A huge occipital osteoblastoma accompanied with aneurysmal bone cyst in the posterior cranial fossa.

Osteoblastoma is an infrequent benign tumor and skull involvement is extremely rare. The occipital bone is much less frequently involved. We report an unusual case of a huge occipital osteoblastoma with aneurysmal bone cyst in the posterior cranial fossa of a 20-year-old young man. MRI scan and CT three-dimensional reconstruction revealed that the tumor (approximately 8.5 cm x 6 cm x 5 cm) occupied nearly half volume of the posterior cranial fossa. The cerebellum, the forth ventricle and brain stem were compressed remarkably and hydrocephalus was noted. The tumor mass was multiloculated cystic and highly vascular. Excessive bleeding occurred during operation and total removal was achieved. The patient was symptom-free and MRI scan revealed no evidence of recrudescence after a follow-up period of 18 months. Pathological examination revealed that the lesion was a benign osteoblastoma with secondary aneurysmal bone cyst (ABC). ABC constitutes a highly vascular lesion while complete surgical resection is often impeded by excessive intraoperative bleeding. Preoperative embolization may reduce the risk. Despite the benign nature of osteoblastoma, local recurrence after incomplete resection is not rare and malignant transformation during recurrence may occur even after adequate surgery. Our case confirms the findings of previous investigators that if osteoblastoma is removed completely, no recurrence is expected even without adjuvant irradiation and chemotherapy.