Definition and Conditions of the Mediastinum (2023)

The mediastinum is an important region of the body located between the lungs. Structures that lie in this region include the heart, the esophagus, the trachea, and large blood vessels including the aorta. The mediastinum is also home to lymph nodes.

Definition and Conditions of the Mediastinum (1)

There are many conditions that can affect the mediastinum or the mediastinal lymph nodes, including cancer, benign tumors, infections, and more. Understanding the different parts of the mediastinum is very helpful in determining the causes of abnormalities in this region. Let's take a look at the different parts of the mediastinum and the conditions that may occur in each area.

Definition of Mediastinum

The mediastinum is the area in the chest between the lungs that contains the heart,part of the windpipe (the trachea), the esophagus, and the great vessels including the ascending aorta (the large artery which carries blood from the left ventricle of the heart on its way to the rest of the body) and right and left pulmonary arteries—essentially all of the organs in the chest except the lungs. It is also home to many lymph nodesand nerves.

The word mediastinum is translated as "midway" in Latin, in reference to the middle part of the chest.

You can visualize this area by seeing the diaphragm as the bottom, the breastbone (the sternum) as the front, the blood vessels that enter and exit the heart (the thoracic inlet) as the top, and the backbone (the vertebral column) as the backside. On the lateral sides (edges), the mediastinum is bound by the membranes that line the lungs.


The mediastinum can be thought of as having two regions, the top, and bottom. The bottom (inferior) half is divided into three main regions. Even though this may sound like a boring description of anatomy, understanding the structures that lie in each of these areas is very important in diagnosing medical conditions in this region.

  • Anterior: The anterior mediastinum is present only on the left side and contains some small arteries as well as lymph nodes.
  • Middle: The middle mediastinum is the largest portion, and contains the heart, blood vessels including those that travel from the lungs to the heart, and lymph nodes.
  • Posterior: The posterior mediastinum contains the esophagus, many blood vessels and nerves, and mediastinal lymph nodes.

Conditions Affecting the Mediastinum

There are many medical conditions which can affect structures in the mediastinum, and early on, most of these conditions do not have symptoms. Some of these include:

  • Cancer: Cancers such as lymphomas (both Hodgkin's lymphomaand non-Hodgkins lymphomas), some germ cell tumors, and thymomas (cancers of the thymus gland) occur in the mediastinum.
  • Benign tumors: Benign germ cell tumors such as teratomas and dermoid cysts may occur in this region.
  • Malignant lymph nodes: The term malignant lymph nodes refers to those lymph nodes that are cancerous. This can occur due to cancers that primarily affect the lymph system, such as lymphomas, as well as cancers that spread to lymph nodes. In addition to cancers such as lymphoma, which is not uncommonly found in these nodes, cancers such as lung cancermay spread to lymph nodes in the mediastinum.
  • Lymphadenopathy: "Swollen" lymph nodes in the mediastinum may occur with some infections, especially viral infections. Fungal infections like histoplasmosis and mycobacterial infections like tuberculosis can also cause mediastinal lymph node enlargements. Another common disease called sarcoidosis can also cause it.
  • Aneurysms: Thoracic aortic aneurysmsare a serious condition involving the mediastinum.
  • Nerve damage: Nerves that pass through the mediastinum may be damaged, for example by pressure from a tumor or cancerous lymph nodes in this area.

Mediastinal Masses

Mediastinal masses are often first noted when a scanis done to evaluate symptoms related to the chest, such as a cough, shortness of breath, or other symptoms. Most masses in the mediastinum are small and do not have any symptoms. When they are large, they can cause respiratory insufficiency (difficulty breathing or getting enough oxygen to the tissues) as well as heart problems, such as a drop in blood pressure or decreased blood flow.

The age of an individual and the location of a mediastinal mass are important in considering a diagnosis. In children, mediastinal masses occur most often in the posterior mediastinum and are often benign (noncancerous).In contrast, mediastinal masses in adults are more common in the anterior mediastinum and often malignant (cancerous.)

Some causes of mediastinal masses based on location include:

  • Anterior mediastinum: Tumors in this regions may include thymomas (tumors of the thymus, an organ in the chest which is fairly large in childhood but essentially disappears in adults), lymphomas, germ cell tumors (such as teratomas), and retrosternal (behind the sternum or breastbone) thyroid masses.
  • Middle mediastinum: Enlarged lymph nodes are a common cause of a mass in the middle mediastinum. These lymph nodes could, in turn, be related to underlying cancer. Bronchogenic cysts may also be seen in this area, as well as cardiac abnormalities such as an enlarged aorta.
  • Posterior mediastinum: Esophageal cancers and other esophageal abnormalities may appear in the posterior mediastinum, and enlarged lymph nodes may also be noted here. Other possibilities include sarcomas, neurogenic tumors, spinal tumors, paraspinal abscesses, and ectopic thyroid tissue (thyroid tissue growing in an area outside of the thyroid gland. A mass in this region could also be extramedullary hematopoiesis. This is a condition in which blood cells are formed in areas outside of the bone marrow, and while often normal in young babies, is usually abnormal in adults.

