Hypertrophic abductor hallucis muscle with nerve compression syndrome

A 13-year-old girl presented with a soft tissue swelling at the posteromedial side of the foot. This swelling had been present since birth but recently started to cause discomfort and radiating pain to the plantar aspect of the first and second toes. A magnetic resonance imaging (MRI) showed a soft tissue mass (2,6 x 3,7 x 13 centimetres) at the posteromedial side of the foot with signal-intensity similar to the intensity of muscle tissue on all the different sequences. There was no pathological contrast enhancement. Anatomically this mass was located at the abductor hallucis muscle (AH), representing a prominence or hypertrophy of the abductor hallucis muscle (Fig A). The diagnosis was made of a hypertrofic abductor hallucis muscle with narrowing the space for the medial plantar branches of the tibial nerve (circle) at the crossover between the flexor hallucis longus and flexor digitorum longus tendons (arrow), the quadratus plantae muscle (QP) and flexor digitorum brevis muscle (FDB) (Fig B). Example of a normal fibromuscular tunnel (Fig. C). Our patient was treated conservatively first and referred to a foot surgeon