Benign osteoblastoma in an unusual mastoid location

Benign osteoblastoma (OB) is an unusual primary bone tumor. The preferred locations are the posterior arch of vertebrae and long bones. We report herein an extremely rare location of an OB in the mastoid process of the temporal bone.

A 22-year-old woman presented with painful left retro-auricular swelling. Computed tomography features were suggestive of an aggressive osteolytic lesion of the left mastoid. The pathologic examination of bone curettage material revealed a benign OB. A complete resection of the tumor was performed later, with no evidence of recurrence at 1 year.

To our knowledge, this is the 14th reported case of OB confined to the mastoid process of temporal bone. Its histological diagnosis can be difficult and osteosarcoma is its principal differential diagnosis. Although generally regarded as benign, OB has potential for recurrence and local invasion. As such, complete resection, whenever possible, is preferred over conventional curettage.