Hemiazygos vein

Anatomy

The hemiazygos vein arises in the upper abdominal region from the confluence of the left ascending lumbar and subcostal veins. In some cases, the hemiazygos vein can also arise from the left renal vein. It runs superiorly, passing either through the aortic hiatus or left crus of diaphragm, to appear in the thoracic cavity. It continues its course superomedially through the posterior mediastinum, traveling on the left hand side of the thoracic spine. It then courses to the right, crossing the aorta, esophagus and thoracic duct posteriorly. This vein terminates by draining into the azygos vein at the level of the T8 vertebra. Occasionally, the hemiazygos vein can be continued by the accessory hemiazygos vein.

Along the way, the hemiazygos vein receives several tributaries including:

• Inferior three left posterior intercostal veins, which help to drain the muscles and skin of the posterior trunk, as well as the vertebral column.
• Mediastinal veins, which help to empty the mediastinum.
• Esophageal veins, which contribute to the venous drainage of the esophagus.

Accessory hemiazygos vein

The accessory hemiazygos vein, or superior hemiazygos vein, courses through the posterior mediastinum, receiving a couple of tributaries along the way.

These tributaries include fifth, sixth, seventh and eighth posterior intercostal veins, left superior intercostal vein and the left bronchial veins.

The accessory hemiazygos vein usually crosses the midline and terminates by draining into the azygos vein at the level of the T7 vertebra.