Saturday, May 31, 2008

Separated Shoulder

This blog was originally conceived as a site for medical professionals, but it's also read by patients looking for more information about their ailment. From this perspective, some of the content is admittedly esoteric; an old (non-medical) friend of mine looked at the blog and commented:

"I found your blog full of information I did not need to understand and was happy I didn't".

Man, that was cold... Good thing we go back more than a few years. Nonetheless, I will be offering him a domestic beer, rather than a selection from my finer imported stock, on his next visit.

Let's look at a common injury, the "shoulder separation". This is a term that sports fans and weekend warriors are familiar with. Shoulder separations are more common in contact sports such as football, rugby, hockey, and wrestling.

Photo by Wouter Verhelst
To understand the nature of this injury, let's examine the shoulder joint area:

(click on image to enlarge)
The true shoulder joint is the articulation between the scapula (red oval) and humerus (black oval). A shoulder separation does not affect this joint, however; rather, it disrupts the articulation between the clavicle (green oval) and the acromion (blue oval) and coracoid (pink oval) components of the scapula. The colloquial term for the clavicle is the "collarbone".

Mild shoulder separations tear the ligament
(black arrow) between the clavicle and the acromion , while more severe separations also disrupt the coracoclavicular ligament, which connects the clavicle and coracoid process of the scapula. The coracoclavicular ligament is composed of the conoid (red arrow) and trapezoid (blue arrow) segments.

OK, enough of the dry vernacular, show me some pictures, please. Forty-two year old male, with shoulder pain after a football injury:

Coronal T2 fat sat and proton-density images reveal widening of the space between the clavicle and acromion and complete disruption of the acromioclavicular ligaments (red arrows). There is also superior displacement of the clavicle with respect to the acromion, implying a disruption of the coracoclavicular ligament as well.

This is confirmed on more anterior images, where the normal coracoclavicular ligament can no longer be identified (red arrow):

For comparison, here is a normal coracoclavicular ligament
from a different patient (blue arrow = conoid segment; black arrow = trapezoid segment):

Most of these injuries are treated nonoperatively. With increasing severity of injury (e.g. clavicle tearing posteriorly through the trapezius muscle and complete loss of suspensory supports of scapula), operative management may be necessary.

Vic David MD

Friday, May 23, 2008

Aerobics and a Painful Foot

Jumping around, getting fit, Pilates...Power 90...Tae-Bo...The Firm...take your pick, they all hurt. They are a necessary evil, the price you pay to fit into the same pants you wore ten years ago.

Photo by stilinberlin

Aerobics has been around since the late 1960s. The term was coined by its inventors, Kenneth H. Cooper M.D., an exercise physiologist, and Col. Pauline Potts, a physical therapist. They came up with this form of exercise while in the Air Force, designing exercise regimens for astronauts. They soon realized that this was not simply for the Tang crowd, and published the book "Aerobics" in 1968. It was a smash hit, and the the craze continues.

Like most forms of exercise, overdoing it can result in injury. Fifty-six year old devoted aerobics instructor with several days of midfoot pain, with negative x-rays:

Coronal T2-fatsat image reveals extensive marrow edema (yellow arrow) within the lateral cuneiform. The corresponding axial image confirms the edema, but also depicts a linear, hypointense line (red arrow) within the subchondral bone, adjacent to the joint between the lateral cuneiform and the base of the third metatarsal, defining a subchondral stress fracture.

(A) Sagittal STIR and (B) sagittal T1 images confirm the subchondral stress fracture (red arrows) of the lateral cuneiform.

Subchondral stress fractures can occur in a variety of bones, but are most often found in the knee. Other relatively common locations are the femoral head (where they might explain some cases of transient osteoporosis), and the head of the metatarsals (AJR 2008; 190:570-575).

In my youth, I adhered to the principle, "No pain, no gain" when it came to exercise. In middle age, I have revised this to, "Always pain, minimal gain". This case is a grim reminder of that adage ;-).

Vic David MD

Friday, May 16, 2008

Disk Herniations and the Hereschmuk Sign

Take a look at this picture and tell me what you see:

Did you recognize the Mona Lisa? How much easier this would have been with the appropriate image contrast...

Image contrast is also important in MRI. Findings can be obscure and hidden on one pulse sequence, and obvious on another, simply due to differences in the contrast of the tissues.

Sixty year-old male with two weeks of severe, non-radiating low back pain after a lifting injury:

Axial T1 and T2-weighted images at the L2-3 disk space reveal a broad-based, left-sided far lateral disk protrusion (herniation). Easy to miss, especially if you are reading through a large stack of cases.

Let's examine sagittal images from the same patient:

The abnormal disk (yellow arrows) can be seen on both T2 and STIR images, but note how the presence of soft-tissue edema (red arrows) on the STIR makes it much easier to pick up this abnormality.

It's an excellent idea to include some form of fluid-sensitive, fat-suppressed sequence in orthopedic MRI. The accentuation of soft tissue edema often gives rise to the famed radiologic "Hereschmuck sign", as in "Here schmuck, don't miss this finding".
Two major types of fat suppression are used in MRI:

1) STIR (short-tau inversion recovery)

2) Chemical selective fat suppression- radiofrequency pulses and gradients are used to suppress the signal from fat protons (the chemical species affected by this technique)

Each technique has its advantages and drawbacks. The major appeal of STIR is uniform, robust fat-suppression, while its most important drawback is relatively poor signal. Chemical-selective fat suppression, with its better signal images, depicts anatomic features better, but nonuniform fat suppression can be a problem. For example, here are sagittal STIR and T2 fatsat images of the ankle:

The T2 fatsat image uses chemical-selective fat suppression, and the uniformity of fat suppression has deliberately been disrupted for this example. Normal fatty bone marrow should be dark on these pulse sequences, but the nonuniform fat suppression results in artifactually high signal in the bone marrow
. Compare this with the robust, uniform suppression of the bone marrow on the STIR images (green asterisks). The nonuniform fat suppression on the T2 fatsat image makes it impossible to identify the pathologic marrow edema in the posterosuperior calcaneus (white arrows).

