Tenosynovial giant cell tumor (TGCT)
TGCT exists in three forms: diffuse, localized, and localized TGCT of tendon sheath:
Tenosynovial giant cell tumor (TGCT) of joints and tendon sheaths: diffuse type (also called pigmented villonodular synovitis [PVNS])
The entire synovium of an affected joint or tendon sheath is involved. It affects individuals in their 30s and 40s with equal sex distribution. Grossly, the synovium is red-brown to mottled orange-yellow and prolific with coarse villi, finer fronds, and diffuse nodularity resembling an Angora rug. It is almost always monoarticular. The most common locations include the knee (80%), hip (15%), and ankle. Swelling and effusion accompanied by moderate discomfort, decreased range of motion, and increased warmth to palpation are typical. Pain is frequently less than anticipated from the degree of swelling.
Localized TGCT of the joint (also called benign giant cell synovioma or localized nodular synovitis)
involves only a portion of a synovial surface in a joint, and the lesion is often pedunculated. It presents with symptoms similar to a loose body. It tends not to be as darkly pigmented and has less villous proliferation than is seen in the diffuse form.
Localized TGCT of the tendon sheath (also called giant cell tumor of tendon sheath or fibroxanthoma of tendon sheath)
This benign condition, which occurs with a slightly increased predilection for females, is second only to the ganglion as a source of localized swelling in the hand and wrist. It occurs less frequently (3% to 10%) in the ankle and foot. These nodular lesions usually occur in association with a tendon sheath (formerly called giant cell tumor of tendon sheath). Excision is curative and recurrences are rare.
Histologically, all three forms of villonodular synovitis are remarkably similar.