The Mediastinum

Key points

• • The mediastinum is the space between the two pleural sacs, running from the breastbone in front to the vertebral column behind, and from the neck to the diaphragm.
• • It is divided into a superior part above and, below that, an anterior, a middle and a posterior part around the heart.
• • The middle mediastinum contains the heart in its pericardium, together with the roots of the great vessels.
• • The superior mediastinum contains the arch of the aorta, the great veins, the trachea, the oesophagus, the thoracic duct, the remnants of the thymus and major nerves such as the vagus and phrenic.
• • The posterior mediastinum contains the descending aorta, the oesophagus, the thoracic duct and the azygos venous system.
• • A mass in a particular part suggests certain causes; the anterior mediastinum is the classic site for the 'four Ts' - thymoma, teratoma, retrosternal thyroid and 'terrible' lymphoma.