Mediastinum

The mediastinum is the central compartment of the thoracic cavity, located between the two pleural sacs and extending from the superior thoracic aperture to the diaphragm. It contains the heart and pericardium, the great vessels (aorta, superior and inferior venae cavae, and their branches), the trachea and main bronchi, the esophagus, the thoracic duct, and a network of nerves and lymph nodes. The mediastinum is traditionally divided into the superior mediastinum and the inferior mediastinum; the inferior mediastinum is further subdivided into anterior, middle, and posterior compartments, based on an imaginary plane through the sternal angle.

The contents by compartment include:

- Superior mediastinum: thymus (more conspicuous in children), brachiocephalic veins, the superior vena cava, the arch of the aorta with its branches (brachiocephalic trunk, left common carotid, left subclavian), the trachea and its bifurcation, the esophagus, the thoracic duct, and various nerves (vagus, phrenic, and the thoracic sympathetic trunk) with accompanying lymph nodes.

- Anterior mediastinum: mostly loose connective tissue, fat, lymph nodes, and thymic remnants.

- Middle mediastinum: the pericardial sac and heart, origins of the great vessels, the tracheal bifurcation, and the main bronchi.

- Posterior mediastinum: the esophagus, descending thoracic aorta and its branches, the thoracic duct, the azygos and hemiazygos venous systems, the vagus nerves, the thoracic sympathetic trunks, and the esophageal plexus.

Clinically, the mediastinum is a common site for tumors and inflammatory processes, such as thymomas, germ cell tumors, lymphomas, and mediastinitis, and imaging often guides diagnosis and management.