A rare location of benign osteoblastoma: case study and a review of the literature.

Osteoblastoma is a solitary, benign bone tumor that is rarely localized in the frontal sinus. It consists of hypocellular mineralized tissue that may form large masses or irregular trabeculae. A 31 year old man came to our attention with a 7 month history of diplopia, photophobia, frontal headhaches and progressive exophthalmos with proptosis of the left eye. The patient was submitted to computed tomography (CT) which allowed to appraise the extension of the lesion. The mass expanded inside the left frontal sinus and the upper ethmoidal cells invading the left orbital roof. Considering the extension of the tumor, the site and the connections with contiguous structures, a combination of endoscopic endonasal technique with intraorbital approach was performed. At histological examination typical features of benign osteoblastoma were observed. The sites of predilection for the tumor are the long bones, vertebral column, and small bones of hands and feet. Its occurrence in the skull and jaw bones is relatively rare and represents only 15% of all osteoblastomas. To our knowledge, only 5 cases of osteoblastoma of the frontal sinus have been previously reported in the English-language literature. This report describes a case of benign osteoblastoma in a rare site, namely, the frontal sinus with particular attention about the differential diagnosis and the treatment.