RESUMEN
Aneurysmal bone cysts are benign bone tumors that most commonly occur in people younger than 30 years. The cysts are most often found in the metaphyses of long bones and rarely affect the skull. We present a 54-year-old woman with a rapidly enlarging mass in the left occipital region that caused tenderness for 2 weeks. Computed tomography (CT) revealed an expansile, osteolytic lesion with characteristic soap-bubble appearance and fluid-fluid levels. Magnetic resonance images showed a dark rim surrounding the lesion, as well as multilocular spaces with fluid-fluid levels. The tumor was soft, fragile, and pulsatile during surgery. The patient was treated with en bloc resection of the tumor with cranioplasty. Follow-up CT 5 months later showed no evidence of recurrence.