Palpable lump on IP joint of the thumb, on extensor side. Evaluate extensor tendon on left thumb for giant cell tumor of tendon sheath. There is a lobulated mass within the soft tissues of the thumb that completely surrounds the interphalangeal joint. Dorsally, the mass lies deep to the extensor tendon, extending from the mid-diaphysis of the proximal phalanx to the level of the interphalangeal joint. The mass extends in both the radial and ulnar directions to surround the head and neck of the proximal phalanx with what appears to be extension deep to the flexor digitorum profundus tendon. There is also a relatively large (14 mm) nodular component of the mass situated superficial and medial to the flexor digitorum profundus tendon at the level of the interphalangeal joint. The mass is of similar signal intensity to muscle on T1-weighted images and shows persistent low signal intensity on T2-weighted images. Although the mass shows relatively mild enhancement following gadolinium administration, the low signal intensity on T2-weighted images favors the suspected diagnosis of tenosynovial giant cell tumor. I see no definite tumor within the joint, nor do I see any definite bone erosions. Both the extensor and flexor tendons can be traced to their insertions on the distal phalanx.
Soft tissue mass in the thumb as described above with MR imaging features compatible with the suspected clinical diagnosis of tenosynovial giant cell tumor.