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Borders, divisions and contents of the mediastinum: want to learn more about it?

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Borders, divisions and contents of the mediastinum

Learning objectives:

Upon completing this study unit you will be able to:

  1. Understand the boundaries of the mediastinum and list the anatomically related structures.
  2. Describe the divisions of the mediastinum.
  3. List the mediastinal contents and place them correctly into each division.

Watch videos

The mediastinum is a compartment of the thorax located in the midline of the body between the left and right pleural cavities, that contains most of the thoracic viscera, apart from the lungs. It extends vertically from the superior thoracic aperture to the diaphragm and is bounded laterally by the medial surfaces of the lungs.

The thoracic plane, also known as plane of Ludwig, is an imaginary line extending from the sternal angle, anteriorly, to the T4-T5 intervertebral space, posteriorly. This plane divides the mediastinum into superior (above the thoracic plane) and inferior (below the thoracic plane) mediastinal divisions.

The inferior division is further subdivided into anterior, middle and posterior compartments by the pericardial sac. Structures located anterior to the pericardial sac belong to the anterior mediastinum, whereas those located posterior to pericardial sac are said to be structures of the posterior mediastinum. Those structures located in and around the pericardial sac belong to the middle mediastinum

Some structures course longitudinally both through the superior and inferior mediastinum: esophagus, azygos veins and vagus and phrenic nerves.

The videos below will give you a better understanding of the boundaries, divisions and contents of the mediastinum:

Take a quiz

Test yourself and your recently acquired knowledge with our quiz on the contents of the mediastinum:

If you would like to explore a broader test, evaluate what you know about all the structures of the thorax with our fully customizable quiz:

Browse atlas

Review the images in our gallery to solidify your knowledge:

Lateral view of the mediastinum

Anterior view of the mediastinum

Summary

Key facts about the mediastinum
Borders Superior: Superior thoracic aperture (delineated by the manubrium of the sternum, superior border of the first rib and T1 vertebral body)
Inferior:
 Diaphragm
Anterior:
 Sternum and costal cartilages of 1st-5th ribs
Posterior:
 Vertebral bodies of superior thoracic vertebrae
Lateral:
 Parietal pleura of each lung
Divisions Thoracic plane: Extends from sternal angle to vertebrae T4/5 intervertebral space
Superior mediastinum:
 Above thoracic plane
Inferior mediastinum:
 Below thoracic plane, further subdivided into anterior, middle and posterior compartments, according to relations with pericardial sac
Contents Superior mediastinum: Thymus, trachea, superior part of superior vena cava, aortic arch and its branches (brachiocephalic trunk, left common carotid artery and left subclavian artery, esophagus
Anterior mediastinum:
 Some remnants of the thymus
Middle mediastinum:
 Pericardial sac and heart; roots of superior and inferior vena cava; pulmonary trunk, arteries and veins; root of aorta; main bronchi; pericardiacophrenic arteries and veins
Posterior mediastinum:
 Descending thoracic aorta and its branches; azygos veins, esophagus

Well done!

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