Mediastinum Anatomy Overview

Mediastinum Overview

• The mediastinum is a median partition separating the two pleural cavities in the thorax.
• It contains vital organs and structures like the heart, great vessels, trachea, esophagus, thymus, and lymph nodes.
• The mediastinum is divided into superior and inferior sections. The inferior mediastinum is further subdivided into anterior, middle, and posterior regions.

Mediastinum Divisions

• Superior Mediastinum: Located above an imaginary plane between the manubrium sterni and the lower border of the 4th thoracic vertebra.
  • Contains the superior vena cava, aorta, trachea, esophagus, thymus, and major blood vessels.
• Inferior Mediastinum: Located below the superior mediastinum.
  • Divided into three further sections:
    • Anterior Mediastinum: Located behind the body of the sternum and in front of the pericardial sac, containing sternopericardial ligaments, internal thoracic artery branches and the lower part of the thymus.
    • Middle Mediastinum: Contains the heart, pericardium, and the roots of the great vessels.
    • Posterior Mediastinum: Situated behind the pericardial sac and in front of the vertebral column from T5 to T12, encompassing the descending thoracic aorta, esophagus, and major nerves.

Boundaries of the Mediastinum

• Superior boundary: Superior thoracic aperture
• Inferior boundary: Diaphragm
• Anterior boundary: Sternum
• Posterior boundary: Bodies of vertebrae T1 to T12
• Lateral boundaries: Mediastinal parietal pleura (left and right)

Contents of the Mediastinum

• Superior Mediastinum: Trachea, esophagus, thymus, major blood vessels, nerves.
• Anterior Mediastinum: Sternopericardial ligaments, lymph nodes, internal thoracic artery branches, lowest part of thymus.
• Middle Mediastinum: Heart, pericardium, major blood vessel roots.
• Posterior Mediastinum: Descending aorta, esophagus, thoracic duct, lymph nodes, splanchnic nerves, sympathetic chain.

Clinical Anatomy

• Mediastinitis: Inflammation of the mediastinum.
• Mediastinal Syndrome: Infiltration, entrapment, or compression of mediastinal structures. Superior vena cava syndrome is the most severe complication. Symptoms include upper body vein engorgement, dyspnea, cough, dysphagia, hoarseness, and pain/neuralgia.
• Lesions of the Mediastinum: Various tumors (thymoma, malignant lymphoma, germ cell tumors, etc.).

Azygos Vein

• A vein that collects deoxygenated blood from the posterior and lateral aspects of the thorax and drains into the superior vena cava.
• It can vary in location, and an anomalous variation can create a pleural septum.
• The arch of the azygos vein (arcus venae azygos) is an important anatomical landmark.
• It connects superior and inferior vena cava systems, providing a pathway for blood when one of the venae cavae is blocked.
• It originates from the union of ascending lumbar veins and right subcostal veins, ascending in the posterior mediastinum and arching over the right main bronchus to join superior vena cava.