An acoustic neuroma is a rare tumour in the brain. The tumour grows on a nerve in the brain near to the ear. Acoustic neuromas tend to grow very slowly and don't usually spread to any distant part of the body.
Acoustic neuroma causes
The cause of most acoustic neuromas is unknown. In less than 1 in 10 people, an acoustic neuroma is caused by neurofibromatosis type 2 (NF2). NF2 is a very rare genetic disorder that causes non-cancerous (benign) tumours of the nervous system. People with NF2 can also develop benign tumours on the spinal cord and the coverings of the brain.
It is not cancerous and so is called a benign tumour.
Acoustic neuromas grow from a type of cell called a Schwann cell. These cells cover the nerve cells in the body. This is why the tumour is also called a vestibular schwannoma.
The tumour grows along a nerve in the brain (these nerves are called cranial nerves) that is called the acoustic or vestibulocochlear nerve. This nerve controls your sense of hearing and also your balance. Therefore acoustic neuromas are sometimes called vestibular schwannomas.
Acoustic neuromas tend to grow very slowly and they don't spread to distant parts of the body. Sometimes they are too small to cause any problems or symptoms. Bigger acoustic neuromas can interfere with how the vestibulocochlear nerve works and so causes symptoms.
For most people with an acoustic neuroma, the cause is not known. About 7 out of every 100 acoustic neuromas are caused by a condition called neurofibromatosis type 2 (NF2). NF2 is a rare genetic disorder that causes benign tumours of the nervous system. It affects about 1 in 25,000 people.
Almost everyone with NF2 develops an acoustic neuroma on both nerves for hearing (acoustic nerves) - ie there is a tumour on the nerves on both sides of the head (bilateral). People with an acoustic neuroma but who don't have NF2 usually only develop a tumour on one side (unilateral). People with NF2 can also develop benign tumours on the spinal cord and the coverings (membranes) that surround the brain.
How common is it?
Acoustic neuromas are rare. Between 1 and 20 people in every million worldwide are diagnosed each year with an acoustic neuroma. Acoustic neuromas account for about 6 in 100 brain tumours. They are more common in middle-aged adults and are rare in children. Acoustic neuromas seem to be more common in women than in men.
Acoustic neuroma symptoms
A small acoustic neuroma may cause no symptoms. If you do have symptoms from an acoustic neuroma, these usually develop very gradually, as the tumour is slow-growing.
A small acoustic neuroma may cause no symptoms. The symptoms that an acoustic neuroma can cause are very common. Remember that acoustic neuromas are very rare. You should see your doctor if you have any of these symptoms, but they are more likely to be due to other conditions than a brain tumour.
The most common symptoms of an acoustic neuroma are:
- Hearing loss. Some degree of deafness occurs in most people with an acoustic neuroma. Usually hearing loss is gradual and affects one ear. The type of deafness caused is called sensorineural deafness and means the nerve for hearing (the acoustic nerve) is damaged.
- Tinnitus. This is the medical name for ringing in the ears. About 7 in 10 people with an acoustic neuroma have tinnitus in one ear. The sounds can vary; it does not have to be ringing like a bell. Tinnitus describes any sounds heard within the ear when there is no external sound being made. Tinnitus is a common symptom and not a disease in itself. Other causes of tinnitus include earwax, ear infections, ageing and noise-induced hearing loss.
Other, common symptoms of acoustic neuroma include:
- Vertigo. This is the sensation of the room spinning, often described as dizziness. It is not a fear of heights as some people incorrectly think. This feeling of movement occurs even when you are standing still. Vertigo can be caused by other conditions affecting the inner ear. Nearly half of people with an acoustic neuroma have this symptom, but less than 1 in 10 have it as their first symptom.
- Loss of feeling (facial numbness), tingling or pain. These symptoms are due to pressure from the acoustic neuroma on other nerves. The commonly affected nerve is called the trigeminal nerve which controls feeling in the face. About 1 in 4 people with acoustic neuroma have some facial numbness - this is a more common symptom than weakness of the facial muscles. However, it is often an unnoticed symptom. Similar symptoms can occur with other problems, such as trigeminal neuralgia or a tumour growing on the facial nerve (a facial neuroma).
