Musculoskeletal and Orthopedic MRI

Bubbles in a Paralabral Cyst

2012-01-17T06:00:00.000-05:00

SLAP lesions and paralabral cysts are well-known lesions of the shoulder. Although classically associated with the throwing athlete, they can be seen with relatively sedentary patients as well. Any busy radiologist will see dozens on SLAP lesions every year, with some of these lesions harboring paralabral cysts.

In this case, a 38 year-old male with a history of a prior distal clavicular resection presented to his orthopedic surgeon with persistent shoulder pain. He was referred for an MR arthrogram, to elucidate the cause of his pain.

A coronal T2 fatsat image demonstrates a SLAP lesion (red arrow) as well as a large paralabral cyst (yellow arrows) that occupies the suprascapular and spinoglenoid notches:

An adjacent coronal image again depicts the SLAP lesion (red arrow), and also reveals an oval focus of decreased signal (green arrow) within the paralabral cyst:

A coronal T1 fatsat image demonstrates additional hypointense foci within the paralabral cyst (green arrows); the paralabral cyst (pink arrows) is primarily hypointense on this pulse sequence, but a portion of the cyst does fill with gadolinium (yellow arrow):

An axial intermediate image depicts the overall anatomy nicely, showing the posterosuperior component of the SLAP lesion (red arrow), paralabral cyst (yellow arrows) and hypointense material (green arrow) within the cyst:

What is the hypointense material within the cyst? Possible explanations include areas of calcification or air. A CT scan of the shoulder shows that the hypointense material is air within the paralabral cyst:

Tung et al. (AJR 174, 1707-1715, 2000) described the MRI features of shoulder paralabral cysts. They observed that:

--> paralabral cysts are strongly associated with labral tears.

--> paralabral cysts can exert local mass effect, and cause a compressive neuropathy, typically affecting the suprascapular nerve.

--> prevailing theory is that these cysts form after the capsulolabral complex is torn or avulsed.

There are few reports of air in paralabral cysts in the literature. Lozano Calderon et al. recently reported a case of a paralabral cyst containing air in a middle-aged woman (Am J Orthop 38, E107-E109, 2009). Air can be more commonly seen in synovial cysts arising from spinal facet joints, but is an uncommon finding in shoulder paralabral cysts. The etiology of air formation in a paralabral cyst is unclear, although the mechanism of air formation in joints has been elucidated (Unsworth et al., Ann Rheum Dis 30, 348, 1971).

The differential diagnosis for hypointense material associated with a paralabral cyst is air, calcification, and prior surgery. Conventional radiographs and/or CT scan will reliably differentiate between these possibilities.

Charlie Brown and a Knee Injury

2011-12-15T07:00:00.000-05:00

Photo by gurana

For those of you that do not recognize the visual allusion above, it is a simulacrum of a famous bit of Americana: Lucy pulling the football away from Charlie Brown. Once I became a doctor, I began to look at this a bit differently, and began wondering what kind of injuries Charlie Brown might sustain thanks to Lucy's wicked intentions. Ah, the loss of innocence....

In this case, a 17 year old female sustained a knee hyperextension injury one day ago, and heard a "pop". The orthopedic surgeon suspected an ACL tear, and referred the patient for an MRI scan.

A sagittal proton-density image reveals that the ACL (pink arrow) and posterior cruciate ligament (PCL, green arrow) are intact, and identifies a tear of the posterior capsule (red arrow).

In a normal patient, the posterior capsule (blue arrows) is easily seen:

A sagittal T2 fatsat image of our patient depicts the tear and the associated edema:

An axial intermediate image also identifies the tear:

In a normal patient, the posterior capsule green arrows) is easily seen:

Posterior capsular tears are associated with hyperextension injuries of the knee. Hyperextension of the knee can result when direct force is applied to the anterior tibia while the foot is planted or from an indirect force, such as a forceful kicking motion (Sanders et al., Radiographics 20, S135-S151, 2000). Hyperextension injuries can result in tears of the posterior capsule, ACL, PCL, anterior bone contusions, and injuries of the posterolateral corner. There may be associated meniscal tears as well. The pattern of injury correlates with the mechanism of injury (Hayes et al., Radiographics 20, S121-S134, 2000).

MRI signs of a tear of the posterior capsule include frank disruption and high signal intensity in or adjacent to the capsule on T2-weighted MR images. In the intercondylar area, however, normal openings for the vascular structures and nerves may be present, and these should not be confused with tears. (De Maeseneer et al., AJR 182, 955-962, 2004).

Posterior capsular tears are commonly associated with PCL injuries, but can occur without significant ligament damage, as in this case.

Figure Skaters and Bursitis

2011-11-14T14:10:00.001-05:00

Photo by YN 08-09

Figure skaters soar and float above the ice, spinning and delighting us with their skill and acrobatics. Skaters spend hours on the ice, and subject their ankles and feet to great stress. When their skates do not fit perfectly, the soft tissues of the foot and ankle can become irritated.

In this case, a 25 year-old female figure skater presented to her orthopedic surgeon complaining of a painful mass over the medial malleolus of her tibia. The physical examination confirmed the presence of a mass along with extensive local soft tissue edema, and she was sent for an MRI for further evaluation.

An axial T2 fatsat image identifies an oval, mass (red arrows) immediately superficial to the medial malleolus (yellow arrow):

A coronal T2 fatsat image again identifies the mass (red arrows) and the medial malleolus (yellow arrow), and also depicts the extensive soft tissue edema (white arrows):

An axial postcontrast T1 fatsat image shows that the majority of the mass fails to enhance. There is thin, circumferential enhancement of the lesion:

Based on these images, a diagnosis of medial malleolar bursitis was made. Brown et al. (AJR 2005, 184:979-983) described the appearance of the medial malleolar fat in an asymptomatic population and described the MRI appearance of the medial malleolar bursa. They described ten patients with medial malleolar bursitis (six figure skaters and four ice hockey players).

The medial malleolar bursa is an adventitial bursa. It develops as a consequence of abnormal, extended pressure over the medial malleolus of the tibia. An adventitial bursa is a reactive bursa that forms as a result of chronic soft tissue irritation. Unlike a true bursa, an adventitial bursa lacks a true epithelial lining. In the foot and ankle, adventitial bursae are most common in the forefoot, typically occurring under the first and fifth metatarsophalangeal joints. They can also be found medial or dorsal to the first metatarsal head, and superficial to the medial malleolus, as in this case.

Medial malleolar bursitis is usually treated nonsurgically, with activity modification, anti-inflammatory medications, and topical treatment. If the patient's symptoms do not resolve over a prolonged period of time, surgical resection of inflamed bursa may be necessary. This injury may be prevented by wearing properly fitted skates, using extra padding, and avoiding overtraining.

High Heels and Morton's Neuromas

2011-10-15T06:53:00.000-04:00

Photo by Amy the Nurse

Through many centuries, high-heeled shoes have been linked to increasing female attractiveness. (For an interesting overview of high-heel footwear, go here). The chronic use of high-heeled footwear comes at the cost of increased foot problems, including toe deformities, bunions, and Morton’s neuromas.

In the following case, a 45 year-old female presented to her podiatrist with metatarsalgia (pain involving the forefoot), and was referred for an MRI scan of the foot. A coronal T1 image reveals mass lesions in the second intermetarsal space (red arrow) and the third intermetatarsal space (blue arrow):

The location and signal features of the lesions are compatible with Morton’s neuromas.

On a coronal T2 fatsat image, the neuromas have different signal features, with the larger second intermetatarsal space lesion (red arrow) primarily hypointense, while the smaller third intermetatarsal space lesion is difficult to see, illustrating the variable appearance of Morton’s neuromas on T2 fatsat images:

An axial T1 image confirms the presence of both neuromas:

A sagittal intermediate image better depicts the fusiform morphology of the neuroma in the second intermetarsal space:

There is a great deal of information about Morton’s neuromas that can be easily found on the internet. Here, we concentrate on imaging of this condition.

What is the best position for MR imaging of Morton’s neuromas?

Weishaupt et al. (Radiology 226: 849-856, 2003) examined this question by scanning 18 patients with 20 Morton’s neuromas in the prone (plantar flexion of the foot), supine (dorsiflexion of the foot), and upright weight-bearing positions. They concluded that:

--> Morton’s neuromas show position-dependent changes in shape in the prone, supine, or weight-bearing body positions.

--> Morton’s neuromas are best visualized in the prone position.

Thus, imaging of the forefoot should be done in the prone position, whenever possible.

What is the clinical significance of a Morton’s neuroma that is detected incidentally, while imaging the forefoot for another reason?>

Bencardino et al. (AJR 175: 649-653, 2000) retrospectively reviewed 85 consecutive foot MR examinations. The patients were subdivided into symptomatic or asymptomatic groups, with regard to Morton’s neuromas. Surgical confirmation was available in eight of 25 symptomatic patients. They diagnosed Morton’s neuromas in 33% of patients with no clinical evidence of this condition. Slightly larger lesions were observed in the symptomatic group of patients; however, significant overlap was noted between the two groups. They found that asymptomatic Morton’s neuromas can be found in a significant number of patients.

Thus, when a Morton’s neuroma is detected on MR imaging, one must correlate the imaging observations with clinical symptoms.

How good is MRI for the diagnosis of recurrent Morton’s neuromas?

Espinosa et al. (Radiology 255: 850-856, 2010) examined this issue in a study where they studied 58 consecutive patients who had undergone resection of a painful Morton’s neuroma. Pre- and postoperative MR imaging, and clinical follow-up for a minimum of 2 years after surgery were available. They concluded:

--> Morton’s neuroma–like abnormalities are commonly encountered on MR images after Morton’s neuroma resection.

--> Although these abnormalities are larger in patients with symptoms, there is a high degree of size overlap; thus, they do not allow differentiation between symptomatic and asymptomatic patients.

Thus, MR imaging is of limited utility in the assessment of recurrent Morton’s neuromas.

Is intravenous contrast (gadolinium) needed for the diagnosis of Morton’s neuromas?

There is conflicting data in the literature on this topic. In 1993, Terk et al. (Radiology 189: 239-241, 1993) published an article which advocated the use of gadolinium in the assessment of Morton’s neuromas. Subsequently, Zanetti et al. (AJR 168, 529-532, 1997) and Williams et al. (Clin Radiol 52: 46-49, 1997) questioned the utility of enhanced T1-weighted fat-suppressed sequences in the assessment of this condition.

In general, intravenous contrast (gadolinium) is not needed for the routine evaluation of Morton’s neuromas.

Expectations, Perceptions, and a Shoulder Fracture

2011-09-18T07:29:00.005-04:00

Our expectations can certainly influence our perceptions. For example, in the figure below, the image "13" is perceived readily as a number when it is surrounded by other numbers (lower line). In the upper line, it is surrounded by letters, and it is perceived differently, recognized more slowly and less readily by the brain.

Expectations influence perception over and over in our lives, and this phenomenon extends to radiology. The clinical setting creates a certain set of expectations in the mind of the radiologist. This situation cuts both ways, enhancing the ability of the radiologist to detect subtle findings (when he is explicitly looking for them), but also detracting from his ability to see these same subtle findings (when the expectation is that they will not be present).

In this case, an 80 year old grandmother tripped over her grandchild's toy and hit a wall 8 weeks ago. She had arthritis in both shoulders, and went to her orthopedic surgeon, since her right shoulder was hurting more than usual. X-rays were negative, and she was sent for an MRI for further evaluation.

A coronal T2 fatsat image reveals an unexpected, easily missed fracture of the spine of the scapula:

An axial gradient echo weighted image of the patient confirms the scapular spine fracture:

Fractures of the scapula are typically associated with major trauma, such as high-speed motor vehicle accidents or other crashes.

In the absence of such trauma, one typically does not think of a scapular fracture as a cause of shoulder pain, but this was indeed the case in this example.

The scapula is also called the "shoulder blade" and helps stabilize the upper extremity against the chest. Here is a posterior view of the chest, showing the scapula:

Scapula, anterior view:

Scapula, posterior view:

The scapula is a flat, triangular bone that lies over the posterior surface of the rib cage. At its upper lateral corner is a cuplike depression called the glenoid fossa (red arrows) which forms the socket for the head of the humerus. The posterior surface of the scapula is divided by a nearly horizontal ridge of bone, the scapular spine (blue arrows). The spine extends laterally to form the acromion (black arrows) which overhangs the glenoid fossa. The anterior surface of the scapula, just medial to the glenoid fossa, has a beaklike projection called the coracoid process (green arrows) that acts as an attachment for muscles and ligaments. (chionline)

Most scapular fractures can be treated nonoperatively. In general, the results are satisfactory with conservative treatment. A sling support for 3-4 weeks and early rehabilitation is the key to successful non operative treatment. Treatment emphasizes symptom relief and early motion to prevent long-term stiffness. After motion is restored in the first four to 6 weeks, therapy is directed at rehabilitating the rotator cuff and strengthening parascapular musculature. (shoulderdoc.co.uk)

This case illustrates that although scapular fractures are traditionally associated with high-energy trauma, they can also occur in elderly osteoporotic patients with a history of a minor trauma.

Mixed Martial Arts and a Chest Injury

2011-08-17T08:20:00.004-04:00

Photo by Michael Connell

The pectoralis muscle is a popular muscle for men and boys to develop. Women are drawn to "chiseled pecs", which is more than enough motivation for men to work on enlarging them.

Weightlifters are particularly prone to injuries of this muscle, and pectoralis tears are seen most often in young, athletic males. Patients with a ruptured pectoralis major present in the acute aftermath of the injury, with pain, extensive swelling, and ecchymosis of the anterior chest wall, axilla, and medial aspect of the affected arm. Injured patients frequently report a "pop" at the time of the injury.

Connell et al. (Radiology 210:785-791, 1999) described the proper technique used to image the pectoralis major. In 2000, Lee et al. (AJR 174:1371-1375) performed a beautiful cadaveric study, and described some salient features of the pectoralis major on MRI:

---> the pectoralis major tendon crosses anterior to the biceps tendon to become a thin, triangular-shaped structure at its insertion at the lateral lip of the intertubercular groove

---> one reliable landmark for the superior margin of the pectoralis insertion is the quadrilateral space, best seen in the axial plane. The superior edge of the pectoralis major insertion typically is identified at the level of, or within 1-1.5 cm inferior to the quadrilateral space (range, 0-1.2 cm).

---> another reliable landmark is the origin of the lateral head of the triceps muscle. The superior edge of the pectoralis major insertion is reliably identified on the anterior aspect of the humerus, approximately 5-10 mm superior to the level at which the lateral head of the triceps is first identified.

Here is an example of axial images through the normal pectoralis major tendon, superior to inferior, illustrating these principles:

(click on image to enlarge)

Green arrow = normal pectoralis major tendon. Orange arrow = latissimus dorsi tendon. Note the proximal aspect of the lateral head of the triceps muscle (pink arrow) and vessels within the quadrilateral space (blue arrow).

In this case, a 25 year old male injured his chest during a take down of an opponent during mixed martial arts training. He presented for his MRI approximately 1 week after his injury.

(A) Axial intermediate image identifies an avulsion of the pectoralis major tendon at its insertion. Note the torn, retracted tendon (red arrows) and the biceps tendon (green arrow) which is displaced anteriorly. MRI clearly identifies the end the torn tendon (yellow arrow). (B) Axial T2 fatsat image better shows the edema associated with the injury.

Compare this appearance with a normal pectoralis tendon:

An oblique coronal T2 fatsat image of our patient shows marked fluid and edema (red arrows) at the myotendinous junction, the pectoralis major muscle (yellow asterisks), and the cephalic vein in the deltopectoral groove (green arrow):

The MRI scan precisely depicted the nature of the injury and allowed appropriate presurgical planning. The patient was operated on three days later, and the tear was repaired successfully.

When ordering an MRI to assess a possible pectoralis tear, it is generally best to order a “MRI of the chest”. If one requests an “MRI shoulder” the MRI technologist may inadvertently use a standard shoulder imaging protocol, which is very different than the protocol used to assess the pectoralis major. The standard shoulder protocol will not answer the clinical question.

In general, early surgical repair is associated with a better outcome for the athlete, with earlier return to full strength and range of motion. Immediate diagnosis avoids surgical delay, which has the advantage of avoiding adhesions, muscle retraction, and atrophy, which can occur as early as 6 weeks after the initial injury (Lee et al. AJR 174:1371-1375).

In the past, tears that have reached the chronic stage have been considered irreparable injuries. More recently, even chronic tears are addressed surgically, and still have a good outcome (Aarimaa et al., Am J Sports Med 32:1256-1262, 2004).

Stairs and a Tendon Tear

2011-07-15T06:30:00.000-04:00

Photo by Susan NYC

Steep stairs are a danger for the very young and very old, who must gingerly pick their way down stairs, to avoid a fall. Inevitably, despite all due care, some individuals will slip and injure themselves.

In this case, a 66 year old man fell going down steep stairs, and presented to his orthopedic surgeon with knee pain and loss of extensor strength.

A sagittal T2 fatsat image depicts a high grade partial tear of the quadriceps tendon. The distal edge (red arrow) of the tendon is well seen, as is the large hematoma (green arrow). The patella (pink arrow) is positioned more inferiorly than normal, and the patellar tendon (white arrow) is lax, suggesting that this is functionally a complete tear. The deep layer of the quadriceps tendon, composed of the vastus intermedius (yellow arrow), remains intact.

An axial image better depicts the size of the hematoma (green arrows) and again identifies the intact vastus intermedius component (yellow arrow) of the quadriceps tendon:

The quadriceps femoris (Latin for "four-headed muscle of the femur"), is a group of four muscles in the anterior thigh:

- rectus femoris
- vastus medialis
- vastus lateralis
- vastus intermedius

These four muscles originate from the pelvis and femur, and form the quadriceps tendon, which inserts on the superior aspect of the patella.

Photo by robswatski

On this frontal view, we can see the rectus femoris (white arrow), vastus medialis (yellow arrow), and vastus lateralis (green arrow). The vastus intermedius is deep to the rectus femoris, and is not seen.

The quadriceps tendon has 3 distinct layers:

- superficial layer, formed by the rectus femoris
- intermediate layer, formed by the vastus lateralis and vastus medialis
- deep layer, formed by the vastus intermedius [you can remember that the deep layer is the vastus intermedius by "intermediate is inside"]

The quadriceps tendon rarely ruptures in the young and healthy; rather, this is a disease of the old, with ruptures most common in the 6th & 7th decade of life. There is a strong male preponderance, with male victims outnumbering females 8:1. Quadriceps ruptures are associated with cortisone injections, diabetes, chronic renal failure, hyperthyroidism, and gout.

