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Anatomy of Azygos Vein: Easy to Understand for Medical Students

Anatomy of Azygos Vein: Easy to Understand for Medical Students

Did you ever hear about the azygos vein? If you have read our previous article then you guys have an idea about this. But if not so don’t worry we will give an amazing article for you on this platform. This article will let you know about the anatomy of the azygos veins, courses, termination, and drainage, etc. 

We agree that medical students have known about azygos vein. It might be difficult for the layman to understand more rapidly than medical students but it’s not unlikely for you. If you are interested in the anatomy of your body then this article is for you. Before going toward the azygos vein let’s have a glimpse of the azygos venous system. The azygos (venous) system is a combined term set to the H-shaped arrangements of the azygos, hemiazygos, accessory hemiazygos veins, and left superior intercostal vein.

It is accountable for clearing the thoracic wall and upper lumbar region by the lumbar veins and posterior intercostal veins. It also supplies chief collateral circulation in the middle of the superior and inferior vena cava. 

What is an azygos vein?

The azygos vein makes from the joint of the right subcostal veins and the ascending lumbar veins. Azygos vein is a unilateral vessel rise in the right posterior mediastinum by the right edge of the inferior eight thoracic vertebrae. In some cases, the azygos vein can proceed in the midline with the head of the thoracic vertebrae. It carries deoxygenated blood forming a collateral pathway between the superior vena cava and the inferior vena cava.

Anatomy of Azygos Vein: Easy to Understand for Medical Students 2 - Daily Medicos

The Function & Structure of Azygos Vein

The azygos vein receiving the right posterior intercostal veins and communicates with the vertebral venous plexus that drain the back, vertebrae, and structures in the vertebral canal. The azygos vein also takes the mediastinal, esophageal, bronchial veins, hemiazygos, and accessory hemiazygos veins. The main function of the azygos vein is; 

  • It carries deoxygenated blood forming a collateral pathway between the superior vena cava and the inferior vena cava. 

Anatomy of Azygos Vein

Origin:

The azygos vein is made by the fusion of the ascending lumbar veins and right subcostal veins at about the T12-L2 vertebral level.

Course:

The azygos vein commonly pierces the chest throughout the aortic hiatus (T12 vertebral level), whereas might invade by entering the right crus of the diaphragm. The azygos vein often begins from the dorsal side of the inferior vena cava at the level of the renal veins. 

It then rises in the posterior mediastinum dorsally at the origin of the right lung (at the level of T5-T6), it connects the superior vena cava just before it enters the pericardium. Although there is a considerable irregularity that the azygos vein takes the accessory hemiazygos vein and the hemiazygos vein at the level of T8 and T9 distributively.

Branches:

The azygos venous system begins from the supra cardinal veins embryologically. The right supra-cardinal vein converts the azygos vein and the left supra-cardinal vein converts into the hemiazygos vein. So let’s move further to describe these branches; 

  • Accessory Hemiazygos Vein:

The accessory hemiazygos vein empties the superior left hemithorax. It originates from the 4th to 8th left posterior intercostal veins and places longitudinally on the left side of the vertebral bodies. It also drains the left bronchial vein. The accessory hemiazygos veins connect azygos veins at the T8 level. 

  • Hemiazygos Vein:

The hemiazygos vein commonly occurs from the left ascending lumbar vein and moves by the left crus of the diaphragm. It clears out the 9th to 11th left posterior intercostal veins and left subcostal vein. The hemiazygos veins connect azygos veins at the T8 level. 

Anatomic Relations:

Relationships of the azygos vein to some other anatomic structures inside the mediastinum are crucial in clinical practice. The following structures are placed dorsal to the azygos vein are:

  • Posterior: vertebral bodies of T5-T12, anterior longitudinal ligament, right posterior intercostal arteries
  • Anterior: inferior vena cava, superior vena cava
  • Right lateral: right greater splanchnic nerve, pleura, lung
  • Left: thoracic duct, aorta, esophagus, trachea, right vagus nerve

Conclusive Thoughts:

The azygos vein makes from the joint of the right subcostal veins and the ascending lumbar veins. Azygos vein is a unilateral vessel rise in the right posterior mediastinum by the right edge of the inferior eight thoracic vertebrae. We have mentioned the important structures and anatomy of the azygos vein in the article. It originates from inferior vena cava and superior vena cava while it drains into superior vena cava. The branches of the azygos vein are; Hemiazygos vein, accessory hemiazygos vein. 

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