16th February 2024

Summary

The mediastinum is bounded anteriorly by the sternum, posteriorly by the spine and laterally by the parietal pleura. This is then divided into superior and inferior mediastinum at the level of sternal angle anteriorly and inferior border of the fourth thoracic vertebra.

The inferior mediastinum is subdivided into anterior, middle and posterior mediastinum. The anterior mediastinum is bordered by the sternum anteriorly and the pericardial sac posteriorly. The posterior mediastinum is bordered by the pericardial sac anteriorly and the thoracic vertebrae posteriorly. 

Image Source: Wikimedia Commons (2006). Mediastinum, Licensed under a creative commons licence. Available for free at: https://upload.wikimedia.org/wikipedia/commons/a/ab/Mediastinum.png (Accessed: 9 January 2024).

The content of each area is as follows:

Superior mediastinum

• Arch of the aorta and associated branches
  • Right brachiocephalic artery
  • Left common carotid artery
  • Left subclavian artery
• Major veins
  • Superior vena cava
  • Right and left brachiocephalic vein
  • Left superior intercostal veins
• Nerves
  • Left laryngeal nerve
  • Phrenic nerve
  • Vagus nerve
  • Sympathetic trunk
• Other major organs
  • Thymus gland ( in most adults)
  • Thoracic duct
  • Trachea
  • Oesophagus
  • Lymph node group

Anterior mediastinum

• Thymus gland ( extension into the anterior mediastinum is possible)
• Lymph node groups

Middle mediastinum

• Heart and origin of the great vessels
• Nerves
  • Cardiac plexus
  • Phrenic nerves ( descends from the superior mediastinum)
• Tracheobronchial lymph nodes
• Trachea and the main bronchi.

Posterior mediastinum

• Thoracic aorta and its associated branches 
  • Bronchial artery
  • Intercoastal arteries
  • Oesophageal arteries
• Oesophagus
• Thoracic duct
• Veins
  • Azygous vein
  • Hemizygous vein
  • Accessory hemiazygous vein
• Thoracic sympathetic trunk and oesophageal vagal plexus