Venous drainage of thoracic wall / azygos system of veins

Venous drainage of thoracic wall / azygos system of veins

Azygos vein of posterior thoracic wall

Location

It is present only on the right side in the upper abdominal wall

Tributaries

·         Right ascending lumbar vein

·         Right subcostal vein

·         Right superior intercostals vein (created by 2-4^th right posterior intercostals veins

·         Hemiazygos vein

·         Accessory hemiazygos vein

·         Right brochial veins

·         Esophageal veins

·         Mediastinal veins

·         Pericardial veins 

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Formation

Its formation is variable:

1.    It is formed by the union of the ascending lumbar veins with the right subcostal veins at the level of the 12th thoracic vertebra, 

2.    Arises from the posterior aspect of the inferior vena cava near the renal veins

3.    As a continuation of right subcostal vein

4.    Occationally it may arise from the right renal or right first lumbar vein

Course

 It enters the thorax via the aortic hiatus in the diaphragm and ascends posteriorly alongside the vertebral bodies, arching over the right main bronchus at T5-T6 and enters the superior vena cava (SVC) at T4 

Variant anatomy

The azygos vein may rarely drain into the right brachiocephalic vein, right subclavian vein, intrapericardial SVC or directly into the right atrium

Drainage area

Thoracic wall and upper lumbar region 

Hemiazygos vein of posterior thoracic wall 

Location

It is also known as inferior hemiazygos vein . it lies on the left side only and corresconds to the lower part of the azygos vein

Tributaries

1.    Lower 3 (9-11^th ) left posterior intercostals veins

2.    Left subcostal vein

3.    Left ascending lumbar vein

4.    Small esophageal and mediastinal veins

Formation

It is formed on the left side 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

Course

The hemiazygos vein enters the thorax either through the aortic hiatus or directly through the diaphragmatic crura. It then courses superiorly to the left of the midline in the posterior mediastinum, adjacent to the thoracic vertebrae until the level of T8 or T9 vertebral bodies, where it crosses the midline anteriorly to the vertebral column to drain into the azygos vein. 

Variant anatomy

·         hemiazygos continuation of the IVC: often occurs with duplicated IVCs

·         interazygos vein: occurs when forming a common trunk with the accessory hemiazygos vein anterior to the aorta

Drainage area

It drains the left inferior hemithorax

Accessory hemiazygos vein

Location

It is also known as superior hemiazygos vein . it lies on the left side only and corresponds to the upper part of azygos vein

Tributaries

·         5^th to 8^th left posterior intercostals vein

·         Left bronchial veins (occationally )

Formation

The accessory hemiazygos vein is formed by the confluence of the middle left posterior intercostal veins. 

Course

It descends to the left of midline, adjacent to the thoracic vertebrae and crosses posteriorly to the aorta at the level of T7-8 to drain into the azygos vein. It normally anastomoses with the left superior intercostal vein.

Variant anatomy

·         drains via a common trunk with the hemiazygos vein into the azygos vein

·         forms a common trunk with the hemiazygos vein that passes anterior to the aorta called the interazygos vein 

·         drains directly into the left brachiocephalic vein (rare) 

Drainage area

It drains the left superior hemithorax.