Anatomy, Thorax, Azygos Veins

The azygos vein forms from the junction of the right subcostal veins and the ascending lumbar veins. The azygos vein is a unilateral vessel that ascends in the right posterior mediastinum along the right border of the inferior eight thoracic vertebrae. In some instances, the azygos vein can travel in the midline along the top of the thoracic vertebrae. This vein carries deoxygenated blood forming a collateral pathway between the superior vena cava (SVC) and the inferior vena cava (IVC). Starting at vertebral levels T12-L2, the azygos vein travels posterior to the right root of the lung (T5-T6) and arches superiorly over the root of the lung, emptying into the SVC. Sometimes, the azygos vein may travel higher to drain into the brachiocephalic or right subclavian vein. There are also instances where the azygos vein can end by draining into the intra-pericardial SVC or even the right atrium.