After a preliminary understanding of the structure of our mediastinum and its location in the body, it is of course necessary to introduce some of the guests who are often present in this villa, which will help in the initial determination of the disease. First of all, I would like to introduce thymoma, a frequent guest of the villa and an active member of the mediastinal tumors. He is often found in the upper part of the mediastinum —- on the second floor of the villa and he likes to stay off to the front. Why is he often found there? Because the root cause of thymoma —- thymus gland is located there. The thymus gland is an important immune organ in our body. After growth and development, it is located and functions in the anterior mediastinum of the body. As we grow older, the thymus gland reaches its maximum during puberty and thereafter gradually degenerates and atrophies, with a gradual increase in fat. Some people will experience incomplete degeneration of the thymus gland, and some will have thymic tumors detected in this area. How can thymoma be detected in time? In fact, the vast majority of thymomas are found by chance. CT or MRI of the chest is a convenient and effective way to detect thymoma (remember, regular medical checkups are good for your health). The main symptoms of discomfort include chest tightness, chest pain, cough, shortness of breath, and swelling of the head, face, neck and chest. If these symptoms are present and you seek medical attention, the thymoma has usually grown to a large size and should be treated urgently. In addition, some people have thymomas that are not very large, but are very vigorous and can affect our body functions in a subtle way, bringing serious damage and systemic symptoms. The most common one is myasthenia gravis, where the symptoms of muscle bundle weakness can affect the eye muscles, the large muscle groups of the trunk, and even the swallowing and breathing muscles, thus endangering life. Thymoma can also affect the hematopoietic function of the bone marrow, which can lead to anemia, weakness, and pallor in the long run. In addition, thymoma may be associated with hypoproteinemia, nephritis nephrotic syndrome, rheumatoid arthritis, lupus erythematosus, and megaesophagus. In short, most thymomas are just growing on their own, and at most they cause discomfort by pressing on the surrounding organs and tissues, while a few thymomas seem to have some magic power, and although they are small, they have a great impact on the human body, and they are relatively difficult to treat. Many people are concerned about the benignity or malignancy of thymomas. In fact, doctors usually classify thymoma by invasive and non-invasive, based on the following criteria: 1) the integrity of tumor envelope; 2) the growth pattern of tumor; 3) the presence of metastasis and implantation; 4) the morphology of tumor cells under the microscope. By combining the above tumor manifestations, doctors will determine whether the patient’s thymoma is aggressive or not. Tumors with aggressiveness may require additional radiotherapy and/or chemotherapy after surgery, depending on the surgery, to prevent the recurrence of thymoma. The treatment of thymoma mainly relies on surgery, and the choice of surgery is based on the size of the tumor, the presence or absence of invasive imaging, and the presence or absence of concomitant symptoms. Currently, minimally invasive thoracoscopic surgery or da Vinci robotic surgery is the most common choice to remove the tumor completely while reducing the damage to the patient. After surgery, the pathological findings and biological characteristics of the thymoma are used to determine whether it is aggressive or not, and radiotherapy may be required. Since the cause of thymoma is not well understood, there is no effective method of prevention. Regular physical examinations can detect tumors early and proper timing of treatment can lead to good results.