Inferior vena cava anatomic variants

Imaging description Inferior vena cava (IVC) anomalies reflect an abnormal regression or persistence of the various embryonic veins, and there are numerous variations. In patients with double (right and left) IVC, two oval structures are seen on both sides of the abdominal aorta on axial images (Figures 99.1 and 99.2). There may be significant discrepancy in the size of the two veins. Typically the right and left IVCs join to form a single right IVC at the level of the left renal vein (Figures 99.1 and 99.2). Different from dilated gonadal vein, the left IVC continues caudally to the left common iliac vein (Figure 99.1). Retrocaval ureter is an anomaly related to the development of the inferior vena cava. The proximal right ureter is positioned posterior to the IVC, and then courses to the left of the IVC, and finally crosses anterior to the IVC (Figure 99.2). Hydronephrosis due to ureteral obstruction may occur in patients with retrocaval ureter. In patients with interruption of the IVC with azygos or hemiazygos continuation, the hepatic segment of IVC is absent (Figure 99.3), and the renal segment of IVC receives blood return from both kidneys and passes posterior to the diaphragmatic crus, and enters the thorax as the azygos or hemiazygos vein (Figure 99.3). The hepatic veins drain directly into the right atrium. In these patients, the azygos or hemiazygos vein is dilated (Figure 99.3), reflecting the increased flow through these vessels. Importance IVC anomalies usually are an incidental finding and do not have a clinical significance. However, it may simulate an abnormal structure such as lymphadenopathy or a mass. Before interventional or surgical procedures, such as IVC filter placement, anomalous anatomy of the IVC is important to be recognized. For example, in patients with double IVC, recurrent pulmonary embolism following placement of an IVC filter is possible. Other uncommon types of IVC anomaly include IVC agenesis, right-sided double IVC, and left IVC with left retrocaval ureter. In patients with IVC agenesis, recurrent deep venous thrombosis may occur.