Azygos Vein Origin & Course: Abdominal to Thoracic Pathway

The azygos vein is a major thoracic venous channel draining the posterior chest wall and mediastinum.

Origin

• Forms at the T12–L2 level as a continuation of the right ascending lumbar vein.
• Receives the right subcostal vein near the diaphragm.
• Enters thorax through the aortic hiatus (with thoracic duct) or posterior to the right crus of diaphragm.

Thoracic Course

• Ascends in posterior mediastinum, right of thoracic aorta, anterior to vertebral bodies.
• Archives over right main bronchus at T4–T5 → arches anterior to hilum → drains into superior vena cava (SVC).

Major Tributaries

• Right intercostal veins (4th–11th)
• Hemiazygos (left lower intercostals, left ascending lumbar)
• Accessory hemiazygos (left upper intercostals)
• Bronchial, esophageal, pericardial, mediastinal veins

Clinical Relevance

• SVC obstruction → azygos dilation (collateral pathway).
• Imaging landmark on CT (azygos lobe if fissure present).
• Thoracic surgery: ligation during esophagectomy, lung resection.