Azygous vein (anatomy)

The azygous vein is present on the right side of the posterior thorax and abdomen. It is formed by the confluence of the right ascending lumbar vein with the right subcostal vein. Also, it is connected to the inferior vena cava by what is usually a fibrous remnant: this represents the caudal section of the developmental right posterior cardinal vein.

It passes superiorly through the aortic aperture, posterior to the right diaphragmatic crus and anterior to the twelfth vertebral body. It then ascends on the right and anterior surfaces of the inferior eight vertebral bodies, posterior to the oesophagus and to the left of the descending aorta. During this course, the azygous vein receives:

• the posterior inferior eight right intercostal veins
• some bronchial veins from the right lung
• some veins from the mediastinum
• oesophageal veins from the middle of the oesophagus
• the hemiazygous veins from the left side at the level of T8 or T9

At the level of T4, the azygous vein arches over the root of the right lung. At its superior limit, the right superior intercostal vein drains into it. On the anterior surface of the root, the azygous vein drains into the superior vena cava.

With the described tributaries, the azygous vein acts as the main vessel of the azygous system and drains:

• the posterolateral thoracic and abdominal walls
• parts of the right lung and mediastinum
• the middle of the oesophagus