Fig. 1. Normal computed tomography venography of the lower extremities.

The venous system of the lower extremities is classified into three groups: deep veins, which lie beneath the muscular fascia (dotted lines); superficial veins, which are situated above the muscular fascia; and perforating veins, which penetrate the muscular fascia and connect the superficial and deep veins. Note the deep vein (femoral vein, arrows), superficial vein (great saphenous vein, open arrows), and perforating vein (femoral canal perforator, arrowheads) of the thigh.