Azygos Vein

What is the azygos vein?

The azygos vein is a blood vessel that runs up the right side of the back of your chest (thorax), next to your spine. This vein is part of your body’s azygous venous system.

What does the azygos vein do?

The azygos vein carries blood from the back of your chest and abdomen to your heart. This vein carries blood upward through your diaphragm and the mediastinum, the space between membranes (pleural sacs) that cover the lungs.

The azygos vein’s function is to drain deoxygenated blood into one of your body’s largest veins (superior vena cava). The superior vena cava carries blood to your heart’s right upper chamber (atrium) so it can reoxygenate blood.

What is the azygos system of veins?

The azygos venous system is a group of veins that work together to help blood circulate. This system creates a pathway for blood between your two largest veins — the inferior vena cava and superior vena cava. This pathway (anastomosis) helps blood return to your heart if the inferior vena cava or superior vena cava become blocked.

The azygos venous system includes two smaller veins, or tributaries, of the azygos vein:

• Accessory hemiazygos vein: This is a vein that starts in the spaces between your middle ribs (intercostal spaces). It runs on the upper left side of your spine and drains down into the azygos vein. The left bronchial vein and a vein in part of your digestive tract (esophagus) drain into the accessory hemiazygos vein.
• Hemiazygos vein: This is a vein that begins where tributaries of other veins meet. These tributaries include mediastinal veins, lumbar veins in your spine and subcostal veins that run along the bottom of your ribs. Several intercostal veins and the left subcostal vein drain into the hemiazygos vein before it joins the azygos vein.

How is the azygos vein different from other veins?

Typically, veins form in pairs. There's usually a vein on your body’s left side and a vein on your body’s right side. But azygos vein anatomy is different. Most people have only one azygos vein on the right side of their body. Occasionally, two azygos veins form during fetal development.

Where is the azygos vein?

Your azygos vein runs along the right side of your spinal column at the back of your chest. This vein begins where the veins between your spinal bones (lumbar) and subcostal veins come together and enter your chest.

Where does the azygos vein drain into?

The azygos vein drains into a large vein that drains into your heart (superior vena cava).

Some people have differences in their veins that they are born with (congenital). These congenital differences can cause the azygos vein to drain directly into the right atrium. It may also drain into the:

• Right brachiocephalic vein: A vein located in your upper right chest (thorax) that's a tributary to the superior vena cava.
• Right subclavian vein: A vein that runs along your arm, shoulder and neck.

How big is the azygos vein?

The azygos vein is usually about 1 centimeter in diameter, about the diameter of an AAA battery.

What is the azygos vein made of?

Veins include tissue and cells that help keep them flexible. Their walls contain three layers:

• Lining made from cells (endothelial cells) that produce chemicals to help veins contract.
• Middle layer of flexible smooth muscle.
• Outer layer of connective tissue (collagen and elastin) that improves elasticity.

What common conditions affect the azygos vein?

Sometimes, changes to the shape of your azygos vein happen because of changes in blood flow due to increased blood pressure or something blocking the vein (obstruction). Your azygos vein may become engorged or enlarged.

The azygos vein may also become damaged due to injury. Cuts (lacerations) or ruptures of your azygos vein can result from car accidents or other hard contacts with your chest, such as a fall or a hard hit during sports.

In addition, injury to your azygos vein can occur during thoracic surgeries (surgeries inside your chest cavity). Complications from implanted devices such as pacemakers can also affect your azygos vein. These changes may cause blood pressure in your azygos vein to become too high or too low.

What tests do healthcare providers do to check for problems in the azygos vein?

Your healthcare provider may recommend an imaging test to check your azygos vein function:

• Arteriogram or venogram, where healthcare providers inject dye and take X-rays to check blood flow.
• Chest X-ray.
• CT scan.
• MRI.

How do healthcare providers treat damage to the azygos vein?

When injury or damage happens, healthcare providers may use procedures to relieve pressure and allow the vein to drain. Providers may make an incision in your chest (thoracotomy) to help blood drain from the space between your lungs (pleural cavity).

When your azygos vein doesn’t form as it should before birth, you may have an abnormality in the vein (congenital defect). Some people with congenital changes to the azygos vein may be at greater risk for:

• Conditions that affect your spleen.
• Congenital heart disease.

What should I do to keep my veins healthy?

These lifestyle habits can help keep your circulatory system, including your veins, healthy:

• Eat healthy foods.
• Exercise regularly.
• Get adequate hydration.
• Manage high blood pressure.
• Quit smoking.

A note from Cleveland Clinic

The azygos vein, part of the azygos venous system, helps move blood from your chest and abdomen back to your heart, where it receives oxygen. Your healthcare provider is a great resource for steps you can take to help keep your veins healthy.