The azygos vein is a vein running up the right side of the thoracic vertebral column draining itself towards the superior vena cava. It connects the systems of superior vena cava and inferior vena cava and can provide an alternative path for blood to the right atrium when either of the venae cavae is blocked. Structure The azygos vein transports deoxygenated blood from the posterior walls of the thorax and abdomen into the superior vena cava. It is formed by the union of the ascending lumbar veins with the right subcostal veins at the level of the 12th thoracic vertebra, ascending to the right of the descending aorta and thoracic duct, passing behind the right crus of diaphragm, anterior to the vertebral bodies of T12 to T5 and right posterior intercostal arteries. At the level of T4 vertebrae, it arches over the root of the right lung from behind to the front to join the superior vena cava. The trachea and oesophagus is located medially to the arch of the azygous vein.The "arch of the azygos vein" (arcus venae azygos) is an important anatomic landmark. As an anatomical variation in 1–2% of the population,...