[X-ray morphology of osseous changes in pigmented villonodular synovitis of the joints].

Pigmented villonodular synovitis (PVNS) of the joints is a rare, benign and generally monoarticular tumour-like soft tissue lesion of the synovium. The secondary bone changes, seen in plain films of 25 patients with PVNS are described. The main radiological features were paraarticular erosions, often with a thin sclerotic border. As a late manifestation these erosions tended to coalesce and to form large multicystic areas. These defects were observed particularly in the more tightly encapsulated joints, such as the hip, wrist, finger and toe. In 3 cases with involvement of the knee the lesions were monostotic. PVNS may be mistaken radiologically for other lesions such as malignant tumours or inflammatory disorders. The differential diagnosis is discussed.