Effect of anatomic variations on deep venous thrombosis of the lower extremity.

Three hundred thirty-seven lower extremities of 256 patients, both symptomatic and asymptomatic, underwent ascending positive contrast venography. Certain anatomic variations were noted to be related to the location and development of deep venous thrombosis (DVT). The thrombus was located entirely in the calf in 44% of asymptomatic limbs and 17% of symptomatic ones (p less than 0.001). There were multiple superficial femoral veins (SFVs) in 31% of the limbs examined, and 40% of those limbs had DVT. This percentage (40%) represented a statistically higher incidence of DVT (p less than 0.001) than those limbs with a single SFV, where the incidence was only 19%. When limbs with multiple SFVs had DVT, only 41% were symptomatic, whereas in those with a single SFV, 72% of the limbs were symptomatic (p less than 0.001). This difference may be the result of internal collaterals due to multiple SFVs. When there were more than five valves in the deep veins between the popliteal fossa and the ischial spine, there was a higher incidence of DVT (35%) as compared to the incidence when there were five or fewer valves (13%) (p less than 0.001).