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Hemiazygos vein

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Major veins of the thorax and abdomen.
Hemiazygos vein (Vena hemiazygos)

The hemiazygos vein (also known as the inferior hemiazygos vein) arises from the confluence of left lumbar ascending and subcostal veins. It is considered to be a left equivalent of the azygos vein. The hemiazygos vein runs in the posterior mediastinum and drains into the azygos vein at the level of the eighth thoracic vertebra.

Along its course, the hemiazygos vein receives several tributaries which include: ninth, tenth and eleventh left posterior intercostal veins, mediastinal and esophageal veins.

This article will discuss the anatomy and function of the hemiazygos vein.

Key facts about the hemiazygos vein
Drains from Left lumbar ascending vein, subcostal vein
Tributaries Inferior three left posterior intercostal, mediastinal and esophageal veins
Drains to Azygos vein
Drainage area Posterior trunk muscles and skin, vertebral column, mediastinum, esophagus
  1. Anatomy
  2. Accessory hemiazygos vein
  3. Sources
+ Show all


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.

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