Osteoblastoma of the orbit. A case report and review of the literature.

We describe a case of benign orbital tumour involving the frontal sinus and ethmoidal cells. CT findings were typical of "bone tumour of the orbit", histological analysis yielded a diagnosis of benign osteoblastoma. A review of the literature disclosed only 13 well documented cases. We compared out radiological findings with the features described in these reports. CT patterns were similar in most cases. The lesion generally appears as a heterogeneous mass where it is possible to appreciate both high density portions and low density areas. On MRI osteoblastoma shows an iso- low signal both in T1 and in T2 sequences. Less frequently the lesion may yield a high signal in T2 images. The orbit is rarely involved by bone tumours, but all bone tumours may theoretically involve the orbit, often making it difficult to establish the right differential diagnosis by imaging. Thirteen cases are insufficient to describe general radiological criteria to improve the specificity in detection of this disease and a broader outlook is essential. For this reason we also examined the radiological signs of bone tumours involving other portions of the body. Even though many literature reports suggest CT is the landmark in bone tumour diagnosis, we think it should always be accompanied by MRI. MRI is known to overestimate local staging, but its contribution to differential diagnosis among various tumours may be decisive.