Giant Cell Tumor of Tendon Sheath in Guyon's Canal Causing Ulnar Tunnel Syndrome A Case Report and Review of the Literature

Objective: Giant cell tumor of tendon sheath is a rare cause of ulnar tunnel syndrome. We present a case of a 37-year-old woman who presented with decreased sensation and weakness of grip of the right hand. Magnetic resonance imaging indicated the presence of a mass in the hypothenar eminence and showed that the mass was associated with the flexor carpi ulnaris tendon and displacing the ulnar neurovascular bundle. A differential diagnosis included desmoid tumor and sarcoma. Methods: Surgical examination showed a mass that was associated with the flexor carpi ulnaris tendon and flexor retinaculum located in the distal portion of Guyon's canal and intertwined with the ulnar nerve and displacing the ulnar artery. The mass was removed and Guyon's canal was released. Results: Histological examination indicated a diagnosis of giant cell tumor of tendon sheath (GCTTS). Postoperatively, the patient had fully restored sensory and motor function of the right hand. Conclusions: Although GCTTS is the most common solid, soft-tissue lesion of the hand, it is rarely diagnosed properly preoperatively. Therefore, it is imperative to always include GCTTS in the differential diagnosis of any mass of the hand.