An acoustic neuroma, also known as a vestibular schwannoma, is a rare benign (non-cancerous) growth that develops on the eighth cranial nerve. This nerve runs from the inner ear to the brain and is responsible for hearing and balance (equilibrium). There is no standard or typical pattern of symptom development, although hearing loss in one ear (unilateral) is the initial symptom in approximately 90 percent of cases. Additional findings include ringing in the ears (tinnitus) and dizziness. The symptoms of an acoustic neuroma occur from the tumor pressing against the eighth cranial nerve and disrupting its ability to transmit nerve signals to the brain. An acoustic neuroma is not cancerous (malignant); it does not spread to other parts of the body. The reason an acoustic neuroma forms is unknown.