Less common symptoms of acoustic neuroma are:
- Headache. This is a relatively rare symptom of an acoustic neuroma. It can occur if the tumour is big enough to block the flow of cerebrospinal fluid in the brain. Cerebrospinal fluid is the clear, nourishing fluid that flows around the brain and spinal cord, protecting the delicate structures from physical and chemical harm. Obstruction to the flow and drainage of cerebrospinal fluid can cause a problem known as 'water on the brain' (hydrocephalus). This results in increased pressure and swelling, and the brain effectively becomes squashed within the skull. This can cause headache and, if untreated, brain damage.
- Earache. This is another rare symptom of acoustic neuroma. There are many more common causes of earache.
- Visual problems. Again, these are a rare symptom. If they do happen, it is due to hydrocephalus (see above).
- Tiredness and lack of energy. These are nonspecific symptoms and can be due to many causes. It is possible that a non-cancerous (benign) brain tumour could lead to this.
How is it diagnosed?
Acoustic neuromas can be difficult to diagnose. If your GP suspects that you have an acoustic neuroma from your symptoms, you would probably be referred to a hospital ear, nose and throat (ENT) specialist.
Any initial tests will depend on the symptoms caused by the acoustic neuroma. If the tumour causes symptoms such as a headache or balance problems, you may also need to have other tests to check for other causes of these symptoms.
The best test to diagnose an acoustic neuroma is a magnetic resonance imaging (MRI) scan of the brain. An MRI scan uses a strong magnetic field and radio waves to take a detailed picture of your brain, and of the structures inside it. It is painless but it can be noisy and can make you feel anxious about being 'closed in' (claustrophobic).
Hearing tests are also needed if an acoustic neuroma is suspected. This is because one of the most common symptoms of an acoustic neuroma is hearing loss.
Acoustic neuroma treatment
If you have a very small acoustic neuroma, your doctors might decide that the best way to treat you is just to observe and monitor it closely.
Acoustic neuromas are very slow-growing and may not cause any symptoms for a long time. Remember, acoustic neuromas are not cancerous (malignant) and do not spread, so it is quite safe to watch things for a while. Also, treatments can have complications and side-effects. Therefore, the risks and benefits of treatment have to be balanced. If observation is recommended, your condition will be monitored with regular scans.
The main treatments for acoustic neuroma are surgery or stereotactic radiosurgery. The treatment you are offered will depend on:
- Your suitability for surgery or radiotherapy. Factors such as age and general health govern how fit you are for different treatments.
- The growth (tumour). The size and position of your acoustic neuroma will influence the type of treatment offered.
The results of the tests and scans you have can also help to determine which type of treatment is best for you and your tumour.
Either a brain surgeon (neurosurgeon) or an ENT surgeon can operate to remove an acoustic neuroma, depending on its size and location on the vestibulocochlear nerve in the brain. The surgery is carried out under a general anaesthetic.
Most people with acoustic neuroma are treated with surgery, and about 95 in 100 tumours can be removed completely. Occasionally (about 5 cases in every 100), a small part of the tumour is left behind. This is usually because it is technically too difficult to remove the whole tumour and/or there is a risk of causing more damage to the nerve or other nearby structures.
If some of the acoustic neuroma is left remaining, it can often be treated with radiotherapy. After surgery for an acoustic neuroma, you will probably have to remain in hospital for a few days for monitoring. You should be fully recovered within 6-12 weeks, and, if your tumour was completely removed, you should not need any more treatment.
This is a newer type of treatment that can be used for acoustic neuromas. Stereotactic radiosurgery involves delivering radiation to an extremely well-defined area within the brain - where your acoustic neuroma is.
Stereotactic means locating a point using three-dimensional (3D) co-ordinates. In this instance, the point is the acoustic neuroma tumour within the brain. A metal frame (like a halo) is attached to your scalp and a series of scans is performed to show the exact position of the tumour. Stereotactic radiosurgery can be given with a normal radiotherapy machine, the CyberKnife® machine, or with a technique known as gamma knife treatment.
