Corpus: Mediastinum

The mediastinum is the central space in the chest cavity, located between the lungs and extending from the upper opening of the thorax (thoracic inlet) to the diaphragm.

The mediastinum is bordered at the front by the sternum and at the back by the spinal column. Its lateral borders are formed by the pleura. The upper boundary is the thoracic inlet, while the lower boundary is the diaphragm.

The mediastinum contains all the organs within the thoracic cavity, except for the lungs.

Anatomically, the mediastinum is divided into the

• upper mediastinum (mediastinum superius) and the
• inferior mediastinum (mediastinum inferius).

The dividing line between the two is the upper border of the pericardium. The lower mediastinum is further subdivided into:

• anterior mediastinum: between the sternum and pericardium
• middle mediastinum: pericardium with its contents
• posterior mediastinum: between pericardium and spine

The upper mediastinum contains the origins of some neck muscles in its superficial layer.

In the deeper layers, it contains:

• organs
  • Thymus or thymus fat body (adulthood)
  • Trachea
  • Esophagus
  • Lymph nodes

• Vessels and nerves
  • Aortic arch
  • Thoracic parts of the brachiocephalic trunk
  • Thoracic parts of the left subclavian artery and common carotid artery
  • Brachiocephalic veins and the upper part of the superior vena cava
  • Thoracic duct
  • Vagus nerve (both sides)
  • Phrenic nerve (both sides)
  • Laryngeal recurrent nerve (left)
  • Sympathetic nerves of the heart

5.1. Anterior mediastinum

The small anterior mediastinum exists only on the left side, where the pleura is displaced laterally by the heart. It contains some small branches of the internal mammary artery and prepericardial lymph nodes and lymphatic vessels.

5.2. Middle mediastinum

The middle mediastinum contains the structures surrounded by the pericardium, i.e.

• Heart
• Lower part of the superior vena cava
• Inferior vena cava
• Ascending aorta
• Pulmonary trunk
• Pulmonary veins
• Azygos vein
• Phrenic nerve
• Pericardiacophrenic arteries
• Bifurcation of the trachea

5.3. Posterior mediastinum

The posterior mediastinum extends down to the diaphragm. It contains:

• Esophagus
• Thoracic part of the descending aorta
• Azygos vein and hemiazygos vein
• Thoracic duct
• Vagus nerve (both sides)
• Posterior intercostal arteries, posterior branches from the aorta
• Greater and lesser splanchnic nerves

Diseases of the mediastinum include mediastinal tumors such as thymomas or lymphomas. Mediastinal shift can occur due to space-occupying masses in the thorax or pneumothorax.

The mediastinum can be visualised with a mediastinoscopy for diagnostic and therapeutic purposes.

• 3D model: Dr Claudia Krebs (Faculty Lead) University of British Columbia