1.What is mediastinal lymph node enlargement? Lymph nodes are an important part of the body’s immune system and an important node in the lymphatic return system, with a normal diameter of mostly within 5 mm. The mediastinum is the area of the human chest located between the two lungs, below the entrance of the thorax and above the diaphragm. Mediastinal lymph nodes, as the name implies, are lymph nodes located in the mediastinum. The enlarged mediastinal lymph nodes are judged based on the results of imaging examinations (such as CT, MRI), and generally refer to lymph nodes with a short diameter greater than 1 cm. 2.What are the common causes of mediastinal lymph node enlargement? A variety of diseases can cause mediastinal lymph node enlargement, and the more common causes are: lung malignant tumor metastasis, lymphoma, nodular disease, tuberculosis, and chronic inflammation. 3.Will enlarged mediastinal lymph nodes be life-threatening? If the enlarged mediastinal lymph nodes are caused by malignant tumors, on the one hand, the progress of the tumors themselves can be life-threatening, and on the other hand, the increasing size of the lymph nodes may compress or invade the important organs in the mediastinum, such as the large airways and large blood vessels, which may lead to respiratory and circulatory system failure. If the enlarged mediastinal lymph nodes are caused by benign diseases (such as nodular disease and tuberculosis), the risk is lower because the disease progresses slowly and can mostly be controlled or relieved by treatment. 4.Does mediastinal lymph node enlargement need treatment? As mentioned above, there are various causes of mediastinal lymph node enlargement, and the key to whether treatment is needed is what the cause is. In general, most of the enlarged lymph nodes need to be treated accordingly. 5.How to diagnose the cause of mediastinal lymph node enlargement? The most direct and clear method is to biopsy the enlarged lymph nodes, obtain cellular or histological specimens, and have the pathology report issued by the pathologist after examination, and then the clinician will make a diagnosis of the cause after a comprehensive judgment with other medical history of the patient. 6.What is bronchoscopy (FOB)? Bronchoscopy is an airway examination technique with a slender scope that can be inserted through the mouth or nasal cavity to enter the trachea, main bronchus, lobar bronchus, segmental bronchus, and even sub-segmental bronchus for examination and biopsy under direct vision, and also for localized puncture biopsy (TBLB) under X-ray fluoroscopy.