Age / Sex : 62 / M

Chief complaint : 4개월 동안의 내측 발바닥 통증

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Courtesy : 정보미 (Bo Mi Chung), 중앙대학교 병원 (Chung-Ang University Hospital)

Medial plantar neuropathy due to ganglion cyst

Discussion

Findings
Denervation change muscles, abductor hallucis muscle, flexor hallucis brevis, flexor digitorum brevis
Ganglion cyst along the medial plantar nerve

Discussion
Entrapment of the medial plantar nerve can occur at the tarsal tun­nel or distal to it, at the level of the Henry knot, between the navicular tuberosity superiorly and the abductor hallucis muscle belly inferiorly. Patients usually present with heel and arch pain, tenderness and a positive Tinel sign posterior to the navicular tuberosity, and numbness along the medial plantar foot. Medial plantar nerve denervation is theorized to lead to increased stress and secondary osteoarthrosis at the first metatarsophalangeal joint.
At MR imaging, space-occupying lesions such as ganglia can be identified, as they replace the normal fat between the abductor hallucis and flexor digitorum brevis muscles. The presence of an excessive amount of tendon sheath fluid at the Henry knot, while usually asymptomatic, should raise the possibility of entrapment of the medial plantar nerve. High signal intensity on T2-weighted images or fatty atrophy involving the abductor hallucis and flexor digitorum bre­vis muscles is indicative of medial plantar nerve entrapment at the ankle.

References
MR Imaging of Entrap­ment Neuropathies of the Lower Extremity Part 2. The Knee, Leg, Ankle, and Foot. RadioGraphics 2010; 30:1001–1019