Intrathoracic goiter (or tumor) is a common mediastinal tumor. Most of them have intact fibrous envelope, are nodular and lobulated, and are soft or moderately hard. Most of them have intact fibrous envelope, nodular and lobulated, soft texture, or moderate hardness. They are white or flesh-colored in cross-section, and may have cystic changes, hemorrhage or necrosis. The cell morphology is divided into epithelial (glandular epithelium-based), lymphocytic (lymphocyte-based), and mixed (both types of cells). In addition, there are spindle cells, which are also classified as epithelial, and thymomas are classified as malignant or benign. Malignant thymomas account for only 20-43% of thymomas. In benign cases, the tumor has an intact envelope and grows non-invasively; in malignant cases, the tumor lacks an intact envelope and invades surrounding tissues. If vascular erosion is found in the tumor tissue, or if deep staining of the nucleus and a large number of dividing phase cells can be seen on cytohistological examination, it may be a malignant lesion. However, most of the malignant lesions do not have this histological feature, so the diagnosis should be confirmed with the clinical operation and the course of the disease. Mediastinal lymphoid tumors and other sarcomas: Lymphomas are located in the middle mediastinum. They are divided into two categories: Hodgkin’s disease and non-Hodgkin’s lymphoma, the latter including lymphosarcoma and reticulocytoma. Other mediastinal sarcomas are fibrous, lipid and smooth muscle tumors. Both mediastinal hemangiomas and lymphangioleiomas are rare. Most of the hemangiomas are located in the anterior and posterior superior mediastinum, and most of the lymphangioleiomas are located in the anterior and posterior superior mediastinum, and their growth locations in the left and right chest are roughly similar. The diagnosis of these tumors can be made by X-ray frontal and lateral chest radiographs, especially lateral and oblique X-ray fluoroscopy and radiography, which can help to localize and differentially diagnose mediastinal tumors. Mediastinal tomography X-ray examination can further determine the location and nature of the lesion in the mediastinum and the relationship between the organs in the mediastinum. Computed tomography (CT) is used for the diagnosis and differential diagnosis of mediastinal tumors. It can not only detect early microscopic tumor foci that cannot be detected by conventional X-ray, but also find out the connection between the tumor and surrounding organs in detail, which is convenient for deciding the method of surgical treatment. In addition, according to the size of CT value, the qualitative differential diagnosis of benign and malignant tumors, cystic, solid and fatty tissue can be made more accurately. Congenital mediastinal cysts: including pericardial cysts, tracheal cysts and esophageal cysts. Clinical manifestations of pericardial cysts rarely compress the heart, have few symptoms and grow slowly. Tracheal cysts are rarely symptomatic in adults, but in children they can cause respiratory distress, compress the esophagus, and break into the bronchi causing secondary infection. Symptoms of esophageal cysts are common in infants and can occur with varying degrees of dyspnea and cough. If ulceration occurs in the wall of the cyst, it can cause bleeding and death. The diagnosis of thoracic X-ray is a simple diagnostic method, which allows to examine the shape and location of the cyst from different positions and the presence of vascular pulsations (differentiation from hemangioma). Pericardial cysts are mostly round or oval shadows in front of the diaphragm angle, with light and uniform density, sharp edges and inseparable from the pericardial shadow, while bronchial cysts are round or oval shadows with sharp edges and uniform image density, connected to the trachea and may have a fluid surface. Esophageal cysts show partial swelling of the esophagus, and the shadow cannot be separated from the esophagus. The three are mainly treated surgically. Diagnosis of mediastinitis, mediastinal hernia and mediastinal emphysema: X-ray examination is an important method. Mediastinitis is manifested by widening of the mediastinum; mediastinal hernia is observed by X-ray from different positions (posterior-anterior and lateral) or by projection tomography, which can show the position of the hernia with the trachea and esophagus and determine whether the mediastinum is displaced. The translucent area extending beyond the trachea to the contralateral side is a herniation into the contralateral lung tissue with sparse lung texture. Bronchograms may lack tracheal images; mediastinal emphysema can be seen on posteroanterior radiographs with white strips of mediastinal pleura pushed to the sides by black inflated mediastinal connective tissue images. The gas band can also be seen along the outer edge of the descending aorta, and gas can be seen along the deep cervical fascial space straight to the neck as a black translucent area. In lateral chest radiographs, a deepened translucent gas shadow can be seen in the posterior sternal space. In the case of pericardial emphysema, the gas is mainly concentrated in the root of the heart, and a reflexed vault of the pericardium can be seen. In contrast, mediastinal emphysema is more obvious on both sides of the upper mediastinum. Mediastinal hernia A part of the mediastinal pleura enters the contralateral pleural cavity through the mediastinum and is called a mediastinal hernia. This is a symptom and not a separate disease. It occurs because there are two anatomically weak areas in the posterior mediastinum: one above the aortic arch and odd vein, corresponding to the level of the 3rd to 5th thoracic vertebrae, with the esophagus, trachea and great vessels in the anterior border and the spine in the posterior border; the other below the aorta and odd vein corresponding to the 5th thoracic vertebrae, with the heart and great vessels in the anterior border and the descending aorta and spine in the posterior border. Previous upper mediastinal hernias are more common. X-ray examination is an important method for the diagnosis of mediastinitis, mediastinal hernia and mediastinal emphysema. Mediastinitis is manifested by widening of the mediastinum; mediastinal hernias can be viewed on X-ray from different positions (posterior-anterior and lateral) or projected tomographically to show the location of the hernia in relation to the trachea and esophagus and to determine whether the mediastinum is displaced. The translucent area extending beyond the trachea to the contralateral side is a herniation into the contralateral lung tissue with sparse lung texture. Bronchograms may lack tracheal images; mediastinal emphysema can be seen on posteroanterior radiographs with white strips of mediastinal pleura pushed to the sides by black inflated mediastinal connective tissue images. The gas band can also be seen along the outer edge of the descending aorta, and gas can be seen along the deep cervical fascial space straight to the neck as a black translucent area. In lateral chest radiographs, a deepened translucent gas shadow can be seen in the posterior sternal space. In the case of pericardial emphysema, the gas is mainly concentrated in the root of the heart, and a reflexed vault of the pericardium can be seen. In contrast, mediastinal emphysema is more obvious on both sides of the upper mediastinum. The first priority in acute mediastinitis is to treat the cause, control infection and supportive therapy (blood, fluids, oxygen). Chronic mediastinitis with severe superior vena cava obstruction requires surgical procedures to establish collateral circulation and vascular bypass. The treatment of mediastinal hernia is mainly to treat the primary disease and remove the cause, which can make the mediastinal hernia recover quickly. If the mediastinal emphysema has only a small amount of gas, it may disappear without treatment. In heavy cases, the cause is also treated (e.g., trauma, emphysema, ruptured alveoli, etc.). If the gas absorption is slow and causes breathing difficulties or affects the patient’s pronunciation, an incision can be made over the sternotomy to reach the subcutaneous tissue for venting.