The portal vein as collateral in inferior vena cava obstruction.

In five patients with obstruction of the inferior vena cava, collateral flow to the portal vein was demonstrated. Although there are many reports on caval occlusion, only 21 cases with this collateral circulation pattern have been reported. The reasons for this are most likely technical: To demonstrate this circulation, a large volume of contrast medium must be used and, because of the low flow velocity in the numerous wide collaterals, delayed films are also necessary.