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 before arching over the right hilum to enter into the superior vena cava (SVC).
The azygos vein is formed by the union of the ascending lumbar veins and right subcostal veins at the level of T12. It ascends in the posterior mediastinum before arching over the right main bronchus posteriorly at the root of the right lung where it joins the SVC. This "arch of the azygos vein" (arcus venae azygos) is an important anatomic landmark.
The azygos vein is unpaired and unique. The hemiazygos vein is a similar structure on the opposite side of the vertebral column and drains into the azygous along with other tributaries such as bronchial veins, pericardial veins, and posterior right intercostal veins. Communication with the vertebral venous plexus also exists. The azygos venous system is a collective term given to the azygous, hemiazygous and accessory hemiazygous veins.
It forms part of the normal cardiomediastinal contour on CXR and normally measures < 7 mm (erect CXR).
An enlarged azygos vein may occur because of a number of factors:
The Greek root zyg refers to a pair and the prefix a- means not; hence, azygos means unpaired.
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- 1. Dähnert W. Radiology review manual. Lippincott Williams & Wilkins. (2003) ISBN:0781738954. Read it at Google Books - Find it at Amazon
- 2. Heitzman, E. R.; Scrivani, J. V.; Martino, J.; Moro, J. Radiology. doi:10.1148/101.2.249
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