Most injuries are treated surgically, optimally within a few days of the injury.

A Forearm Lump

2011-06-15T05:40:00.002-04:00

Patients vary in their approach to lumps they find in their body. Some will seek medical attention immediately, while others will wait for the mass to enlarge or cause symptoms before going to see a physician.

A 50 year-old female presented to a hand surgeon with a slowly enlarging forearm mass:

The surgeon referred the patient for an MRI scan, to further characterize the mass. Coronal and sagittal T1-weighted images identify an encapsulated, fat-containing mass (red arrows) along the dorsal aspect of the forearm, with a few, thin internal septations (blue arrows):

An axial T1 image better depicts the relationship of the mass to the radius (R) and ulna (U):

An axial T2 fatsat image confirms that the lesion is composed of fat, and also better defines the deep extension of the lesion to the level of the interosseous membrane and anterior interosseous neurovascular bundle (green arrow):

An axial T1 fatsat image obtained after the administration of gadolinium shows that the lesion does not enhance:

Thus, the forearm mass is well-encapsulated, contains only a few-thin septations, has no nodular areas, and fails to enhance after the administration of gadolinium. The diagnosis of a simple lipoma was made, and important anatomic relationships were described in the radiology report, for preoperative planning. The lesion was excised, and was confirmed to be a simple lipoma.

MRI is often used to characterize soft tissue masses. The initial questions are usually:

- is the mass benign or malignant?

- what are the anatomic boundaries of the mass, and what is its relationship to critical structures such as major nerves and arteries?

- can a specific tissue diagnosis be provided?

A simple, but useful approach is to put the mass into one of three categories, which MRI can do with a high degree of reliability:

--> ganglion cyst

--> lipoma or other fat-containing mass

--> does not fit criteria for ganglion cyst or fat-containing mass, and needs further analysis

When a discrete, homogeneous fat-containing mass is encountered, a simple lipoma can be diagnosed with certainty. When an inhomogeneous fat-containing mass is found, further analysis is required. Gaskin and Helms examined 126 fat-containing masses, to better understand how to differentiate simple lipomas from well-differentiated liposarcomas (AJR 162:733-739, 2004) and concluded:

--> MRI is 100% specific for a simple lipoma, when the lesion has a characteristic appearance

--> infiltrating intramuscular lipomas also have a characteristic appearance, and can be diagnosed with confidence

They also noted that when a fat containing mass is heterogeneous (thickened or nodular septa, significant nonadipose tissue, prominent foci of high T2 signal, and prominent areas of enhancement), the lesion may be benign or malignant. In their series, 10/16 (63%) of the lesions suspicious for malignancy were benign lipoma variants, such as chondroid lipoma, osteolipoma, hibernoma, angiolipoma, lipoleiomyoma, and necrotic lipoma.

Thus, about two-thirds of soft tissue masses that contain fat and are suspicious for malignancy will actually turn out to be benign in nature. Nonetheless, it is important for the radiologist to alert the clinician and pathologist to the possibility of a liposarcoma, so that the patient can be managed appropriately.

A common question that is asked is, "Does the MRI need to be done with intravenous contrast?". When a simple lipoma or a typical ganglion cyst is found, there is usually no need to administer intravenous contrast for further characterization. Unfortunately, one does not know the nature of the mass before doing the MRI, so it is often best if the clinician orders the examination with intravenous contrast, "at the discretion of the radiologist".

Rock Climbers and Pulleys

2011-05-15T19:38:00.001-04:00

Photo by groundzero

"There are only 3 real sports: bull-fighting, car racing and mountain climbing. All the others are mere games."— Ernest Hemingway

Critical to mountain and rock climbing are extraordinarily strong fingers, which can find small cracks in the rock, and propel the ardent climber skyward. Flexion of the fingers is generated by the flexor digitorum profundus and flexor digitorum superficialis (sublimus) tendons, which attach to the distal phalanx and middle phalanx, respectively. These tendons are held close to the underlying bone by five annular or "A" pulleys, that prevent bowstringing during flexion:

Figure courtesy of Nicros

Of the five annular pulleys, the A2 pulley is the most commonly injured. Injuries can vary from partial tears to complete tears. Rock climbers are particularly prone to pulley injuries, due to the tremendous load placed on the pulleys when the climber grips tightly, and levers himself upward. The traditional rock climbing grip ("crimp position"), which involves hyperflexion of the proximal interphalangeal (PIP) joint and hyperextension of the distal interphalangeal, puts high stress on these pulley structures. Tears can develop over time, or be acute in nature.

Pulley tears can be imaged using MRI or ultrasound. On ultrasound, a partially torn pulley is thickened and hypoechoic (Martinoli et al., Skel Rad 29, 387-291, 2000). On both ultrasound and MRI, complete pulley tears will manifest with an increased distance between the flexor tendon and the underlying bone, since the pulley is no longer holding the flexor tendon in place, with this sign accentuated during finger flexion. High resolution imaging will easily identify the normal A2 and A4 pulleys, allowing direct detection of pulley injuries.

In this case, a 36 avid rock climber complained of a painful ring finger, with pain maximal at the base of the finger. He began to notice the pain after a day of climbing, six weeks before seeking medical attention. Physical examination revealed swelling at the base of finger, but no bowstringing of the tendons. The patient was referred for an MRI to assess the A2 pulley, and to exclude a flexor tendon sheath ganglion cyst.

An axial intermediate image reveals diffuse thickening of the A2 pulley of the ring finger (red arrow). The pulley remains continuous, without focal discontinuity. The normal middle finger A2 pulley (green arrow) is also seen.

Here is the corresponding axial T2 fatsat image:

A coronal intermediate image depicts the abnormally thickened A2 pulley:

Sagittal images of the ring finger were also performed:

(A) Gradient echo and (B) T2 fatsat images show the abnormally thickened A2 pulley, along with local soft tissue edema. In normal patients, the A2 pulley cannot be seen on sagittal images, since it is a diaphanous structure tightly applied to the underlying flexor tendons.

MRI yields the diagnosis of a partial, interstitial tear of the A2 pulley with reactive local soft tissue inflammation, and allows proper treatment.

Treatment of partial pulley tears is usually conservative, although complete annular pulley ruptures may be addressed surgically. Rock climbers are tough individuals, and some of them will attempt to "climb through" partial pulley tears, but rest is the recommended approach.

Torn Tendon with Two Heads

2011-04-15T19:42:00.006-04:00

Photo by toksuede

Football (or soccer) is a venerable game that existed for several hundred years. The original balls were made out of animal bladders, which were cleaned, inflated, and kicked around. Not surprisingly, injuries related to the kicking motion have also existed for hundreds of years. The kicking motion can place a high degree of stress on muscles and tendons that originate in the pelvis, such as the rectus femoris muscle.

The rectus femoris muscle has two distinct origins. The direct (straight) head arises from the anterior–inferior iliac spine (AIIS), while the indirect (reflected) head originates from the superior acetabular ridge and hip capsule. The indirect (reflected) head is the primary head. The two heads unite, and form the rectus femoris muscle, shown in red below:

A frontal view of the pelvis depicts the origin of the direct head (red) from the AIIS, and the origin of the indirect head (blue) from the superior acetabular ridge:

Remember that the indirect head in inferior (both words begin with "i"). An oblique view of the pelvis better depicts the relationship of the two origins to the acetabulum:

The two heads of the rectus femoris tendon are well depicted on the following oblique axial image, which depicts the origin of the direct head (red) from the AIIS, and the origin of the indirect head (blue) from the superior acetabular ridge:

In the following case, a 14 year old boy experienced sharp pain while kicking a soccer ball. A coronal STIR image shows an avulsion of the direct head of the rectus femoris (red arrow) from the AIIS:

Axial images show the avulsed bone fragment (red arrow) and the attached tendon, as well as the intact indirect head (yellow arrow) of the rectus femoris:

Consecutive sagittal images show the avulsed bone fragment (red arrow), direct arm of the rectus femoris (green arrow) and indirect arm of the rectus femoris (yellow arrow):

Rectus femoris tears typically affect the direct head, but one can also involvement of the indirect head, alone or in concert with direct head tears. With direct head tears, one often sees a flake of bone on conventional radiographs, corresponding to an avulsion fragment. MRI can help confirm the diagnosis.

Avulsion of the anterior superior iliac spine can simulate this injury if the fragment is retracted inferior to the level of the anterior inferior iliac spine (Stevens et al. Radiographics 19:655-672, 1999). Rectus femoris tears can lead to a soft tissue mass, and a chronic rectus femoris tear can mimic a tumor (Temple et al, AJSM 26:544-548, 1998).

Injuries of the rectus femoris typically respond well to conservative therapy. Avulsions of both the anterior superior and anterior inferior iliac spines tend to be less symptomatic and disabling than avulsions of the ischial tuberosity, and recovery typically occurs over a few weeks (Combs JA, Physician Sports Med 22:41-49, 1994). Fortunately, rectus femoris tears usually respond well to conservative therapy, and heal over several weeks.

Supernovas and Hand Creases

2011-03-15T18:11:00.026-04:00

NASA’s Chandra X-ray observatory has given us this image of an unusual hand-shaped nebula, a result of a star gone supernova. The pulsar remaining from this supernova spins at seven complete rotations a second, expelling particles and gas into space, creating the fingers of the hand.

Closer to earth, our hands are critical parts of being human, enabling us to caress, grasp tools, and change the world around us. As part of our body, the hand falls prey to many of the ills that affect all our tissues, including tumors. Some of these tumors must be excised by the hand surgeon, and when that is necessary, the creases of the hand can become important anatomic landmarks for the surgeon.

While radiologists are used to describing lesions in reference to easily observable deep structures such as bones and joints, it is often more useful to describe lesions with reference to surface landmarks. In the hand, one should remember that skin creases are not in the same position as the underlying joint. Hand skin creases are named as follows:

The surface anatomy of the hand was reviewed by Bugbee and Botte in 1993 (Clin Orth and Rel Res, 296: 122-126, 1993). In this diagram, the position of the skin creases is depicted by lines:

Bugbee and Botte point out the following:

---> DIP crease is consistently proximal to the DIP joint, with a mean distance of 7-7.8 mm proximal to the joint.

---> PIP crease is consistently proximal to the PIP joint, with a mean distance of 1.6-2.6 mm proximal to the joint.

---> palmar digital crease is consistently distal to the MCP joint, with a mean distance of 14.4-19.6 mm distal to the joint.

---> distal palmar crease averages 7.9 mm proximal to the little finger MCP joint, 10.3 mm proximal to the ring finger MCP joint, and 6.9 mm proximal to the long finger MCP joint.

---> proximal palmar crease averaged 9.1 mm proximal to the index MCP joint, 18 mm proximal to the long finger MCP joint, and 22.1 mm proximal to the ring MCP joint.

The MRI correlate is seen in this sagittal T2 fatsat image:

Green arrow = palmar digital crease; Red arrow = distal palmar crease; Blue arrow = proximal palmar crease.

The distal and proximal palmar creases can sometimes be identified on MRI by the presence of air between the skin folds. Coronal T1 weighted images, posterior to anterior, depict air in the distal palmar crease (red arrow) and the proximal palmar crease (blue arrow):

This movie better depicts the various hand creases, in relation to the underlying joints:

Green arrow = palmar digital crease; Red arrow = distal palmar crease; Blue arrow = proximal palmar crease; Yellow arrow = thenar crease.

In this case, a 47 year- old male came to the hand surgeon complaining of focal pain along the palmar surface of hand. No mass was present on physical examination. The patient was referred for an MRI, to localize a suspected glomus tumor.

An axial gradient echo image reveals a 2 mm mass (red arrow) near the site of pain:

A coronal T1 weighted image also depicts the mass, which was not palpable:

The location of the lesion with respect to surface landmarks is best depicted on this sagittal T1 weighted image:

The lesion (red arrow) is located proximal to the palmar digital crease (green arrow), distal to the metacarpophalangeal joint (yellow arrow).

MRI precisely localized of the tumor in reference to the surface landmark, and enabled the surgeon to make the appropriate incision, and excise the tumor easily. Pathologic analysis confirmed the presence of a glomus tumor.

Zumba and a Painful Toe

2011-02-15T05:53:00.004-05:00

Zumba is a dance fitness program that is a modern variant of aerobics. The program combines Latin and international music with dance in an effort to make exercise fun (if that is possible). There is a whole lot of body and foot movement, and generally one leaves a class with endorphins flooding your brain, or so I am told.

Like every activity, though, there is some risk of injury. In this case, a 28-year-old female presented to her podiatrist complaining of one year of great toe pain, recently increased with Zumba dancing. She was referred for an MRI.

An axial T1 image reveals fragmentation of the anterior aspect of the tibial sesamoid of the hallux (red arrows). The bone fragments are abnormally dark (compare with the normal signal intensity of the fibular sesamoid (green arrow):

Here is a magnification view of the same area:

An axial T2FS image reveals that the bone fragments remain dark, and are separated by a small amount of fluid:

A sagittal intermediate image again depicts the abnormally dark anterior half of the sesamoid (red arrow), and also depicts the proximal half of the sesamoid (yellow arrow), which remains normal in signal:

Thus, the anterior portion of the tibial sesamoid is fragmented and devascularized (avascular necrosis).

The sesamoid bones of the hallux (great toe) are embedded within the medial and lateral slips of the flexor hallucis brevis tendon at the level of the first metatarsal head. The sesamoids are usually unipartite, but there is a significant incidence of bipartite or multipartite sesamoids, especially in the case of the tibial sesamoid. Afflictions of the sesamoids include acute trauma and chronic increased stress, which can manifest as sesamoiditis, stress fractures, and osteonecrosis (avascular necrosis). The classic findings of avascular necrosis include pain and tenderness to palpation, with osseous fragmentation or mottling noted on conventional radiographs. On MRI, the marrow will be hypointense on both T1, T2FS and STIR images; in contradistinction, the marrow will be hyperintense on T2FS and STIR images in cases of sesamoiditis and stress fractures.

The great toe is a well-known stress point in ballet dancers, but can also be injured with less intense forms of dancing, such as Zumba.

Magic Angle and the Meniscus

2011-01-16T07:20:00.001-05:00

Photo by Brother O'Mara

The way MRI images structures deep inside the body can seem like magic. Ironically, there is also an imaging artifact in MRI with the tag "magic" attached to it— the magic angle artifact, also know as the magic angle phenomenon or effect.

In an earlier post, I discussed the magic angle phenomenon. If you recall, the magic angle effect results in artifactual increased signal in structures with ordered collagen, such as tendons, fibrocartilage, and hyaline cartilage.

One well-known structure that contains ordered collagen is the meniscus of the knee. Magic angle effects can lead to artifactual increased signal in the meniscus, and can be confused with meniscal degeneration or a meniscal tear.

Knees are often imaged on both closed and open MRI scanners, and the magic angle effect has different manifestations, depending on what type of MRI scanner is used.

Here is a conventional, high-field closed MRI scanner:

The main magnetic field is horizontal in nature, and runs directly through the center of the magnet (red arrow). In the following diagram, we are looking down the bore of the magnet, with the "X" the back of an arrow denoting the direction of the main magnetic field:

Open MRI scanners have two parallel "plates", with the patient lying between the plates. The main magnetic field is vertical in nature; this can be diagrammed in the following way:

Now let's do an experiment to see how an ordered, collagenous structure behaves in these two environments. Take a beef hamstring tendon, and fold it into a C-shape, to mimic the shape of the normal knee meniscus. Once we do that, place it into a water bath, and perform a T2-weighted image, using a TE (echo time) of 50 ms:

As expected, the ordered collagen in this tendon is completely black, except for some fatty tissue at the inner margin of the tissue (yellow arrow).

Now let's take our model meniscus, and perform a scan in an open MRI, using a TE of 15 ms:

At this TE, magic angle artifacts will become evident. Note the bright signal (red arrows) at the edges of the meniscus, where the collagen fibers are close to the magic angle (55 degrees with respect to the main magnetic field, which is straight up and down in this open magnet). There is also bright signal at the inner margin of the specimen from the fatty tissue, which you can ignore for this illustration.

OK, now let's take our model meniscus, and move it to a closed MRI, and repeat the scan, using the same TE (15 ms).

Note that the artifactual signal has completely disappeared. The main magnetic field is perpendicular to the plane of the picture (going into the plane of the picture), and none of the collagen fibers are at the magic angle, so there is no artifactual signal.

From this example, it should be apparent that in open, vertical field magnets, magic angle artifact will be found in two locations: 1) junction of anterior horn and body of meniscus and 2) junction of posterior horn and body of meniscus. Here is one such example:

Ah, but only if it were that simple! Magic angle artifact can also occur in closed MRI scanners, but it will occur at different locations. Remember that in closed scanners, the main magnetic field runs from head to foot. The upsloping posterior horn of the lateral meniscus is often close to 55 degrees to the main magnetic field, and one will often see magic angle artifact in this region, as in this example:

The inner edge of the posterior horn of the lateral meniscus is the classic location for magic angle artifact, due to the upsloping nature of this area of the meniscus in many patients. Although less frequent, the posterior horn of the medial meniscus can also be upsloping, and magic angle can be encountered in medial meniscus as well. In rare cases, magic angle artifact can also be associated with the anterior horns of the menisci.

If you made it this far, congratulations, you now have a good grasp of some situations where magic angle artifact can confound the interpretation of meniscal pathology in both open and closed MRI.

Shoulder Instability and Upside Down Pears

2010-12-18T07:00:00.007-05:00

Have you ever seen someone that reminds you of someone else? Above is a striking comparison between Gordan Freeman from Half-Life and Dr. House from the TV show House. There is even a website devoted to this topic, that you may find amusing. Doctors are no different, and when they see something in the body that looks like something else, they will often point that out, as we will see below.

The shoulder joint is composed primarily of the humeral head (red arrows), which fits into the glenoid portion of the scapula (blue arrows):

The glenoid portion of the scapula is best seen looking at the shoulder from the side, with the humeral head removed:

The shape of the glenoid can be compared to a pear:

Photo by Magalie L'Abbé

The normal pear shape of the glenoid helps keep the humeral head in place. With repeated anterior dislocations, bone along the anterior margin of the glenoid can become worn down, and the glenoid can lose its normal shape. The curve of the anterior glenoid becomes flattened, and the loss of the normal convexity of the glenoid can be part of the syndrome of recurrent anterior instability. The normal pear shape of the glenoid is lost; when the inferior part of the glenoid appears narrower than the superior part, one is said to have an "inverted-pear" glenoid.

