Pigmented Villonodular Synovitis

     Pigmented villonodular synovitis (PVNS) is a locally aggressive synovial tumor. There are two forms of PVNS: diffuse and nodular. Nodular occurs most commonly in the hands and diffuse is found most commonly in the knee. PVNS may also occur in the hips and ankle. PVNS has the highest
prevalence during the third and fourth decades and it affects males and females equally. It presents as a painless or mildly painful joint with swelling.
The radiological appearance of PVNS depends on the location. A nodule in the hand may have soft tissue swelling and bone erosion on plain x-ray. The knee usually only has a soft tissue mass but bone erosion or cysts will be present in tighter joints like the hip, elbow, ankle or wrist. The joint space is
usually preserved and there may be an effusion. CT scan is able to pick up the hemosiderin and demonstrates the extent of the synovial involvement as well as bone erosion and cysts. Hemosiderin appears as low or absent signal on both T1 and T2 weighted images.
     On gross examination, the diffuse form of PVNS is a tan mass of villi and folds of synovium. The lesion may be sessile or have several pedunculated nodules. Bony invasion through the joint capsule is possible. The local form of PVNS is a pedunculated firm nodule.
     Microscopically, PVNS is characterized by synovial cell hyperplasia both on the surface and below the synovium. Also present are scattered giant cells, hemosiderin and foam cells. The location of the polyhedral cells below the synovial membrane suggests that perhaps the cell of origin is a fibrohistiocyte. The pathologic differential includes hemosiderotic synovitis, rheumatoid arthritis and synovial chondromatosis.
     Treatment of PVNS is surgical excision. Recurrences are common due to the difficulty of complete surgical excision.


References
l Bullough, Peter, Orthopaedic Pathologv (third edition), Times Mirror International Publishers Limited, London, 1997.

Huvos, Andrew. Bone Tumors: Diagnosis. Treatment and Prognosis, W.B.
Saunders, Co., 1991.

Bravo, SM et al., Pigmented Villonodular synovitis, Radiologic Clinics of North America, 34(2):311-325, March, 1996.

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