Accessory hemiazygos continuation of left inferior vena cava: CT demonstration.

The first CT description of accessory hemiazygos continuation of a left-sided inferior vena cava is presented. This venous anomaly appears as a mediastinal mass on plain chest films and may simulate an aortic dissection on CT or angiography. Careful attention to the various abnormal vascular pathways will obviate the need for further invasive testing.