Osteoblastoma of the ethmoid sinus in a nine-year-old child--an unusual occurrence.

Osteoblastoma is a benign bone tumor which is common in the vertebral column and long bone of the extremities. The paranasal sinus involvement is rare. We reported a case of benign osteoblastoma of the ethmoid sinus in a nine-year-old boy who presented with exophthalmos. The tumor had aggressive growth with cranial base involvement. Radiologic finding was a mottled soft tissue mass with sclerotic margin. Histologic features were the presence of osteoblast, small trabeculae of woven bone and rich vascular fibrous stroma. Differential diagnoses consist of various kinds of fibro osseous lesions; the closest one is osteoid osteoma. Surgery is the treatment of choice, external ethmoidectomy with lateral rhinotomy was performed in this case. Recurrence is common according to previous reports. Previous literature were reviewed and discussed.