A rare human variation: a major branch of the ulnar artery found in the carpal tunnel.

During a routine anatomic dissection of a 60-year-old female cadaver, a large branch of the ulnar artery in the carpal tunnel was found in the left forearm. This branch crossed the median nerve anteriorly. Guyon's canal contained another branch of the ulnar artery and the ulnar nerve. There was no superficial palmar arch in the left hand. The right forearm was without any vascular anomalies. This anomaly has considerable consequences for surgeons considering endoscopic carpal release, because there is a significant risk of injury to the ulnar artery branch.