Vessel
Hemiazygos vein
A lower left thoracic tributary of the azygos system
High-yield
Hemiazygos flow commonly joins the right-sided azygos pathway after crossing the midline in the lower thorax.
Overview
The hemiazygos vein collects lower left posterior intercostal drainage and ascends beside the vertebral column. It usually crosses behind the aorta, esophagus and thoracic duct to reach the azygos vein. Its formation and crossing level are variable.
Reference facts
- Origin
- Usually left ascending lumbar and subcostal channels, with variable renal or lumbar connections
- Course
- Ascends through or beside the left diaphragmatic crus, then crosses toward the azygos, commonly near T8–T9
- Branches
- Lower left posterior intercostal and variable mediastinal tributaries
- Supplies
- Returns blood from the lower left posterior thoracic region
- Drains to
- Usually the azygos vein, directly or through a shared communicating channel
Clinical correlation
Hemiazygos channels may enlarge as part of collateral circulation. Normal variants include unusual crossings, shared trunks or absence of a separate named vein, which can affect image interpretation.
Frequently asked questions
Where does the hemiazygos vein originate?
Usually left ascending lumbar and subcostal channels, with variable renal or lumbar connections.
What does the hemiazygos vein supply?
The hemiazygos vein supplies the returns blood from the lower left posterior thoracic region.
Where does the hemiazygos vein drain to?
Usually the azygos vein, directly or through a shared communicating channel.
What are the branches of the hemiazygos vein?
Branches of the hemiazygos vein include the lower left posterior intercostal and variable mediastinal tributaries.