Left maxillary sinus cysts have different causes depending on the type. Common types of cysts are mucus cysts, mucous membrane cysts, odontogenic cysts, etc. It is recommended to go to the otolaryngology department of the hospital for treatment. 1. Mucous cyst: When the sinus opening of left maxillary sinus is blocked due to various reasons, the secretion cannot be discharged in time in the sinus, and a large amount of retention and accumulation will form mucous cyst in the left maxillary sinus. 2. Mucous membrane cyst: the mucous gland of the mucous membrane is blocked, which leads to the secretion in the gland can not be discharged, and a large amount of retention and accumulation will lead to the left maxillary sinus mucous membrane cyst. 3. Odontogenic cysts: abnormal development of fish oil teeth, immature teeth wrapped in the alveolar bone, stimulating the tissue to produce proliferative lesions, resulting in increased secretion and the formation of odontogenic cysts. Suspected left maxillary sinus cysts, it is recommended that patients need to go to the hospital, follow the doctor’s instructions to improve the relevant examination and treatment.