Radiological reasoning: Acutely painful swollen finger.

Objective: The purpose of this article is to review the differential diagnosis of finger masses and their imaging appearances.

Conclusions: Giant cell tumor of the tendon sheath is a slowly growing, benign tumor of the synovium that commonly presents as a painless nodular mass in the hand or wrist. Also termed "localized nodular tenosynovitis," these tumors are the most common soft-tissue tumors of the hand. Occasionally, these tumors can present with pain when traumatized, and they should be suspected when a firm, rubbery mass is found at the location of a tendon sheath.