A 3-year-old girl was presented to the hospital due to gradual hearing loss. She had been healthy and there was no history of head trauma or injury. Physical examinations were unremarkable. Pure tone audiometry (PTA) revealed a down-sloping curve and an asymmetrical severe high frequency hearing loss. Acoustic immitance examination showed a normal tympanogram and an absent acoustic reflex. A high resolution CT (HRCT) examination was requested to further investigate the cause of the hearing loss.