The area in the middle of the two chests is the mediastinum, which is a general term for the organs, structures and connective tissues between the right and left mediastinal pleura. The mediastinum is sagittal, located in the middle of the chest cavity to the left of the center, narrow at the top and wide at the bottom, shorter at the front and longer at the back, the anterior border of the mediastinum is the sternum, the posterior border is the spine, and the mediastinal pleura is at both sides. Under normal circumstances, the position of the mediastinum is relatively fixed, and when pneumothorax occurs on one side, the mediastinum may be displaced to the opposite side. Clinically, the trichotomy method is often used to divide the anterior mediastinum into anterior mediastinum and posterior mediastinum, with the anterior walls of the trachea and bronchus, and the posterior wall of the pericardium as the boundary. The plane of the sternal angle is divided into the upper and lower mediastinum. The mediastinal space is a narrow gap between the organs of the mediastinum, which is filled with loose connective tissue and is suitable for organ activity and changes in thoracic volume. The connective tissue in the interstices is continuous with the connective tissue around the organs of the neck and in the retroperitoneal space.