Hemiazygos vein of posterior thoracic wall

Hemiazygos vein of posterior thoracic wall 

Location

It is also known as inferior hemiazygos vein . it lies on the left side only and corresconds to the lower part of the azygos vein

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Tributaries

1.    Lower 3 (9-11^th ) left posterior intercostals veins

2.    Left subcostal vein

3.    Left ascending lumbar vein

4.    Small esophageal and mediastinal veins

Formation

It is formed on the left side similar to the azygos vein by the union of left ascending lumbar vein and left subcostal vein

It may arise from the posterior surface of the left renal vein

Course

The hemiazygos vein enters the thorax either through the aortic hiatus or directly through the diaphragmatic crura. It then courses superiorly to the left of the midline in the posterior mediastinum, adjacent to the thoracic vertebrae until the level of T8 or T9 vertebral bodies, where it crosses the midline anteriorly to the vertebral column to drain into the azygos vein. 

Variant anatomy

·         hemiazygos continuation of the IVC: often occurs with duplicated IVCs

·         interazygos vein: occurs when forming a common trunk with the accessory hemiazygos vein anterior to the aorta

Drainage area

It drains the left inferior hemithorax