Lymph nodes are important immune organs of human body, and there are about 500-600 lymph nodes in normal people, with a diameter of 0.2~0.5M, often distributed in groups, with soft texture, smooth surface, no pressure pain, and no adhesion to surrounding tissues. 1, etiology Infection Acute infection: bacteria and viruses such as rickettsia caused by acute cellulitis, upper respiratory tract infection, infectious mononucleosis, scrub typhus, etc. Chronic infections: bacteria, fungi, helminths, chlamydia, screw borreliosis, filariasis, venereal disease, lymph node granuloma, syphilis, AIDS, etc. Tumors Reactive hyperplasia Necroproliferative lymphadenopathy. Serum sickness and serum sickness-like reactions. Allergic subsepsis. Systemic lupus erythematosus rheumatism, etc. Abnormal cell proliferation metabolism Langerhan histiocytosis (histiocytosis X): including Letterer-Sive (Hand-Schüller-Christian) disease and eosinophilic granuloma of bone. Lipid deposition diseases: include sphingomyelin disease also known as Niemann-Pick disease glucocerebrosidosis also known as Gautier’s disease . Nodal disease The accompanying symptoms can provide important clues to the etiology of lymph node enlargement. Pain at the site of the lesion (alcohol pain) occurs about 20 minutes after drinking alcohol is seen in some patients with Hodgkin’s disease. 2. Main functions of lymph nodes Filtration and phagocytosis Immune function Hematopoietic function 3. Mechanism of occurrence Inflammatory enlargement Enlarged lymph nodes with painful acute lymphadenitis, usually secondary to infection in the corresponding drainage area. Effective antibiotic treatment can reduce the size of the enlarged inflammatory lymph nodes. Tumor enlargement Unrestricted proliferation of tumor cells in the lymph nodes occupies and destroys the normal tissue structure of the lymph nodes, and also causes proliferation of fibrous tissue and infiltration of inflammatory cells in the lymph nodes, resulting in enlargement of the lymph nodes. Cancerous lymph nodes are often hard as stones and relatively fixed. Reactive hyperplasia includes both nonspecific reactive lymphocytic hyperplasia and immunoreactive hyperplasia. Histiocytic hyperplasia is a large number of histiocytes in the lymph nodes, with a focal or diffuse distribution in the form of sheets, and granuloma formation may be present.