Revision 31 for 'Morton neuroma'

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Morton neuroma

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’s metatarsalgia. The condition is thought to be due to chronic entrapment of the nerve by the intermetatarsal ligament.

Epidemiology

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’s 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.

Clinical presentation

Patients typically present with forefoot pain which radiates from mid foot to toes 5. Symptoms are often progressive and worsened by activity. 

Location

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. 

Pathology

It is characterized by neural degeneration with epineural and endoneural vascular hyalinization, and perineural fibrosis around an intermetatarsal nerve 2

Radiographic features

Ultrasound

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.

MRI

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.

Differential diagnosis

MR Imaging differential considerations include

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