Pigmented villonodular synovialitis. Rare differentialdiagnosis of a popliteal space-occupying lesion

Pigmented villonodular synovitis (PVNS) is a disease that involves the lini ng of joints, bursae and tendon sheaths. The incidence is low and estimated to be 1.8 patients per million population. The cause of PVNS is unclear an d discussed to be either inflammatory or neoplastic. PVNS has been describe d in 2 forms different for prognosis and treatment (nodular and diffuse). T he articular form almost appeares in the knee joint as we describe below in a 14 year-old patient. PVNS was first defined in 1941 by Jaffe e.a. [7]. Because of the uncommon o ccurence of the disease it is difficult to amass patient series to allow co nfirmed statements on therapy and outcome. Larger patient series raise out of long periods of time. Differences in outcome and recurrence rates exist for the nodular and diffuse form. Clinical findings are moderate pain and s welling of joints due to effusion and synovial proliferation. Magnetic reso nance imaging shows typical findings. Surgical procedures are recommended a s open or arthroscopic synovectomy for the diffuse form of PVNS,local excis ion for the nodular form and arthrodesis or prosthetic replacement for join t destruction.