Pigmented villonodular synovitis. A clinicopathologic study of 52 cases.

Clinicopathologic, enzyme histochemical and electron microscopic findings in 52 patients with pigmented villonodular synovitis (PVS) are reported. The lesion was by far the most common in the knee joint (48%), followed by the ankle joint (25%). As to sex incidence, there seemed to be no predilection (46% in men, 54% in women). Microscopically, the PVS showed thin or thick villous projections of the involved synovial membrane, associated with or without nodular formation. The nodule of PVS consisted essentially of a proliferation of histiocyte-like cells with phagocytic activities. Another characteristic feature was large clefts and pseudoglandular or alveolar spaces lined by synovial cells. Enzyme histochemical studies revealed that the lesional cells had functional properties of macrophages. Electron microscopically, the lesion consisted essentially of histiocyte-like and fibroblast-like cells, together with intermediate cells and myofibroblasts.