Abstract
A huge, calcified intracranial mass continuous with the left frontal bone was revealed in the plain craniogram of an 11-year-old boy suffering from convulsive seizure. Preoperatively meningioma involving the left frontal bone was suspected by tomography, cerebral angiography and brain scan. Total removal of a yellowish gray, hard and sharply circumscribed tumor weighing 230g together with the left frontal bone was successfully performed. The tumor was compressing frontal lobes and was not infiltrative bilaterally. Microscopically numerous bone trabeculae associated with the osteocytes were scattered in the intermingled fibrous connective tissue. At the junction of the skull and the tumor, the dura mater was folded and the bone trabeculae with a high osteoblastic activity in the tumor were continuous with the thickened inner table of the skull. A typical lamellar appearance was seen under polarized light. The tumor was finally diagnosed as ossifying fibroma which miginated in the left frontal bone and developed into the cranial cavity compressing the brain. Differential diagnosis between ossifying fibroma and fibrous dysplasia was discussed especially from the histological and pathogenetical points of view.
