Morton's neuroma: is it always symptomatic?

We determined the prevalence of clinically silent Morton's neuroma and searched for distinguishing MR imaging features of Morton's neuroma in patients with clinical complaints related to this entity and in patients with clinically silent lesions.

One radiologist who was unaware of clinical findings retrospectively reviewed 85 consecutive foot MR examinations. MR imaging criteria for Morton's neuroma included a low- to intermediate-signal-intensity soft-tissue mass in the intermetatarsal space. The size, location, and signal intensity of each neuroma and the presence of intermetatarsal bursae were recorded. The patients were subdivided into symptomatic or asymptomatic groups on the basis of the patients' answers on a questionnaire documenting the locations and characteristics of symptoms and discussions with each referring physician about clinical findings. Surgical confirmation was available in eight of 25 symptomatic patients.

The prevalence of Morton's neuroma in patients with no clinical evidence of this condition was 33% (19/57). Twenty-five patients had symptomatic Morton's neuroma, 19 had Morton's neuroma based on MR imaging findings with no clinical manifestations, and 41 did not have Morton's neuroma. Slightly larger lesions were observed in the symptomatic group, although significant overlap was noted between the two groups. The mean transverse diameter of symptomatic neuromas was 5.3 mm (standard deviation, 2.14) compared with 4.1 mm (standard deviation, 1.75) for asymptomatic neuromas; this difference was marginally significant (p = 0.05).

The MR imaging diagnosis of Morton's neuroma does not imply symptomatology. Careful correlation between clinical and MR imaging findings is mandatory before Morton's neuroma is considered clinically relevant.