The term “benign osteoblastoma” was independently proposed by Jaffe (1956) and Lichtenstein (1956) to define a vascular osteoid and bone-forming tumor containing numerous osteoblasts and rich vascularized delicate fibrous stroma with a benign appearance.4
Benign osteoblastoma is a rare tumor that constitutes ~1% of all primary bone tumors and 3% of all benign bone tumors.5
Osteoblastomas usually occur in patients <30 years of age with a peak incidence in the second decade of life and a range of 3 to 78 years. The tumor shows a predilection for the male gender. It is most commonly located in the vertebral column and metaphysis or diaphysis of long bones. It rarely develops in the skull, but when it does, it has a preference for the temporal and frontal bones.6,7
Its occurrence in the sphenoid bone is exceptional.8,9,10,11
It is a painful tumor and usually grows slowly, becoming symptomatic only when it invades important structures, such as the cranial nerve foramina. Neuroradiological examination, namely with CT and MRI, is particularly important to make a preoperative diagnosis. Besides, it is essential to define the nature and extent of soft tissue involvement or compromise. The typical image is a “lytic” zone surrounded by bony condensation and a minimal osteosclerotic reaction peripherally, rarely invading the soft tissues. Generally, CT reveals a bony destruction and focal calcification with variable patterns of contrast enhancement. MRI is characterized by a hypointense or isointense mass on a T1-weighted image with homogeneous or heterogeneous enhancement after the administration of gadolinium and by a hypointense mass on a T2-weighted image, unlike our case that showed a heterogeneous lesion, with some small areas that have low signal intensity on T1- and T2-weighted images, suggesting a mixture of bone and fibrous tissue.12
Benign osteoblastoma should be differentiated from other similar bone-forming tumors, such as osteomas, osteoid osteomas, osteosarcoma, ossifying fibroma, calcifying meningioma, giant cell tumor, aneurysmal bone cyst, and fibrous dysplasia.13
Definitive diagnosis is made by histological examination that reveals osteoblast-like cells disseminated in an abundant conjunctive background surrounded by immature richly vascularized bone. No malignant features such as anaplasia, necrosis, or abnormal mitosis are found. The majority of the authors currently recommended that benign osteoblastoma, despite its benign biological behavior, should be treated with total resection of the tumor. Prognosis after complete removal is uniformly good.14
There is no definitive role for adjuvant radiotherapy or chemotherapy, and radiation therapy currently is reserved for specific cases in which only subtotal resection has been achieved or for unresectable lesions in symptomatic patients. To our concern, this is the fifth reported case of benign osteoblastoma in the sphenoid bone. MRI proved to be effective for the evaluation of the intracranial and intraosseous extensions of the tumor. The mass was totally excised and no recurrence was observed, for at least 15 years, confirming that total surgical resection is the treatment of choice of benign osteoblastoma.