Aneurysmal Bone Cyst at the Anterior Skull Base Arising from the Perpendicular Plate of the Ethmoid Bone

Aneurysmal bone cysts (ABCs) are benign cystic lesions most commonly observed in long bones. Expansile bone destruction and blood-filled cavities separated by fibrous septa characterize these lesions. We present a case of a 20-year-old woman who presented with recurrent epistaxis for seven months and progressive anosmia over the preceding three months. Nasal endoscopy revealed a mass located in the midline of the nasal cavity. Radiological imaging demonstrated a bone-origin cystic lesion with dense content occupying the nasal cavity and extending to the anterior skull base. The patient underwent endoscopic surgery, and the cystic lesion was removed together with a portion of the nasal septum. No postoperative complications occurred during follow-up.ABCs are typically diagnosed at a young age and are rarely encountered in the paranasal sinus region. Although imaging modalities do not demonstrate pathognomonic findings, computed tomography and magnetic resonance imaging play an important role in diagnosis and surgical planning. ABCs involving the skull base are extremely rare. Complete surgical excision remains the preferred treatment whenever feasible.