Pigmented villonodular synovitis. Diagnosis and differential diagnosis.

PVNS is a proliferative disorder that can affect joints, tendons and bursae. Its etiology is unknown. The most widely accepted theories attribute this disorder to a chronic inflammatory response or a benign neoplasm of fibrohistiocytic origin. On gross specimens, the synovial changes are characterized by villous and/or nodular hyperplasia. This disorder occurs most frequently in the third or fourth decades of life and has no sex predilection. As a joint problem, it favors the knee and hip. As a tendon abnormality, it favors the digits. Plain film findings include 1) soft tissue swelling, 2) increased density of the synovium secondary to hemosiderin deposition, 3) multiple subchondral cysts, and 4) extrinsic cortical pressure erosions. Cartilage space narrowing, if present, is gradual and occurs later than the other plain film findings. Arthrography can demonstrate the nodular synovial changes and determine if the process is diffuse or focal. MRI can, in some cases, reveal areas of decreased signal within the hyperplastic synovium reflecting the deposition of hemosiderin. The major roentgen differential diagnoses of articular PVNS include uncalcified synovial chondromatosis, tuberculous arthritis, and hemophilic arthropathy.