Carpal Tunnel Syndrome Caused by Bifid Median Nerve in Association with Anomalous Course of the Flexor Digitorum Superficialis Muscle at the Wrist

Secondary carpal tunnel syndrome (CTS) can be caused by vascular anomalies usually involving persistent median artery, variations of the median nerve, and space-occupying lesions in the wrist and palm. High division of the median nerve proximal to the carpal tunnel (known as a bifid median nerve) is a median nerve anomaly with a reported incidence of 2.8% per wrist. The bifid median nerve is often associated with various abnormalities such as persistent median artery and aberrant muscles, causing clinical features of CTS. Most reported cases of bifid median nerves are associated with CTS due to its higher cross-sectional area compared to a non-bifid median nerve. We report a rare case in which an anomalous tendinous course of the flexor digitorum superficialis muscle is associated with bifid median nerve proximal to the flexor retinaculum at the distal wrist. Surgeons should consider the possibility of median nerve variation in patients with unilateral severe CTS and be aware of this anomaly during elective carpal tunnel release.