Mediastinum Anatomy
The central
part of the thorax between the two pleural cavities contains a group of
structures collectively termed the mediastinum. These include the heart and
great vessels, the trachea and the oesophagus. The mediastinum extends from the
superior thoracic aperture above to the diaphragm below and from the sternum in
front to the thoracic vertebral bodies behind (Fig. 2.28).
By convention, the mediastinum is divided into superior and inferior parts by
an imaginary horizontal plane passing through the manubriosternal joint and the
lower part of the fourth thoracic vertebra. The superior mediastinum lies
between this plane and the superior thoracic aperture and contains the superior
vena cava and its tributaries, the arch of the aorta and its branches and the
trachea. Also passing through this region are the oesophagus, the thoracic duct
and the right and left vagus and phrenic nerves.
The inferior mediastinum lies between
the imaginary plane and the diaphragm and consists of three compartments. The
largest of these is the middle mediastinum, containing the heart and its
covering of fibrous pericardium. In front of the middle mediastinum lies the
anterior mediastinum, consisting of a small amount of fat and the remnants of
the thymus gland. Behind the fibrous pericardium lies the posterior
mediastinum, traversed by the descending thoracic aorta, the oesophagus, the
thoracic duct and the azygos venous system. The sympathetic trunks run alongside
the thoracic vertebral bodies.
