Mediastinum

What is the mediastinum?

Your mediastinum is a space within your chest that contains your heart and other structures.

Your mediastinum is one of the three main compartments that make up your thoracic cavity. The other two compartments are your left pleural cavity (holds your left lung) and your right pleural cavity (holds your right lung). Your mediastinum is the space between these two pleural cavities.

Your mediastinum is the middle section of your thoracic cavity. It's located between your two pleural cavities (left and right).

What structures are in the mediastinum?

Your mediastinum contains many different structures, including organs and blood vessels.

Organs in your mediastinum include your:

• Esophagus: Your esophagus (food tube) passes through your mediastinum as it travels from your throat to your stomach.
• Heart: Your heart is a muscular organ that pumps blood throughout your body. It’s located in the middle of your mediastinum. Your heart is surrounded by a protective sac called your pericardium.
• Thymus: Your thymus supports your immune system and is most active before puberty. It’s located in the front, upper part of your mediastinum.
• Trachea: Your trachea (windpipe) helps you breathe. It’s located just in front of your esophagus. It travels from your lower neck into your chest, before branching in two and traveling into each of your pleural cavities.

Blood vessels in your mediastinum include your:

• Left brachiocephalic vein: Your left brachiocephalic vein helps blood from the left side of your upper body return to your heart. It empties into your superior vena cava.
• Superior vena cava: Your superior vena cava carries blood from your upper body to your heart. It empties directly into your right atrium (top right heart chamber).
• Pulmonary trunk: This blood vessel connects with your heart’s right ventricle at your pulmonary valve. After leaving your heart, your pulmonary trunk splits into your right and left pulmonary arteries. These vessels send blood to each of your lungs to gain oxygen.
• Thoracic aorta: Your aorta is the largest artery in your body. It’s responsible for sending oxygen-rich blood to all your organs and tissues. Your aorta connects with your heart’s left ventricle at your aortic valve. From there, it passes through your chest (thorax) and abdomen (belly). The section in your chest (thoracic aorta) is contained in your mediastinum. Segments of your thoracic aorta are your ascending aorta, aortic arch and descending thoracic aorta.

Other structures in your mediastinum include:

• Fatty and connective tissues.
• Lymph nodes.
• Nerves.
• Thoracic duct.
• Thoracic spine.

What is the function of the mediastinum?

Your mediastinum has several important functions, including:

• Serving as a “house” for your heart and the roots of your great vessels. These are the blood vessels that attach directly to your heart to carry blood into or out of your heart.
• Protecting your thymus, heart and other structures. Fatty tissue and connective tissue in your mediastinum provide cushioning. Your mediastinum sits behind your sternum, or “breastbone,” which provides additional protection to this important area.
• Providing a passageway for structures to travel between your neck and your chest, and between your chest and your belly. For this function, you can think of your mediastinum as a railroad station. It contains body structures that act as railroad tracks, transporting cargo (like food or air) where it needs to go. For example, your esophagus carries foods and liquids through your mediastinum to get from your throat to your stomach.

Where is the mediastinum located?

Your mediastinum is located in the middle of your chest between your lungs. Mediastinum means “midway” in Latin. Its boundaries are as follows:

• The superior (upper) border is the root (base) of your neck.
• The inferior (lower) border is your diaphragm. This muscle separates your thoracic cavity from your abdominal cavity.
• The anterior (front) border is your sternum (breastbone).
• The posterior (back) border is your spine.
• The lateral (at each side) borders are the pleural sacs that surround your left lung and right lung.

What are the parts of the mediastinum?

Your mediastinum is divided into several parts, which researchers call compartments. There are different classification systems for organizing these compartments. The main idea to know is that your mediastinum can be divided into either three or four parts. And their names refer to their position in your chest.

Traditional four-compartment classification

The traditional or classical model divides your mediastinum into four parts:

• Superior mediastinum: The top part, located superior to (above) your heart.
• Anterior mediastinum: The part anterior to (in front of) your heart, between your heart and your sternum (breastbone).
• Middle mediastinum: The part that contains your heart.
• Posterior mediastinum: The part posterior to (behind) your heart.