Lung cancer may cause a mass in any part of the mediastinum.

(Video) Mediastinum and Heart in situ: Clinical anatomy of mediastinum & pericardium

It's important to note that there are many more causes of abnormalities in the mediastinum, and most often further testing is needed to define the exact cause.

Terms Involving the Mediastinum

The mediastinum may also be included in names of conditions involving this region, such as:

  • Pneumomediastinum refers to the presence of air in the mediastinum, most commonly related to thecollapse of a lung (pneumothorax.)
  • Mediastinitis is a term referring to an infection involving the mediastinum. Mediastinitis is a life-threatening condition that most often develops after cardiac surgery.

Mediastinoscopy Procedure

With cancers such as lung cancer and lymphomas, doctors often evaluate the mediastinum to see if any cancer has spread to this region. One procedure that allows surgeons to visualize this area is called a mediastinoscopy. If a cancer has spread to nodes in the mediastinum, it is often treated differently than a cancer that has not spread to this region; the presence of mediastinal lymph nodes is important in the staging of lung cancer.

Mediastinoscopy was a common procedure for those diagnosed with lung cancer, but the same information may sometimes be available now via a PET scan.

Examples: Joy had a procedure done to see if her lung cancer had spread to lymph nodes in her mediastinum.

Frequently Asked Questions

  • Where is the mediastinum located?

    The mediastinum is located inside the thoracic cavity (the chest area) between the lungs. It is divided into four compartments: the superior, anterior, middle, and posterior. Each one houses different structures such as the heart and arteries.

  • Where is the heart located in the body?

    The heart is located within the middle mediastinum, alongside many blood vessels and lymph nodes. The middle mediastinum is its largest compartment.

  • What is inside the posterior mediastinum?

    (Video) Enlargement of the Mediastinum

    The posterior mediastinum houses the esophagus, the descending thoracic aorta, veins, and nerves.

Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.

  1. Terán MD, Brock MV. Staging lymph node metastases from lung cancer in the mediastinum. J Thorac Dis. 2014;6(3):230-6. doi:10.3978/j.issn.2072-1439.2013.12.18

  2. Juanpere S, Cañete N, Ortuño P, Martínez S, Sanchez G, Bernado L. A diagnostic approach to the mediastinal masses. Insights Imaging. 2013;4(1):29-52. doi:10.1007/s13244-012-0201-0

  3. Lee AY, Choi SJ, Jung KP, Park JS, Lee SM, Bae SK. Characteristics of Metastatic Mediastinal Lymph Nodes of Non-Small Cell Lung Cancer on Preoperative F-18 FDG PET/CT. Nucl Med Mol Imaging. 2014;48(1):41-6. doi:10.1007/s13139-013-0244-2

    (Video) Mediastinum

  4. Tiwari MK, Yadav R, Mathur RM, Shrivastava CP. Mediastinal bronchogenic cyst presenting with dysphagia and back pain. Lung India. 2010;27(2):86-8. doi:10.4103/0970-2113.63612

  5. Kouritas VK, Papagiannopoulos K, Lazaridis G, et al. Pneumomediastinum. J Thorac Dis. 2015;7(Suppl 1):S44-9. doi:10.3978/j.issn.2072-1439.2015.01.11

  6. Mclean AEB, Barnes DJ, Troy LK. Diagnosing Lung Cancer: The Complexities of Obtaining a Tissue Diagnosis in the Era of Minimally Invasive and Personalised Medicine. J Clin Med. 2018;7(7). doi:10.3390/jcm7070163

  7. Stoddard N, Heil JR, Lowery DR. Anatomy, thorax, mediastinum. StatPearls.

Additional Reading

Definition and Conditions of the Mediastinum (2)

By Lynne Eldridge, MD
Lynne Eldrige, MD, is a lung cancer physician, patient advocate, and award-winning author of "Avoiding Cancer One Day at a Time."

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(Video) Disorders of the pleura and mediastinum - Emergency Medicine - Detailed explanation


What's the definition of mediastinum? ›

(MEE-dee-uh-STY-num) The area between the lungs. The organs in this area include the heart and its large blood vessels, the trachea, the esophagus, the thymus, and lymph nodes but not the lungs.

What is mediastinum and its function? ›

The mediastinum houses many vital structures including the heart, great vessels, trachea, and essential nerves. It also functions as a protected pathway for structures traversing from the neck, superiorly, and into the abdomen, inferiorly.

What are the common mediastinum diseases? ›

Mediastinal diseases are conditions that arise from tissues in this cavity. They include cancerous tumors (thymomas, lymphomas, germ cell tumors, carcinoids) and noncancerous tumors (lipoma, teratoma), masses, enlarged lymph nodes, and cysts (bronchogenic, pericardial, esophageal).

What and where is the mediastinum? ›

mediastinum, the anatomic region located between the lungs that contains all the principal tissues and organs of the chest except the lungs.

