The mediastinum is located between the two sides of the lungs, with the sternum and thoracic vertebrae as its anterior and posterior boundaries. There are many important organs inside, including large blood vessels, trachea, main bronchus, pericardium, esophagus, thymus and a large amount of fat, nerves and lymphatic vessels and other tissues, which become mediastinal tumors due to abnormal developmental process in the congenital or acquired cyst or tumor formation. There are many kinds of mediastinal tumors, both primary and metastatic, and benign tumors are common among primary tumors, but a considerable part of them are also malignant. In order to indicate where the lesion is located in the mediastinum, the mediastinum can be divided into several parts, with the level of the sternum and the lower edge of the 4th thoracic vertebra divided into upper and lower parts, the mediastinal space containing many important organs is called “visceral organ mediastinum” (middle mediastinum), the space in front of the right trachea and pericardium is the anterior mediastinum; behind the trachea and pericardium (including esophagus and spine) is called posterior mediastinum. The posterior mediastinum is called the posterior mediastinum. According to the domestic statistics, the incidence of mediastinal tumors is the first among neurogenic tumors, followed by teratomas, thymic tumors and thyroid tumors, and the least among various cystic tumors. Common mediastinal tumors: neurogenic tumors: mostly originate from sympathetic nerves, and a few originate from peripheral nerves. These tumors are mostly located in the posterior mediastinum within the paravertebral area and are unilateral in nature. They are usually asymptomatic, but pain can occur when they grow up to compress the nerve trunk or malignantly erode. Teratomas and dermatomal cysts: Mostly located in the anterior mediastinum, near the base of the heart in front of the great vessels of the heart, teratomas are mostly substantial and contain cysts of different sizes and numbers. 10% of teratomas are malignant. Thymoma: Mostly located in the anterior superior mediastinum, mostly benign, but often considered clinically potentially malignant, easily infiltrating nearby tissues and organs, about 15% combined with myasthenia gravis. Conversely, more than half of patients with myasthenia gravis have thymoma or thymic hyperplasia abnormalities. Intra-thoracic ectopic tissue tumors: there are post-thoracic goiter, parathyroid adenoma, lymphogenic tumors, etc. The latter are mostly malignant, and the masses are often bilateral and irregular, and lymphomatous tumors should not be operated, but mostly treated with radiotherapy or chemotherapy. Mediastinal cysts: the more common ones are bronchial cysts, esophageal cysts and pericardial cysts, all of which are benign, mostly round or oval in shape, with thin walls and clear borders. Other tumors: vascular origin, adipose tissue, connective tissue, mesenchymal tissue tumors from muscle tissue are less common. Clinical manifestations: Generally speaking, mediastinal tumors do not have many positive signs, and their symptoms are related to tumor size, location, growth mode, texture and nature. Benign tumors grow slowly and can grow to a considerable size without symptoms or very mild. On the contrary, malignant tumors are highly invasive and progress rapidly, and symptoms may appear when they are small. Common symptoms include chest pain, chest tightness, cough, head and facial edema, no sweating on one side of the face, and difficulty in swallowing. In addition, some specific symptoms related to the nature of tumor may appear: for example, up and down movement with swallowing is post-sternal goiter, coughing up hair-like hairs or bean curd-like sebum is teratoma that has broken into the lung; with severe muscle weakness is thymoma, etc. Diagnosis: Chest X-ray examination: it is an important means to diagnose mediastinal tumor. Fluoroscopy can observe whether the mass moves up and down with swallowing, whether there is morphological change with breathing and whether there is pulsation, etc. X-ray frontal and lateral chest X-ray can show the tumor location, density, shape, smoothness of edges, whether there is calcification or bone shadow, etc. CT or MRI can further show the relationship between tumor and adjacent tissues and organs, which is an essential examination. If necessary, cardiovascular and bronchogram can be performed. Ultrasound can identify substantial, vascular or cystic tumors. Radionuclide can assist in the diagnosis of retrosternal goiter. Biopsy of enlarged lymph nodes in the neck. Tracheoscopy, esophagoscopy, mediastinoscopy. Thoracoscopic mediastinal mass biopsy. Diagnostic radiation therapy, whether it can shrink in a short period of time, helps to identify tumors sensitive to radiation, such as malignant lymphoma. Treatment: Except for malignant lymphogenic tumors for which radiotherapy and chemotherapy are applicable, most primary mediastinal tumors should be treated surgically as long as there are no contraindications. Even if benign tumors or cysts are asymptomatic, surgery is appropriate because they will grow up and compress the adjacent organs, and even become malignant or secondary infections. The choice of specific surgical methods can be based on the characteristics of the patient and tumor by conventional open or minimally invasive thoracoscopic surgery (VATS). If malignant mediastinal tumor has invaded adjacent organs and cannot be removed or has distant metastasis, surgery is contraindicated and radiotherapy or chemotherapy can be given according to the pathology.