Morton neuroma and fluid in the intermetatarsal bursae on MR images of 70 asymptomatic volunteers.

PURPOSE: To determine the prevalence and size of presumed Morton neuromas and fluid in the intermetatarsal bursae on magnetic resonance (MR) images.

MATERIALS AND METHODS: In 70 asymptomatic subjects, transaxial T1-weighted spin-echo and T2-weighted turbo spin-echo images were obtained of the right forefoot. The prevalence and size of presumed Morton neuromas (diagnosed with MR imaging criteria) were evaluated, and the sizes were compared with those of 16 symptomatic, surgically proved Morton neuromas. The prevalence and diameter of fluid collections in the intermetatarsal bursae were evaluated on the T2-weighted images.

RESULTS: Twenty-four Morton neuromas were diagnosed in 21 subjects (prevalence, 30%). The transverse diameter of the neuromas was 3-7 mm (mean, 4.5 mm) versus 4-8 mm (mean, 5.6 mm) in symptomatic subjects; this difference was significant (P = .0075). The prevalence of fluid in the intermetatarsal bursa was 20%, 47%, 49%, and 0% for the first through fourth intermetatarsal spaces. The transverse diameter of the fluid collection was 1-4 mm.

CONCLUSION: The diagnosis of Morton neuroma at MR imaging may be relevant only when the transverse diameter is 5 mm or more and can be correlated to clinical findings. Fluid collections in the first three intermetatarsal bursae with a transverse diameter of 3 mm or less can be considered physiologic.