**4. Etiology of cysts localized in the maxillary sinus**

A cyst is a lesion consisting of an epithelial sac, filled with fluid or semisolid material, and is surrounded by a connective tissue capsule. Cysts are more commonly seen in the maxilla than the mandible. The most common causes of cysts localized in the maxillary sinus are chronic infection, allergic sinonasal disease, trauma, previous surgery, obstruction of the sinus ostium, accumulations of secretions, ectopic teeth, foreign bodies (e.g., dental implant, tooth roots, graft materials), dental infections, incomplete sealing of all communications between the root canal system and periradicular tissues during endodontic treatment, mechanical obstruction of mucociliary flow, defects in ciliary capabilities to propel the mucous blanket and genetic factors. Pathologically, a cyst can develop and grow in the sinus until it reaches a large size with no serious complaint by the patient because of the anatomy of the sinus. [14-16]
