Accessory hemiazygos vein

The accessory hemiazygos vein (also known as superior hemiazygos vein, Latin: vena hemiazygos accessoria, vena hemiazygos superior) is a blood vessel that runs along the left side of the vertebral column. Both the hemiazygos vein and the accessory hamiazygos vein together serve as the left-sided equivalent of the azygos vein.

The accessory hemiazygos vein is mainly formed by tributaries from the fourth to eighth intercostal spaces on the left side of the thorax. Sometimes the left bronchial veins also contribute to creating this vein. The accessory hemiazygos vein descends on the left side of the vertebral column, crosses the 7th thoracic vertebra (T7) and usually drains in the azygos vein. However, sometimes it flows in the hemiazygos vein. In that case, their common trunk joins the azygos vein.