Aneurysmal bone cyst on top of fibro-osseous lesion of the ethmoid sinus with orbital and intracranial extension in a child

OBJECTIVE: Aneurysmal bone cysts (ABCs) rarely involve the cranium. We report a case arising in the ethmoid sinus with orbital and intracranial invasion. Imaging suggested an associated fibro-osseous lesion. The lesion was completely resected. Histology confirmed the imaging diagnosis of ABC on top of an ossifying fibroma. A multidisciplinary approach is essential for optimal surgical outcomes. METHODS: We report a case of an 8-year-old boy with a 5 week history of painless, increasing prominence of the left eye. Clinical examination revealed non-pulsatile left proptosis. Visual acuity and ocular movements were normal. CT and MRI scans of the maxillofacial regions showed a large space-occupying lesion involving the left ethmoid air cells with left orbital and left inferior frontal intracranial extension. Multiple fluid levels with blood products were seen. Areas of the bony component of the lesion showed ground-glass density on CT. Imaging was consistent with an ABC with an underlying fibro-osseous lesion; probably fibrous dysplasia which was confirmed after surgical removal of the lesion. A multidisciplinary team of maxillofacial, neurosusugery and ENT surgeons performed the surgery. RESULTS: ABC arising from an osseous fibroma of the skull is rare. Total resection can be achieved with a multidisciplinary surgical approach. Post-operative histology confirmed by the imaging findings.