Anatomical variation of the azygos vein in human cadavers

Thirty embalmed adult human cadavers irrespective of age, sex and cause of death, were selected for this study over a period of one year to determine the azygos vein formation and drainage patterns. This study revealed four varieties regarding azygos vein formation. In twenty two cases (73.3%), the azygos vein formed by the confluence of the right subcostal and right ascending lumbar vein. It formed by the right subcostal vein with a contribution from the inferior vena cava (IVC) in three cases (10.0%) while, it formed by the right and left subcostal veins in three cases (10.0%) and in two cases (6.7%) formed by the right subcostal vein only. Moreover, in twenty three cases (76.67%), the azygos vein showed usual course and tributaries. Five cases (16.67%) revealed midline azygos vein with independent left lower eight posterior intercostal and subcostal veins. One case (3.33%) showed (H) shape azygos system. Independent double azygos veins were found in one case (3.33%). Based on the results, the azygos vein can take different developmental variations. Such variations are important in mediastinal surgery, imperative for reporting radiologists and have clinical importance. Variations in the formation and drainage pattern of the azygos vein are not clearly described in the literature. In this study the possible causes of these types of variations are discussed in view of the embryological development.