In this case, a 29 year old male with a history of multiple left shoulder anterior dislocations was sent for an MR arthrogram. An axial intermediate image shows a large Bankart lesion:

A sagittal T1 weighted image reveals extensive flattening of the anterior margin of the glenoid, with an inverted pear appearance:

A CT scan shows the loss of the normal cup shape of the left glenoid on axial images (red arrow), with maintenance of the normal glenoid shape (green arrow) in the asymptomatic right shoulder:

A 3D volume rendered CT image better depicts the abnormal shape of the left glenoid:

For comparison, here is the shape of a normal glenoid:

Joe de Beer and his colleagues have recently written an excellent article on anterior shoulder instability in the elite athlete, with specific reference to bony deficiencies (Shoulder & Elbow 2010 2, pp 63–70). They note that:

--->Diagnosis of anterior glenoid bone loss can be missed at arthroscopy if one looks examines the glenoid solely from the posterior portal. This diagnosis is best made using the antero-superior portal.

--->Significant bone loss cut-off has been widely quoted as greater than 25%. This may not be the correct number in all patients: "What experience has taught us is that....the higher the demand, the less bone loss that is tolerated. We therefore deem significant even small bony deficiencies in the elite athlete".

Percentage bone loss can be measured on imaging studies (Griffith et al., AJR 2003;180:1423-1430) as well as at arthroscopy (Burkhart et al., Arthroscopy 2002; 18:488–91). The radiologist should alert the surgeon when there is appreciable bone loss along the anterior margin of the glenoid, as this information can alter the surgical procedure that is used to treat the patient.

Football and a Meniscal Tear

2010-11-15T13:40:00.004-05:00

Between Thanksgiving and Christmas, citizens in the United States eat too much, and watch a lot of football. They also get out in the backyard, and play the game, typically "touch" or "flag football".

Photo by frohner1

There is a spike of football-related injuries during this time, typically resulting in bone contusions, ligament injuries, and meniscal tears. Most of these are typical in character, but every once in a while one will see an unusual variant.

In this case, a 38 year-old male was playing flag football, and sustained an injury. His knee swelled almost immediately, and he had an MRI a few days after the injury.

There is an obvious ACL tear:

A coronal image through the posterior knee identifies the medial meniscus (green arrow), but the posterior horn of the lateral meniscus is missing in action, with only fluid found in the expected location of the lateral meniscus (red arrow):

A coronal image through the mid-joint reveals that the torn posterior horn has been flipped out of the joint:

An axial image identifies the torn, flipped meniscus (red arrow), situated between the fibular collateral ligament (yellow arrow) and the popliteus tendon (green arrow).

Most flap tears of the meniscus that are displaced out of the joint are found inferior to the joint line, but these flap tears can also displace superiorly, as in this case. MRI can provide valuable preoperative information, allowing the surgeon to counsel the patient and plan his surgical approach.

Football is a great sport (both the American and European versions), but it does come with its risks...

Tennis and Hand Pain

2010-10-18T00:04:00.004-04:00

High level tennis players place a great deal of stress on their hands:

Photo by splitmilk

In an earlier entry, we looked at the shape of the hamate, which has a hook (blue arrow):

In sports where an instrument is swung, fractures of the carpal hamate bone can be due to blunt trauma or a sharp strike against the hook of the hamate. The swinging motion that accompanies golf, baseball, tennis racquet are all well-known causes of this injury. Patients present with pain localized over the ulnar aspect of the wrist and reduction in grip strength.

In this case, a 40 year-old female tennis player presented with ulnar-sided pain of two weeks duration. She had no direct trauma to hand, but developed the pain after playing tennis. Axial T2 fatsat images reveal intense bone marrow edema in the body of the hamate (yellow arrow) and a fracture of the hook of the hamate (red arrow), with accompanying bone marrow edema:

A sagittal T1 weighted image confirms the presence of the fracture:

(click on image to enlarge)

Thus, one should consider this injury when assessing an athlete with ulnar-sided hand pain.

Shadows in the Knee

2010-09-19T23:08:00.001-04:00

Photo by ambrown

In the early days of medical imaging, radiologists used only x-rays to image the body. These pioneers saw shadowy representations of the tissue that is inside all of us. With the advent of cross-sectional imaging techniques such as CT, ultrasound, and MRI, we are now able to visualize anatomic structures directly, and no longer have to deduce the anatomy from a shadow-like representative object.

Occasionally, however, events conspire to create ghost-like shadows even on cross-sectional imaging such as MRI. In this case, a 31 year old male presented with knee pain, and was referred for an MRI:

(A) Sagittal proton-density image reveals an unusual appearance to the bones, with visualization of the ghostly outline of the femoral secondary epiphysis (blue arrows) and the tibial secondary epiphysis (red arrows). (B) Sagittal T2 fatsat image is less striking, with areas of nonspecific increased signal visualized in the femur and tibia.

A sagittal proton-density image through the patella reveals the ghostly outline of the patellar epiphysis:

A manifestation of growth arrest was suspected. Further questioning of the patient revealed that he had a serious ski accident in childhood, resulting in a femur fracture requiring prolonged immobilization, confirming the diagnosis. Epiphyseal growth arrest lines have been described (Yao L, Seeger LL, Clin Imaging. 1997 Jul-Aug;21(4):237-40) and can lead to a "bone-in-bone" appearance, as in this case. Causes of a "bone-in-bone" appearance on conventional radiographs include bone infarction, osteopetrosis, and Paget's disease. On MRI, however, this appearance is highly suggestive of an epiphyseal growth arrest event in the patient's past.

"Pop" and an Unusual Meniscus

2010-08-07T06:21:00.001-04:00

A common complaint that is heard in doctor's offices after a knee injury is, "I heard a pop, and then my knee swelled up". This complaint is usually related to a tear of the anterior cruciate ligament, but can sometimes also indicate a tear of the meniscus.

Occasionally, a "pop" can be felt by the examining physician as well, but this is relatively rare. Conditions that may cause painful snapping about the knee include congenital snapping knee, discoid lateral meniscus in children, a torn meniscus, intraarticular rheumatoid nodules, synovial plicae, and iliotibial band syndrome. Subluxation of tendons has been reported to cause this painful snapping syndrome about the knee, medially by the gracilis and semitendinosus tendons, and laterally by the biceps femoris and popliteus tendons (Bach and Minihane, AJSM 2001, 29:93-95).

In this case, a 32 year-old female presented to her orthopedic surgeon with knee pain. The surgeon noted that as the patient extended her knee into full extension, there was a "pop" in the posterolateral knee. She was referred for an MRI, to evaluate for internal derangement.

A sagittal proton-density weighted image reveals abnormal signal in the anterior horn of the lateral meniscus (red arrow), but is otherwise unremarkable:

The astute MRI technologist (a former naval medic) was puzzled by the relatively innocuous nature of the finding in the anterior aspect of the meniscus, particularly given the strong clinical history of a pop in the posterolateral knee. At the end of the examination, he asked the patient if she could do anything that would elicit the "pop". She obliged, and squatted downwards, and the "pop" occurred. The MRI technologist gingerly placed her back in the magnet, and repeated the sagittal:

Here, after the provocative maneuver, we see a striking peripheral tear of the posterior horn of the lateral meniscus which has been displaced anteriorly, leaving only fluid where the meniscus should be (green arrow).

An axial image better reveals the avulsed lateral meniscus (blue arrows), which has been displaced anteriorly:

Compare this to the position of the meniscus (yellow arrow) on the initial (before the provocative maneuver) axial scan:

Intermittent meniscal dislocation has been discussed in the literature (Lyle et al.Br J Radiol. 2009, 82:374-9). They described three patients with a strong history of intermittent knee locking, who had negative initial MR scans. The patients were able to reproduce locking of their knee voluntarily, as in our case. Further MR imaging of the knee in the "locked" position demonstrated meniscal dislocation in all three patients. All three were confirmed arthroscopically to have deficiency of the corresponding menisco-capsular ligaments (as was our patient).

When there is a strong clinical history of knee locking, all the structure of the knee must be carefully inspected on MRI, particularly the menisci, anterior cruciate ligament, and the hyaline cartilage. When no abnormality can be detected, it is a good idea to scrutinize the peripheral attachments of the meniscus. The meniscocapsular junction is a difficult area to analyze, with abnormalities easily missed (and overcalled as well). With higher resolution imaging now becoming increasingly common, it has become easier to detect abnormalities in this area with greater confidence.

In the exceptional case, provocative imaging can be performed, and may help demonstrate an intermittently dislocating mensicus.

Ants and a Shoulder Mass

2010-07-09T19:29:00.001-04:00

Photo by TillinKa

A surgical suture is used to close the edges of a wound or incision and to repair damaged tissue. The closure of wounds has a dramatic history, with some inventive methods. In ancient times, beetles or ants were used to close wounds. The living creatures were attached to the edges of the wound, which they clamped shut with their pincers. The insect body was then cut off, leaving the jaws in place. Army ants can be used for this purpose, due to their impressive pincers

We have made some advances since that time, and here is a nice summary:

Sutures are made from both man-made and natural materials. Natural suture materials include silk, linen, and catgut, which is actually the dried and treated intestine of a cow or sheep. Synthetic sutures are made from a variety of textiles such as nylon or polyester, formulated specifically for surgical use. A suture can also be classified according to its diameter. In the United States, suture diameter is represented on a scale descending from 10 to 1, and then descending again from 1-0 to 12-0. A number 9 suture is 0.0012 in (0.03 mm) in diameter, while the smallest, number 12-0, is smaller in diameter than a human hair.

64 year-old woman with a history of a humeral fracture, who presents with an arm mass. Oblique sagittal T1-weighted image reveals a 7 mm subcutaneous mass (red arrow), along with extensive metal artifact (yellow arrows):

The presence of extensive metal artifact made fat suppression difficult, and an ultrasound was performed to determine if the mass was solid or cystic:

The ultrasound confirmed the existence the mass, depicting an oval mass (red arrows) with irregular margins and no posterior acoustic enhancement. The mass was thus confirmed to be solid. In addition, within the posterior aspect of the mass, there was a linear, hyperechoic focus (yellow arrow), not conforming to a tissue plane.

Pathologic analysis revealed a suture granuloma. Suture granulomas can mimic neoplasms, especially at imaging. They are most commonly reported in the setting of inguinal herniorrhaphy, but can occur in other post-surgical settings as well. They can present as enhancing masses on MRI or CT, and can be associated with increased uptake at F-18 fluorodeoxyglucose (FDG)-positron emission tomography (PET)/CT imaging (Kim et al., Kor J Rad 2009; 10:313-318). Suture granulomas have been reported to mimic recurrent thyroid carcinoma on ultrasound (Chung et al., Yonsei Med J. 2006; 47:748-751) and urachal tumor on CT (Gan and Wastie, J HK Col Radiol 2007; 10:59-61).

A recent report assessed the ultrasound features of suture granulomas at the thyroid bed after thyroidectomy for papillary thyroid carcinoma with an emphasis on their differentiation from locally recurrent thyroid carcinomas. Shape, heterogeneity, and the presence of central or paracentral internal echogenic foci (as in this case) were helpful criteria for differentiating suture granulomas from locally recurrent tumors in the thyroid bed.(Kim et al., Ultrasound in Med Biol 2009; 35,1452-1457). Thus, if you suspect that a mass may be a suture granuloma on MRI, a follow-up ultrasound may identify linear hyperechoic suture material within the lesion, and help suggest the diagnosis of a suture granuloma.

Jujitsu and a Shoulder Injury

2010-06-06T06:45:00.014-04:00

Photo by icantcu

Hand-to-hand, testosterone-fueled combat has existed for centuries. As long as violence, power, and sex exist (and I see no signs of them going away soon), fighting will thrive. Boxing and ultimate cage fighting are the more recent variations of an ancient drive to display power and conquer the other.

Jujitsu, a form of hand-to-hand mayhem, is a Japanese martial art style that emphasizes pins, joint locks, and throws. This sport can cause significant torque forces on the body, and lead to injury.

In this case, a twenty-six year old male experienced an upper body injury two weeks ago during jujitsu. He had torso pain and a clinical exam notable for glenohumeral instability. An MR arthrogram of the shoulder was obtained to clarify the extent and nature of his injuries.

An oblique coronal intermediate-weighted image from an MR arthrogram depicts a tear of the latissimus dorsi and teres major tendons (red arrows), with increased fluid (yellow arrow) adjacent to the torn tendons:

An oblique sagittal T2 fatsat image demonstrates the torn, retracted latissimus dorsi (red arrow) and teres major (green arrow) tendons. Also seen is a paralabral cyst (yellow arrow) adjacent to the posterior labrum. There is fluid in the joint (blue arrow) related to the MR arthrogram:

The pectoralis major, latissimus dorsi, and teres major tendons all insert on the humerus, next to one another. A good mnemonic for the pattern of insertion is "lady between two majors", with "lady" = latissimus dorsi (red line) and "major" = pec major (blue line) and teres major (green line):

Sagittal images from a normal patient (medial to lateral) illustrate the anatomy of latissimus dorsi (red arrows) and teres major (green arrows).

(click on image to enlarge)

The teres major tendon is smaller and more compact than the tendon of the latissimus dorsi. The quadrilateral space (Q) is found between the teres minor (blue arrows) and teres major (green arrows) muscles. T = long head of the triceps

Oblique axial intermediate images through the upper arm of our injured patient better demonstrate the torn, retracted latissimus dorsi (red arrows) and teres major (green arrows) tendons.

(click on image to enlarge)

Note the intact pectoralis major (pink arrow) tendon, as well fluid (yellow arrow) at the expected insertion site of the latissimus dorsi and teres major tendons. The footprint of the latissimus dorsi and teres major tendons is "naked".

For comparison, consider these oblique axial images from a normal patient (superior to inferior), showing the intact latissimus dorsi (red arrows) and teres major (green arrows) tendons at their insertion. The intact pectoralis major (pink arrow) tendon is also seen:

In addition to tears of the latissimus dorsi and teres major, this patient had a posterior labral tear (red arrow) and an associated paralabral cyst (yellow arrows), additional information provided by the MR arthrogram:

Tears of the latissimus dorsi and teres major are uncommon injuries, usually seen in competitive athletes, such as baseball pitchers (Leland et al., J. Shoulder Elbow Surg.18, e1-e5, 2009). The clinical signs and symptoms for both injuries are similar (Schickendantz et al., AJSM 37, 2016-2020, 2009).Typical management is non-operative, as operative intervention does not seem to improve outcome (although published studies are small in number and limited in study design). Tears or reactive tendinosis of the latissimus dorsi tendon at its insertion may present as a pseudotumor (Anderson et al., AJR 185, 1145-1151, 2005).

It is important to note that these injuries will often be seen only at the edge of the field-of-view of a standard shoulder MRI (or completely missed). Thus, if this injury is suspected clinically, it is a good idea to alert the radiologist, so that the anatomic coverage of the examination can be increased (as was done in this case).

Orchids and Subscapularis Tears

2010-05-10T06:30:00.004-04:00

Photo by van swearingen

The Star of Bethlehem orchid is one of the best arguments for the existence of evolution and natural selection.

This orchid (the Madagascan star orchid Angraecum sesquipedale) has a foot long nectar tube that hangs from its back. Darwin predicted what the pollinator of this orchid would look like, over forty years before its actual discovery:

"In several flowers sent to me by Mr. Bateman I found nectaries eleven and a half inches long, with only the lower inch and a half filled with nectar....It is, however, surprising that any insect should be able to reach the nectar....In Madagascar there must be moths with proboscides capable of extension to a length of between ten and eleven inches! This belief of mine has been ridiculed by some entomologists."

In 1903, a giant Madagascan hawk moth with such a long tongue was discovered, and was given the name Xanthopan morganii praedicta, Latin for "predicted moth".

Photo by kqedquest

Darwin was able to predict the existence of an unexpected moth in Madagascar, a striking example of the predictive and explanatory power of the theory of evolution.

In a different sphere of science, the powerful technology of MRI can predict the existence of an unexpected clinical condition. Twelve year-old boy who is a baseball pitcher, with pain after an injury:

Axial T2 fatsat image reveals a complete avulsion of the subscapularis muscle and tendon (yellow arrows). The avulsed bone and cartilage fragment (red arrows) are also seen.

A sagittal T2 fatsat image depicts visualizes the subscapularis tendon footprint, which is now replaced by fluid:

Injuries to the rotator cuff of children are often not suspected by the clinician, due to their rarity. There are only a few reports in the literature, and most of these describe injuries to the subscapularis, often avulsion fractures. The few reports that do exist about subscapularis tendon injuries often describe this injury in throwing athletes, although other sports can be involved, including wrestling and hockey.

Conventional radiographs and CT may reveal a flake of bone related to the avulsion injury. Even when radiographs are initially normal, repeat radiographs several weeks after injury may reveal soft tissue calcification in some cases (Tarkin et al, AJSM 2005, 33:596-601). MRI is very useful in this patient population, as it will assess the shoulder area for multiple causes of pain, including growth plate injuries, rotator cuff tears, and glenohumeral instability.

Thus, when evaluating an adolescent athlete with shoulder pain, one must keep in mind the possibility of an injury to the rotator cuff, particularly when symptoms suggest rotator cuff dysfunction.

References
1) Tarkin et al., "Rotator Cuff Tears in Adolescent Athletes", AJSM 2005, 33:596-601.
2) Kleposki et al., "Rotator Cuff Injuries in Skeletally Immature Patients", Orthop Nursing 2009, 28:134-138.
3) Sugalski et al., " Avulsion Fracture of the Lesser Tuberosity in an Adolescent Baseball Pitcher", AJSM 2004, 32:793-796.
4) White and Riley, "Isolated avulsion of the subscapularis insertion in a child. A case report". JBJS Am 1985, 67:635-636.

Ecclesiastes and an Ankle Fracture

2010-04-11T15:12:00.001-04:00

Photo by jimforest

"What has been will be again, what has been done will be done again; there is nothing new under the sun."

This is perhaps the most famous quote from Ecclesiastes, one of the books of the Bible, and it certainly rings true. Although there are many exciting new developments in medicine every year, patients still contract the same illnesses and undergo the same injuries they did long ago.

24 year-old male with a history of a twisting injury to the foot:

(A) Sagittal T2 fatsat and (B) sagittal T1 images reveal an avulsion fracture (red arrows) of the extensor digitorum brevis (EDB) tendon, at its origin from the calcaneus.

A small flake of bone can be seen on a conventional radiograph:

(A) Oblique axial intermediate and (B) oblique axial T2 fatsat images also show avulsed bone fragment (red arrows):

This injury was described by Norfray et al. in 1980 (AJR 134:119-123, 1980), who described the distinctive conventional radiographic findings of this injury. Radiographs of 100 consecutive emergency room patients with clinically suspected ankle fractures occurring during the winter of 1978-79 were reviewed. Most resulted from slipping on ice, or falling over snow-covered obstacles. The avulsion fracture was identified in 10 of 100 patients. Clinically, the point of maximum tenderness was similar to the area of maximum tenderness in fractures of the anterior process of the calcaneus. Thus, these fractures of the anterior process of the calcaneus and EDB avulsion fractures cannot be differentiated clinically, but only by imaging.