What causes Mediastinitis? ›

Mediastinitis usually results from an infection. It may occur suddenly (acute), or it may develop slowly and get worse over time (chronic). It most often occurs in person who recently had an upper endoscopy or chest surgery. A person may have a tear in their esophagus that causes mediastinitis.

Where is mediastinal located? ›

The mediastinum is an area found in the midline of the thoracic cavity, that is surrounded by the left and right pleural sacs. It is divided into the superior and inferior mediastinum, of which the latter is larger. The inferior mediastinum is further divided into the anterior, middle and posterior mediastinum.

What type of tissue is mediastinum? ›

The mediastinum is the fibrous, loose areolar connective tissue in the center of the thoracic cavity.

Where does mediastinum start? ›

The mediastinum lies within the thorax and is enclosed on the right and left by pleurae. It is surrounded by the chest wall in front, the lungs to the sides and the spine at the back. It extends from the sternum in front to the vertebral column behind. It contains all the organs of the thorax except the lungs.

Which gland is located in the mediastinum? ›

The thyroid gland is located in the cranial part of the mediastinum along either side of the distal part of the trachea, cranial to its bifurcation into the bronchi (in sea lions, but not in other marine mammals, the bifurcation is cranial to the thoracic inlet).

Which diseases can be diagnosed with mediastinoscopy? ›

Why might I need mediastinoscopy?
  • Cancer of the bronchi.
  • Cancer of other structures in the mediastinum.
  • Infection or inflammation.
  • Cancer that starts in the lymphatic system (lymphoma), including Hodgkin disease.
  • Sarcoidosis, a condition that causes areas of inflammation in the organs such as the liver, lungs, and spleen.

What syndrome is associated with anterior mediastinal masses? ›

Manifestations of paraneoplastic syndromes can occur with anterior mediastinal masses, especially thymomas. The constellation of ptosis, dysphagia, weakness, and fatigue point to the most commonly associated paraneoplastic syndrome, myasthenia gravis.

What are the boundaries of the mediastinum? ›

Boundaries of Mediastinum are:
  • Posteriorly: thoracic spine.
  • Anteriorly: sternum and costal cartilages.
  • Laterally: mediastinal pleura.
  • Superiorly: thoracic inlet.
  • Inferiorly: diaphragm.

Is mediastinum a bone? ›

The mediastinum is the area that separates the lungs. It is surrounded by the breastbone in front and the spine in back, with the lungs on either side. It encompasses the heart, aorta, esophagus, thymus (a gland in the back of the neck) and trachea (windpipe).

What is not found in the mediastinum? ›

The esophagus, heart, thymus gland, and trachea are found in the mediastinum. The lungs are not found in the mediastinum.

How is mediastinitis diagnosed? ›

Diagnosis of Mediastinitis

The diagnosis is confirmed by a chest x-ray or CT. When mediastinitis occurs in a person who has had median sternotomy, doctors may insert a needle into the chest through the breastbone and remove fluid for examination under a microscope (aspiration biopsy).

Is mediastinitis life threatening? ›

There are multiple etiologies that can cause mediastinitis. Since many vital structures lie within the mediastinum, the disease process is life-threatening and requires emergent intervention and treatment.

What bacteria causes mediastinal widening? ›

Optimal treatment includes adequate drainage of the neck and mediastinum and broad spectrum intravenous antibiotics. Commonly implicated organisms are alpha-hemolytic streptococci and Bacteroides fragilis.

What is mediastinum in chest xray? ›

A widened mediastinum will often be first noted in the emergency department on a chest x-ray. The mediastinal borders are composed of the right heart, ascending aorta, superior vena cava, aortic knob, descending aorta, and the left heart. These structures are all contained between the right and left lungs.

What is a mediastinal tumor? ›

Definition. Mediastinal tumors are growths that form in the mediastinum. This is an area in the middle of the chest that separates the lungs.

How do you remember the content of mediastinum? ›

The contents of mediastinums and their mnemonics - YouTube

What does mediastinal lymph nodes mean? ›

Mediastinal lymph nodes are lymph nodes located in the mediastinum. The mediastinum is the area located between the lungs that contains the heart, esophagus, trachea, cardiac nerves, thymus gland, and lymph nodes of the central chest. The enlargement of lymph nodes is referred to as lymphadenopathy. 1.

Where does mediastinum start? ›

The mediastinum lies within the thorax and is enclosed on the right and left by pleurae. It is surrounded by the chest wall in front, the lungs to the sides and the spine at the back. It extends from the sternum in front to the vertebral column behind. It contains all the organs of the thorax except the lungs.

Which of the following organs are not located in the mediastinum? ›

Which of these structures is NOT found in the mediastinum? The esophagus, heart, thymus gland, and trachea are found in the mediastinum. The lungs are not found in the mediastinum.

What is the root of the word mediastinum? ›

Etymology. From New Latin mediastīnum, from Medieval Latin mediastīnus (“middling; middle”), from Latin mediastīnus (“a common servant”).


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