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Mediastinum

Mediastinum

For medical students2 min readUpdated 2026-10-10

The mediastinum is the central anatomical compartment of the thoracic cavity, located strictly between the right and left pleural cavities. This space densely packs vital thoracic organs, major blood vessels, and nerve trunks.

LocalizationBounded laterally by the pleural cavities of the lungs
ClassificationA horizontal plane divides the region into the superior and inferior mediastinum
Middle compartmentIncludes the heart with the pericardium and great vessels
Anterior compartmentForms a narrow cleft containing loose connective tissue

Borders and Fascial Apparatus of the Mediastinum

The anatomical space of the mediastinum is tightly bounded laterally by the pleural cavities of the lungs, known anatomically as the regiones pleuropulmonales.

Special attention should be paid to the fascial apparatus of this region. The parietal pleura covering the mediastinum fuses closely with the fascia endothoracica. Depending on the level, this fascia forms specific structures:

Topographically, the entire mediastinal space is divided into two major tiers: the superior mediastinum (mediastinum superius) and the inferior mediastinum (mediastinum inferius).

Superior Mediastinum

The superior mediastinum (mediastinum superius) occupies the upper thoracic compartment. Its boundaries are clearly defined:

This compartment concentrates numerous critical anatomical structures. These include the thymus (in children) or its adipose remnant (in adults), the aortic arch with its branching vessels, the superior vena cava, and the brachiocephalic veins. The trachea, upper esophagus, and thoracic duct also pass through this space. Neural structures include branches of the vagus and phrenic nerves, as well as the sympathetic trunks. Additionally, the superior mediastinum contains lymph nodes.

Inferior Mediastinum and Its Subdivisions

The inferior mediastinum (mediastinum inferius) lies below the imaginary plane passing through the tracheal bifurcation. For study and clinical application, this large area is further subdivided into three independent compartments: anterior, middle, and posterior.

  1. Anterior mediastinum (mediastinum anterius) is located between the posterior surface of the sternum and the anterior surface of the pericardium. Visually, it forms a narrow cleft. Its contents consist primarily of loose connective tissue containing lymphatic vessels and nodes.
  2. Middle mediastinum (mediastinum medium) is the largest volume compartment. Its main contents are the heart enclosed within the pericardium. It also contains the proximal segments of the great vessels: the ascending aorta and pulmonary trunk. Additionally, the middle mediastinum includes the lower part of the trachea, main bronchi, tracheobronchial lymph nodes, and the lower half of the phrenic nerves.
  3. Posterior mediastinum (mediastinum posterius) occupies the position between the posterior wall of the pericardium (anteriorly) and the vertebral column (posteriorly). The thoracic aorta and esophagus pass through this compartment. The lymphatic system is represented by the thoracic duct, and the nervous system by the vagus nerves and sympathetic trunks.

Mnemonic

To quickly remember the borders: the main dividing 'axis' is the tracheal bifurcation. Everything above it is the superior mediastinum. Everything below it is the inferior mediastinum, which the pericardium (as the central figure) divides into anterior, middle (the pericardium itself), and posterior.

Frequently asked questions

What branches does the aortic arch give off in the superior mediastinum?

In the superior mediastinum, three major trunks arise from the convex surface of the aortic arch. From right to left, these branches are:

  • Brachiocephalic trunk (truncus brachiocephalicus) — ascends upward and to the right, dividing into the right common carotid and right subclavian arteries.
  • Left common carotid artery (a. carotis communis sinistra) — arises directly from the aortic arch.
  • Left subclavian artery (a. subclavia sinistra) — courses upward and to the left toward the cervical region.
Which blood vessels are located in the middle mediastinum?

The middle mediastinum contains the intrapericardial segments of the great vessels as well as vessels accompanying nerves. These include:

  • Ascending aorta.
  • Pulmonary trunk (truncus pulmonalis).
  • Pulmonary arteries and veins (aa. et vv. pulmonales).
  • Pericardiacophrenic vessels (a. et v. pericardiacophrenica) — accompanying the phrenic nerves.
What anatomical structures pass through the posterior mediastinum?

Blood and lymphatic vessels, nerves, and digestive organs pass through the posterior mediastinum. It contains the following anatomical structures:

  • Thoracic aorta (descending aorta).
  • Azygos vein (v. azygos) and hemiazygos vein (v. hemiazygos).
  • Esophagus (esophagus).
  • Thoracic duct (ductus thoracicus).
  • Vagus nerves (nn. vagi).
  • Sympathetic trunks (trunci sympathici) and splanchnic nerves (nn. splanchnici).
  • Lymph nodes, fatty tissue, and extensions of the endothoracic fascia.
Which nerves and nerve trunks pass through the superior mediastinum?

The following pass through the superior mediastinum:

  • Vagus nerves (nn. vagi) and their branches.
  • Phrenic nerves (nn. phrenici).
  • Sympathetic trunks (trunci sympathici).
What are the contents of the anterior mediastinum?

The contents of the narrow, cleft-like anterior mediastinum include fat, vessels, lymph nodes, and glandular tissue. It houses:

  • Loose connective tissue (fat) and extensions of the endothoracic fascia.
  • Internal thoracic vessels (a. et v. thoracicae internae).
  • Lymphatic vessels and nodes (parasternal, prepericardial, anterior mediastinal).
  • The bulk of the thymus (thymus).
The convergence of which veins forms the superior vena cava?

The superior vena cava (v. cava superior) is formed by the union of two large venous vessels collecting blood from the head, neck, and upper extremities. It is formed by:

  • Right brachiocephalic vein (v. brachiocephalica dextra).
  • Left brachiocephalic vein (v. brachiocephalica sinistra).

The brachiocephalic veins themselves are formed by the junction of the jugular and subclavian veins.

Where is the border between the superior and inferior mediastinum?

The border is an imaginary horizontal plane drawn at the level of the tracheal bifurcation.

In which mediastinal compartment is the heart located?

The heart, along with its surrounding pericardium, is located in the middle compartment of the inferior mediastinum.

What is found in the anterior mediastinum?

It is a narrow, cleft-like space between the sternum and pericardium containing loose connective tissue, lymphatic vessels, and nodes.

How is the endothoracic fascia related to the pleura?

The mediastinal parietal pleura fuses with the endothoracic fascia. At the level of the costal pleura, it forms the suprapleural membrane, and near the diaphragmatic pleura, it forms the phrenicopleural fascia.

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