Pigmented villonodular synovitis: keys to early diagnosis.

Pigmented villonodular synovitis is a synovial proliferative disorder that remains a diagnostic difficulty. Many clues in the history, physical examination, and radiographic studies can aid in the diagnosis. A patient in the third or fourth decade of life often will present with vague monoarticular complaints. Symptoms include intermittent, extreme deep pain localized to the hip, occasionally relieved by position. Decreased active and passive range of motion may be found. Small erosions in the head of the femur and acetabulum may occur early in the course of the disease. Magnetic resonance imaging is the imaging modality of choice and will show the characteristic findings of a joint effusion, synovial proliferation, and bulging of the hip. The synovial lining has a low signal on T1- and T2-weighted images, secondary to hemosiderin deposition. Pigmented villonodular synovitis should be included in the differential diagnosis of young patients with unexplained hip pain.