Alterations in CT mediastinal anatomy produced by an azygos lobe.

Computed tomographic (CT) scans of 11 patients with an azygos lobe were compared with similar scans of age- and gender-matched normal controls. The reflections of the right lung against the superior mediastinum were evaluated, and particular attention was directed to five specific areas: the azygos vein and arch, the superior vena cava, the pretracheal and retrotracheal areas, and the esophagus. With an azygos lobe, the azygos arch is at a more cephalad position than normal. The axis of the superior vena cava is oriented toward the left. The azygos lobe intrudes into the pretracheal and retrotracheal mediastinum contacting the anterior wall of the trachea, the medial wall of the superior vena cava, and most of the posterior wall of the trachea in the majority of patients. The presence of an azygos lobe significantly alters the contour of the right mediastinum and changes the relation of lung to the superior vena cava and trachea.