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Remote Fellowship – Foot & Ankle Fundamentals – 11/2/2020

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Diagnosis

Morton Neuroma

Case Discussion

A Morton neuroma, also known as an intermetatarsal neuroma, is a focal area of symptomatic perineural fibrosis around a plantar interdigital nerve. The condition is considered a chronic entrapment neuropathy caused by the distal extent of the deep transverse intermetatarsal ligament. It is histologically characterized by neural degeneration with epineural and endoneural vascular hyalinization, and perineural fibrosis. The condition is more prevalent in women than men, with the onset of symptoms most commonly in the 5th decade, and the 3rd intermetatarsal space is most frequently affected.

MRI findings of a Morton neuroma include a dumbbell/ovoid shaped lesion in the intermetatarsal space just proximal to the metatarsal head, with intermediate signal intensity on T1-weighted images and low to intermediate signal intensity on T2. Enhancement characteristics are variable and depend on the proportion of fibrous tissue.

T2 high signal intensity between the metatarsals may be mass like and represent some bursitis.  The morton neuroma never demonstrates fluid signal; bursitis does.  Sometimes the two co-exist.

Key Images

Two Morton neuromas in an 80-year-old man with a several-year history of a painful “lump” on the bottom of his left foot.

A. Axial T1 image of the left foot shows a large intermetatarsal mass (M3-M4) with intermediate signal intensity measuring approximately 3.0 x 2.0 cm (red arrow). A similar, smaller, intermetatarsal mass (M2-M3) with intermediate signal intensity is also present (green arrow).
B. Axial T1 FS image shows a large intermetatarsal mass (M3-M4) with high signal intensity peripherally and intermediate signal intensity centrally, measuring approximately 3.0 x 2.0 cm (red arrow). A similar but smaller intermetatarsal mass (M2-M3) has high signal intensity (green arrow).

References

  1. Torres-Claramunt R, Gines A, Puig L, de Zabala S. MRI and ultrasonography in morton’s neuroma: Diagnostic accuracy and correlation. Indian J Orthop 2012; 46(3) 321-325
  2. Sharp RJ, Wade CM, Hennessy MS, Saxby TS. The role of mri and ultrasound imaging in morton’s neuroma and the effect of size of lesion on symptoms. J Bone Joint Surg Br 2003; 85(7) 999-1005