Dilatation of the hemiazygos system on plain films of the chest.

The enlargement of the hemiazygos system and the superior intercostal vein as a collateral pathway in cases of obstruction of the superior or the inferior vena cava is recognizable on the frontal and lateral plain chest films. It appears in frontal radiographs as an additional line parallel to the left paraspinal line with a bulging at the level or superiorly to the aortic knob and continuing with the shadow of the left brachiocephalic vessels. In the lateral chest view it is evident as an inhomogeneous soft tissue density posteriorly to the lower third of the trachea.