[Pseudothrombophlebitis due to an expansive popliteal cyst associated with Reiter's syndrome].

Popliteal cysts presenting as thrombophlebitis are unusual diseases of the popliteal fossa and are commonly associated with rheumatoid arthritis or meniscal tears. The authors report the case of a 38-year-old man with Reiter's syndrome in which a synovial cyst of the popliteal space, mimicking symptoms suggestive of deep venous thrombosis, complicated the course of the arthritis. Clinical and diagnostic features of this rare popliteal pathology are discussed and the usefulness of noninvasive diagnostic methods for detecting this disease, in particular that of echotomography, is emphasized. The authors stress the importance of a correct diagnosis in order to avoid the risks of an erroneous anticoagulant treatment.