Bilateral maxillary sinus mucosal cysts are cystic lesions that occur under the mucosa of the maxillary sinuses due to an increased secretion of secretory cells in the mucosa of the maxillary sinuses, which leads to localized accumulation of secretory fluid. Bilateral maxillary sinus mucosal cyst is a cystic lesion that occurs under the mucosa of the maxillary sinus bilaterally, because the secretory cells in the mucosa of the maxillary sinus secrete excessive body fluids, which accumulate locally to form bilateral maxillary sinus mucosal cysts. Most of the mucosal cysts of the maxillary sinus do not have any symptoms, and are usually reviewed on a regular basis. A few bilateral maxillary sinus mucosal cysts may cause blockage of the maxillary sinus openings, which in turn leads to inflammation of the maxillary sinus caused by the lack of drainage of the maxillary sinus, which may lead to headache, nasal congestion, runny nose, and loss of sense of smell and other symptoms.