Flexor carpi radialis brevis muscle presenting as a painful forearm mass: case report.

This case report describes an anomalous muscle, the flexor carpi radialis brevis (FCRB), that presented as a painful, enlarging volar forearm mass. After magnetic resonance imaging (MRI) characterization, surgical exploration confirmed that the FCRB tendon crossed over the flexor carpi radialis (FCR) tendon and the resultant tenosynovitis was the apparent cause of the patient's symptoms.