Pigmented villonodular synovitis of the hip and knee.

Pigmented villonodular synovitis is an uncommon disease that remains a diagnostic challenge. Presenting complaints commonly involve one joint, most often the knee or hip. Symptoms of pain and swelling characteristically have an insidious onset and are slowly progressive. The physical examination may be completely normal. Radiographs of the knee may appear normal or may show a periarticular soft tissue density, expansion of the suprapatellar pouch and local osseous changes confined to the patellofemoral articulation. Radiographs of the hip may show erosions in the head and neck of the femur and acetabulum. Magnetic resonance imaging usually demonstrates key diagnostic features, which include joint effusion, elevation of the joint capsule, hyperplastic synovium and low signal intensity resulting from hemosiderin deposition. The diagnosis of pigmented villonodular synovitis is confirmed by biopsy, and the treatment of choice is synovectomy.