Azygos vein

The azygos vein is a unilateral vessel that ascends in the thorax to the right side of the vertebral column, carrying deoxygenated blood from the posterior chest and abdominal walls. It forms part of the azygos venous system

The azygos vein is formed by the union of the ascending lumbar veins and right subcostal veins at around the level of T12-L2 vertebral level.

If originating at a lumbar level, the azygos vein typically enters the chest through the aortic hiatus (T12 vertebral level), although may enter by piercing the right crus. It then ascends in the posterior mediastinum before arching over the right main bronchus posteriorly at the root of the right lung (at the level of T5-T6) where it joins the SVC. This arch of the azygos vein (arcus venae azygos) is an important anatomical landmark. 

  • hemiazygos vein is a similar structure on the opposite side of the vertebral column and drains into the azygos vein
  • accessory hemiazygos vein
  • posterior right intercostal veins
  • right superior phrenic vein
  • right superior intercostal vein
  • tracheal veins
  • oesophageal veins
  • bronchial veins
  • pericardial veins

The azygos vein freely anastomoses with the vertebral venous plexus. 

It forms part of the normal cardiomediastinal contour on chest x-rays and normally measures <7 mm (erect projection). 

The Ancient Greek root "ζυγόν" (zygon) means a yoke, as holds two oxen together, and thus came to mean a pair, and the prefix "α-" (a) means not; hence, azygos means a non-paired structure.

Anatomy: Thoracic
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Article information

rID: 955
System: Vascular, Chest
Section: Anatomy
Synonyms or Alternate Spellings:
  • Azygous vein

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Cases and figures

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    Figure 1: azygos vein diagram
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    Case 1: contrast enhancing on CTPA
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    Figure 2: azygos vein diagram
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    Case 2: azygos fissure
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    Case 3: azygos fissure and lobe
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    Bronchovascular m...
    Case 4: chest x-ray with azygous vein impression
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