[Monostotic fibrous dysplasia of the occipital bone]

A case of monostotic fibrous dysplasia of the occipital bone in a 18-year-old female is described. She was admitted to our hospital with a hard, painless mass (5 x 5 cm) in the occipital region. Neurological examination and laboratory data revealed no abnormalities. Skull x-rays showed a radiolucent lesion with a sclerotic margin in the occipital bone. CT scan revealed an intradiploic multilocular mass separated by bone trabeculae. RI bone scan showed an abnormal uptake in this lesion. T1 and T2 MR image showed an abnormal low-intensity lesion in the occipital region. Operation was performed to verify the nature of the lesion, which was histologically confirmed to be an inactive fibrous dysplasia. Postoperative course was uneventful. Although its occurrence in the occipital bone is uncommon, fibrous dysplasia should be considered in the differential diagnosis of skull tumors.