Morton neuromas are focal areas of symptomatic perineural fibrosis around a plantar digital nerve of the foot. The abnormality is non-neoplastic and does not represent a true neuroma. It may more correctly be known as Morton metatarsalgia. The condition is thought to be due to chronic entrapment of the nerve by the intermetatarsal ligament.
It most often occurs in middle-aged individuals and is many times more common in women than men. ~30% of asymptomatic middle-aged persons have the radiologic pathologic findings of a Morton neuroma. Symptomatic lesions tend to be slightly larger (mean 5.3 mm vs. 4.1 mm in one large series 1). Lesions >5 mm are very likely to be symptomatic. 10% of lesions are bilateral.
Patients typically present with forefoot pain which radiates from mid foot to toes 5. Symptoms are often progressive and worsened by activity.
The 3rd web-space (between 3rd and 4th metatarsal heads) is the most commonly affected site. The 2nd web-space is less commonly involved while the remaining web-spaces are rarely involved.
It is characterized by neural degeneration with epineural and endoneural vascular hyalinisation, and perineural fibrosis around an intermetatarsal nerve 2.
Typically seen as a round to ovoid, well-defined, hypoechoic lesion in the intermetatarsal space proximal to the metatarsal head 4. A small proportion can have mixed echotexture 5.
Dumbbell/ovoid-shaped lesion at a similar position to that described on ultrasound.
- T1: typically low-to-iso signal 1-2
- T2: typically low signal but can sometimes be intermediate in signal
- T1 C+ (Gd): tends to show intense enhancement
Treatment and prognosis
Ultrasound-guided interdigital injection of steroid and local anesthetic has been shown to have a relatively good success rate 9.
Surgical excision can also be performed, also with a relatively good success rate (~ 80% 6).
History and etymology
It was initially described by Thomas Morton in 1876 4.
MR Imaging differential considerations include
- changes secondary to a plantar plate tear/disruption 7-8