Vessel
Azygos vein
The main right paravertebral venous channel
High-yield
The azygos arch crosses above the right lung root before entering the SVC.
Overview
The azygos vein ascends through the posterior thorax and arches over the right lung root to join the superior vena cava. It receives posterior chest-wall and mediastinal tributaries, including the left-sided hemiazygos channels. Connections with lumbar veins provide an alternative route between the caval systems.
Reference facts
- Origin
- Usually right ascending lumbar and subcostal venous channels, with variable caval connections
- Course
- Through the diaphragm near the aortic opening or right crus, up the right posterior thorax, then over the right lung root
- Branches
- Posterior intercostal, hemiazygos, accessory hemiazygos and mediastinal visceral tributaries
- Supplies
- Drains posterior thoracic tissues and contributes to collateral venous return
- Drains to
- Usually the superior vena cava
Clinical correlation
The azygos system can enlarge when it carries collateral flow around venous obstruction. Enlargement may also reflect altered central venous pressure or a congenital continuation of the inferior caval pathway.
Frequently asked questions
Where does the azygos vein originate?
Usually right ascending lumbar and subcostal venous channels, with variable caval connections.
What territory does the azygos vein serve?
Drains posterior thoracic tissues and contributes to collateral venous return.
Where does the azygos vein drain to?
Usually the superior vena cava.
What are the branches of the azygos vein?
Posterior intercostal, hemiazygos, accessory hemiazygos and mediastinal visceral tributaries.