This model is based on X-ray images of your heart. So, it takes a two-dimensional view of your heart.

ITMIG three-compartment classification

The International Thymic Malignancy Interest Group (ITMIG) developed the more recent three-compartment model. It’s based on cross-sectional imaging (CT scans) and takes a three-dimensional view of your heart. This model divides your mediastinum into three parts:

Prevascular compartment

The prevascular compartment is in front of your heart, between your heart and your breastbone. Structures inside this compartment include:

• Fat.
• Left brachiocephalic vein.
• Lymph nodes.
• Thymus.

Visceral compartment

The visceral compartment is the middle part, which contains your heart. Structures inside this compartment include:

• Esophagus (part of it).
• Heart.
• Lymph nodes.
• Pulmonary trunk.
• Superior vena cava.
• Thoracic aorta.
• Thoracic duct.
• Trachea (part of it).

Paravertebral compartment

The paravertebral compartment is the part behind your heart, between your heart and your spine. Structures in this compartment include:

• Paravertebral soft tissues.
• Thoracic spine.

It’s also helpful to remember that your mediastinum is a three-dimensional (not flat) space. It’s a bit like a diorama that you build inside a small box. The structures inside are arranged in a particular way to help your body function. But certain conditions can affect the organs and tissues in your mediastinum and disrupt its careful balance.

What common conditions affect the mediastinum?

Many different conditions can affect the organs and tissues in your mediastinum. Some conditions begin in the mediastinum, such as primary tumors or cysts. Other times, a disease (like cancer) spreads to your mediastinum from somewhere else in your body. Infections that affect your whole body (systemic) can also impact your mediastinum.

Some conditions that may affect your mediastinum include:

• Aortic dissection.
• Cardiac tamponade.
• Esophageal cancer.
• Goiter.
• Heart disease.
• Lymphoma.
• Mediastinal tumors.
• Mediastinitis (swelling or infection).
• Myasthenia gravis.
• Thoracic aortic aneurysm.

These conditions have a wide range of symptoms and treatments. Talk with your provider about your condition to learn more about what you can expect.

What is a widened mediastinum?

A widened mediastinum means that your mediastinum is at least 8 centimeters wide. This is a clinical sign your healthcare provider sees when viewing your mediastinum from back to front on an X-ray.

A widened mediastinum could indicate a wide range of conditions, including:

• Aortic dissection.
• Broken ribs or vertebrae.
• Cardiac tamponade.
• Mediastinal tumor.
• Mediastinitis.
• Thoracic aortic aneurysm.

What tests check the health of the mediastinum?

Tests your provider may use to check your mediastinum include:

• Chest X-ray.
• Computed tomography (CT) scan.
• Magnetic resonance imaging (MRI) scan.
• Mediastinoscopy.
• Ultrasound.

Your provider may order testing to find the cause of symptoms you’re having. Or, you may need testing on a regular basis to monitor an issue. Talk with your provider about the testing you need, why you need it and how to prepare.

How can I keep my mediastinum healthy?

A healthy lifestyle can help lower your risk of many conditions that affect your mediastinum. Some tips include:

• Avoid smoking and all tobacco products. Ask your provider for resources to help you quit.
• Eat a heart-healthy diet.
• Exercise regularly. Check with your provider before starting a new exercise plan.
• Limit your alcohol intake.
• Take your medications as prescribed.
• Visit your provider for yearly check-ups.

A note from Cleveland Clinic

Your mediastinum is a space in your chest that holds your heart and other important structures. It’s the middle compartment within your thoracic cavity, nestled between your lungs.

It can be easy to forget that your mediastinum is there. That’s because most people focus on what’s inside it (like your heart). But it’s helpful to learn mediastinum anatomy and the terms scientists use, especially if you or a loved one are diagnosed with a related condition. Talk with your provider if you have questions about your mediastinum or its role in your health.