Anomalous muscle of the wrist

A case of an anomalous muscle found in the right wrist of a 52-year-old man during routine carpal tunnel decompression surgery is reported. The muscle was observed lying transversely across the carpal tunnel superficial and parallel to the flexor retinaculum. Its further definition was subsequently demonstrated by postoperative magnetic resonance imaging (MRI). No similar structure was detectable on MRI of the left wrist.