Azygos

Azygos Vein

The azygos vein is an important component of the venous system of the thorax. It is a vessel that drains the thoracic wall and upper lumbar region into the superior vena cava. The azygos vein is part of the azygos venous system, which also includes the hemiazygos and accessory hemiazygos veins.

Anatomy

The azygos vein originates from the right ascending lumbar vein or the posterior aspect of the inferior vena cava. It ascends through the aortic hiatus of the diaphragm, running along the right side of the vertebral column.

Course

The azygos vein travels superiorly in the posterior mediastinum, receiving blood from the right posterior intercostal veins, the right superior intercostal vein, and the hemiazygos and accessory hemiazygos veins. It arches over the root of the right lung and empties into the superior vena cava.

Tributaries

The main tributaries of the azygos vein include:

• Right posterior intercostal veins
• Right superior intercostal vein
• Hemiazygos vein
• Accessory hemiazygos vein
• Esophageal veins
• Bronchial veins
• Mediastinal veins

Function

The azygos vein serves as a collateral pathway for venous return from the thorax and abdomen to the heart, especially when the inferior vena cava is obstructed. It plays a crucial role in maintaining venous return in cases of increased intra-abdominal pressure or inferior vena cava obstruction.

Clinical Significance

The azygos vein can become enlarged in conditions such as portal hypertension, where it serves as an alternative pathway for blood to return to the heart. It may also be involved in certain congenital anomalies or be affected by pathological conditions such as thrombosis or compression by tumors.

Imaging

The azygos vein can be visualized using various imaging modalities, including:

• Chest X-ray: May show an enlarged azygos vein as a paratracheal stripe.
• CT scan: Provides detailed images of the azygos vein and its relationship to surrounding structures.
• MRI: Useful for assessing the azygos vein in cases of suspected vascular anomalies or thrombosis.

See Also

• Hemiazygos vein
• Accessory hemiazygos vein
• Superior vena cava
• Inferior vena cava

References

• Gray's Anatomy: The Anatomical Basis of Clinical Practice.
• Moore, K. L., Dalley, A. F., & Agur, A. M. R. (2013). Clinically Oriented Anatomy.