The authors paid attention to revealing as precisely as possible anatomical and haemodynamic conditions in venous vascular bed in the course of ultrasonographic examination of 309 lower extremities with clinical manifestations of chronic venous insufficiency (CVI). A combined reflux in the superficial and deep venous system (53.7 %) or isolated reflux in superficial veins (25.9%) proved to be the most frequent pathogenic bases of CVI. Pathophysiology of varices was mostly based on the venous reflux and the primary idiopathic CVI was mostly present (98.1%). The post-thrombotic partial obstruction of the deep venous system (post-thrombotic venous changes on the walls) was demonstrated exceptionally (1.9 %). A high coincidence of reflux in the deep and superficial venous system points out to s.c. secondary eflux in the deep veins originating on the basis of primary reflux in the large or small saphena. An attempt was made to clarify, whether the development and frequency of incompetent perforators is directly connected with the presence and seriousness of reflux in the large and small saphena. The presence and severity of large saphena insufficiency does not univocally indicate the presence of dilated or insufficient perforators on the medial side of the crus, where these anastomoses are present most frequently. The large saphena is a long vein typically suffering from segmental insufficiency, i.e. reflux affecting a certain portion, whereas other parts of the vein may be fully competent. Anatomical venous variability and abnormalities on lower extremities were demonstrated in every fifth extremity (62 extremities, 20.1 %). Most of them concerned large saphena (39 extremities, 62.8 %), small saphena being second (15 extremities, 25.2 %). Other anatomical deviations occurred sporadically as solitary findings. In the large saphena, duplication was present most frequently (54.8 %). Insufficient variable superficial veins and anatomical venous anomalies were mostly not the only pathogenic basis of CVI, but were predominantly associated with insufficiency in the area of deep veins and perforators (84 %). In our cohort there were altogether 55 extremities (17.8 %) after the operation on superficial venous system, where relapses of varices were found. The causes of post-operation relapse of varices may be divided into three groups: 1. insufficiency of the large saphena, 2. insufficiency of the small saphena and 3. insufficiency of the deep veins. A combined simultaneous insufficiency in several venous systems was found most frequently (27 extremities, 49.1 %). Even though the reflux in the deep veins was demonstrated in 50.9 % of these extremities, a combination with the reflux in superficial veins and perforators (49.1 %) was present with the exception of one case of isolated insufficiency. The insufficiency of the large and small saphena was clearly the leading single cause (15 extremities, 27.3%) of varix relapses. The patients should never be operated on the venous system of lower extremities without previous detailed ultrasonographic examination. It is the only way to increase probability of the operation success and to decrease the risk of relapses of CVI manifestations.

        Key words: Color duplex sonography - Chronic venous insufficiency - Anatomical venous anomalies - Variable veins - Secondary venous reflux - Post-operation varix relapse