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Azygos Vein

Contents

Introduction

The azygos venous system is located on either side of the vertebral column and drains the viscera within the mediastinum, as well as the back and thoracoabdominal walls. This system consists of the azygos vein and its two main tributaries: the hemiazygos vein and the accessory hemiazygos vein. This article will discuss the anatomical course, relations and variations of the azygos vein as well as its tributaries. This will be followed by a discussion of any related clinical pathology.

Azygos vein - ventral view

Anatomical Course

The azygos vein usually originates from the posterior aspect of the inferior vena cava, at the level of the renal veins. It ascends within the posterior mediastinum to the level of T4 before it arches above the right pulmonary hilum. It drains into the superior vena cava just before it pierces the pericardium.

Azygos vein - lateral-right view

Anatomical Relations

Relationships of the azygos vein to other structures within the mediastinum can be important in clinical practice. The following structures are located posterior to the azygos vein:

  • the anterior longitudinal ligament
  • right posterior intercostal arteries
  • the bodies of T4-T12 

In the posterior thorax, the azygos vein is located posterior to the recess of the right pleural sac and the oesophagus.

Azygos vein - cross-sectional viewM​edial to the vein one can find:

  • the thoracic duct
  • aorta
  • oesophagus
  • trachea
  • right vagus nerve

The following structures are located laterally to the axygos vein:

  • the right greater splanchnic nerve
  • lung
  • pleura

The azygos vein is also in close proximity to the right posterolateral aspect of the descending thoracic aorta. Pulsations within the aorta may aid venous return in the azygos vein, as well as the hemiazygous vein.

Anatomical Variations

The origin and anatomical course of the azygos vein are quite variable. Usually, there is a singular azygos vein on the right side of the body. However, the azygos vein is occasionally located in the midline or two independent veins may be present like in early embryonic development.

The azygos vein usually originates at the level of the lumbar vertebrae, but may originate further up. The lumbar aspect of the azygos vein can ascend anterior to the lumbar vertebrae and pass behind the right crus of the diaphragm or cross the aortic hiatus (where the aorta pierces the diaphragm) to the right of the cisterna chyli, a dilated lymph sac.

The common trunk of the right ascending lumbar vein and the right subcostal vein joins the azygos vein anterior to the body of T12. However, if the lumbar segment is absent, this trunk may form the azygos vein.

Tributaries

The azygos vein has two tributaries, which are referred to as the hemiazygos vein and the accessory hemiazygos vein.

The hemiazygos vein is often connected to the left renal vein. It is formed by the oesophageal and mediastinal tributaries, the common trunk of the left ascending lumbar vein and left subcostal vein, and by the lower three posterior intercostal veins. It ascends anterior to the vertebral column before crossing the column posterior to the aorta, oesophagus and thoracic duct at the level of T8.

Hemiazygos vein - ventral view

The accessory hemiazygos vein is formed by veins from the fourth to eighth intercostal spaces and sometimes by the left bronchial veins. It descends to the left of the vertebral column before crossing T7, where it joins with the azygos vein. Sometimes it joins the hemiazygos vein and, in this case, their common trunk drains into the azygos vein.

Accessory hemiazygos vein - ventral view

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Show references

References:

  • C. McDermott, G. O’Connor, E. McGovern, G. McMahon: Conservative Mangaement of Azygous Vein Rupture in Blunt Thoracic trauma. Case Reports in Critical Care (2012), volume 2012, Article ID 147614, 3 pages.
  • J.Y. Yang, D.H. Kim, J. H Lee, E. H. Suk: Evaluating a Thrombosed Azygous Vein Aneurysm Combined with Pulmonary Arterial Thromboembolism by ECG-Gated Multidetector CT: a Case Report. Korean J Radiol (2011), volume 12, issue 6, p. 754-6.
  • R. Vikayvergiya, M.N. Bhat, R.M. Kumar, S.G. Vivekanand, A Grover: Azygos continuated of interrupted inferior vena cava in association with sick sinus syndrome. Heart (2005), volume 91, issue 4, e. 26.
  • H. Knipe, Radswiki et al: Azygos continuation of the inferior vena cava. Radiopaedia.org (accessed 24/07/2015)
  • S. Standring: Gray’s Anatomy The Anatomical Basis Of Clinical Practice, 40th Edition, Elsevier Health Sciences UK (2008), p. 1723-6.

Author, Review and Layout:

  • Charlotte O'Leary
  • Catarina Chaves

Illustrators:

  • Azygos vein - ventral view - Yousun Koh
  • Azygos vein - lateral-right view - Yousun Koh
  • Azygos vein - cross-sectional view - National Library of Medicine
  • Hemiazygos vein - ventral view - Yousun Koh
  • Accessory hemiazygos vein - ventral view - Yousun Koh
© Unless stated otherwise, all content, including illustrations are exclusive property of Kenhub GmbH, and are protected by German and international copyright laws. All rights reserved.

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