Anomalies of the inferior vena cava.

The inferior vena cava is formed by a complex process of embryogenesis during the sixth to tenth week of gestation. Improper completion of the process may result in four anatomic anomalies: duplication of the inferior vena cava, transposition or left-sided inferior vena cava, retroaortic left renal vein, and circumaortic left renal vein. The first two anomalies can be diagnosed by sonography and all four anomalies can be seen on CT scan of the abdomen. Duplication and transposition of the inferior vena cava should be further delineated by preoperative phlebography. Preoperative diagnosis of the anomalies should reduce the complication rate of abdominal aortic operations.