Mediastinum – is the median septum of thorax, between 2 lungs. It is divided into superior and inferior mediastinum. Superior mediastinum: is separated from inferior by sternal angle and lower border of body of 4th thoracic vertebra. Inferior mediastinum is subdivided into 3 parts by pericardium: anterior, posterior and middle mediastinum. Area in front of pericardium is anterior mediastinum; behind pericardium – is posterior mediastinum. The pericardium and its contents -is middle mediastinum.
Organs of superior mediastinum: trachea, esophagus, thymus, thoracic duct.
Organs of anterior mediastinum: the lowest part of thymus, areolar tissue.
Organs of middle mediastinum: heart, bifurcation of trachea, the right and left bronchi principal.
Organs of posterior mediastinum: esophagus. Pericardium – is a fibroserous sac which encloses the heart and the roots of the great vessels. It’s situated in middle mediastinum. It consists of fibrous and serous pericardium. Fibrous pericardium – conical sac made up of fibrous tissue. Serous pericardium – is thin, double-layered serous membrane lined by mesothelium. The outer layer is fused with fibrous pericardium, and inner layer is fused to the heart. Sinuses of pericardium: The passage behind the aorta and pulmonary trunk is called the transverse sinus of pericardium. The space bounded below and to the right by the inferior vena cava and to the left by left pulmonary veins is the oblique sinus of pericardium.