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Mediastinum

The mediastinum is an area found in the midline of the thorax 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. Every compartment of the mediastinum contains many vital organs, vascular and neural structures that are closely related one to another.

Such a rich content of the mediastinum indicates its significance from the aspect of the anatomy.

Key Facts
Superior mediastinum Borders: first rib (superior) - T4 (inferior)
Content: esophagus, trachea, thymus; phrenic nerve, vagus nerve, left recurrent laryngeal nerve; superior vena cava, brachiocephalic veins, aortic arch, thoracic duct
Anterior inferior mediastinum Borders: T4 (superior) - T9 (inferior);  sternum (anterior) - pericardium (posterior)
Content: remnants of the thymus, lymph nodes
Middle inferior mediastinum Borders: T4 (superior) - T9 (inferior); anterior aspect of pericardium (anterior) - posterior aspect of pericardium 
Content: phrenic nerve, heart, pericardium, ascending aorta, pulmonary trunk, superior vena cava, pericardiacophrenic artery
Posterior inferior mediastinum Borders: T4 (superior) - T12 (inferior); posterior aspect of pericardium (anterior) - spine (posterior)
Content: esophagus, thoracic aorta, azygos veins, hemiazygos veins, accessory hemiazygos veins, thoracic duct, cisterna chyli, vagus nerve, esophageal plexus, greater, lesser and least splanchnic nerves
Clinical relations Mediastinitis (inflammation of the structures within the mediastinum)

In this article, the borders of each section of the mediastinum and their contents will be discussed. Lastly, a pathological condition known as mediastinitis will be mentioned.

Borders

Superior Mediastinum

The superior mediastinum begins at the level of the first rib and descends to the horizontal plane of the thoracic vertebra T4.

Anterior Inferior Mediastinum

The anterior inferior mediastinum starts from the thoracic vertebra T4 and continues to the diaphragm at the level of the thoracic vertebra T9.

It extends posteriorly from the body of the sternum and transversus thoracis muscle to the fibrous pericardium.

Middle Inferior Mediastinum

The middle inferior mediastinum begins in the same area as the anterior inferior mediastinum and finishes also in the same area between the T9 and T10 vertebrae. It extends posteriorly between the width of the fibrous pericardium.

Posterior Inferior Mediastinum

The posterior inferior mediastinum again originates in the same place as the other two subdivisions but extends the deepest, to the vertebra T12. Sagittally, it runs from the posterior aspect of the fibrous pericardium to the vertebral column.

Contents

Superior Mediastinum

The superior mediastinum contains three visceral organs including the esophagus, the trachea and remnants of the thymus. The nerves that run through this area are three and there are also two different nervous plexuses. The phrenic nerve, the vagus nerve and the left recurrent laryngeal nerve are the singular nerves, while the cardiac plexus branches and the pulmonary plexus branches make up the peripheral neurological plexuses.

Arterial and venous constituents are comprised of:

The termination of thoracic duct is also found in the superior mediastinum.

Anterior Inferior Mediastinum

The anterior inferior mediastinum has no major contents save remnants of the thymus and some lymph nodes.

Middle Inferior Mediastinum

The middle inferior mediastinum contains a single nerve which is the phrenic nerve, the heart and the pericardium. The vessels present include:

Posterior Inferior Mediastinum

The posterior inferior mediastinum has possibly the most anatomical structures. It encompasses:

  • the esophagus
  • the thoracic aorta and its branches which include the posterior intercostal arteries, the bronchial arteries and the esophageal arteries
  • the azygos venous system
  • the hemiazygos veins
  • the accessory hemiazygos veins
  • the thoracic duct
  • the cisterna chyli
  • the vagus nerve
  • the esophageal plexus.
  • several branches of the sympathetic trunk, like the greater splanchnic nerve, the lesser splanchnic nerve and the least splanchnic nerve.
Recommended video: Mediastinum
Contents of the mediastinum seen from the lateral views.

Mediastinitis

Mediastinitis is a term used to describe the inflammation of the tissue within the chest or the mediastinum. This disorder can be acute or chronic and is quite serious because the infection is in close proximity to so many essential organs and vessels. The most likely cause of this infection today is post surgical complications of cardiovascular or endoscopic surgery. This situation can become chronic, if a patient has an underlying disease such as tuberculosis or they are undergoing radiation therapy. Treatments depend on the patients case and can include therapy or even surgical decompression of the vessels.

Mediastinum - want to learn more about it?

Our engaging videos, interactive quizzes, in-depth articles and HD atlas are here to get you top results faster.

Sign up for your free Kenhub account today and join over 852,397 successful anatomy students.

“I would honestly say that Kenhub cut my study time in half.” – Read more. Kim Bengochea Kim Bengochea, Regis University, Denver

Show references

References:

  • Neil S. Norton, Ph.D. and Frank H. Netter, MD: Netter’s Head and Neck Anatomy for Dentistry, 2nd Edition, Elsevier Saunders, Chapter 22 Introduction to the Upper Limb, Back, Thorax and Abdomen, Page 584 to 585.
  • Michael Schuenke et al.: Atlas of Anatomy: Neck and Internal Organs, First Edition, Thieme, Thorax Chapter 1, 1.2 Divisions of the Thoracic Cavity and Mediastinum, 1.3 Overview of the Mediastinum and 1.4 Contents of the Mediastinum, Page 60 to 68.

Author:

  • Dr. Alexandra Sieroslawska

Illustrators:

  • First Illustration Gallery - Yousun Koh
  • Second Illustration Gallery - Yousun Koh
  • Third Illustration Gallery - Yousun Koh
  • Fourth Illustration Gallery - Yousun Koh
  • Fifth Illustration Gallery - Yousun Koh, Irina Munstermann
  • Sixth Illustration Gallery - Yousun Koh, Stephan Winkler
© Unless stated otherwise, all content, including illustrations are exclusive property of Kenhub GmbH, and are protected by German and international copyright laws. All rights reserved.

Related Atlas Images

Contents of the mediastinum

Lymphatics of the mediastinum

Thoracic surface of the diaphragm

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