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

This report describes an unusual case of pure bilateral ulnar innervation o f 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 la boratory investigation findings were normal, but on electroneuromyography u lnar to median nerve anastomosis of the motor fibers in the palm was detect ed bilaterally. However, there was no anastomosis between the sensory fiber s. On investigation of focal neuropathy the anomaly known as Riches-Cannieu anastomosis may surprise the electroneuromyographer and change the clinica l signs and symptoms. It should be suspected when the hand muscles are clin ically intact in the presence of a severe median nerve lesion in the forear m. 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 eve ry surgical intervention to the hand, this anomaly should be kept in mind a nd should be investigated electrophysiologically.