Mediastinum: The Vital Region of the Chest

The mediastinum is the compartment located between the two lungs, housing many vital organs of the body. The location of the mediastinum is bounded by:

• Anterior: Sternum

• Posterior: Thoracic vertebrae

• Lateral: The outer walls of the pleura

• Superior: Thoracic inlet

• Inferior: Diaphragm

The superior mediastinum is the upper part of the mediastinum, containing important structures such as:

• Major arteries, veins and nerves:

• Veins: Brachiocephalic veins, internal thoracic veins, superior intercostal veins, left inferior thyroid vein connecting to the right inferior thyroid vein to form the thyroid venous plexus.

• Arteries: Aortic arch and its ascending branches.

• Right vagus nerve: Descends from the neck, slightly inwards, lying posterior to the brachiocephalic vein and the superior vena cava.

• Left vagus nerve: Crosses the anterior surface of the aortic arch, and separates into the recurrent laryngeal nerve.

• Other structures:

• Thymus: Located anteriorly in the superior mediastinum.

• Brachiocephalic vein: Located anteriorly in the superior mediastinum.

• Brachiocephalic artery: Located anteriorly in the superior mediastinum.

• Left common carotid artery: Located anteriorly in the superior mediastinum.

• Left subclavian artery: Located anteriorly in the superior mediastinum.

• Trachea: Located in the middle of the superior mediastinum.

• Esophagus: Located posteriorly in the superior mediastinum.

Esophagus: is a smooth muscle tube connecting the pharynx to the stomach, passing through the superior mediastinum and the posterior mediastinum. The esophagus has 4 constrictions, respectively distanced from the incisors:

• 15 cm: Upper end

• 22.5 cm: Where the esophagus crosses the aortic arch

• 27.5 cm: Where the esophagus crosses the thoracic aorta

• 40 cm: Where the esophagus passes through the diaphragm

Relations of the esophagus in the posterior mediastinum:

• Anterior: Right brachiocephalic vein

• Posterior: Thoracic duct

• Left: Thoracic aorta

Thoracic aorta:

• Branches: Divides into 5 branches nourishing the bronchi, esophagus, 9 pairs of intercostal spaces, supplying the pericardium, and providing blood to the upper surface of the diaphragm.

Thoracic duct:

• Formation: From 3 trunks: intestinal trunk, 2 lumbar trunks.

• Intestinal trunk: Drains the digestive tract.

• Lumbar-sacral trunk: Drains the abdominal wall and pelvis.

• Lymphatic ducts: Flowing from the lower abdomen and upper chest will drain into the brachiocephalic vein or the superior vena cava.

Lymphatic drainage:

• Organs below the diaphragm are drained by the azygos vein, except for the digestive tract.

Conclusion: The mediastinum is a vital area containing many important organs, ensuring the body’s respiratory, circulatory and digestive functions.