Saturday, October 15, 2011

High Heels and Morton's Neuromas

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.

Vic David MD