Hemiazygos Vein

vena hemiazygos

The hemiazygos vein is the left-sided counterpart of the lower azygos system, draining the lower left posterior intercostal veins (typically T9-T11). It ascends on the left side of the vertebral column, crosses the midline at T9 posterior to the aorta and thoracic duct, and drains into the azygos vein. The accessory hemiazygos vein drains the upper left intercostal veins (T5-T8) and joins either the hemiazygos or the azygos directly.

Region: Chest

Clinical Relevance

Clinical Notes

The hemiazygos and accessory hemiazygos provide left-sided posterior chest wall venous drainage and are encountered during left thoracotomy and left-sided thoracoscopic procedures. They must be controlled during posterior spinal approaches from the left side. In cases of IVC obstruction or SVC syndrome, the azygos system including the hemiazygos serves as a major collateral pathway to maintain venous return. Embolisation of hemiazygos feeding vessels is occasionally performed in thoracic venous malformations.

Pathology

Common Injuries & Conditions

Hemiazygos Injury in Left Thoracotomy

The hemiazygos vein crossing the midline posterior to the aorta can be injured during left thoracotomy and anterior spinal surgery, requiring suture ligation for control; its division is sometimes planned in posterior left thoracic approaches to gain access to the vertebral bodies.