Aneurysmal bone cyst at the base of the skull.

Aneurysmal bone cysts have been described as pseudocysts in view of their lack of an epithelial lining. These cysts are uncommon, but when they do occur they typically involve the long bones of the extremities, the membranous bones of the thorax and pelvis, and the vertebrae. Skull involvement is uncommon. We present the case of a 14-year-old girl who presented with nasal obstruction and a swelling of the right cheek. Contrast-enhanced computed tomography detected a heterogeneous cystic mass involving the sphenoid and ethmoid bones. The mass was excised via a lateral rhinotomy approach, and it was identified as an aneurysmal bone cyst on histologic examination. The patient experienced a recurrence in the right sphenoid sinus within 3 months, and the lesion was removed via transnasal endoscopy.