Laboratory Studies

No laboratory studies are indicated for the diagnosis of Morton's neuroma.

Imaging Studies

Results of plain films are normal in Morton's neuroma.

Ultrasonography is gaining in popularity and may be equivalent in sensitivity to MRI in detecting Morton's neuroma.^{[6, 7, 8]} Indeed, a literature review by Bignotti et al indicated that ultrasonography and MRI are equally accurate for the diagnosis of Morton neuroma, with the modalities having sensitivities of 0.91 and 0.90, respectively.^[14]

Computed tomography (CT) scanning has been used but may not be as sensitive as MRI or ultrasonography. MRI, while not needed in most cases for establishing diagnosis of Morton's neuroma, has been studied widely.^{[4, 5]}Sensitivity of 87% and specificity as high as 100% have been reported. Asymptomatic neuromas may occur and confound accurate diagnosis.

Indications exist that Morton's neuromas smaller than 5 mm in diameter may not be significant clinically and that other diagnoses may be excluded carefully before such a small lesion is diagnosed as a symptomatic Morton's neuroma. Imaging with T1 weighting in a coronal plane is recommended for best visualization. In addition, on T2 imaging, the low signal of a Morton's neuroma may help to differentiate it from a true neuroma, ganglion cyst, or intermetatarsal bursal fluid collection.

Contrast enhancement usually is demonstrated with Morton's neuromas.

Other Tests

Electromyography and nerve conduction study (EMG/NCS) of Morton's neuroma are not used often because of the technical difficulty in performing them; needle stimulation of the common digital nerve and pickup on the adjacent toe or toes, which may be of short distance, is required. Surface stimulation results most often in volume conduction through the skin to the pickups because of the short distance involved and the large amount of stimulation needed to penetrate the deep tissue separating the nerve from the skin surface.

Procedures

Temporary elimination of pain and numbness in the associated webspace by a common digital nerve block with an anesthetic agent supports a diagnosis of Morton's neuroma. If numbness of the associated webspace occurs but no decrease in pain is noted, other diagnoses should be considered.

Histologic Findings

Tissue biopsy is neither needed nor recommended for Morton's neuroma.

Treatment & Management

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Media Gallery

Plantar view showing the relationships between the metatarsal heads, the intermetatarsal ligament, and the neuroma.
Neurectomy: typical incision location.
Neurectomy: superficial exposure.
Neurectomy: deeper dissection.
Neuroma and adherent fibrofatty tissue.