Accessory hemiazygos vein

Last revised by Yoshi Yu on 8 Apr 2023

The accessory (or superior) hemiazygos vein forms part of the azygos system and along with the hemiazygos vein, it is partially analogous to the right-sided azygos vein. It drains the left superior hemithorax. 

Spelling it "hemiazygous" when referring to the vein is incorrect, regardless of whether British or American English 5. In the context of anatomy, see Terminologia Anatomica, hemiazygos vein is the sole correct spelling.

The accessory hemiazygos vein is formed by the confluence of the 4th to 8th left posterior intercostal veins.

It descends to the left of midline, adjacent to the thoracic vertebrae and crosses posteriorly to the aorta at the level of T7-8 to drain into the azygos vein. It normally anastomoses with the left superior intercostal vein superiorly.

  • drains via a common trunk with the hemiazygos vein into the azygos vein

  • forms a common trunk with the hemiazygos vein that passes anterior to the aorta called the interazygos vein 2

  • drains directly into the left brachiocephalic vein (rare) 2

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Cases and figures

  • Figure 1
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  • Case 1: appearance on CTPA
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  • Case 2 : drains into left brachiocephalic vein
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