superior mediastinum (anatomy)

Last reviewed 01/2018

The superior mediastinum is the region bounded by:

• anteriorly: the sternum
• posteriorly: the upper thoracic vertebral bodies
• inferiorly: an arbitrary plane passing horizontally and posteriorly from the manubriosternal joint to the inferior border of the T4 vertebra
• superiorly: thoracic inlet
• laterally: apices of the lungs The key structures within the superior mediastinum are:
• trachea
• oesophagus
• great vessels, particularly the arch of the aorta
• thymus
• phrenic and vagus nerves

The principal difference between the right and left of the superior mediastinum is that the great veins are generally disposed to the right whereas the arteries are on the left. Correspondingly, there is more room for potential expansion on the right side of the superior mediastinum to accommodate the volume changes of the venous system. Also, the greater expansibility of the right side encourages space-occupying masses to project first in this direction.

The superior mediastinum has been divided up in the submenu according to the relationship of structures to the arch of the aorta; a description of the route taken by the aortic arch is given in the submenu:

• anterior and to the right
• anterior and to the left
• posterior to the arch and to the right
• inferior to the arch Also, anatomical compartments are formed by the continuation of the fascial sheets from the neck:
• prevertebral fascia - attached to the anterior surface of the T4 vertebra
• pretracheal fascia - blends with anterior surface of pericardium