- The azygos lobe is a normal variant that is found in 1% of anatomic specimens and on about 0.4% of chest radiographs.
- It occurs when the right posterior cardinal vein, one of the precursors of the azygos vein, fails to migrate over the apex of the lung and penetrates it instead, carrying along pleural layers that entrap a portion of the right upper lobe.
 Imaging Findings
 Plain film
- The azygos lobe is usually well seen on the chest radiograph, where it is limited by a fine, convex (relative to the mediastinum) line that crosses the apex of the right lung.
- CT shows the deep penetration of the lung behind the SVC and the trachea.
- The azygous fissure ends anteriorly at the right brachiocephalic vein and SVC, and posteriorly at the lateral aspect of the vertebral body near the location of the right superior intercostal vein.
- The azygos vein is seen as a thicker structure following the same path as the fissure. The position of the arch is higher than when it follows an intramediastinal course
- The azygous vein ends in the SVC and occasionally in the right brachiocephalic vein
Patient #1: CT images demonstrate an azygous lobe
 See Also
 External Links
- Mata, J, Caceres, J, Alegret, X, Coscojuela, P, De Marcos, JA. Imaging of the azygos lobe: normal anatomy and variations. Am. J. Roentgenol. 1991 156: 931-937