Avulsion fractures of the calcaneus can occur at multiple sites, including the attachment of the Achilles tendon, bifurcate ligament, plantar fascia, and the abductor hallucis (Pelletier and Kanat, J Foot Surg, 29:268-271, 1990). All of these injuries can be identified by MRI.

Avulsion fractures were common thirty years ago, and were usually found on x-rays. Avulsion fractures are still common today; there truly is nothing new under the sun. The only thing that is different is that some of these patients will have MRI scans, and the radiologist must be able to recognize these injuries.

A Torn Meniscus and the Moon

2010-03-14T20:02:00.004-04:00

The menisci of the knee are crescent-shaped pieces of cartilage which lie between the femur and tibia, and serve to cushion the weight of the body and reduce friction during movement. Here is a view of the menisci from above, looking down on the tibia, depicting the medial meniscus (blue arrows) and the lateral meniscus (green arrows):

You can see why these pieces of cartilage are called menisci, from the Greek "meniskos", or "lunar crescent". Consider the similarity to the crescent of the moon:

Images from a knee MRI of a 59 year old male, who heard a "pop" walking down some steps, and had subsequent knee pain:

This coronal T2 fatsat image identifies a torn medial meniscus, with an inferiorly displaced meniscal fragment (red arrow). There is a trace of marrow edema (yellow arrow) subjacent to the torn meniscus.

A series of sagittal images (medial to lateral) identifies the displaced meniscal fragment (red arrows) as well as the adjacent truncated undersurface of the meniscus (blue arrows):

An axial intermediate image also visualizes the displaced meniscal fragment:

A magnification of this axial view better shows the meniscal fragment (red arrows) underneath the posterior oblique ligament (green arrow):

Inferiorly displaced flap tears were first described in the radiology literature by Lecas et al. (AJR 2000; 174:161-164). More recently, McKnight et al. (Skel Rad 2010: 39:279-283) have described common patterns of displaced meniscal tears on MRI. They noted that meniscal fragments can be displaced inferiorly or superiorly, and displaced tears can affect both the medial and lateral meniscus. As noted by both authors, flap tears that are displaced peripherally can be overlooked at arthroscopy, as they are not immediately visible to the arthroscopist.

The patient in this case was taken to arthroscopy. In this arthroscopic image, we see the torn meniscus located between the femur and tibia. Note that the displaced meniscal fragment is not apparent:

The arthroscopist was alerted to the presence of the fragment by the preoperative MRI, and used a hook to probe the region in question:

This enabled the arthroscopist to deliver the displaced fragment back into the joint:

The displaced fragment was then resected, and the meniscus trimmed back to a stable rim.

This case illustrates the type of important information a preoperative MRI can provide to the orthopedic surgeon. This information enhances appropriate pre-operative planning, and maximizes the ability of the surgeon to provide optimal care to the patient.

Pearls and Ganglion Cysts

2010-02-14T15:19:00.008-05:00

Our bodies can develop various lumps and bumps, and when they are near the skin surface, they become noticeable. Various terms are used to describe these bumps, often at the whim and creativity of the clinician e.g. "pea-sized", "pearl sized", and the like.

A real pearl is a hard, rounded object composed of calcium carbonate, created within a living mollusk:

They come in various colors, and are treasured for their beauty. The vast majority of pearls are cultured pearls, as natural pearls are quite rare.

A common pearl-sized bump in the area of the wrist is a ganglion cyst. Here is an example of a ganglion cyst on the volar side of the wrist:

Photo by Glen E. Malone

When they arise from the volar aspect of the wrist, common locations include the radioscaphoid/scapholunate interval, scaphotrapezial joint, pisotriquetral joint, and the metacarpotrapezial joint. When they arise dorsally, they are typically near the scapholunate joint and dorsal wrist capsule. Other sites include the extensor tendons, the carpal tunnel, and the Guyon canal. Ganglions may also arise within bone; these are called intraosseous ganglion cysts. Finally, ganglions can also arise near and within tendons and ligaments.

In this case, a 34 year-old female presented with a dorsal wrist mass. Axial T1 image reveals a smoothly marginated mass (red arrows) deep to the ECRL and ECRB tendons:

Axial T2 fatsat image shows the mass to be of homogeneous fluid signal intensity:

Coronal intermediate and T2 fatsat images depict the ganglion cyst (red arrows) and demonstrate a small neck (green arrows) leading to the scapholunate ligament (yellow arrows):

Dorsal ganglion cysts are often related to the scapholunate (SL) ligament. The SL ligament typically can still be identified, but is often increased in signal, indicating tissue degeneration.

When one detects a ganglion cyst on imaging, it is important to look for a "neck" or "pedicle", as in this case. The neck often points to the origin of the cyst, which can be important presurgical information.Small dorsal ganglia may not be palpable clinically, but may be painful. Cysts can get larger and smaller over time, and can resolve spontaneously in some cases. An excellent review of wrist ganglion cysts has been written by Gude and Morelli, and is worth reading. They have a nice section on management of ganglion cysts, with a fascinating description of alternate, historical methods of treatment:

Heister in 1743 had this recommendation: “The inspissated matter of a ganglion may often be happily dispersed by rubbing the tumor well each morning with fasting saliva and binding a plate of lead upon it for several weeks successively … Others … prefer a bullet that has killed some wild creature, especially a stag. Sometimes, indeed, a recent ganglion will speedily vanish … by adding a repeated pressure with the thumb or a wooden mallet. If none of these means prove effectual … they may be safely removed by incision provided you are careful to avoid the adjacent tendons and ligaments. But as for rubbing them with the hand of a dead man and the like … I presume, my reader will excuse me from insisting on them”

We now have different means to manage ganglion cysts, typically surgical excision. Not as creative as the methods described by Heister, but more effective....

Ankle Sprains and a "New" Lateral Ligament

2010-01-16T22:00:00.004-05:00

Photo by sarowen

Ankle sprains are extremely common injuries, with virtually every active individual sustaining one sometime in their lives. The most frequent ankle sprain is an inversion injury, typically resulting in injuries of the lateral ligaments.

The commonly known lateral ligaments are the anterior talofibular, calcaneofibular, and posterior talofibular ligaments. A recent article by Pastore et al. (AJR 192:967-973, 2009) beautifully describes some lesser known ligaments of the ankle, including the lateral talocalcaneal ligament.

The lateral talocalcaneal ligament (LTCL) is located in close proximity to the calcaneofibular ligament, but is just anterior and medial to it. The LTCL can be difficult to separate from the calcaneofibular ligament on MRI due to their close relationship. With 3T MRI, one will typically see the LTCL as a distinct structure, and it should not be confused with the calcaneofibular ligament.

Coronal intermediate images, posterior to anterior, reveal the familiar calcaneofibular ligament (green arrows) coursing from the calcaneus, superiorly and anteriorly, to attach on to the fibula. The LTCL ligament (red arrows) is easily identified, clearly distinct from the calcaneofibular ligament.

Axial proton density images, superior to inferior, show the relationship of the calcaneofibular ligament (green arrow) and the LTCL (red arrow):

The clinical significance of injuries of LTCL injuries is still uncertain, but I have seen this ligament injured in many individuals, often in conjunction with ATFL injuries.

Hydrogen Precession Frequencies and a Trillion Dollars

2009-12-20T14:24:00.005-05:00

The microcosmic, relativistic, and quantum worlds often work in counter-intuitive ways. The twin paradox is a famous example of a puzzling, non-intuitive phenomenon in the theory of special relativity.

Photo by phil h

Our real-world experiences often do not apply to the quantum universe, where strange particles such as quarks and leptons rule the roost. The scale of this world is difficult to comprehend, let alone the bizarre behavior that one encounters in this realm.

In this world, we run into the terms "micro" and "million", and often encounter the terms "nano, "pico", "billion", and "trillion". These are hard terms to understand at a gut level.

Clinical MRI depends on the physical properties of the hydrogen atom, which has a precession frequency of 64 million hertz at 1.5 Tesla. Perhaps we can grasp the size of this number by looking at something that has been in the news over the last few months— trillion dollar financial deficits in the United States. How bad is that, really?

Some time ago, I heard a story on NPR radio that helped me better understand how big these numbers are.

Let's ask a simple question: how long does it take to count to a million, if we assume that it takes one second to say each number out loud? How about a trillion? Here is a table that gives the results:

(click on image to enlarge)

It takes 12 days to count to 1 million, 32 years to count to 1 billion, and 32,000 years to count to 1 trillion.

If we step back twelve days, what we were doing is easily in our memory. If we step back thirty two years, that is in the memory of most readers of this blog (even if that memory is a bit dim). If we step back thirty two thousand years, we would find Neanderthals huddling in caves!

Hydrogen atoms spinning 64 million times a second are the basis of clinical MRI at 1.5 Tesla. Pretty fast, but not as fast as a government can spend money every year....

Hemarthrosis and a Stable Knee

2009-11-25T19:40:00.003-05:00

Photo by speedye

November is football season in America, and physicians will see a surfeit of gridiron-related knee mishaps in this month. The usual culprits are injuries to the anterior cruciate ligament, medial collateral ligament, and the menisci, but occasionally one will see rarer injuries.

In this case, a 16 year-old high school football player felt a "pop" over the lateral aspect of his knee, and presented with pain and swelling, but had a stable knee on exam.

Sagittal T2 fatsat image reveals a hemarthrosis with a fluid-fluid level (red arrow) and moderate edema within the popliteus muscle (yellow arrow).

The popliteus muscle originates from the posterior shaft of the tibia, and inserts on the lateral femoral condyle:

Axial images from (A) the patient and (B) a normal individual for comparison reveal an irregular popliteus tendon (red arrows) in the injured football player. Compare with a normal popliteus tendon (green arrow):

Coronal intermediate images from (A,B) the patient and (C,D) a normal comparison individual delineate the nature of the injury:

(click on image to enlarge)

There is an avulsion fracture involving the popliteus (red arrows = abnormal popliteus; green arrows = normal comparison popliteus). Note the hypointense bone avulsion fragment (blue arrows), which was confirmed on conventional radiographs (not shown)

More coronal images, posterior to anterior:

(click on image to enlarge)

Red arrows = popliteus tendon; black arrows = fibular collateral ligament; blue arrows = avulsed bone fragments; pink arrow = combination of torn tendon and bone.

The patient had no other injuries, with normal menisci, collateral ligaments and cruciate ligaments. Isolated avulsion of the popliteus tendon is a rare injury. It was originally described by Naver and Aalberg in 1985, and this injury was also reported in two adolescent patients by Garth et al. in 1992 (JBJS 74:130, 1992). They stated that isolated avulsion of popliteus should be considered in the setting of a traumatic hemarthrosis. One may see a small flake of bone next to the lateral femoral condyle on radiographs, a clue to the diagnosis. In some patients, the tendon may retract out of the joint.

Thus, in the setting of lateral pain, traumatic hemarthrosis and a stable knee, one should examine the popliteus tendon carefully for signs of an avulsion injury.

Weightlifting and the Distal Clavicle

2009-10-30T06:04:00.001-04:00

Photo by greg westfall

Weightlifting is an ancient sport, dating back to ancient China, Egypt, and Greece. I'm sure that even before these recorded competitions, there were plenty of contests of brute strength, including lifting heavy rocks:

The original Olympics did not include weightlifting as an event, but it was still a popular pastime in ancient Greece. Weightlifting continues to this day, and one popular exercise is the bench press:

Photo by Justin Berndt

This exercise places a great deal of strain on the glenohumeral (shoulder) joint and the adjacent acromioclavicular (AC) joint. One consequence of repeated increase strain on the AC joint can be osteolysis of the distal clavicle.

In this case a 36 year-old female felt the gradual increase of shoulder pain while increasing the number of pushups she was doing daily. She then experienced an abrupt increase in her pain after moving luggage from overhead compartment in a plane. Her orthopedic surgeon sent her for an MRI:

Sagittal T2 fatsat image reveals striking bone marrow edema (yellow arrow) within the distal clavicle.

On an axial T2 fatsat image, there is a linear, hypointense fracture line (yellow arrows) within the subchondral bone:

A coronal intermediate-weighted image confirms the presence of the subchondral fracture:

Repetitive stress can lead to bone marrow edema and a subchondral fracture line within the distal clavicle. Demineralization and bone resorption may follow. (Textbook of Arthroscopy; Miller, M. and Cole, B.; 178-179, 2004 and Kassarjian et al.; Skel. Rad. 36:17-22, 2007)

On physical examination, patients have point tenderness over the affected AC joint. The range of motion of the glenohumeral joint is typically not affected.

Thus, a subchondral stress fracture may be the earliest MRI manifestation of distal clavicular osteolysis.

Horse Racing and Foreign Bodies

2009-10-03T10:02:00.001-04:00

Photo by raymond

Horse racing is an ancient sport. Its origins date back to about 4500 B.C, among the nomadic tribesmen of Central Asia (who first domesticated the horse). The sport has a history of nobility, but interest in the sport can be found at all rungs of the societal ladder. In the modern world, organized horse racing is done at a racetrack. Many horse racing tracks are quite old, and are constructed mostly of wood.

In this case, a 71 year old woman went to a race track four weeks ago, and felt a sharp pain as she ran her hand along a wooden railing. Her clinician suspected a wooden splinter, but was unable to detect one on clinical examination. She was sent for an MRI:

Sagittal T2 fat sat image reveals a linear structure (red arrow) surrounded by fluid.

Axial and coronal T2 fatsat images confirm the presence of a wooden splinter:

What is the best test for a foreign body? While MRI can reveal foreign bodies, it is not very sensitive for the presence of non-metallic foreign bodies. Thus, despite what we see in this case, if the clinical question is "rule out foreign body", one should generally start with an x-ray. If this is negative, one can go on to CT or ultrasound, with the choice depending many times on local clinical practice.

Remember— while MRI can detect foreign bodies, it is not the ideal test, particularly if the foreign body is non-metallic in nature.

Extensor Digitorum Brevis Muscle Edema

2009-09-06T07:00:00.000-04:00

A 32 year-old male suffered an MVA 3 months ago, and was sent for an ankle MRI due to persistent ankle pain.

(A) Oblique coronal T1-weighted and (B) Oblique coronal T2 fatsat images at slightly different slice positions reveal mild atrophy and striking edema within the extensor digitorum brevis (EDB) muscle.

The traumatic event was three months ago, and it would be unusual for muscle edema to persist this long after an injury. After digging into the clinical history a little further, it came to light that the patient had suffered an injury to his common peroneal nerve at the level of the fibular head, due to a motor vehicle accident.

Thus, the atrophy and edema of the EDB muscle in this case is due to denervation. The differential diagnosis for intramuscular edema is quite broad, and includes trauma, infection, myositis of various etiologies, and systemic diseases such as dermatomyositis.

The most common cause of extensor digitorum brevis muscle edema is trauma. In the proper clinical context, one should also consider the possibility of anterior tarsal tunnel syndrome. In this disorder, the deep peroneal nerve is trapped/compressed as it travels under the extensor retinaculum. Patients complain of dorsal foot pain. Examination will reveal a sensory deficit in the area between the first and second toes and paresis and atrophy of the extensor digitorum brevis. This syndrome is further discussed in a beautiful review of foot and ankle entrapment by Delfaut et al. (Radiographics 23:613, 2003).

Sesamoids and Lateral Ankle Pain

2009-07-18T06:02:00.002-04:00

The term 'sesamoid', coined by Galen, is derived from the flat, oval seeds of the Sesanum indicum plant.

Sesame Plant

The largest sesamoid bone in the body is the patella, a sesamoid within the extensor mechanism of the knee.

The peroneus longus muscle plantar flexes and everts the foot. A sesamoid bone called the os peroneum may be present within the peroneus longus tendon. Many support the idea that the os peroneum is always present, but the os peroneum is completely ossified in only about 20% of the population. It may also be cartilaginous or fibrocartilaginous in nature. The os peroneum is multipartite in some individuals.

In this case, a 23 year old female presented with lateral ankle pain.

(A) Oblique axial intermediate and (B) Oblique axial T2 fatsat images depict globular areas of abnormal signal red arrows) within the peroneus longus tendon. There is adjacent soft tissue edema (yellow arrows)

Examination of a lateral radiograph of this area reveals a markedly enlarged, multipartite os peroneum (red arrows):

(A) Oblique axial intermediate and (B) Oblique axial T2 fatsat images immediately proximal to the enlarged, fragmented os peroneum identify focal longitudinal splits (red arrows) within the peroneus longus tendon.

This is an example of painful os peroneum syndrome, with superimposed partial tearing of the peroneus longus. Painful os peroneum syndrome is associated with a spectrum of conditions that includes one or more of the following: (1) acute os peroneum fracture or a diastasis of a multipartite os peroneum, either of which may result in a discontinuity of the peroneus longus tendon; (2) chronic os peroneum fracture or diastasis of a multipartite os peroneum with callus formation; (3) attrition or partial rupture of the peroneus longus tendon, proximal or distal to the os peroneum; (4) frank rupture of the peroneus longus tendon with discontinuity proximal or distal to the os peroneum; (5) enlarged peroneal tubercle on the lateral aspect of the calcaneus which entraps the peroneus longus tendon and/or the os peroneum during tendon excursion (Foot Ankle Int. 15:112-24, 1994).

One must be careful not equate abnormal signal within the peroneus longus tendon at the level of the calcaneocuboid joint with a tendon tear. I have had more than one phone call from a foot and ankle surgeon asking why a radiologist commented on a peroneus longus tear, and did not mention the os peroneum, which was clearly present on x-rays.

While the os peroneum is obvious on x-ray, it is often much less apparent on MRI, which is insensitive to the presence of calcification and mineralized bone (unless it contains fatty marrow).

When abnormal signal is present in the peroneus longus tendon at the level of the calcaneocuboid joint on MRI, one should consider the possibility of os peroneum syndrome, and correlate with conventional radiographs.

Cellular Hyperplasia and a Thumb Bump

2009-06-20T08:04:00.005-04:00

Hypertrophy and hyperplasia are common medical terms. Doctors, like lawyers, tend to come up with single words or short phrases to summarize important concepts. Both professions develop a lexicon that is sometimes impenetrable to the uninitiated.

