= INTERDIGITAL NEUROMA (neuroma is a misnomer)

= benign nonneoplastic lesion due to fibrosis + degeneration around a plantar digital nerve

Age: highest prevalence in 5^th + 6^th decade; M÷F = 1÷4

Path: perineural fibrosis entrapping a plantar digital nerve

Often associated with: intermetatarsal bursitis

Histo: dense collagenous + fibrous tissue

• numbness; burning / tingling electric forefoot pain increasing with activity + wearing of narrow shoes
• Mulder sign = painful palpable click when metatarsal heads are squeezed together with one hand + involved metatarsal space simultaneously compressed between thumb and index finger of the other hand

Location: plantar side of deep transverse intermetatarsal ligament beyond MTP joint

Site: typically 2^nd / 3^rd intermetatarsal space (rarely 1^st / 4^th)

• splaying of metatarsal heads in large lesion

MR (87% sensitive, 100% specific):

• Best depicted prone (positional changes)
• small well-demarcated teardrop-shaped mass isointense to muscle on T1WI + hypointense to fat on T2WI
• variably hyperintense on gadolinium-enhanced fat-suppressed T1WI (easier to see)
• ± fluid in intermetatarsal bursa (vertically oriented between metatarsal heads)

Rx: conservative treatment; surgical excision for neuromas >5 mm in transverse diameter (more commonly symptomatic)