[Popliteal vein entrapment, popliteal cyst, desmoid tumor and fabella syndrome].

The popliteal fossa is a relatively small, muscle-bound strategic anatomical area where is found, on the posterior aspect of the knee, a vasculonervous pedicle and where both vascular and pseudovascular disease may develop, the latter originating from wall-constituting parts. Among non-typical popliteal diseases, the authors have singled out four rare syndromes. The popliteal vein may be trapped due to fibrous strangulation or, more often, to compression by the hypertrophied gastrocnemius muscle. This requires proper diagnosis and surgical management prior to thrombosis onset. Synovial cysts raise no diagnostic problems, unless they mimic an episode of phlebitis; echotomography has now become essential for diagnosis. Desmoid tumors for which predominant extra-abdominal occurrence sites are the popliteal fossa, the leg and thigh, are difficult to excise completely, especially at the popliteal level, and are a major technical challenge because of the inclusion of the vasculonervous pedicle. Lastly, in sports pathology, one must be able to recognize the painful fabella syndrome (osteochondritis of sesamoid fibrocartilage in lateral head of gastrocnemius), so as not to mistakenly implicate vascular disease. New developments in imaging (namely, real time CT-echography) are of major help to clinicists, who should, nonetheless, remain chiefly responsible for detecting these diseases.