Fibroma of a tendon sheath causing Guyon's canal syndrome: case report.

This report presents a rare case of a 41-year-old woman with decreased sensation and weakness of grip of her left hand. On examination she had a well-defined mass on the ulnar-volar aspect of the wrist. Magnetic resonance imaging showed a focal nodular mass in Guyon's canal. Examination showed that the mass, 2.1 × 1.1 × 1.0 cm in size, originated in the proximal portion of the canal and was loosely associated with the tendon sheath of the flexor carpi ulnaris. The mass was removed and Guyon's canal released. Histological examination confirmed a diagnosis of fibroma of tendon sheath. Postoperatively, she had fully restored sensory and motor function of her left hand. The tumor has not recurred.