Sonography of Morton's neuromas

The objective is to evaluate the sonographic characteristics of Morton's neuromas and the usefulness of sonography in detecting them.

Thirty intermetatarsal spaces were evaluated with sonography to diagnose Morton's neuromas. The prospective sonographic reports were correlated with surgical and pathologic findings. Each sonogram was then blindly and retrospectively reviewed to characterize mass echotexture, location, size, and continuity with the plantar digital nerve when present.

Surgery revealed 27 Morton's neuromas, one synovial cyst with infarcted tissue, one ganglion cyst, and one giant cell tumor of the tendon sheath. The prospective sonographic reports correctly identified neuromas in 85% of the cases. Retrospectively, 79.2% (19/24) of the neuromas were characterized as hypoechoic compared with muscle, whereas 12.5% (3/24) were of mixed echotexture and 8.3% (2/24) were anechoic. One half (50%) of the neuromas were located dorsal to the plantar aspect of the metatarsal heads, and 50% were both dorsal and plantar to this level. No statistical difference in height and width was found between neuromas and nonneuromas; however, nonneuromas were statistically greater in length than neuromas. All 15 masses in which presumed plantar digital nerve continuity with the mass was identified were neuromas.

Sonography can reveal a Morton's neuroma in 85% of cases. Identification of the presumed plantar digital nerve in continuity with the mass improves diagnostic confidence. The finding of an interdigital mass greater than 20 mm in length should raise suspicion of an abnormality other than a neuroma.