What Is The Mediastinum?

The mediastinum is the space between the right and left lungs in the chest.  The mediastinum is in the middle of the chest extending from the spine to the front of the chest and the breast bone (sternum). We can see the mediastinum on all imaging studies which cover the chest.

What structures does the mediastinum contain?

The mediastinum contains the heart and great vessels that arise from it.  The esophagus which goes from the throat to the stomach.  The trachea or windpipe.  The mediastinum contains nerves, lymphatics and lymph nodes.  The thymus gland is also within the anterior mediastinum.

Divisions of the mediastinum

The mediastinum is further divided into superior and inferior compartments.   This is a plane that goes from the upper breast bone to the fourth thoracic vertebra.  The inferior mediastinum is further divided into anterior, middle and posterior compartments going from front to back.

The division of the inferior mediastinum is primarily based on the pericardium or the covering of the heart. In front of the pericardium or covering of the heart is the anterior mediastinum.  Within the pericardium is the middle mediastinum.  Posterior or behind the pericardium is the posterior mediastinum.

Why is the mediastinum divided into compartments?

The contents of the mediastinal compartments helps us with diagnosing abnormalities.  There are different structures in each mediastinal compartment.  Diagnosis of Masses in the mediastinum can be narrowed down by their precise location.

For example, a mass in the anterior mediastinum can be narrowed down to tumors arising from the thymus.  Masses which arise from the thyroid or parathyroid glands in the lower neck.  Lymphoma which arises from the lymph nodes.  Germ cell tumors also arise in the anterior mediastinum.  Some vascular masses such as aneurysms can extend into the anterior mediastinum.  Disease which involves multiple areas of the mediastinum can be cancerous, from infection such as that after surgery or bleeding.

What is the best test for the mediastinum?

The best test to evaluate the mediastinum is a chest CT.  We can see detailed anatomy of the entire mediastinum.  We can also see some diseases of the mediastinum on chest X-ray.  Usually this will be seen as a widened appearance or mass.  Often a chest CT is needed to provide a diagnosis.

The mediastinum is an important compartment in the chest between the lungs.  Many diseases involve the mediastinum.   Chest X-ray is often the first test done but chest CT is better for diagnosis.  Dividing the mediastinum into compartments and seeing where the abnormality is located, helps us narrow the diagnosis.


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