Abstract
Popliteal cysts are frequently found in association with rheumatoid arthritis of the knee; in contrast, lymphangioma of the knee is rare in adults. This report describes a lymphangiolipoma and popliteal cyst located in the leg of a 70-year-old man with poorly controlled rheumatoid arthritis. In the right knee and elbow, similar granulomatous elevations and effusions were observed, and magnetic resonance imaging suggested the presence of effusion from a Baker's cyst in the right knee. However, operatively, the skin tissue was found not to be continuous with the synovial capsule, and the skin tissue was histologically diagnosed as a lymphangioma. Another unique finding in this case was that the effusion appeared to be derived from the Baker's cyst. Synovial fistulae occur only rarely as a spontaneous complication of rheumatoid arthritis. We are unaware of synovial fistulae in relation to a knee joint having been previously described either as a spontaneous occurrence or as a complication of surgery. Particular attention is needed when making the differential diagnosis of lymphangiolipoma and synovial fistulae in the knee.