Fortunately, hypertrophy and hyperplasia are simple concepts. In hypertrophy, cells increase in size. In hyperplasia, cells increase in number:

In this case, a 15 year old patient presented with a thumb mass that had been present for about 6 months:

Axial images of the thumb reveal an oval mass (red arrow) corresponding to the clinically palpable abnormality. The mass has a tubular-appearing T2 hyperintense rim which enhances following the administration of gadolinium.

(A) Sagittal and (B) Coronal intermediate weighted images with fat saturation through the lesion reveal hypointense material within the center of the lesion.

Here are images from a different patient, also with a thumb mass:

(click on image to enlarge)

Multiple images through the lesion reveal that this lesion has an appearance almost identical to the first, with a tubular T2 hyperintense rim that enhances following the administration of gadolinium (red arrows). This lesion also has hypointense material more centrally (green arrows).

Both of these lesions were excised, and were confirmed to be cases of intravascular papillary endothelial hyperplasia (IPEH), also known as Masson's tumour. An excellent description of this condition is provided by Dr. Sampurna Roy.

IPEH is a reactive condition representing an unusual form of organizing thrombus. Masson's tumour may either occur in pure form (primary), as a focal change in a preexisting vascular lesion (hemangioma, pyogenic granuloma, or vascular malformation) and rarely in an extravascular location as a result of organization of a hematoma.

The lesion may occur in any blood vessel in the body, but is commonly located on the fingers, head and neck and trunk. It is typically seen as a small (less than 2 cm in diameter), firm, blue or purple nodule. This lesion has been reported to occur deep in the body, including the liver (J Korean Med Sci 19:305, 2004) and renal sinus (Jap J Clin Oncol 27:433, 1997)

Multiple small, delicate papillary structures project into the lumen and these are associated with thrombus. These projections and associated thrombus presumably give rise to the T2 hypointense material seen in the central aspect of the lesions presented here.

This lesion has an excellent prognosis and is usually cured by simple excision.

If you see a hand lesion with a tubular T2 hyperintense rim that enhances, with a T2 hypointense center, one should think of the diagnosis of IPEH.

Blogs and Google Analytics

2009-06-05T19:45:00.000-04:00

One of the benefits of blogging on the Google platform is that you have access to Google Analytics. This service will give you insight into who is reading a given blog.

Here, for example, is a snapshot of where traffic to this blog comes from:

(click on image to enlarge)

Blogging is a great way to distribute information. It is not a replacement for other forms of communication, but is a valuable adjunct. You don't have to supersede a format to be relevant.

This blog has been included in the "Top 50 Radiology and Sonography Technician Blogs", and I thank them for the inclusion. I hope that this blog stimulates its readers, and helps medical caregivers take better care of their patients.

Oily Fish and Enhancing Masses

2009-05-23T07:20:00.000-04:00

This is a photograph of a herring, a small, oily fish of the genus Clupea found in the shallow, temperate waters of the North Pacific and the North Atlantic, including the Baltic Sea.

Most people are familiar with the term "red herring". In the investment world, a red herring is associated with initial public offerings (IPOs). A red herring is a preliminary registration statement that must be filed with the SEC describing a new issue of stock and the prospects of the issuing company.

Outside the financial world, a red herring is an item or event that distracts the observer from what is truly important. The origin of the term is somewhat controversial but most associate it with hunting. When herrings are cured, they turn red and acquire a distinctive smell. Hunting dogs were taught to follow a trial by following the scent of a herring that was dragged along the ground. Red herrings may also have been used to confuse the hounds in order to prolong a fox hunt or to test their ability to stay with a scent.

Occasionally, we run across red herrings in medicine as well. In this case, a 35 year-old female presented to her physician with a mass behind the elbow. She was sent for an MRI:

(A) Coronal T1-weighted and (B) T2 fatsat images reveal a T2 hyperintense mass (red arrows) corresponding to a clinically palpable abnormality.

An axial T2 fatsat image confirms the mass (red arrows) under a skin marker placed by the technologist (yellow arrow):

(A) Axial precontrast T1 fatsat and (B) postcontrast T1 fatsat images obtained immediately after IV contrast administration reveal strong enhancement associated with the lesion, which has irregular margins:

The history obtained by the MRI technologist reported no history of recent trauma. Given this, a differential of various neoplastic entities was offered, and the patient was referred to an orthopedic oncologist.

Up to this point, the patient had proceeded at a breakneck pace through the medical system. At the orthopedic oncologist, things finally slowed down. The astute orthopedic oncologist obtained a careful history, which included a possible history of a bleeding disorder. After careful consideration, he opined that this was likely a hematoma, despite the strong enhancement seen on MRI.

Over the next several weeks, the mass decreased in size, and a follow-up scan eight weeks later confirmed resolution of the hematoma:

This case illustrates many things, not the least of which is the importance of an accurate clinical history. It is also a good example of how hematomas can rarely enhance, particularly along their periphery. Cases have been described of chronically expanding hematomas which enhance, simulating a neoplasm (Skel Rad 35:1432, 2006)

Although gadolinium enhancement is often associated with neoplasms, in some cases it can be a red herring, as this case illustrates.

Shoulder MR Arthrography and Butterflies

2009-05-08T22:29:00.002-04:00

Insects often uses camouflage to hide from predators. Can you find the butterfly in this picture?

Photo by plj.johnny

Click on image to enlarge

Although arthrography (the placement of contrast within a joint) generally increases the accuracy of MRI, on occasion the contrast can camouflage important findings.

In this case, a patient with chronic shoulder pain was sent for an MR arthrogram. Here is a T1-weighted image with fat saturation:

Here is the corresponding T2-weighted image with fat saturation:

Do you see anything important?

Here are the two images next to each other:

(A) T1-weighted image with fat saturation and (B) T2-weighted image with fat saturation reveal a lobulated paralabral cyst (red arrows) adjacent to the anterosuperior labrum. Note how the hyperintense fluid within the joint on makes this lesion more difficult to perceive on the T2-weighted image. As expected, the paralabral cyst is hypointense on the T1-weighted image.

I have seen several cases where paralabral cysts are missed, because they blend in with the hyperintense joint fluid on T2-weighted images. This is unfortunate, as the presence of a paralabral cyst in the shoulder is highly predictive of a labral tear.

Axial image from the same patient identifies the paralabral cyst (red arrow) and the adjacent tear of the anterosuperior labrum (yellow arrow):

Thus, on MR arthrograms, be careful not to miss paralabral cysts on T2-weighted images, due to the presence of adjacent bright joint fluid.

Did you manage to find the butterfly? Here it is (yellow arrows):

Shoulder MR Arthrography

2009-04-25T05:42:00.003-04:00

Photo by Cesar R.

Many different people from all walks of life look at this blog. The kaleidoscopic panoply that the web offers to both the writer and viewer is astounding.

The intended main audience of this blog is the radiology community, but orthopedic surgeons, other health care professionals and patients also view this blog. In this entry, we will address an area that will interest primarily orthopedic surgeons— the interpretation of shoulder MR arthrograms.

A potential point of confusion in MR arthrography is the similar image contrast of two pulse sequences that are often used: T1-weighted image with fat saturation, and T2-weighted images with fat saturation.

Note how similar these images appear:

(A) T1-weighted image with fat saturation and (B) T2-weighted image with fat saturation depict hyperintense contrast within the joint (yellow arrows) and fluid in the subacromial-subdeltoid bursa (green arrows).

It is quite important not to confuse T1-weighted images with T2-weighted images. Pure fluid will be bright only on the T2-weighted image, while contrast will be bright on both pulse sequences. In this example, the bursal fluid is hypointense on the T1-weighted image, and hyperintense on the T2-weighed image, while contrast in the joint is hyperintense on both pulse sequences, as expected.

Since the overall appearance of these pulse sequences is so similar, how is one to quickly distinguish between these two images? For coronal images, most centers use spin echo images, and do not use gradient echo in the coronal plane. With this assumption, one can easily identify a T1-weighted image simply by looking at the TR that is used. If the TR is less than 900, it can be considered a T1-weighted image:

The TR in this case is 566 (yellow arrow). Thus, we know that this is a T1-weighted image. Again, this rule holds true for spin echo images, not for gradient echo images.

In MR arthrography, one reliable sign of a rotator cuff tear is contrast entering the tendon. If the tear is full-thickness, the contrast will leak into the subacromial-subdeltoid bursa.

There are two exceptions to this rule. First, in the case of a partial-thickness bursal surface tear (a tear of surface of the tendon facing away from the joint), contrast will not enter the tendon. The tear is on the bursal surface and contrast is contacting the intact articular surface of the tendon. The other exception to this rule is when there is an intrasubstance tear of the tendon; contrast cannot enter the tear because there is a layer of intact tendon separating the tear from the contrast within the joint.

Consider this full-thickness tear:

(A) T1-weighted image with fat saturation and (B) T2-weighted image with fat saturation depict contrast within the joint (yellow arrows). Note the presence of contrast within the subacromial-subdeltoid bursa (red arrows) due to the full-thickness tear within the distal supraspinatus tendon (green arrow)

This is contradistinction to this case of a partial-thickness, articular surface tear of the supraspinatus tendon:

(A) T1-weighted image with fat saturation and (B) T2-weighted image with fat saturation depict a partial-thickness articular surface tear (red arrows) of the supraspinatus tendon. Contrast enters the tear, and the tear is seen as a hyperintense area on both pulse sequences. Although there is a small amount of hyperintense fluid in the subacromial-subdeltoid bursa on the T2-weighted image, no contrast enters the bursa. Thus, this is a partial thickness tear.

Finally, consider this case:

(A) T1-weighted image with fat saturation and (B) T2-weighted image with fat saturation depict contrast within the joint (yellow arrows). Note the intrasubstance tear (red arrow) of the distal supraspinatus tendon, seen as a hyperintense zone on the T2-weighted image. Note that contrast does not enter this area since the tear does not communicate with the articular surface of the tendon. There is hyperintense fluid in the subacromial-subdeltoid bursa on the T2-weighted image, but this area is hypointense on the T1-weighted image. This fluid should not be confused with contrast in the bursa.

Accurate interpretation of MR arthrograms hinges on your ability to distinguish between various pulse sequences. It's worth remembering this little trick of simply looking at the TR to distinguish between T1-weighted and T2-weighted images.

Fruit Flies and Tarsal Coaltion

2009-04-11T07:00:00.005-04:00

Those of you who took genetics in college might recognize this little creature:

This is the fruit fly, Drosophila melanogaster, which has delighted geneticists and tortured premed students for decades. I still can smell the ether we used to anesthetize these buggers as we struggled to understand Mendelian inheritance in my college genetics class.

Far apart in the tree of life, humans and Drosophila nonetheless share major portions of DNA. One such DNA sequence is the homeobox, which encodes transcription factors that play a major role in limb development. These DNA sequences are conserved across vast distances in the phylogenetic tree— for example, a fly can function perfectly well with a chicken homeotic gene in place of its own.

Hox genes are a subgroup of homeobox genes. In vertebrates these genes are found in gene clusters on the chromosomes. In mammals four such clusters exist, on four different chromosomes.

Mutations in hox and other genes can cause multiple genetic anomalies, including segmentation errors. Segmentation errors can lead to fusion of bones in the foot, a phenomenon known as tarsal coalition.

Tarsal coalition has been know about for hundreds of years, although the genetic basis is only being investigated in the modern era. The first written description of tarsal coalition was by Buffon in 1769. The first radiologic depiction of tarsal coalition took place in 1898, only three years after Roentgen described x-rays.

The most common types of tarsal coaliton are calcaneonavicular and talocalcaneal coalitions, These variants are commonly seen by every busy radiologist that reads MRI scans of the foot and ankle.

39 year old female training for 10 mile run, who recently increased running up to seven miles a day, and complained of distal leg pain:

(A) Sagittal T1 and (B) Sagittal T2 fatsat images depict a stress fracture (red arrow) of the distal tibial metaphysis. Note the striking marrow edema, seen best on the T2 fatsat image.

One must be cautious about satisfaction of search, however, and examination of the remainder of the examination reveals a second finding:

(A) Sagittal T1 and (B) Sagittal T2 fatsat images display a predominantly fibrous coalition (red arrow) between the navicular (green arrow) and the cuboid (blue arrow) bones.

The coalition (red arrow) is nicely seen between the navicular (green arrow) and the cuboid (blue arrow) on this coronal intermediate image:

An oblique axial T2 fatsat image reveals marrow edema on both sides of the abnormal joint, reflecting abnormal stress:

Coalitions between the cuboid and navicular are rare, accounting for less than one percent of tarsal coalitions. Coalitions are often treated nonsurgically, but when necessary, they can be surgically resected.

Humans run and flies use their wings to get from place to place, but they both share common DNA. Errors in the DNA code in critical areas of either species can lead to segmentation anomalies in both.

Dislocated Sesamoid Bone

2009-03-27T19:08:00.009-04:00

What is the largest sesamoid bone in the body?

Medical and biologic mavens will regard this question as a "gimme"— the largest sesamoid bone is the patella. A sesamoid bone is a bone embedded within a tendon. These bones often resemble a sesame seed, hence the name.

Sesamoid bones are said to increase the moment arm of the tendon in which they are embedded.

The patella can sometimes dislocate from its normal position in the trochlear groove of the femur. This dislocation event is typically lateral in direction, and can be confused clinically with a tear of the anterior cruciate ligament. The MRI findings of lateral patellar dislocation events have been described in several excellent articles. These findings can include osteochondral injuries to the medial patella and lateral femoral condyle, tears of the medial patellofemoral ligament, and bone bruises of the inferomedial patella and anterolateral femoral condyle.

In this case, a forty-year old male sustained a knee injury while doing martial arts 1 week ago. Axial T2-weighted image with fat saturation identifies bone bruises (red arrows) in the medial patella and anterolateral femoral condyle.

An axial intermediate-weighted image depicts a large osteochondral defect in the patella (red arrows). Note the undamaged patellar cartilage (green arrows) in the lateral patella:

Interestingly, there is a corresponding large chondral defect (red arrows) in the lateral femoral condyle:

This chondral defect is at the posterior margin of the bone bruise, a characteristic location described by Sanders et al. (AJR 187:1332, 2006). Chondral debris (white arrow) is found in the suprapatellar joint recess. There is also a tear of the anterior horn of the lateral meniscus (yellow arrow) in this patient:

An axial T2 weighted image with fat saturation better defines the jagged nature of this chondral lesion:

Thus, shearing cartilage injuries of the lateral femoral condyle can occur in the setting of lateral patellar dislocation events. This lesion is more common in young patients, but can occasionally be seen in older individuals as well, as this case illustrates.

Calf Pain- is it my Achilles Tendon?

2009-03-13T20:40:00.008-04:00

Achilles was a mythical Greek warrior, most famous for his role in the Trojan war. A mighty fighter, Achilles killed the Trojan Hector, as reenacted in this scene from the movie "Troy".

Achilles was the son of the nymph Thetis and Peleus, the king of the Myrmidons. When Achilles was born, his mother tried to make him immortal by dipping him in the river Styx. However, he was left vulnerable at the part of the body she held him by, his heel (Wikipedia).

The Achilles tendon is aptly named- a complete tear of this structure is a devastating injury, often career ending for many athletes.

The Achilles tendon (also known as the triceps surae), is formed by the confluence of the medial gastrocnemius, lateral gastrocnemius, and soleus muscles. Achilles tendinopathy and strains are a common problem, and can be clinically difficult to distinguish from tears of the distal gastrocnemius muscle, particularly the medial head of the gastrocnemius muscle.

Another tendon that is in close proximity to the Achilles is a thin, rope-like tendon known as the plantaris. This tendon typically tears in the upper leg, and the examiner can be hard-pressed to distinguish between a tear of the medial head of the gastrocnemius muscle, a high Achilles strain/tear, and a plantaris tear.

In this case 36 year old male felt calf pain. His physician sent him for an MRI, with a prescription stating, "MRI right distal leg, possible Achilles tear".

The MRI technologist read the prescription, and (appropriately) imaged the distal leg:

Note that the Achilles tendon is absolutely pristine on this T1-weighted image.

It is at this point that the MRI technologist proved himself a master of his craft. He had interviewed the patient, and noted that the pain was actually in the mid calf, more than the distal calf. The technologist then slid the patient out of the MRI magnet and switched coils (a coil is a device used to pick up the MRI signal), and reimaged the patient. All this takes extra thought, extra time and extra care, but this is what separates the good MRI technologist from the excellent technologist.

This coronal STIR was then obtained, showing fluid in the upper calf, in a location and morphology highly characteristic of a tear of the plantaris tendon (Helms et. al, radiology 195:201-203, 1995):

The patient's fear of an Achilles tendon tear was assuaged, and the much more sanguine diagnosis of a plantaris tear was given.

The plantaris muscle originates from the lateral aspect of the distal femur, courses down the calf, and then inserts on to the calcaneus bone of the foot. Plantaris tendon tears are treated conservatively, and have an excellent prognosis, unlike Achilles tears, which have a much more prolonged recovery, and may need to be addressed surgically.

Primates, Thumbs, and de Quervain Syndrome

2009-02-27T18:29:00.001-05:00

The opposable thumb is said to be one of the key features that distinguishes humans from much of the animal world. Not all primates have an opposable thumb; only Old World monkeys and apes have this unique adaptation.

Photo by ucumari

The thumb is powered by numerous muscles. Two muscles contribute to the motion of radial abduction- the extensor pollicis brevis (EPB) and abductor pollicis longus (APL). The tendons for these muscles pass through the first dorsal compartment of the wrist, where they are surrounded by tendon sheaths. Inflammation of these tendon sheaths was first described by the Swiss surgeon Fritz de Quervain in 1895, who also described an inflammatory condition of the thyroid gland ("de Quervain thyroiditis")

In this case, a 36 year-old woman presented with wrist pain. Radiographs were obtained, and an erosion was noted at the base of the radial styloid, along with adjacent soft tissue calcification. There was some concern that this could represent a soft-tissue mass, and the patient was referred for an MRI. Coronal intermediate weighted image reveals the erosion (red arrow) at the base of the radial styloid:

A coronal gradient echo image again depicts the erosion (red arrow), and a fleck of soft tissue calcification (yellow arrow):

Chien et al. described focal radiographic abnormalities of the radial styloid as a manifestation of de Quervain disease (AJR 177:1383-1386, 2001). Axial images from our patient:

(A) Axial T1 image depicts erosion in distal radius. (B) Axial T2 fatsat image shows inflammation surrounding the APL and EPB tendons (green arrow).

Chein et al. noted that "in the appropriate clinical context, radiographic visualization of focal cortical erosion, sclerosis, or periosteal bone apposition of the radial styloid should suggest the diagnosis of de Quervain tenosynovitis". Although their report described the x-ray manifestations of de Quervain syndrome, the same findings can be depicted on MRI, as demonstrated in this case.

