Ulnar to median nerve anastomosis in the palm (Riches-Cannieu anastomosis).

This report describes an unusual case of pure bilateral ulnar innervation of the thenar and hypothenar muscles of the hands. The patient was a healthy 36-year-old woman who presented with neck pain. Examination and routine laboratory investigation findings were normal, but on electroneuromyography ulnar to median nerve anastomosis of the motor fibers in the palm was detected bilaterally. However, there was no anastomosis between the sensory fibers. On investigation of focal neuropathy the anomaly known as Riches-Cannieu anastomosis may surprise the electroneuromyographer and change the clinical signs and symptoms. It should be suspected when the hand muscles are clinically intact in the presence of a severe median nerve lesion in the forearm. In this case, a complete lesion of the median nerve at the forearm might erroneously be interpreted as a partial lesion of the median nerve. In every surgical intervention to the hand, this anomaly should be kept in mind and should be investigated electrophysiologically.