Infected dentigerous cyst of maxillary sinus arising from an ectopic third molar

A dentigerous cyst or follicular cyst is a form of odontogenic cyst. It is believed that it forms during the development of the tooth and is associated with pressure exerted by the crown of an unerupted (or partially erupted) tooth on the fluid within the follicular space. Typically, dentigerous cysts are painless and discovered during routine radiographic examination. However, they may be large and result in a palpable mass. Additionally, as they grow they displace adjacent teeth. They almost exclusively occur in permanent dentition. The cyst is lined by stratified squamous non-keratinizing epithelium. About 70% of dentigerous cysts occur in the mandible and 30% in the maxilla. Dentigerous cysts associated with ectopic teeth within the maxillary sinus are very rare. We report radiologic and pathologic features in a rare case of infected dentigerous cyst of maxillary sinus arising from an ectopic third molar in a 21-year-old female patient.