AZYGOUS VENOUS SYSTEM
AZYGOUS VENOUS SYSTEM
- The azygos (venous) system is a collective term given to the H-shaped configuration of the azygos, hemiazygos, accessory hemiazygos veins and left superior intercostal vein.
- It is responsible for draining the thoracic wall and upper lumbar region via the lumbar veins and posterior intercostal veins .
- It also provides important collateral circulation between the superior and inferior venae cavae should they become obstructed.
Development
- The azygos venous system arises from the supracardinal veins embryologically.
- The right supracardinal vein becomes the azygos vein, while the left supracardinal vein becomes the hemiazygos vein.
AZYGOUS VEIN
- Azygous vein connects SVC & IVC. It also connects portal venous system & caval venous system.
- The azygous vien is formed by union of the lumbar azygous , right subcostal & right ascending lumbar veins.
- It enters the thorax by passing through the aortic opening of the diaphragm.
- Then it ascends upto T4 vertebra where it arches forwards over the root of right lung & ends by joining the SVC in the middle mediastinum.
Its tributaries are:
- Right superior intercostal vein
- 5th to 11th right posterior intercostal veins.
- Hemiazygous vein at lower border of T8.
- Accessory azygous vein at upper border of T8.
- Right bronchial vein, last tributary
- Several oesophageal, pericardial & mediastinal veins
HEMIAZYGOUS VEIN
- It is also called inferior hemiazygous vein.
- It is formed by union of left lumbar azygous, left ascending lumbar & left subcostal veins.
- It pierces the left crus of diaphragm & ascends upto T8 level where it turns to right & joins azygous vein.
- It drains 9th to 11th left posterior intercostal veins & oesophageal veins.
ACCESSORY HEMIAZYGOUS VEIN
- It is also called superior hemiazygous vein.
- It descends from 4th or 5th intercostal space down to upper border of T8 where it turns to right & joins azygous vein.
- It receives 5th to 8th left posterior intercostal veins & sometimes left bronchial vein.
Left superior intercostal vein
- The left superior intercostal vein drains the left posterosuperior hemithorax and is considered to be part of the azygos venous system even though it does not directly drain into the azygos vein.
Exam Important
- Azygos venous system arises from the supracardinal veins.
- Azygous vein drains into Superior vena cava.
- Azygous vein ascends through the aortic opening in the diaphragm.
- The azygous vien is formed by union of the lumbar azygous , right subcostal & right ascending lumbar veins.
- The Last tributary of azygous vein is Right bronchial vein.
- Azygous vein & hemiazygous vein drain into Middle mediastinum.
- Hemiazygous vein crosses left to right at the level of T8.
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