Azygos Venous System
The azygos venous system provides essential collateral drainage for the thoracic wall and serves as a critical bridge between the inferior and superior vena cava systems.
Key Components
- Azygos Vein: Primarily on the right. Ascends in the posterior mediastinum and arches over the root of the right lung to drain into the superior vena cava (SVC).
- Hemiazygos Vein: On the left (inferior). Typically crosses the midline at T8–T9 to join the azygos vein.
- Accessory Hemiazygos Vein: On the left (superior). Typically crosses at T7–T8 to join the azygos vein.
Clinical Significance
| Condition | Key Detail |
|---|---|
| Caval Obstruction | If the SVC or IVC is obstructed, the azygos system can become significantly dilated to provide an alternative venous return route. |
| Esophageal Varices | The azygos vein receives esophageal veins; in portal hypertension, these form part of the portosystemic shunt, leading to risk of hemorrhage. |
High-Yield Exam Pearl:
On a plain chest X-ray, the azygos vein appears as an “azygos node” or “azygos knob” in the right tracheobronchial angle. Enlargement of this structure can be a sign of SVC obstruction or portal hypertension.