Four major anomalies of the venous system were encountered during abdominal aortic surgery. These were transposition of the inferior vena cava, duplication of the inferior vena cava, circumaortic venous collar, and retroaortic left renal vein. Although these anomalies are not common, each poses a particular problem related to its recognition, protection from injury, and intraoperative management.
Brener BJ, Darling RC, Frederick PL, Linton RR. Major Venous Anomalies Complicating Abdominal Aortic Surgery. Arch Surg. 1974;108(2):159-165. doi:10.1001/archsurg.1974.01350260019004