Twist, Turns and Tibial Torsion

2009-02-13T20:30:00.009-05:00

Twists and turns occur in nature, sometimes with great beauty, as in this nautilus shell:

The nautilus shell is an example of a logarithmic spiral, a spiral curve whose shape is unaltered with each successive curve. The logarithmic spiral was first described by Descartes and later extensively investigated by Jakob Bernoulli, who called it Spira mirabilis, "the marvelous spiral". Possibly as a result of this unique property, the spira mirabilis has evolved in nature, appearing in certain growing forms such as nautilus shells and sunflower heads. (Wikipedia).

Twists and turns can also occur in the human body. The cochlea of the ear is spiral-shaped. Spiral shapes can also be pathologic— spiral electrical waves have been linked to cardiac arrhythmias, and pathologic twists of the intestine can be life-threatening.

Pathologic twists are sometimes referred to as "torsion", as in intestinal torsion, testicular torsion, and ovarian torsion. The word "torsion" comes from the Latin and old French, meaning "wringing pain in the bowels, and "to twist".

In the musculoskeletal realm, one can encounter tibial torsion, defined as the degree of twisting between the proximal and distal articular surfaces of the tibia. There is a normal, physiologic amount of tibial torsion, but when it is excessive, tibial torsion is harmful.

Excessive tibial torsion is usually a disease of childhood, but on occasion one can encounter excessive tibial torsion in adulthood as well.

Tibial torsion can be measured using the cross-sectional imaging techniques of MRI and CT. Conventional radiographs are less reliable and reproducible than MRI and CT. There is no general consensus on where exactly to draw the reference lines used to calculate the tibial torsion angle, but one reasonable method is illustrated here:

(A) Transverse CT section through proximal tibia, just below proximal articular surface. A line is drawn bisecting the tibia. (B) Transverse CT section through distal tibia, just above distal articular surface. A line is drawn bisecting the tibia. (C) The angle between these two lines is calculated.

There are ethnic and gender differences in the tibial torsion angle, with reports studying Caucasians reporting values centered at 30-35 degrees, while studies of Japanese and Indian subjects reporting values centered at 22-24 degrees.

In the patient depicted above, the tibial torsion angle in the right leg was 56 degrees. The contralateral limb had a tibial torsion angle of 31 degrees (normal).

The abnormally high angle in the symptomatic limb was due to a tibial fracture which healed with rotation:

Although tibial torsion is typically measured on CT, one can obtain this angle using MRI as well, as long as the proximal and distal tibia are imaged in the axial plane on the same study.

Further information on the measurement of tibial torsion can be found in a nice paper by Mullaji et al. (IJO 43:309-313, 2008).

Mummies and Metal Artifact

2009-02-06T22:12:00.001-05:00

Is it a mummy or a Mummy? Sometimes your occupation determines your reaction to a word. For example, here is an artifact:

Photo by Shain Etin

To an archeologist, an artifact such as this is a boon, an insight into a past age. To a radiologist, the word means something very different. An artifact is an annoyance, a pox on what could have been a beautiful image.

Yi Zhao at the University of Chicago summarizes how the "artifact" can mean very different things:

An artifact (artefact in British spelling; from Latin arte, ablative of ars, art, and factum, neutral past participle of facere, to make), according to the Oxford English Dictionary, is “[i]n technical and medical use, a product or effect that is not present in the natural state (of an organism, etc.) but occurs during or as a result of investigation or is brought about by some extraneous agency.” This meaning of the term artifact has been in use since 1908, and contrasts with the first meaning: “Anything made by human art and workmanship; an artificial product. In Archæol. applied to the rude products of aboriginal workmanship as distinguished from natural remains,” which appeared in the early 19th century. In all meanings of the word, it signifies the presence of an artificial object or element, in contrast with a natural medium.

The word artifact has come into popular use mainly due to wide developments in imaging technologies, starting with the telescope, but especially since the invention of photography, and most recently with the proliferation of digital technologies. Although the applications of such technologies were at first primarily technical and scientific, they quickly became parts of people's daily lives (the telescope has always been a curiosity for the public, and digital photography has recently become a regular practice for most households). Therefore the current definitions of the word, not totally acknowledged by the Oxford English Dictionary, depend heavily on context, and the contexts in turn depend on technologies with which the artifact is associated.

Thus, with the advent of scientific technology and digital imaging in particular, the archeologist artifact has been transmuted to a word with negative connotations. In MRI, a common cause of artifact is metallic hardware. The degree of metal artifact is variable, and depends on many factors. Lee et al. have written a nice summary on overcoming metal artifact from metallic orthopedic implants (Radiographics 27:791-803, 2007). They point out that the degree of artifact will depend on the composition of the metal hardware, with stainless steel causing much more artifact than titanium.

Unfortunately, it can be hard to predict how much artifact a particular piece of hardware will cause. As long as the hardware is not directly in the area of interest, however, in many cases it is possible to obtain diagnostic information. For example, here is a CT topogram image from a patient with shoulder pain. She has a humeral rod in place, due to a fracture:

The presence of this much metal might lead you to think that an MRI would be markedly degraded by metal artifact, and be nondiagnostic. I am sure that many MRI scans are not ordered in this setting because the clinician thinks that the study will be nondiagnostic.

In fact, despite the presence of the rod, and resulting metal artifact, the shoulder MRI is able to clearly depict a full thickness tear of the supraspinatus tendon:

Thus, MRI may remain a reasonable option in patients with indwelling metal hardware, particularly if the hardware is titanium, and is not directly in the area to be imaged. Some modifications can be made to pulse sequences to decrease metal artifact, but these improvements are typically not dramatic. In addition, this is one setting where low-field strength MRI can be a good option, as metal artifact will be less pronounced at low field strength.

Finally, for questions about metal hardware and MRI safety, it's worth visiting Dr. Frank Shellock's outstanding website, MRIsafety.com.

Darwin and an Anomalous Muscle

2009-01-24T07:01:00.004-05:00

The theory of evolution posits that natural selection acts on the phenotypic expression of genetic variation, driving population changes over time. The classic example of genetic variation, observed by Charles Darwin, was the different appearance of the beaks of finches in the Galapagos islands:

The different beak shapes are adapted to different food sources, and affect the relative survival of various finch species. From these seminal observations, Darwin developed his theory of evolution.

Humans, like finches, also exhibit variations in their bodies. This variation is often plain to see, with different body shapes and sizes, skin color, and the like. Other variations are more subtle, and require cross-sectional imaging to detect.

In this case, a 34 year-old woman presented to a hand surgeon with a lump on the dorsum (back) of her wrist. The lump had been present for a few years, but had become more bothersome recently, exacerbated by certain activities. She was sent for an MRI:

Axial T1 and T2 fatsat images reveal a mass-like area (red arrows) corresponding to the clinical finding. The mass is close to muscle in signal intensity. A coronal image depicts the sharp contours of the mass-like area (red arrow), situated between the extensor tendons (green arrows):

Sagittal images help confirm the diagnosis of an accessory muscle, the extensor digitorum brevis manus (red arrow, figure A). Compare to an image from a normal individual (image B):

The extensor digitorum brevis manus (EDBM) muscle occurs in 1-3% of the population and may be mistaken for a mass or ganglion. The EDBM origin is variable, but the most common origin is the dorsal wrist capsule deep to the extensor retinaculum. The muscle may also arise from the distal radius or the deep carpal fascia. It typically inserts onto the extensor hood of the index finger or middle finger but may also insert into the extensors of the fourth and fifth fingers by way of either a tendon or a slip.

On MRI, extensor tendons should not have a muscular component at and distal to level of carpus. The presence of muscle tissue in this region indicates the presence of an accessory muscle.

The EDBM is usually asymptomatic, but increased use of the hand may lead to pain. Conservative treatment is pursued in most cases, but surgical removal may be necessary. Note that resection of EDBM should be avoided in cases where the EDBM is compensating for the absence of the extensor indicis proprius.

In this particular case, the patient elected to modify her activity level, rather than undergo surgery.

Nature gives finches different beaks, and humans different muscles.

Acetabular Retroversion and the Library of Congress

2009-01-16T19:16:00.008-05:00

Above is the Library of Congress— it is impressive looking, but it's very physical presence dooms it to obsolescence. Information wants to be free of physical presence and physical restraints. Wikipedia and Google "own" the Library of Congress, as my kids would say, when it comes to the accessibility of information.

Background information on the hip joint, straight from Wikipedia, one of those free sources of information:

There are three bones of the os coxae (hip bone) that come together to form the acetabulum. Contributing a little more than two-fifths of the structure is the ischium, which provides lower and side boundaries to the acetabulum. The ilium forms the upper boundary, providing a little less than two-fifths of the structure of the acetabulum. The rest is formed by the pubis, near the midline. The word acetabulum means "little vinegar cup", and was the Latin word for a small vessel for storing vinegar.

In the last few years, femoroacetabular impingement (FAI) has become recognized as a cause of hip pain in adults. Much has been written about this entity, and most physicians are now aware of FAI. The topic is complex, from a diagnostic as well as treatment standpoint.

The two main types of FAI are termed the "cam" and "pincer" forms. In this entry, we will not review FAI; rather, we will focus on how to recognize the condition of acetabular retroversion, which is associated with the pincer form of FAI.

In the normal hip, the acetabular opening is anteverted (opens anteriorly). In the retroverted condition, the superior aspect of the acetabulum is tilted posteriorly. In both normal and retroverted hips, the opening gradually tilts anteriorly as one proceeds inferiorly.

On X-ray, the anterior rim of acetabulum should always project medial to the posterior wall, in a normal anteverted acetabulum:

(A) Edge of anterior acetabular wall (green arrow) is medial to the edge of posterior wall, even in superior aspect of acetabulum. (B) Green and yellow lines denote the anterior and posterior edges of acetabular wall. Note that these lines never cross.

In cranial acetabular retroversion, the anterior rim will project lateral to the posterior wall in the superior aspect of the acetabulum. Views from a CT topogram, in a hip with cranial acetabular retroversion:

(A) Edge of anterior wall (green arrow) is medial to the edge of posterior wall (yellow arrow) in inferior segment of the hip, but in the superior segment, this relationship reverses. This leads to the "crossover sign". (B) Illustration of crossover sign, with lines drawn.

On CT and MRI, cranial acetabular retroversion is recognized by examining the first axial image that includes the femoral head. If the acetabulum is retroverted, the anterior rim of the acetabulum will be lateral to the posterior rim:

(A,C) Axial images that contain the top of the femoral head demonstrate cranial acetabular retroversion (B,C) Axial images from a different patient at a similar slice position demonstrate normal acetabular configuration at this level (anteversion).

Thus, one can recognize acetabular retroversion on both conventional radiography and cross-sectional imaging. Just know what to look for....

All that Meets the Eye

2009-01-03T07:12:00.000-05:00

Photo by badboy69

"There is more than meets the eye"— a nice summary of the ability of MRI to peer deep inside tissues.

If we compare MRI and arthroscopy, it is clear that the arthroscopist has an unparalleled visualization of surface anatomic features. Once the arthroscope is introduced into a joint, the surgeon has a marvelous view of the surfaces of cartilage, ligaments, bone, and soft tissue. While diagnostic arthroscopy is a powerful tool, it is important to remember that it only sees what is on the surface.

MRI does not approach the resolution that arthroscopy provides, but enables us to look inside tissues. Exclusive reliance on what is seen at arthroscopy can lead to underestimation of pathology.

In this case, a 36 year-old female with shoulder pain was referred for an MR arthrogram. Coronal T1 weighted images with fat saturation demonstrate a SLAP lesion (yellow arrows). There is also globular hypointense signal within the distal supraspinatus tendon (red arrows), consistent with an area of calcification within the tendon. Calcification in this area was confirmed by a CT scan (not shown).

At arthroscopy, the SLAP tear was repaired, but the calcification within the substance of the tendon could not be observed. It is clearly present, but because it is within the tendon, it was not apparent at arthroscopy.

In this case, there was no edema within the tendon or in the peritendinous tissues on MRI, suggesting that this was a clinically silent area of calcification, rather than active calcific tendinitis. The patient responded well to her SLAP repair, and became pain-free postoperatively.

The radiologist should remember that the surface resolution of arthroscopy far exceeds that of MRI. The surgeon should remember that all that is important does not meet the eye of the arthroscopist. Thus, MRI and diagnostic arthroscopy are complementary techniques. Melding the information gleaned from each discipline provides the orthopedic surgeon with maximal information.

Hunchbacks and Bony Variants

2008-12-19T22:33:00.000-05:00

Photo by TCM Hitchhiker

The Hunchback of Notre Dame is a novel by Victor Hugo, set in 1482 in Paris, in and around the cathedral of Notre Dame de Paris. It has had numerous theatrical and movie interpretations. I'm no literary snob, and have to confess that my only real exposure to this story is via Walt Disney. One of the perils of having several children is unrelenting exposure to Uncle Walt and his minions.

There are hunchbacks in the medical world as well. The os styloideum was first described by the Frenchman Fiolle, in 1932. He termed this entity the "carpe bossu", which can be translated as "hunchback carpal bone". This anatomic variant is located on the dorsal side of the wrist, at the base of the third metacarpal. It is typically a separate ossicle, but can fuse with the adjacent bones, typically the second and third metacarpals, but sometimes with the trapezoid or capitate.

The carpe bossu is usually an incidental finding, but can cause symptoms in some patients, and can be confused with a ganglion cyst. When troublesome, patients will complain of focal dorsal pain, and a tender bone mass. The lesion usually becomes symptomatic in adulthood, but can rarely present in childhood.

In this case, a fourteen year old boy presented with wrist pain, and was discovered to have a scaphoid fracture on MRI. Review of the coronal images along the dorsal aspect of the hand reveals a carpal boss (red arrows) located between the bases of the second and third metacarpals:

The carpal boss is also well seen on this sagittal T1-weighted image:

The patient also had edema-like changes within the os styloideum and the base of the third metacarpal, seen on this coronal T2-weighted image:

Interestingly, the patient did not report any symptoms referable to this region. One wonders whether this area will eventually become symptomatic, given the degree of abnormal signal in this area.

Lumbar Spine MRI— See More, Miss Less

2008-12-12T22:34:00.000-05:00

What do you see in this diagram?

Some see a vase while others see two faces looking at each other. They are both there.

"You see what you look for and recognize what you know". This is a hoary but true dictum in radiology.

When looking at an MRI, radiologists will detect a greater percentage of abnormalities if they are specifically looking for them. Radiologists are in part a product of their training, and carry with them biases learned during that process.

One place where this tends to show up is in lumbar spine MRI scans, which are interpreted by radiologists with significant differences in their training. It's easy to miss subtle abnormalities that are clinically relevant on this exam.

Early in their post-training career, musculoskeletal-trained radiologists tend to miss small disk herniations, while neuroradiology-trained radiologists tend to miss bone findings such as stress reactions and stress fractures.

Here is an example of a subtle right foraminal disk herniation:

Here is an example of stress-related changes in the posterior elements of L4:

Both are subtle findings, but in my experience, musculoskeletal-trained radiologists will be more likely be miss the first example, while neuroradiology-trained radiologists will be more likely to miss the second example.

If you keep this in mind, whatever your training, you will be less likely to miss either type of finding.

Osteomyelitis and Fly Larvae

2008-12-05T21:48:00.006-05:00

Musculoskeletal infections can be a vexing, serious problem. For example, consider knee replacement surgery, a common procedure that is done over 400,000 times a year worldwide. If postoperative infection is avoided, the outcome is typically excellent. A post-operative infection, however, will often spell trouble, and a prolonged recovery.

Over time, we have gotten better at treating infections of bones and joints, particularly with the advent of antibiotics. In the pre-antibiotic era, some novel treatments were tried, including fly larvae:

In World War II, combat induced wounds to the extremities had a 20-25% rate of osteomyelitis. By the Vietnam War, this figure had dropped to about 8%, thanks to better treatment.

In the civilian world, infection is much rarer, but can still occur. Radiologists are often asked to assess for the possibility of bone, joint, or soft tissue infection, and the define its extent.

The question of whether or not osteomyelitis is present comes up most often in the foot. Collins el al. wrote an excellent article on the use of T1-weighted images when looking for pedal osteomyelitis (AJR 185:386-393, 2005). While signal abnormalities on T2-weighted and STIR images tend to be nonspecific, they noted that T1 signal abnormality that is medullary and confluent is highly suspicious for osteomyelitis.

Since then, I have used the principles outlined in their article when analyzing pedal osteomyelitis, and have had good success. I am not aware of any articles that address the MRI analysis of osteomyelitis in the hand and wrist. Given that the hand and foot are ontogenic homologs, I have transferred the principles of Collins et al. to analysis of osteomyelitis of the hand and wrist.

In this case, a 37 year-old man was sent for a finger MRI, due to pain and swelling. He suffered an injury at his work five weeks before the MRI.

A sagittal STIR image shows extensive marrow edema (red arrows) in the middle and distal phalanx, as well as a distal interphalangeal joint effusion (white arrow):

Marrow edema and excess joint fluid are worrisome findings, but tend to be nonspecific. Next, we examine the corresponding T1 weighted image:

The T1-weighted image depicts confluent medullary signal abnormality in the head of the middle phalanx (red arrow), and depicts extensive soft tissue edema. The presence of confluent medullary signal abnormality allows us to predict the presence of osteomyelitis with a high degree of confidence. Osteomyelitis and septic arthritis were confirmed at surgery.

SOS and a Rheumatoid Knee

2008-11-28T22:40:00.004-05:00

The phenomenon of "satisfaction of search" (SOS) is the bane of all radiologists. ("Bane" comes form the old English word for "slayer, murderer"; it means "that which causes ruin or woe", so it is a felicitous choice for this context). In SOS, the radiologist detects an obvious lesion, becomes satisfied with his perceptions, and misses less obvious abnormalities on the same study.

Satisfaction of search has been described by several authors, including Samuel et al. (Radiology 194:895-902, 1995), who studied this phenomenon in the detection of nodules on chest radiographs. They concluded that "obvious abnormalities capture visual attention and decrease vigilance for more subtle abnormalities". SOS also occurs in musculoskeletal radiology, as documented by Ashman et al (AJR 175:541-544, 2000).

Not surprisingly, radiologists continue to wrestle with this phenomenon. The more striking the findings, the more you have to increase your vigilance for subtle findings.

In this case, a 22 year-old female with rheumatoid arthritis presents with knee pain:

Sagittal and coronal T2 fat sat images show a large joint effusion with rice bodies (yellow arrow) and inflammatory pannus (green arrows). There is also a bone infarct in the tibia (red arrows). There seem to be more than enough findings to explain the patient's pain!

