Morton's Neuroma (Interdigital Neuroma)

The interdigital neuroma is not a tumor, but a degenerative, fibrosing process occurring in and about the plantar digital nerve. It is most frequent between the ages of 25 and 50 years, and 80 percent of cases occur in women. Pain at the distal metatarsal interspace is noted, which may radiate distally and transversely through the toes. They most often arise at the second or third intermetatarsal space between the metatarsophalangeal joints and deep to the plantar transverse metatarsal ligament. The etiology is unproven, but may be an entrapment neuropathy that develops secondary to repetitive trauma and fibrous degeneration of the nerve. MR diagnosis is best accomplished in the coronal or axial plane. Lesions have low to intermediate signal intensity on T1 and proton density weighted images and low signal intensity on T2W images, likely representing dense fibrous composition of the lesion. Avid contrast enhancement is also noted in these lesions, best demonstrated by fat suppressed contrast enhanced T1 weighted sequences.

49-year-old female with a 1.2 x 1.0 cm mass in the second intermetatarsal space, which has low-intermediate signal on T1 W images, and diffuse enhancement on the post-gadolinium fat suppressed T1 W images