CT appearance of the retroaortic anastomoses of the azygos system.

The terminations of the hemiazygos and accessory hemiazygos veins can be mistaken for normal or enlarged posterior mediastinal lymph nodes on CT scans of the chest. These terminations are termed the retroaortic anastomoses by anatomists. We studied the CT appearances of these veins on scans of one cadaver and seven patients. We found that the retroaortic anastomoses usually were clearly recognizable because of their continuity with the hemiazygos or accessory hemiazygos vein. However, it is sometimes possible to mistake these vessels for lymph nodes, especially when only short segments of the vessel are visible on a CT image or when the vessel is not clearly opacified by contrast material. Familiarity with the CT appearances of the hemiazygos and azygous veins can prevent their being mistaken for normal or enlarged lymph nodes.