Inverted papilloma of the sphenoid sinus.

Inverted nasosinusal papilloma is a benign tumor accounting for less than 4% of all nasal masses. The lesion originates in the mucosa lining the nasal cavities, the locations in decreasing order of frequency being the lateral wall of the nasal fossa, ethmoid sinus, and maxillary sinus; the sphenoid sinus is only rarely affected. Despite its benign histology, the tumor shows aggressive behavior and can be associated to carcinomas. Surgery is therefore indicated in such cases.