Pigmented villonodular synovitis-like lesions in association with rare cases of rheumatoid arthritis, osteonecrosis, and advanced degenerative joint disease. Report of five cases.

Five synovial lesions that were incidental microscopic findings during routine pathologic assessment of tissue removed during joint arthroplasties are described. The five lesions were comparable in that they were circumscribed nodular mononuclear spindle cell proliferations similar morphologically to the most common neoplasm-like conditions of joints and tendon sheaths, the so-called pigmented villonodular synovitis (PVNS) or giant cell tumor of tendon sheaths (GCTTS). Their location in the fibrohistiocytic layer of the synovium beneath the membrane lining cells is morphologic evidence of the site of origin of PVNS/GCTTS, a heretofore poorly understood but troublesome clinical entity. Whether these lesions represent true subclinical PVNS or rare reactions to bone, synovium, and cartilage breakdown products leading to a histologic pattern that mimics PVNS remains unclear.