The origin of thrombi in the deep veins of the lower limb: a venographic study.

A series of 952 patients was examined by ascending venography; 812 with clinically diagnosed deep vein thrombosis (DVT) (group 1) and 140 with clinical features suggestive of pulmonary embolism (group 2). Thrombus was demonstrated in 401 (49.4 per cent) of group 1 and in 74 (53 per cent) of group 2 patients. A total of 535 limbs contained thrombus. In 493 (92 per cent) thrombus was present in the calf with either no further clot, or clot in continuity with that in more proximal veins. In the remaining 42 legs (8 per cent) thrombus either originated from multiple discontinuous sites in the legs and pelvis, or in proximal major veins without concomitant calf involvement. The clinical implications of these findings are discussed.