[A case of ossifying fibroma of the skull].

A 23-year-old woman was admitted to our hospital because of a soft, painful mass in the right parietal region for a month. Neurological examination revealed no abnormality. Laboratory data including serum Ca, P and alkaline phosphatase were normal. Skull x-ray film showed a partially osteolytic, not well circumscribed lesion in the right frontal, parietal and occipital bone. No remarkable sclerotic area was seen in the lesion. CT scan showed that the lesion was located in the diploë, destroying both inner and outer tables of the bone. Right external carotid angiogram revealed that the lesion is supplied by the branches of superficial temporal artery and middle meningeal artery. 99mTc bone scan showed increased uptake in the lesion. The patient underwent a right parietal craniectomy. The skull bone was invaded by the tumor, which was yellow-brown in color, thickened and fragile. We could easily perforate it through. The tumor didn't invade the dura mater or periosteum. It was extensively removed with an airtome and rongeurs. A cranioplasty was carried out using a plastic resin. The pathological specimen showed that the tumor was mainly composed of mature, regularly-aligned bone and intermingled fibrous tissue. Neither mitosis nor atypical cellular features was seen. These findings were compatible with the diagnosis of ossifying fibroma. The postoperative course was uneventful and the patient was discharged in a good condition. There was no evidence of local recurrence 10 months later. Ossifying fibroma is a rare, benign bone tumor that mainly involves the craniofacial bone. The differential diagnosis of ossifying fibroma versus fibrous dysplasia is difficult. These diseases can be differentiated on combined clinical, radiological and morphological grounds.