Azygos system

authentic anatomy

1. Azygos system Dr. Vibhash Kumar Vaidya

2. Azygos system The term azygos means single. Azygos system of veins consists of: azygos , hemiazygos , and accessory hemiazygos veins. These veins lie in front of thoracic part of vertebral column and play an important role in the venous drainage of the thorax .

3. AZYGOS VEIN Present only on the right side in the upper part of the posterior abdominal wall and the posterior mediastinum. It connects the inferior vena cava with the superior vena cava. It is provided with valves and may appear tortuous . The functions of azygos vein are as follows: It drains venous blood from the thoracic wall and upper lumbar region. It forms an important collateral channel connecting the superior vena cava and inferior vena cava.

4. formation of azygos vein Formed by the union of right subcostal and right ascending lumbar vein at the level of T12 vertebra (common ). Arises from the posterior aspect of the inferior vena cava (IVC) near the renal veins. As a continuation of right subcostal vein. Occasionally , it may arise from right renal or right first lumbar vein.

5. COURSE AND TERMINATION The azygos vein after formation ascends up and leaves the abdomen by passing through the aortic opening of the diaphragm and enters the posterior mediastinum. There it ascends vertically lying in front of vertebral column up to the level of T4 vertebra, where it arches forwards above the hilum of the right lung to terminate in the superior vena cava at the level of the 2nd costal cartilage.

6. RELATIONS Anterior : Esophagus (right edge). Posterior : 1 . Lower 8th thoracic vertebrae. 2 . Right posterior intercostal arteries. To the right : 1 . Right lung and pleura. 2 . Greater splanchnic nerves. To the left : 1 . Thoracic duct. 2 . Descending thoracic aorta. 3 . Esophagus (right border).

7. TRIBUTARIES 1. Lower 7th right posterior intercostal veins except first. 2 . Right superior intercostal vein (formed by union of 2nd, 3rd, and 4th right posterior intercostal veins ). 3 . Hemiazygos vein (at the level of T7 or T8 vertebra ). 4 . Accessory hemiazygos vein (at the level of T8 or T9 vertebra ). 5 . Right subcostal vein. 6 . Right bronchial vein. 7 . Right ascending lumbar vein. 8 . Esophageal veins with the exception of those at its lower end. 9 . Mediastinal veins. 10 . Pericardial veins

8. TRIBUTARIES

9. HEMIAZYGOS VEIN The hemiazygos vein lies on the left side only and corresponds to the lower part of the azygos vein (i.e., mirror image of the lower part of the azygos vein ). It is Formed on the left, similar to the azygos vein. by the union of left ascending lumbar vein and left subcostal vein. It may arise from the posterior surface of the left renal vein

10. TRIBUTARIES 1 . Lower three (9th–11th) left posterior intercostal veins. 2 . Left subcostal vein. 3 . Left ascending lumbar vein. 4 . Small esophageal and mediastinal veins.

11. ACCESSORY HEMIAZYGOS VEIN The accessory hemiazygos vein. lies on the left side only and corresponds to the upper part of the azygos vein. ( i.e., mirror image of the upper part of the azygos vein ). It begins at the medial end of left 4th or 5th intercostal space and descends to the left side of the vertebral column. At the level of T8 vertebra.

12. TRIBUTARIES 1 . Fifth to eighth (5th–8th) left posterior intercostal veins. 2 . Left bronchial veins (sometimes).

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