Large, expansile odontogenic cyst with bilateral maxillary sinus involvement.

Residual cysts are common odontogenic lesions of the tooth-bearing areas of the jaws. A case of an unusually large residual cyst that crosses the maxillary midline and occupies portions of the maxillary sinuses is being reported. Investigations included a panoramic radiograph, CT scan and a biopsy. The differential diagnoses were common odontogenic lesions, including cysts and benign tumors. The value of advanced imaging modalities is stressed when determining the presence and extent of lesions in complex structures such as the maxilla. The need to visualize the entire lesion beyond what may be seen on intraoral views, as well as panoramic radiographs, is discussed.