The radiology of the right superior intercostal vein.

The right superior intercostal vein is visualised on CT examination as a circular opacity laterally at the right aspect of the vertebral body at the T4-T5 level. In venographic examination the RSIV appears to be formed by the confluence of the venous channels, the right second, third and fourth intercostal veins. In superior vena cava obstruction the RSIV is an important collateral pathway: the flow through the vein depends on the site of the obstruction, anterograde if the obstruction is superior or parallel to the level of the vena azygos, and retrograde if the obstruction is below the vena azygos.