The possible causes of unilateral lymph node enlargement in the neck include lymphadenitis, lymph node tuberculosis, lymph node metastasis of malignant tumors, lymphoma and so on. 1. Lymphadenitis: Neck lymphadenitis is mostly due to the spread of infections in neighboring tissues, such as gingivitis, tonsillitis, bronchitis, etc. Generally, the enlarged lymph nodes can dissipate by themselves after the primary infections are controlled. 2. Lymph node tuberculosis: cervical lymph node tuberculosis is mostly spread from oropharyngeal or pulmonary tuberculosis foci of infection, mostly seen in adults or children, the lymph nodes are painlessly enlarged, hard, and can be pushed, and the lymph nodes can be fused with each other to form lumps in the late stage. 3. Lymph node metastasis of malignant tumors: many malignant tumors can have lymph node metastasis, and the ones that can easily metastasize to the lymph nodes of the neck include thyroid cancer, squamous carcinoma of head and neck, esophageal carcinoma, lung cancer and so on. Patients with a history of malignant tumor or suspected cancer should be highly suspicious of metastasis when they have enlarged lymph nodes on one side of the neck. 4. Lymphoma: Lymphoma is a malignant tumor originated from lymphatic tissues, theoretically, it can occur in lymph nodes all over the body, and it is more common in cervical lymph nodes. Patients manifest painless progressive lymph node enlargement, accompanied by low fever, night sweating (abnormal sweating after going to sleep and stop sweating after waking up), itching, emaciation and other systemic manifestations. It is recommended to go to the hospital as soon as possible to clarify the nature of the enlarged lymph nodes on one side of the neck, and then give medication and surgical treatment.