Circumaortic venous ring: incidence and significance.

A left circumaortic renal vein was found in 11% of 74 left renal venograms, an incidence similar to that at autopsy. Cavography proved to be an unsatisfactory method of demonstrating the renal veins. Prior knowledge of a venous ring is important when blood samples from the adrenal or renal veins are to be collected. When caval interruption is planned, a circumaortic venous ring may provide a fully developed collateral pathway immediately after surgery if the procedure is planned without awareness of its presence.