Mindful of the SOS phenomenon, a careful inspection of the entire knee was done. This revealed a tear of the posterior horn of the lateral meniscus:

This case reinforces the idea that the bigger and more spectacular the findings, the more you should look carefully at the entire study. Otherwise, human nature and SOS will tend to lead you astray.

Hamstrings and Filet Mignon

2008-11-21T22:09:00.001-05:00

The reason I gave up eating red meat can be traced back to my experiences as a medical student dissecting cadavers in gross anatomy. I learned that filet mignon was a cut from the psoas major muscle of the steer. Knowing that, and looking simultaneously at the psoas major of a human (albeit a dead one), did the trick— instant vegetarian. Eventually I gained back my appetite for meat, but it's now pretty much restricted to fish and chicken.

The "hamstrings" are the muscles that compose the posterior thigh. Roughly speaking, they run from the pelvis to the knee, and are composed of the biceps femoris, semitendinosus and semimembranosus muscles. The ham of the dinner table is typically the hamstring of the pig:

Photo by cactusbones

The verb "hamstring", meaning "to disable or render useless", derives from the observation that cutting the hamstring tendons renders a person or animal lame.

Hamstring injuries are common in sports. Many people consider these to be fairly innocuous injuries, but Askling et al. recently pointed out that these can be extremely debilitating injuries (AJSM 36:1799-1804,2008).

Consider this case, a 55 year-old female athlete, with sustained a sports injury three weeks ago:

A coronal T1-weighted image depicts a near-complete avulsion of the right hamstring tendon (red arrow) from the ischial tuberosity. Note the normal left hamstring (green arrows).

An axial T2-weighted image with fat saturation shows the nearly naked right ischial tuberosity (red arrow), where the hamstring tendon has been avulsed. Note the normal left hamstring tendon (green arrow):

Askling et al. examined 30 subjects from 21 different sports. All the hamstring injuries they studied were located proximally in the posterior thigh, close to the ischial tuberosity. They found that a large percentage of patients (47%) actually chose to give up their sport after an extended time of rehabilitation (median, 63 weeks). Of those patients that returned to sports, 88% of the subjects still reported symptoms from the injury.

Thus, high-grade partial or complete proximal hamstring tears can be an extremely debilitating, serious injury that can have a prolonged recovery time. It is important to give an accurate description of the location and degree of tear when interpreting the MRI examination.

Iliotibial Band Friction Syndrome (or Not)

2008-11-14T23:47:00.003-05:00

Running is a great way to get exercise, if your ankles and knees will tolerate it:

Photo by ziga-zaga

Runners can develop a condition called, iliotibial band friction syndrome, as can cyclists. In this condition, there is inflammation of the tissues around the iliotibial band (ITB). Patients present with lateral knee pain. On MRI, one can see edema around the iliotibial band, typically deep to the iliotibial band (arrows), as in this example:

Recently, I ran across a case of a young female patient with knee pain, with edema around the iliotibial band:

Although the edema is closely associated with the ITB, the preponderance of edema is superficial to the ITB, rather than deep to it, as would be expected for ITB friction syndrome.

This seemed a bit odd, so I picked up the phone and called the patient. She informed me that she had received a cortisone shot in this location about 3 hours prior to the MRI, and had a bruise in that location. A little clinical history can go a long way...

Thus, if you see edema concentrated in a focal area in the superficial soft tissues, without a history of trauma or infection, consider the possibilty of iatrogenic mischief. This is also true for other joints, such as the shoulder.

Icebergs and Fractures

2008-11-07T23:45:00.007-05:00

The word "fracture" comes from the Latin word fractura, meaning "a breach, break, cleft". The word is used in various ways— for example, when icebergs fracture from a glacier, that process is known as "calving":

Photo by Hometown Invasion Tour

In medicine, "fracture" is usually used in the context of a bone break. MRI is excellent for depicting acute fractures, because most acute fractures are accompanied by extensive bone marrow edema, as in this radial head fracture in my 14 year-old son:

In the subacute or chronic setting, however, MRI becomes less sensitive for fractures, in part because bone marrow edema often subsides or resolves entirely. This can be particularly problematic in small joints. The bones are smaller, and are often curving in character, creating volume-averaging artifact.

One way to increase the sensitivity of the exam for small chip or avulsion fractures is to use a thin-section 3D (volume) gradient echo sequence. This is often the best sequence for picking up these subtle injuries.

Here are MRI and CT images from a 35 year-old male with a history of trauma four months ago:

(click on image to enlarge)

There is a subtle chip fracture of the lunate (red arrows), which is seen best on the GRE (gradient echo) and CT images. Note how difficult the fracture is to see on the intermediate fatsat (Int FS) image. When reading wrist MRI, I try to scrutinize the 3D GRE images very carefully, as this can often be the only sequence where a fracture is well-seen.

Thus, it's generally a good idea to run a thin-section GRE sequence for wrist MRI. Fractured icebergs off glaciers are easy to see, but small bone chip and avulsion fractures can be hard to detect without this sequence.

Gadolinium and MR Arthrography

2008-10-29T16:51:00.015-04:00

We do a great deal of MR arthrography in our practice. In this test the radiologist first instills contrast into the joint, typically under imaging guidance. Immediately thereafter, the patient has an MR examination. The contrast that is typically used for this examination is dilute gadolinium, mixed in iodinated contrast, saline, or a mixture of the two. There have been excellent articles published about what concentration of gadolinium to use; for example, see this article by Montgomery et al.

I have seen some unusual contrast properties on various MRI pulse sequences, sometimes varying with the brand of iodinated contrast that is used in the cocktail. I finally decided to try to gather some additional data, to see how various mixtures performed under the pulse sequence parameters that we use.

The following graph summarizes the results:

Saline = normal saline
Iodine = iodinated contrast (240mg iodine/ml)
Gad = Magnevist

The graph plots the signal intensity for several different mixtures, using sequences routinely used for MRI arthrography at 1.5 Tesla.

There are a number of interesting conclusions that can be drawn from this data. Most importantly, the highest signal intensity for all pulse sequences is obtained by using a 1:1 mixture of iodinated contrast and normal saline, with a gadolinium concentration of 1.25 mmol/L. This is the mixture we currently use for MR arthrography. Next, signal intensity for T2 weighted sequences is lower for all mixtures when one goes from TE=36 ms to a TE=70 ms. This is not surprising, but emphasizes that one should use TE values that are at the lower end of T2 values that give T2 weighting.

MR arthrography, properly done, is an excellent test that can give a great deal of valuable information about the joint and its environs. Some of this information can be difficult to see or inapparent using conventional (noncontrast) MRI. This data helps validate the techniques that we use to perform MR arthrography.

Special thanks to John Murphy, Jamie Stephens, and Raymond Stephenson, MRI technologists par excellence, for their help with this data collection.

Ankle Sprains and the ATFL

2008-10-24T23:30:00.000-04:00

Ankle sprains are extremely common injuries, and occur in a wide variety of sports:

The anterior talofibular ligament (ATFL) is a major component of the lateral collateral ligament complex of the ankle joint and plays an important role in stabilizing the ankle. The ATFL is the most frequently torn ligament in ankle sprains.

The ATFL is usually thought of as a single structure, but the ATFL can have more than one band (Milner and Soames;J. Anat 191, 457-458, 1997). These investigators carefully dissected 26 cadaver ankles. In 38% of ankles, the ATFL had a single band; in 50% of ankles, the ATFL had two bands, and in 12% of ankles, the ATFL had three bands. The overall width of the ATFL did not vary greatly, irrespective of the number of bands present.

This variation in structure can be seen on MRI as well. In the following patient, the ATFL has a single band:

In this ankle, the ATFL has two bands:

In the final example, we see an ATFL composed of three bands:

The individual bands of the ATFL are best perceived on coronal images. Thus, do not confuse variations in the fascicular structure of the ATFL for a tear of this ligament.

Skier's Thumb and Partial Stener Lesions

2008-10-19T13:39:00.000-04:00

Skiing in the crisp mountain air, beneath a blue sky, is one of life's true pleasures.

Photo by Spatial Mongrel

Eventually, every skier falls backward in a fall, and hyperabducts the thumb MCP joint. That places them at risk for "skier's thumb", the eponym for a tear of the ulnar collateral ligament. Historically, the UCL was often chronically injured in gamekeepers, who killed rabbits and other small game by breaking their necks between the ground and their thumbs and index fingers.

Bertil Stener was a Swedish hand surgeon who elucidated the cause of chronic instability in patients with ulnar collateral ligament tears:

Stener noted that in some patients with UCL tears, the torn ligament would retract superficial to the aponeurosis of the overlying adductor pollicis muscle. The interposed adductor aponeurosis prevented healing of the torn UCL.

In most cases, a Stener lesion represents a complete rupture of the UCL. This is not always true however, as pointed out by Romano et al. (Can Assoc Radiol J 2003;54(4):243-8) in an excellent article on the spectrum of ulnar collateral ligament injuries. They observed that in some patients, "a large component of the redundant ligament was displaced proximally and dorsally, as would be found in a Stener’s lesion, but the distal end remained beneath the aponeurosis, which distinguished it from a classic Stener’s lesion".

This article goes on to note that "this contradicts previous claims that adductor aponeurosis interposition cannot occur in partial ruptures".

Twenty-seven year old patient with trauma to the thumb, and clinical evidence of a thumb UCL tear, who was referred for an MRI, to rule out a Stener lesion:

Coronal T2-weighted images with fat saturation reveal a torn, retracted UCL (red arrows), superficial to the adductor aponeurosis (yellow arrows). Note that although the majority of the UCL is retracted proximally, there remains a portion of the ligament (white arrow) that remains underneath the aponeurosis.

Thus, although a Stener lesion typically reflects a complete tear of the UCL, in a minority of cases one can have partial tears of the UCL leading to a Stener configuration.

Profundus Laceration

2008-10-11T00:24:00.001-04:00

The word "laceration" comes from the latin "laceratio", Latin for "tearing, lacerating". Fingers are often cut:

Photo by amanky

These injuries are often treated in the emergency room, as described by in this blog entry by an an ER doc in Texas. Worth reading....

Finger lacerations are often superficial, but a deep injury can transect a tendon. In this case, a thirty-two year old female lacerated her ring finger on a food preparation machine, and presented to a hand surgeon. The clinical examination was difficult, and the patient was referred for an MRI to better delineate the nature of the flexor tendon injury.

Sagittal gradient-recalled echo image:

The flexor digitorum profundus tendon is completely cut, with a 7 mm gap (red arrow) in the distal tendon. Interestingly, there is a second gap in the tendon (yellow arrow), just proximal to its insertion. Thus, there are two separate lacerations of the tendon, with a free-floating segment. These findings were confirmed at surgery. At surgery, it was discovered that the volar plate of the PIP joint was also cut.

Compare this to a normal flexor digitorum profundus tendon:

Lacerations usually are not referred for MR imaging, but when the clinical exam is difficult or confusing, a high-resolution MRI can often yield valuable pre-operative information.

Beckham and the Posterior Tibial Tendon

2008-10-04T00:32:00.002-04:00

Tears of the posterior tibial tendon (PTT) are rare in athletes. Overuse syndromes leading to tendinopathy and tenosynovitis are more common in sports such as tennis and soccer, which require a great deal of side to side movement. As long as the feet are happy, stars like David Beckham can make great plays:

An uncommon ankle injury worth remembering is dislocation of the posterior tibial tendon. Thirty year-old male with medial ankle pain:

Axial proton-density (PD) and T2-weighted images reveal a medially dislocated posterior tibial tendon (red arrows).

Here are comparison images from a normal individual, depicting the normal posterior tibial tendon (green arrow), behind the medial malleolus (yellow arrows). (The bright oval laterally is a skin marker, and can be ignored):

A coronal intermediate image from the abnormal patient confirms the abnormal position of the PTT, superficial and medial to the medial malleolus:

Dislocation of the PTT is a rare condition, and diagnosis is often delayed. The MRI diagnosis of this condition has been described by Bencardino et al. (AJR 169:1109-1112, 1997). Most lesions involve tearing of the flexor retinaculum, but some cases are due to an incompetent flexor retinaculum (AJSM 29:656-689, 2001). Conservative therapy is not effective, and surgical repair is usually necessary.

Efficient PACS Reading

2008-09-27T01:04:00.001-04:00

Radiologists are reading more cases every year, and anything that makes our day more efficient is a good thing. In a computer-centric environment, the workday revolves around digital imaging, the monitor, mouse, and keyboard.

A great scripting program called Autohotkey can save you thousands of repetitive mouse clicks and keystrokes a year. If you are a heavy computer user like me, it can make your computing experience significantly better, and save you from repetitive strain injury.

It's simple to learn, if you let your inner geek run wild and free. It can be run off a USB stick, so administrative privileges are not required.

Learn more about it:

Autohotkey in Radiology

Using AHK

Examples

Heart Surgeons, Abscesses, and Lytic Lesions

2008-09-14T21:06:00.000-04:00

Michael DeBakey M.D. died at the age of in July 2008. He was best known as a pioneering heart surgeon, operating on celebrities and commoners alike, saving thousands of lives.

Debakey was a creative surgeon even early in his career. With his mentor Alton Ochsner, he devised a new way to drain subphrenic abscesses, through a transthoracic approach. An abscess is a collection of pus (infected fluid), and is typically found within the soft tissues. In some cases, however, abscesses can also occur within the bone.

In 1832 the surgeon B.C. Brodie described three cases of a chronic abscess within the tibia:

The patients were young adults, and each presented with chronic tibial pain and swelling. Brodie was a good writer, and his description is compelling:

"The lower extremity of the left tibia was considerably enlarged; the skin covering it was tense, and adhered closely to the parts below. The patient complained of a constant aching pain, which he referred to the enlarged bone. Once in two or three weeks there was an attack of pain more severe than usual, during which his sufferings were excruciating, lasting several hours, and sometimes one or two days, and rendering him altogether incapable of following his usual occupations. The pain was described as shooting or throbbing, worse during the night, and attended with such exquisite tenderness of the parts in the neighborhood of the ankle that the slightest touch was intolerable."

Recently, I saw a case of a 12 year-old girl with a lytic lesion in the tibia. Of course, the clinical history on the prescription was a little less eloquent than the description above: "Pain, MRI ankle".

Sagittal T1-weighted and STIR images depict an oval lesion (red arrows) in the distal tibial metaphysis. The lesion crosses the physis (yellow arrow), to involve the epiphysis as well. There is a great deal of marrow edema surrounding the lesion. A close-up of the lesion reveals that the lesion is heterogeneous, with a rind of T2 hyperintensity representing granulation tissue (red arrow) surrounding a relatively hypointense core (blue arrow):

The appearance is highly suggestive of a chronic bone abscess (Brodie's abscess), which was confirmed at surgery. In some cases, the lesion can be difficult to distinguish from a tumor, such as osteoid osteoma. Conventional radiographs and CT are often helpful, and depict a lytic lesion with surrounding sclerosis. This sclerotic response typically has a sharp interface with the lesion, but merges gradually with the surrounding bone (Musculoskeletal Imaging: A Teaching File. Felix S. Chew, Catherine C. Roberts; Lippincott Williams & Wilkins, 2005)

A Brodie's abscess develops when osteomyelitis is contained by the host immune response, but is not cured. The infection is walled off, but remains active. The lesion usually is within the metaphysis, but can occur anywhere. When it occurs in the epiphysis, it can be mistaken for a chondroblastoma.

Nearly 200 years have flashed by since Brodie's original description, but chronic bone abscess remains an important medical diagnosis. These lesions are eminently treatable, once the diagnosis is established.

Diving and the Thumb CMC Joint

2008-09-12T22:00:00.002-04:00

Platform diving is acrobatic and beautiful:

Photo by shutterhack

Inevitably, there are some serious g forces exerted on the human body, especially if the rapid deceleration is less like a knife-like entry into the water, and more like one of my dives, the classic belly-flop:

Photo by j. cliss

Recently, a hand surgeon called me and told me about a set of patients who are platform divers, with intractable pain at the base of the thumb, at the thumb carpometacarpal (CMC) joint. She remarked that it would be nice to get some imaging information about the ligamentous structures supporting this joint, particularly along the dorsal aspect of the joint, a region that is difficult to visualize at arthroscopy.

There is not a great deal written about MR imaging of the thumb CMC joint. One good article was written by Connell et al.; there is also a Wandering Radiologist blog post.

There is some variability in how these ligaments are named, but if we follow the convention of Connell et al., there are four main ligaments:

1. Anterior oblique (beak) ligament- extends from the trapezium to the first metacarpal base, on the volar side of the joint.

2. Posterior oblique ligament- extends from dorsoulnar trapezium to the first metacarpal base.

3. Dorsoradial ligament- extends from the dorsoradial aspect of trapezium to the first metacarpal base. This ligament is reinforced by the abductor pollicis longus tendon.

4. Intermetacarpal ligament- runs from the radial base of the index metacarpal to the ulnar aspect of the thumb metacarpal base.

The combination of direct coronal and oblique sagittal images of the CMC joint visualize the first three of ligamentous structures quite well, at 1.5 Tesla. The intermetacarpal ligament can also be seen, but is more wispy in character.

Consecutive oblique sagittal intermediate-weighted images of a normal volunteer:

The anterior oblique ligament (red arrows) is well seen, as is the posterior oblique ligament (green arrows). The dorsoradial ligament is depicted on this next set of images:

(A) Oblique sagittal and (B) direct coronal images delineate the normal dorsoradial ligament (pink arrows).

Direct coronal images are usually the best way to visualize the anterior oblique (beak) ligament:

The MRI technologists I work were instrumetal in determining the optimal imaging planes for us to visualize these structures. This post illustrates once again the vital role the MR technologist plays in producing high-quality MR images.

Movies and ACL Tears

2008-09-05T19:15:00.014-04:00

Movement is essential to life. Our brain is hard-wired to detect motion, and we respond to video much more than static pictures. Consider these two different depictions of a horse galloping:

Now, the video version:

Clearly, the video version is more appealing. Moreover, the video version contains important information that the still picture does not. This video, made by Eadweard Muybridge in 1878, was the first motion picture ever made. Muybridge was commissioned by Leland Stanford (California governor/ Stanford University) to answer a popularly debated question of this era— are all four of a horse's hooves ever off the ground at the same time while the horse is galloping? Muybridge's time-motion photography proved they were off the ground simultaneously. Video analysis had answered a scientific question for the first time in history.

Although cross-sectional imaging has revolutionized radiology, video representations of anatomic detail are the exception in MRI and CT. Volume-rendering techniques enable us to depict 3D data sets, but these techniques are diffusing into clinical practice in a sluggish fashion.

