Complete absence of the inferior vena cava presenting as a paraspinous mass.

Dilatation of the azygos-hemiazygos venous system presenting as paravertebral masses may be seen in intrahepatic and extrahepatic portal vein obstruction, anomalous pulmonary venous return, occlusion of the superior and inferior vena cava, persistence of the left superior vena cava, hepatic vein obstruction, eleva- tion of central venous pressure as in congestive heart failure, pericardial effusion, constrictive pericarditis, pregnancy, and isolated aneurysms of the azygos vein.' a : :