What are the azygos and hemiazygos veins?

The azygos system of veins consists of three unpaired veins that drain the thoracic wall: the azygos vein, hemiazygos vein, and accessory hemiazygos vein. They lie anterior to the thoracic vertebrae and provide an important venous drainage pathway.

Where is the azygos vein located and what does it do?

The azygos vein is located on the right side of the posterior thoracic wall. It drains the thoracic wall and upper lumbar region and forms a collateral pathway between the superior vena cava (SVC) and inferior vena cava (IVC).

How do the hemiazygos and accessory hemiazygos veins differ from the azygos vein?

The hemiazygos and accessory hemiazygos veins are located on the left side of the posterior thoracic wall, mirroring parts of the azygos vein. They drain left-sided structures and cross the midline to join the azygos vein, unlike the azygos vein which stays on the right.

What is the clinical significance of the azygos vein?

The azygos vein serves as a collateral pathway to the inferior vena cava (IVC) in cases of superior vena cava (SVC) obstruction, helping to maintain venous return from the upper body.

What structures drain into the azygos vein?

The azygos vein receives tributaries from right posterior intercostal veins (2nd–11th, except 1st), the right superior intercostal vein, hemiazygos and accessory hemiazygos veins, and right bronchial, esophageal, mediastinal, and pericardial veins.

Where does the azygos vein terminate?

The azygos vein ascends in the posterior mediastinum, arches over the right lung root at the T4 vertebral level, and drains into the superior vena cava (SVC) at the level of the second costal cartilage.

Azygos System – Azygos & Hemiazygos Veins Explained