Mediastinal lesions include mediastinal tumors (benign and malignant), cysts, acute and chronic mediastinitis, mediastinal hernia, and mediastinal emphysema. The human thoracic cavity is divided into two pleural cavities, right and left, and the middle part of the two pleural cavities is called the mediastinum. The mediastinum contains the heart, large blood vessels in the chest, trachea, esophagus, nerves and lymphatic tissues. The mediastinum can be divided into several regions, from the sternal angle (i.e., the junction of the sternal stem and the sternal body, which can be palpated on the body surface as a distinct transverse ridge) to the lower edge of the fourth thoracic vertebrae, the upper mediastinum is called the upper mediastinum above the line, and the lower mediastinum below the line. The upper mediastinum is divided into the anterior superior mediastinum and the posterior superior mediastinum, with the trachea as the boundary. The lower mediastinum is subdivided into anterior, middle, and posterior portions, with the anterior mediastinum in front of the pericardium, the middle mediastinum where the pericardium is located, and the posterior mediastinum between the pericardium and the spine. The first priority in acute mediastinitis is to treat the cause, control infection, and supportive therapy (blood transfusion, fluids, and oxygenation). Chronic mediastinitis with severe superior vena cava obstruction requires surgical creation of collateral circulation and vascular bypass. For the treatment of mediastinal hernia, the main treatment is to treat the original disease and remove the cause of the disease, which can make the mediastinal hernia recover quickly. A mediastinal emphysema with only a small amount of gas may resolve without treatment. In severe cases, the cause of the disease is also treated (e.g., trauma, emphysema, ruptured alveoli, etc.). If the slow absorption of gas causes dyspnea or affects the pronunciation of the patient, an incision on the sternal notch can be made to reach the subcutaneous tissue to exhaust the gas. Except for malignant lymphoid tumors, most primary mediastinal tumors should be treated surgically as long as there are no other contraindications. Even if benign tumors or cysts are asymptomatic, they will grow gradually and compress the adjacent organs, or even develop malignant changes or secondary infections, and thus it is appropriate to take surgery; if malignant mediastinal tumors have invaded the adjacent organs and cannot be resected, or have metastases in distant places, surgery is contraindicated, and surgery can be given according to the nature of pathology. If the malignant mediastinal tumor has invaded into the adjacent organs and cannot be removed or has distant metastasis, surgery is contraindicated and radiotherapy or chemotherapy can be given according to the pathological nature.