Title:
Bifid median nerve causing carpal tunnel syndrome: MRI and surgical correlation.

Abstract:
Carpal tunnel syndrome can be secondary in some patients, and vascular anomalies (usually a persistent median artery), median nerve variations, or both are among the etiologic factors. High division of the median nerve proximal to the carpal tunnel (known as a bifid median nerve) is a median nerve anomaly that has an incidence rate of 2.8%. This rare entity is often associated with various abnormalities that are clinically relevant, such as vascular malformations (persistent median artery), aberrant muscles, and carpal tunnel syndrome. The bifid median nerve is one cause of carpal tunnel syndrome because of its relatively higher cross-sectional area compared with a nonbifid median nerve. Obtaining magnetic resonance imaging and ultrasounds of bifid median nerves has helped surgeons avoid potential surgical hazards.This article describes 3 men with 4 bifid median nerves associated with a persistent median artery. Mean patient age was 38 years (range, 37-40 years). Mean follow-up was 7 years (range, 3-11 years). Patients were diagnosed with carpal tunnel syndrome and underwent open carpal tunnel release. To reveal a morphological etiology in patients in whom it the possibility of having idiopathic carpal tunnel syndrome is unlikely, preoperative imaging studies should be obtained. Bifid median nerves associated with a persistent median artery in the carpal tunnel are important to understand for their clinical and surgical significance. A secondary nature should be suspected in patients with unilateral symptoms, especially those with a history of symptoms and when the symptomatic hand shows severe neurophysiologic impairment but the contralateral hand is neurophysiologically intact. Inadvertent injury to the median nerve during carpal tunnel surgery can be minimized if the variations of the median nerve are recognized.