A rare case of sino-nasal aneurysmal bone cyst

Aneurysmal bone cysts (ABC) are rare in the paranasal sinuses. They are benign expansile multicystic masses containing blood-filled spaces which typically occur in the long bones of pediatric patients. The lesion often produces symptoms due to the compression of adjacent structures or pathological fracture and depends on localization. In this case report, we discuss a 28-year-old female who presented with left-sided headache, left eye proptosis, and diplopia. Radiologic evaluation revealed a left paranasal sinus expansile multicystic mass with internal blood fluid levels displacing and thinning the left medial orbital wall which suggested the diagnosis of ABC. Radiologists should be familiar with and comfortable diagnosing ABC in the head and neck, and be able to differentiate this entity from others, such as telangiectatic osteosarcoma. Biopsy can be challenging since blood products may be the only material identified and may produce tissue that is difficult to interpret or misdiagnosed.