Stereotactic radiosurgery is a very specialised type of treatment and is only available in some large hospitals. These hospitals are usually ones with both neurosurgery and cancer treatment (oncology) centres. The main advantage of this treatment is to prevent tumour growth and preserve any remaining (residual) hearing. It tends to shrink rather than remove or destroy the acoustic neuroma. It can be used for very small tumours.
What are the possible complications from the treatments for acoustic neuroma?
- Damage to the facial nerve, causing a facial nerve palsy. The facial nerve is the nerve in the brain that controls movements in the muscles of the face. If an acoustic neuroma has grown quite large, removal during surgery can potentially lead to damage of this neighbouring nerve. If the nerve is damaged, there will be paralysis of part of the face. This can cause a problem with drooping of one side of the face. In some cases, physiotherapy will help but, in others, the damage is permanent. Obviously, during surgery, great care is taken to identify and avoid damage to surrounding nerves.
- Damage to the vestibulocochlear nerve, leading to deafness. As mentioned, a degree of hearing loss is normal after treatment for acoustic neuroma. If you have NF2 and bilateral tumours, there is a strong chance that after surgery, you will completely lose the hearing in both of your ears.
- Damage to the trigeminal nerve, leading to loss of feeling (facial numbness). In the same way that the facial nerve can be damaged during surgery to remove an acoustic neuroma, the trigeminal nerve can also be injured. If this occurs, there is loss of sensation to parts of the face.
What are the possible complications?
The possible complications due to the acoustic neuroma include:
- Hearing loss:
- The most common symptom of an acoustic neuroma is hearing loss.
- The extent to which you will be affected by hearing loss varies from person to person.
- 'Water on the brain' (hydrocephalus):
- If your acoustic neuroma grows very large, a complication called hydrocephalus can occur. This happens because the flow of fluid in the brain (cerebrospinal fluid) is obstructed.
- Pressure can build up inside the brain, leading to permanent brain damage if not identified and treated.
- The condition can be treated by inserting a drainage tube (called a shunt) to relieve the pressure and allow the cerebrospinal fluid to flow.
- Hydrocephalus is very unlikely if you have treatment for an acoustic neuroma.
- Damage caused by pressure on other nerves in the brain, or on the brainstem:
- If the acoustic neuroma is growing and untreated, it can cause problems by pressing on nearby structures in the brain. Long-term pressure can cause permanent damage.
- For example, it is possible that the trigeminal nerve (which controls feeling in the face) or the facial nerve (which controls movements of the muscles of the face) can be affected.
- If you have treatment for your acoustic neuroma before it has had the chance to grow very big (remember, it is a slow-growing tumour), this sort of complication is very unlikely.
What is the outlook?
The outlook (prognosis) is generally very good. Acoustic neuromas usually respond well to treatment and complications are uncommon. However, there is often some hearing loss in the affected ear after treatment.
Fewer than 5 in every 100 acoustic neuromas come back. So it is uncommon, but possible. It is more likely if you have NF2. It could cause any of the symptoms mentioned earlier, or any of the complications. After treatment for acoustic neuroma you will generally be followed up in an outpatient clinic to check for any symptoms or signs of it coming back.
Further reading and references
; Risk Factors of Acoustic Neuroma: Systematic Review and Meta-Analysis. Yonsei Med J. 2016 May57(3):776-83. doi: 10.3349/ymj.2016.57.3.776.
; Acoustic neuroma growth: a systematic review of the evidence. Otol Neurotol. 2010 Apr31(3):478-85. doi: 10.1097/MAO.0b013e3181d279a3.
; Factors associated with anxiety and depression in the management of acoustic neuroma patients. J Clin Neurosci. 2012 Feb19(2):246-51. doi: 10.1016/j.jocn.2011.06.006. Epub 2011 Nov 2.
; Acoustic neuroma observation associated with an increase in symptomatic tinnitus: results of the 2007-2008 Acoustic Neuroma Association survey. J Neurosurg. 2013 Oct119(4):864-8. doi: 10.3171/2013.5.JNS122301. Epub 2013 Jun 21.
; Radiosurgery, a treatment for acoustic neuroma. Ten years' experience. Acta Otorrinolaringol Esp. 2014 May 17. pii: S0001-6519(14)00087-9. doi: 10.1016/j.otorri.2014.03.003.