Extra-tunnel Compression Mimicking Tarsal Tunnel Syndrome: Ultrasound Imaging for a Plantar Ganglion Cyst.

We reported a 43-year-old man with right-foot numbness under the tentative diagnosis of tarsal tunnel syndrome. The initial ultrasound examination did not identify any remarkable findings at the level of the medial malleolus. Owing to the failure of conservative treatments, he was referred for US-guided injection of the tibial nerve. When tracking the entire course of the nerve, a ganglion cyst was observed on top of the tibial nerve, in proximity to the medial and lateral plantar branches. The symptom disappeared after surgical excision. The present case highlights the importance of sonoantomy and tracking of the entire course of affected nerve in peripheral nerve disorders and scout scanning prior to any perineural injections.