Acoustic neuroma is a noncancerous (benign) and usually slow-growing tumor that develops on the main nerve leading from your inner ear to your brain. Because branches of this nerve directly influence your balance and hearing, pressure from an acoustic neuroma can cause hearing loss, ringing in your ear and unsteadiness. A type of schwannoma, this tumor arises from the Schwann cells responsible for the myelin sheath that helps keep peripheral nerves insulated.