Pathological case of the month.

A 12-YEAR-OLD male child had a history of swelling in the left knee joint since age 4 years. There was no pain or other constitutional symptoms. On physical examination the swelling was soft and boggy. There was no tenderness and the movements were not painful or restricted. Results of routine blood investigations were within normal limits. Aspiration of the knee joint did not reveal any fluid. X-ray films revealed synovial thickening. Arthrotomy with subtotal synovectomy resulted in exuberant grapelike, soft, fleshy synovium (Figure 1, Figure 2, and Figure 3). About 100 g of tissue was received for pathologic examination.