Almost everyone reads off PACS now, which is clearly superior to reading from film for many reasons. One advantage of PACS is the ability to rapidly scroll through a stack of images. This video-like representation of data sets will sometimes enable you to quickly recognize abnormalities that are subtle and easily missed on static images.

One example is the analysis of the anterior cruciate ligament (ACL), a key stabilizer of the knee. It is important to recognize tears of this structure, as the presence of an ACL tear will often change the treatment algorithm. There have been many excellent articles written about the MRI analysis of ACL tears, and these tears are usually easy to recognize on MRI.

The key word here is usually. These tears can be subtle in some patients. The ACL should be examined in the sagittal, axial, and coronal planes to maximize your accuracy. One common error is to rely solely on the sagittal plane to determine the status of the ACL. The axial and coronal planes will often yield additional information about this critical structure.

In the coronal plane, the normal ACL has an oblique course, arising from the lateral femoral condyle, and coursing anteriorly and medially before inserting on the anterior tibia. In the following figure, the green arrow depicts the normal oblique course of the ACL:

Any significant deviation from this normal oblique course of the ACL on coronal images is abnormal.

Here is a movie of a stack of coronal images, depicting a normal ACL. Note how the ACL tracks from the top left of the figure to the bottom right, following its normal oblique course:

Next, let's look at a sagittal image from a 37 year-old patient with knee pain:

The ACL is visualized (red arrow) throughout most of its course. The femoral origin (green arrow) is hazy , but on the adjacent image, this part of the ACL can be seen:

The ACL looks "funny", but it would not shock me if a busy reader passed this off as volume averaging, or a partial tear of the ACL.

A complete analysis of the ACL, however, requires scrutiny of the axial and coronal planes as well, particularly in complex cases. Here is a movie of a stack of coronal images from the same patient. The ACL (red arrow) no longer follows its normal oblique course through the intercondylar notch. Its path is now curvilinear, and the inferior aspect of the ACL is deviated laterally:

With these additional images, we can confidently diagnose a complete tear of the ACL, which was subsequently confirmed at arthroscopy.

One of the less-advertised benefits of PACS is its ability to give us video-like representations of the imaging data.

Perhaps one day video imaging will kill static images, as video killed the hegemony of Top 40 Radio, through MTV. For those of you that missed the advent of MTV, the first video played on MTV was the aptly titled "Video Killed the Radio Star":

Lost in Translation and a Hip Tumor

2008-08-29T17:42:00.004-04:00

Some things are easily lost in translation. Witness the ineptly named Chinese Barbie-doll knock-off, "Benign Girl":

Something tells me that the manufacturer was trying to conjure up resonances of something besides a benign tumor when they named this product.

Clearly, language is important. For example, what is the difference between a benign and malignant tumor? The essential difference is their biologic behavior— benign tumors classically do not metastasize (spread to other sites), and typically grow more slowly than their malignant counterparts. Despite their less aggressive behavior, however, benign tumors can still be quite symptomatic.

Teenage boy who presents with left hip pain:

Coronal STIR image reveals a rounded, mixed-signal mass (red arrow) in the epiphysis of the left femoral head. There is extensive surrounding bone marrow edema, as well as a joint effusion.

(A) Axial T1-weighted and (B) T2-weighted images confirm the presence of the lesion, which is nearly isointense to the edematous cancellous bone:

Intravenous gadolinium was administered, and a subtraction image was obtained, confirming the presence of an enhancing tumor in the femoral epiphysis:

A CT scan was obtained for lesion characterization:

The lesion has internal matrix, with a pattern of rings and arc calcifications, characteristic of chondroid matrix. The lesion is well defined, and has a sclerotic rim. A pathologic fracture (blue arrow) is also identified.

The overall findings are highly suggestive of a chondroblastoma, which was confirmed at pathologic analysis.

Chondroblastomas typically arise in patients between the ages of 10 and 30. They almost always arise in the epiphysis. Although are regarded as a benign lesion, a small percentage can metastasize to the lungs.

On MRI, chondroblastomas are typically heterogeneous, but will often have some dark areas on T2-weighted images. They tend to generate a great deal of bone marrow edema, and will enhance after the administration of gadolinum. A subchondral epiphyseal tumor in the immature skeleton, associated with significant edema, is usually a chondroblastoma (Kan,J.H., & Kleinman,P.). The differential diagnosis includes a Brodie's abscess and Langerhans histiocytosis. Also to be considered, but much less likely, is an epiphyseal osteosarcoma or ganglion cyst filled with granulation tissue.

Snapping Hip- Internal or External?

2008-08-22T19:25:00.000-04:00

High-performance athletes learn to live with many injuries. I am always amazed to see what the joints of some professional athletes look like- many of them are walking around with pain that would make me admit myself to the hospital for a pain pump.

Some ailments are more confusing to diagnose than others. In the "snapping hip" syndrome, there is an audible snap or click that occurs in the region of the hip joint. Athletes that are particularly prone to this sydrome include ballet dancers, track and field competitors, soccer players, and gymnasts, where repetitive hip flexion is common.

Photo by Angela Radulescu

Snapping hips can be caused by intraarticular and extraarticular conditions. The most common intraarticular cause is a tear of the acetabular labrum. There are many extraarticular causes, including movement of the iliotibial band over the greater trochanter, snapping of the iliopsoas tendon, and movement of the gluteus maximus tendon over the greater trochanter.

15 year-old female with snapping left hip, referred for MRI to see if snapping is intraarticular (usually due to a labral tear) or extraarticular in origin. Oblique axial T2-weighted image reveals local soft tissue edema (red arrow) associated with the iliopsoas tendon (yellow arrow):

The iliopsoas tendon can snap over the lesser trochanter, the joint capsule, or the iliopectineal eminence. With reptitive snapping, the local soft tissues can become edematous, as in this case. The iliopsoas bursa can also become inflamed.

Oblique coronal T2-weighted image confirms the edema (red arrow) tracking along the iliopsoas tendon (yellow arrow):

Axial T2-weighted image depicts the unilateral nature of the edema (red arrow) associated with the left iliopsoas tendon (yellow arrow). Note the normal right iliopsoas tendon (green arrow):

Snapping can be asymptomatic, but can be painful in some patients. Althoug nonoperative treatment is usually successful, in recalcitrant cases, one can perform a total or partial release of the posteromedial tendinous portion of the iliopsoas muscle at the pelvic brim.

Volume Averaging Artifact

2008-08-15T19:36:00.001-04:00

"Partial volume artifact" and "volume averaging" are terms that are thrown about willy-nilly by radiologists, because we run into this phenomenon every day. Here, we aim to give a brief explanation of this phenomenon.

This artifact occurs when an object is only partially within the slice (i.e. volume) that is imaged. When this occurs, the pixel value at that location is the average of the object and its surroundings.

To reify this concept, let us conduct an experiment. We will take a piece of plastic shaped like this:

Place this plastic piece in a water bath, and put the water bath into an MRI scanner. Next, perform two MRI pulse sequences, varying only slice thickness, keeping all other parameters the same:

(click on image to enlarge)

Each row contains consecutive slices through our plastic piece. At 0.7 mm slice thickness, the margins of the plastic object are relatively sharp, particularly at the center of the object.

At 1.2 mm slice thickness, however, we see something different. As we get to the edge of the object, there is marked blurring (red arrows). Why does this occur?

Remember that in this area, the slice encompasses both the object and the surrounding water. Thus, the signal value of the pixels in this area is the average of the pixel value of the object and the pixel value of the surrounding water. Voila, volume averaging artifact.

This has real world implications in radiology- to minimize volume averaging artifact, we want the smallest possible pixels. Unfortunately, as we make pixels smaller, the signal from those pixels also decreases. Thus, one must balance the desire for high resolution with the need for adequate signal. If done correctly, optimal image quality and diagnostic information is achieved.

Swimmers and Unstable Shoulders

2008-08-08T19:27:00.006-04:00

The 2008 Summer Olympics are coming up, and one of the main events will be swimming. Many eyes will be on Michael Phelps, who won eight medals at the 2004 Summer Olympics:

Swimmers like Michael Phelps are athletes who repeatedly stretch the shoulder girdle, and the capsular attachments of the glenohumeral joint. This can lead to ligamentous laxity, particularly in patients predisposed to this condition on a genetic basis. Ligamentous laxity can lead to shoulder instability, with repeated subluxations and dislocations.

Shoulder instability can be in one direction (anterior or posterior), or be multidirectional. Most cases of multidirectional instability are atraumatic in nature, and are related to increased joint volume and capsular laxity.

22 year-old male with history of multidirectional instability. An MR arthrogram was requested to evaluate the capsule and labrum. Axial image reveals a markedly capacious posterior joint:

For comparison, here is a patient without a history of posterior instability; note that the posterior capular volume is markedly smaller:

Sagittal image from the patient with multidirectional instability confirms the patulous nature of the posterior joint, particularly posteroinferiorly (yellow arrows). Green arrow= coracoid process, an anterior structure:

Dewing et al. published an analysis of this issue recently (AJSM 36:515-522, 2008). They analyzed capsular area in patients with anterior, posterior, and multidirectional instability. They found that capsular area is increased in the setting of posterior and multidirectional instability, but not in patients with anterior instability. They pointed out that it may be difficult to reproducibly measure joint volume, due to variability in the amount of contrast injected between patients. In addition, they also noted that gravity might play a role in the relative size of the anterior aspect of the joint. (Patients are scanned in the supine position, and it is unclear what would happen to the relative volume of the anterior and posterior aspect of the joint in the prone position).

My own experience suggests that one should examine the capacity of the glenohumeral joint when analyzing an MR arthrogram, particularly in patients with a history of multidirectional instability. Some of these patients will have no labral abnormality whatsoever, but will have clear evidence of increased posterior or posteroinferior joint capacity. I will comment on this in my report, noting the absence of a labral tear, but the presence of an abnormally increased joint volume. In addition, my anecdotal observations of increased anterior joint volume in the setting of repeated anterior dislocations are consonant with the observations of Urayama et. al, (AJSM 31:64-67, 2003) who reported capsular elongation in patients with recurrent anterior dislocation.

Korn and the Extensor Pollicis Longus

2008-08-01T19:13:00.005-04:00

My teenage son recently went through his musical Korn phase. Delicate music, this is not. Lots of ear-splitting, pounding guitar, twisted transistors, and a drummer that loves to pound his kit:

Photo by Mark McLauglin

Drumming has been around for a few hundred years, and it should come as no surprise that drummers can get injured from their repetitive acrobatics. In 1876 Duplay described "drummer boy's palsy" in Prussian drummers, due to rupture of the extensor pollicis longus (EPL) tendon. Patients with rupture of the EPL tendon present with pain and loss of thumb extension.

The EPL tendon is classically torn as a result of a distal radius fracture. In this setting, the tendon usually ruptures at the level of Lister's tubercle, typically one to three months following the fracture. The EPL can also experience attritional tearing in the setting of systemic diseases such as rheumatoid arthritis, lupus, and gout. Rarely, the EPL tendon can be torn at the level of the distal phalanx of the thumb.

The EPL tendon can also rupture due to trauma, although this is less common. Twenty-eight year old gentleman, who sustained an injury playing lacrosse, and complained of dorsal wrist pain, radiating to the thumb. Axial T2-weighted image reveals a small amount of fluid surrounding the EPL tendon, which is markedly abnormal in signal:

On sequential coronal images, the EPL tendon (yellow arrows) is still continuous, but has a striated appearance, and it is surrounded by a thin rim of increase fluid:

Note the normal cross-over of the EPL tendon over the extensor carpi radialis brevis [ECRB] tendon (green arrows). These images define the presence of a partial tear of the tendon, with reactive inflammatory fluid in the tendon sheath.

The patient was treated conservatively, but several weeks later suffered an additional traumatic event, and presented with acute loss of thumb extension, with a recurrence of dorsal wrist pain radiating to the thumb. An EPL rupture was diagnosed clinically, but an MRI was obtained to exclude a concurrent intercarpal ligament injury. An axial T2-weighted image reveals that the third dorsal compartment, which normally houses the EPL tendon, is nearly empty, with only a small amount of debris in the tendon sheath:

A coronal image better depicts the fluid in the essentially empty tendon sheath:

A slightly more anterior coronal image identifies the torn, retracted EPL tendon (red arrow).

Ruptures of the EPL tendon are not repaired directly. This situation has not changed for many decades, as demonstrated from this letter in the British Medical Journal in September, 1937:

EPL ruptures are treated with a tendon transfer, typically using the extensor indicis.

The EPL tendon can be challenging to image on MRI, due to the thin nature of the tendon, and the complications of magic angle artifact. Nonetheless, with high-resolution, thin section MR imaging, much information can be gained.

Soccer Players and the Plantar Plate

2008-07-25T18:53:00.004-04:00

"I spent all my money on booze, girls and fast cars. The rest I just squandered."—George Best, English soccer star

A talented winger, George Best was renown for his extravagant lifestyle and soccer majesty. Here is a video of one of his goals, demonstrating his sheer athletic brilliance:

Football players, whether they are soccer or American football players, are prone to injuries of the foot and ankle. The hallux (great toe) can be a source of great pain, with injuries of the first metatarsophalangeal joint particularly common.

The term "turf toe" is used to describe various injuries of the 1st MTP joint, but classically refers to a hyperdorsiflexion injury of this joint. Other mechanisms of turf toe injury include valgus and varus injuries, as well as hyperflexion-related damage (Ohlson, B; emedicine). Structures that can be injured include the plantar plate, joint capsule, sesamoids, and adductor hallucis tendon.

Professional soccer player, who felt a "pop" and subsequent pain in the first MTP joint:

There is a tear of the plantar plate (red arrow), with fluid at the expected location of the plantar plate.

For comparison, here is an image from a normal patient, showing an intact plantar plate (green arrow). Also note the normal dorsal capsular recess (yellow arrow):

The plantar plate of the hallux arises primarily from the sesamoids and inserts on the plantar aspect of the base of the proximal phalanx.

The plantar plate supports the undersurface of the metatarsal head and resists hyperextension of the MTP joint. Injuries of the plantar plate can be extremely painful and debilitating, but these injuries usually respond to conservative treatment. When conservative management fails, surgery can be performed, and the avulsed plantar place can be reattached.

High-resolution MRI scans of the metatarsophalangeal joint can yield valuable information about the joint and surrounding soft tissue structures, particularly in high-performance athletes.

Thigh Swelling and Veils

2008-07-18T21:10:00.011-04:00

Radiologists have an unparalleled ability to look inside the human body, using our myriad machines. Starting with X-rays in the early part of the 20th century, radiologists eventually integrated ultrasound, CT, and MRI into their imaging armamentarium. These technologies, and others, give physicians the ability to noninvasively display the inner topography of our bodies.

In many cases, however, pictures alone do not give the answer. There is a veil over our understanding, and we cannot always make the correct diagnosis. The phrase "lifting the veil" seems to fit here; once the veil is lifted, the answer is often apparent. The phrase has been associated with wedding rituals from the dawn of civilization. In ancient Judaism, the veil was lifted prior to the consummation of the marriage. Modern brides often still wear a veil:

Photo by junebugweddings

What, then, lifts the veil for the radiologist? Often, it is the clinical history that delivers the correct diagnosis. We live in the dark ages of medical informatics— in fifty years we will look back and marvel at all the errors that are made in medicine today simply due to a lack of accurate clinical history about the patient.

Radiologists usually read their examinations in an informational vacuum. I am fortunate enough to work with great MRI technologists, who ask the patient the right questions, and usually obtain the information I need to interpret the examination properly. If the pictures do not "fit" the clinical history, then it is time for me to call the patient and/or the physician, to get the information I need to lift the veil.

Forty-five year-old woman with thigh pain and swelling:

Coronal STIR image (above) reveals a fluid collection (red arrow) in the mid right thigh, with extensive soft tissue edema.

(A) Axial T1 and (B) Axial T2 fatsat images show that the fluid collection is associated with the vastus intermedius muscle, and confirm the extensive surrounding soft tissue edema.

The patient was given intravenous gadolinium, and additional imaging was performed:

Axial postcontrast T1 fatsat image depicts rim enhancement of the fluid collection, with some associated enhancement of the adjacent muscle.

The images are there, but the veil is in place— the prescription states "MRI thigh, pain and swelling". Why would a 45 year old woman develop an angry-looking fluid collection in her thigh? The additional clinical history obtained by the technologist tells us that there is no history of blunt trauma or athletic injury, and that the symptoms have come on over the last two weeks. The mystery remains.

So.... it's time to get more information. I call the patient, and after a few questions, the mists part. She suffers from multiple sclerosis, and injects herself in the thigh with the immunomodulator Avonex. This additional information tells us that this is a case of pyomyositits. The fluid collection is an abscess within the vastus intermedius muscle, and it will have to be drained, and the patient put on antibiotics.

This is not a difficult case, but it illustrates what Professor William Osler taught us over 100 years ago— the importance of accurate information about the patient. Fundamental truths rarely change.

Buttock pain and the Tour de France

2008-07-11T18:40:00.003-04:00

The Tour de France is a monument to human endurance. Cyclists cover over 2000 miles in just over 20 days, with some prodigious climbing through the Pyrenees mountains. Participants can consume 8000-9000 calories a day, with metabolic rates rising to 4-5 times normal. Cyclists are some tough hombres.

Photo by l--o-o--kin thru

Endorphin highs are intoxicating, and even nonprofessional cyclists are willing to undergo a great deal of pain to keep doing their favorite activity. Many cyclists are addicted to their sport, and are out riding several days a week. Perched on top of a gangly two-wheeled contraption, unusual forces can be exerted on the human body.

Forty-five year-old avid biker with six weeks of bilateral buttock pain, left greater than right:

Coronal STIR and T1 images demonstrate subcutaneous edema and soft tissue thickening in the area (red arrows) where the biker sits on his bicyle seat.

Six weeks ago, he had adjusted the stem of his seat, and also changed his handlebar position. Riding position is a balance between comfort and power. This patient was getting older, and wanted a less aggressive riding position. He made the changes, and quickly experienced buttock pain. Interestingly, the skin overlying this area was completely normal, with no evidence of saddle sores. This edema is the result of abnormal, unrelenting pressure on the subcutaneous tissues of the buttocks. The cyclist will have to forego his endorphin high for a few weeks (as mentally painful as that might be), and alter his riding position.

One can speculate that similar changes could be seen in any riding sport. I have occasionally ridden horses, and can state unequivocally that this can be remarkably unpleasant. I did not realize just how much pain ischial tuberosities can cause until I rode a horse for a full day in Colorado, on a dude ranch last summer. I was hobbling around and sitting gingerly for a few days following that experience. I did not need an MRI to tell me that I was not cut out to be a cowboy....