Despite the fact that acoustic neuromas are not normal, they can cause serious or life-threatening problems whether left to chance or addressed. This is somewhat surprising because they are completely benign with non-cancerous growth, derived from cells that surround and insulate the nerves of balance. These cells are called Schwann cells and the nerve of balance is the vestibular nerve and thus the technically correct name for these lesions would be “vestibular schwannoma”. This name is often used in medical literature.
When the nerves of hearing and balance leave the inner ear they move inwards, through a narrow canal called inner auditory canal. Then there is a gap between the inner surface of the skull and the brain called the cerebellopontine angle. This space is filled with fluid surrounding the brain (cerebrospinal fluid). The two nerves cross the space and connected to each other enter the brainstem. The stem controls many vital functions such as breathing, blood pressure, beats, balance, eye movements and many of the unconscious functions we take for granted. From the same area come the nerves that control swallowing, speech, chewing and the sensation of the skin. A very important nerve in this region is the facial nerve. This is located near the outlet of the nerves of hearing and balance and is moving along with these two nerves inside the inner auditory canal through the end of the canal. Then, following a complicated route, the facial nerve runs through the middle ear and mastoid bone to get to the muscles of the facial expression – that is the smile, the eyelid fluttering, closing the eyes and the wrinkling of the forehead.
When acoustic neuromas begin to grow, they compress the surrounding structures and affect their function, eventually causing symptoms. If the volume growth starts within the inner auditory canal there can occur unilateral tinnitus, impaired hearing and hearing loss. Loss of balance may rarely occur. If the tumor starts further inside, it may remain asymptomatic for a long time until it starts to compress the brainstem, thus developing clumsiness of movement, pain or numbness of the face and speech disturbances. Finally, compression of the brainstem reduces the flow of cerebrospinal fluid and increased intracranial pressure. This will cause nausea, vomiting, headache, fever, severe disruption to the movement, blurred vision and a decrease in consciousness, possibly leading to seizures and death.
Generally, unilateral symptoms related to hearing must be investigated thoroughly and MRI provides safe and accurate diagnosis of these neoplasms. Therefore there is no reason for the symptoms not to be investigated, though of course usually it is not an emergency, unless there are major signs that indicate the presence of a large tumor, or presence of increased intracranial pressure.