Figure 1. (a) Coronal straight and (b,c) curved planar thin-slab maximum intensity projection CT angiography images showing atretic segment of the inferior vena cava (IVC) (double arrows), right perirenal retroperitoneal (small arrows), left paravertebral-gonadal (large arrows) collateral veins, and perirectal-haemorrhoidal venous collateral veins (small arrows in (c)). Large renal veins are seen as a sign of collateral circulation. Left varicocele is also seen (curved arrow in (a)). (d) Coronal curved planar maximum intensity projection MR angiography image showing no detectable flow in the atretic segment of the IVC (double arrows).