[Benign osteoblastoma of the parietal bones]

Benign osteoblastoma accounts for less than 1% of the primary bone tumors and the calvarial lesion is extremely rare. There are only 12 reported cases in the literature as far as we could collect. We have presented a case of benign osteoblastoma originated from the parietal bone. This 9-year-old boy struck his head on the parietal region and noticed the bulging at the same site. A month later he visited to Fukuoka University Hospital because of persistent bulging of the same site. Neurological examinations were normal. Plain skull roentgenogram on Towne view showed radiolucent area in the midline of parietal bones with irregular margins and in tangential view the outer table revealed thinning and expanding. Coronal CT scan demonstrated same abnormality and intact inner table. The tumor was located within the dipole in the bilateral parietal bones and was removed by a simple curettage. The microscopic feature showed numerous osteoblasts, osteoblastic rimming and many multinucleated giant cells. These indicated a typical benign osteoblastoma. He has been doing well one year after the operation without any evidence of recurrence.