Accessory Hemiazygos Vein

vena hemiazygos accessoria

The accessory hemiazygos vein drains the upper left posterior intercostal veins (T5-T8), running inferiorly on the left side of the vertebral column before crossing the midline at T8 to drain into the azygos vein, or descending to join the hemiazygos vein. It connects superiorly with the left superior intercostal vein and communicates with the left brachiocephalic vein. Together with the hemiazygos, it forms the left-sided equivalent of the azygos venous system.

Region: Chest

Clinical Relevance

Clinical Notes

The accessory hemiazygos and hemiazygos veins are encountered during left-sided thoracic procedures, particularly left-sided thoracotomy and left posterolateral approaches to the thoracic spine. These veins must be controlled during anterior thoracic vertebral body surgery at their respective levels. The accessory hemiazygos provides an important venous collateral pathway in SVC obstruction and caval anomalies. Awareness of its variable anatomy prevents inadvertent injury during intercostal vessel ligation in left thoracotomy.

Pathology

Common Injuries & Conditions

Accessory Hemiazygos Injury in Left Thoracotomy

The accessory hemiazygos vein crossing the left lateral spine at T7-T8 is at risk during left posterolateral thoracotomy and anterior spinal approaches, where inadvertent avulsion from the azygos junction causes difficult haemorrhage in the midline paravertebral space requiring careful suture ligation.