Also note the water suppression that is evident on the T2 fatsat image- the chemical selective pulse intended to suppress signal from fat is instead of suppressing signal from water protons in some areas, including the flexor hallucis longus muscle (red arrows) and cartilage within an enchondroma (pink arrows). This example illustrates the importance of uniform fat suppression in orthopedic MRI. As long as fat suppression is uniform, however, chemical selective fat suppression is typically preferred over STIR, due to superior depiction of anatomic detail.

This case also illustrates the occasional importance of the "scout" images obtained during an MRI. Scout (also known as "localizer") images are obtained by the MRI technologist at the beginning of the MRI examination. These preliminary, large field-of-view images are used to prescribe the MRI sequences used to study the area in question. In some cases, these scout images can give additional information. For example, a coronal scout image from this examination confirmed the presence of the far lateral disk:

Finally, here is another image of the Mona Lisa from the beginning of this post. This version has the appropriate contrast. I think you will agree that the Mona Lisa is a bit easier to see with the proper contrast, just like pathologic findings on MRI:

Vic David MD

Friday, May 9, 2008

Red Marrow and Lady Chatterly's Lover

"Oh literature, oh the glorious Art, how it preys upon the marrow in our bones. It scoops the stuffing out of us, and chucks us aside. Alas!" - D.H. Lawrence

Overheated language is to be expected from D.H. Lawrence, the author of the novel Lady Chatterly's Lover. Hard as it is to believe, this novel was once regarded as pornographic, in a long gone era. These days it can be found in most community libraries:

Radiologists look at bone marrow all the time. Marrow does not scoop up even a soup├žon of stuffing out of me, since I am too busy trying to make sure that it is normal. Marrow is evaluated primarily on T1-weighted, T2 fat suppressed, and STIR images. Most of us tend screen the marrow quickly using STIR or T2 fat suppressed images, since most marrow abnormalities tend to be bright on these images.

Occasionally your eye will be drawn to marrow that looks more hyperintense than typical. Forty-nine year old female, imaged for elbow pain:

(A) Coronal T2 fat sat and (B) T1-weighted images depict areas of differential signal within the radius. These areas are hyperintense on T2 fat sat images (red arrow); corresponding areas are decreased in signal on T1-weighted images (green arrows).

Does this patient have an infiltrating process in the marrow such as a tumor, or perhaps bone marrow edema from trauma or ischemia? If the radiologist raises such possibilities, alarm bells will ring, with patient anxiety and referring clinician consternation resulting.

Fortunately, these areas of differential signal simply represent red marrow, and are not pathologic. Areas of red marrow should not be confused with bone marrow edema.

The different signal of red and yellow marrow is a result of the higher water content of red marrow. Adults will have variable amounts of red marrow, and these areas can be quite prominent, particularly in the metaphysis of long bones. Red marrow is typically amorphous and feathery in character on T1-weighted images. On fluid-sensitive images, red marrow is isointense or minimally hyperintense to skeletal muscle, and can be flame-shaped. These features, and the metaphyseal and metadiaphyseal location of red marrow is a strong clue to the benign diagnosis. Red marrow is classically prominent in the setting of smoking and obesity, particularly in middle-aged female patients.

Overcalling red marrow can be hazardous to your radiology reputation- it's a good idea to become familiar with its appearance.

Vic David MD

Sunday, May 4, 2008

Lawn Mowers and a Painful Shoulder

There are few things in life I find more unappealing than mowing the lawn. Spending a few hours pushing this thing around, breathing in gas fumes, is my idea of hell:

I am always looking to for ways to justify my anti-lawnmower position, besides the obvious environmental justification. Recently, I ran across a case that helped me convince my wife that mowing can be hazardous to your health.

Thirty-four year old woman with severe right shoulder pain one week after trying to start a gas-powered lawn mower:

Sagittal T2 fatsat and T1-weighted images show patchy edema in the teres minor (yellow arrow), infraspinatus (red arrow) and posterior edge of supraspinatus (white arrow) muscles, representing a moderate strain of these muscles. She was yanking on the starter cord with all her might, when the cord abruptly froze, torquing her shoulder. She immediately felt a sharp pain, and sought medical attention.

Without this compelling clinical history, one might have to consider other diagnostic possibilities, including a myositis or a form of Parsonage-Turner syndrome (although the patchy involvement seen in this case would be atypical).

It was very helpful for the patient and her treating physician to have this information. There was no rotator cuff tear, and no intra-articular abnormality. Thus, one can tell the patient with a high degree of confidence that her symptoms will abate over a few weeks, with conservative therapy.

Some might call this study a waste of imaging dollars, since the patient will be better in 3-4 weeks, whether or not she had an MRI scan. I respectfully disagree with those individuals. I learned early in my training that one of the most valuable things a physician can provide for their patients is a diagnosis and prognosis. There are few things worse than being in pain, and not knowing why you are in pain.

If the pain is in your shoulder, or a shoulder of a loved one, you will tend to agree with me on this one.

Vic David MD