Acoustic neuroma (vestibular schwannoma)
An acoustic neuroma (vestibular schwannoma) is a benign tumor that develops on the balance (vestibular) and hearing, or auditory (cochlear) nerves leading from your inner ear to the brain, as shown in the top image. The pressure on the nerve from the tumor may cause hearing loss and imbalance. In some cases, the tumor may grow and affect the cerebellum or other brain tissues, as shown in the magnetic resonance imaging (MRI) scan and illustrations above.
Acoustic neuroma, also known as vestibular schwannoma, is a noncancerous and usually slow-growing tumor that develops on the main (vestibular) nerve leading from your inner ear to your brain. Branches of this nerve directly influence your balance and hearing, and pressure from an acoustic neuroma can cause hearing loss, ringing in your ear and unsteadiness.
Acoustic neuroma usually arises from the Schwann cells covering this nerve and grows slowly or not at all. Rarely, it may grow rapidly and become large enough to press against the brain and interfere with vital functions.
Treatments for acoustic neuroma include regular monitoring, radiation and surgical removal.
Signs and symptoms of acoustic neuroma are often easy to miss and may take many years to develop. They usually happen because of the tumor's effects on the hearing and balance nerves. Pressure from the tumor on nearby nerves controlling facial muscles and sensation (facial and trigeminal nerves), nearby blood vessels, or brain structures may also cause problems.
As the tumor grows, it may cause more noticeable or severe signs and symptoms.
Common signs and symptoms of acoustic neuroma include:
- Hearing loss, usually gradually worsening over months to years — although in rare cases sudden — and occurring on only one side or more severe on one side
- Ringing (tinnitus) in the affected ear
- Unsteadiness or loss of balance
- Dizziness (vertigo)
- Facial numbness and weakness or loss of muscle movement
In rare cases, an acoustic neuroma may grow large enough to compress the brainstem and become life-threatening.
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When to see your doctor
See your doctor if you notice hearing loss in one ear, ringing in your ear or trouble with your balance.
Early diagnosis of an acoustic neuroma may help keep the tumor from growing large enough to cause serious consequences, such as total hearing loss.
The cause of acoustic neuromas can be linked to a problem with a gene on chromosome 22. Normally, this gene produces a tumor suppressor protein that helps control the growth of Schwann cells covering the nerves.
Experts don't know what causes this problem with the gene. In most cases of acoustic neuroma, there is no known cause. This faulty gene is also inherited in neurofibromatosis type 2, a rare disorder that usually involves the growth of tumors on the hearing and balance nerves on both sides of your head (bilateral vestibular schwannomas).
Neurofibromatosis type 2
Autosomal dominant inheritance pattern
In an autosomal dominant disorder, the altered gene is a dominant gene located on one of the nonsex chromosomes (autosomes). You need only one altered gene to be affected by this type of disorder. A person with an autosomal dominant disorder — in this case, the father — has a 50% chance of having an affected child with one altered gene (dominant gene) and a 50% chance of having an unaffected child with two typical genes (recessive genes).
The only confirmed risk factor for acoustic neuroma is having a parent with the rare genetic disorder neurofibromatosis type 2. However, neurofibromatosis type 2 only accounts for about 5% of acoustic neuroma cases.
A hallmark characteristic of neurofibromatosis type 2 is the development of noncancerous tumors on the hearing and balance nerves on both sides of the head, as well as on other nerves.
Neurofibromatosis type 2 (NF2) is known as an autosomal dominant disorder, meaning that the mutation can be passed on by just one parent (dominant gene). Each child of an affected parent has a 50-50 chance of inheriting it.
An acoustic neuroma may cause a variety of permanent complications, including:
- Hearing loss
- Facial numbness and weakness
- Difficulties with balance
- Ringing in the ear
Large tumors may press on your brainstem, preventing the normal flow of fluid between your brain and spinal cord (cerebrospinal fluid). In this case, fluid can build up in your head (hydrocephalus), increasing the pressure inside your skull.