An acoustic neuroma (also called a vestibular schwannoma) is a rare growth (tumour) in the brain. It often grows in size but does not spread to other parts of the body. This means it is benign.
The tumour grows on a nerve in the brain near to the ear. It can cause problems with hearing and balance, and also ringing in the ears (tinnitus). In most cases, the cause is unknown. However, some acoustic neuromas are associated with the disease neurofibromatosis type 2.
Acoustic neuromas are usually slow-growing and are rarely life-threatening. Treatment is most often with surgery, but radiotherapy can also be used. Some permanent deafness in one ear is common after treatment for an acoustic neuroma.
What is an acoustic neuroma?
An acoustic neuroma is a rare type of brain tumour (growth). It is not cancerous and so is called a benign tumour. The tumour grows along a nerve in the brain (a cranial nerve) that is called the acoustic or vestibulocochlear nerve. This nerve controls your sense of hearing and balance.
Acoustic neuromas grow from a type of cell called a Schwann cell. These cells cover nerve cells. This is why the tumour is also called a vestibular schwannoma. 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 the vestibulocochlear nerve.
What is the cause of acoustic neuromas?
The cause of most acoustic neuromas is unknown. About 7 out of every 100 acoustic neuromas are caused by neurofibromatosis type 2 (NF2). NF2 is a very rare genetic disorder that causes benign tumours of the nervous system. It affects about 1 in 350,000 people. Almost everyone with NF2 develops an acoustic neuroma on both nerves for hearing (acoustic nerves) - ie bilateral tumours. People with NF2 can also develop benign tumours on the spinal cord and the coverings of the brain.
How common are acoustic neuromas?
Acoustic neuromas are rare. About 13 people in every million are diagnosed each year with an acoustic neuroma in the UK. Brain tumours themselves are rare. Brain tumours can be non-cancerous (benign) or cancerous (malignant). Brain tumours are divided into two main groups:
- Primary brain tumours originate in the brain. An acoustic neuroma is a primary brain tumour.
- Secondary brain tumours are tumours in the brain that have spread from other parts of the body. They are often referred to as secondaries or brain metastases. These are malignant tumours.
Acoustic neuromas account for about 8 in 100 primary brain tumours. They are more common in middle-aged adults and rare in children. Acoustic neuromas seem to be more common in women than in men.
What are the symptoms of an acoustic neuroma?
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. 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.
What tests are needed to diagnose an acoustic neuroma?
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) surgeon.
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). No X-rays are used (so it is different to a CT scan which does use X-rays). See also the separate leaflet called MRI Scan for more information.
Hearing tests may also be performed if an acoustic neuroma is suspected. This is because one of the most common symptoms of an acoustic neuroma is hearing loss. If an acoustic neuroma is found on a scan, it is useful to know what your hearing in both ears is like before treatment.
What is the treatment for acoustic neuroma?
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. This is because acoustic neuromas are very slow-growing and may not cause any symptoms for a long time. Remember, acoustic neuromas are not 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.
- Your 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 a very precise single dose (usually) of 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 location 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.
Are any complications likely from an acoustic neuroma?
Complications can be thought of as:
- Due to the tumour itself.
- Due to treatments for acoustic neuroma.
- Return (recurrence) of an acoustic neuroma.
Possible complications due to the acoustic neuroma
- Hearing loss. The most common symptom of an acoustic neuroma is hearing loss. This is due to damage to the vestibulocochlear nerve that the acoustic neuroma is growing on. Even if the acoustic neuroma is removed with surgery, or destroyed with radiotherapy, a degree of permanent hearing loss in one ear is usual. The extent to which you will be affected by hearing loss varies from person to person. It can depend on things such as how big the tumour is, how much damage has been caused and how difficult treatment was. It is possible to be left with severe or even complete deafness on the side of the acoustic neuroma.
- 'Water on the brain' (hydrocephalus). If your acoustic neuroma grows very large, a complication called hydrocephalus can occur. This happens because the flow of cerebrospinal fluid is obstructed (see above, under 'Less common symptoms of acoustic neuroma'). 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. This can lead to some of the symptoms of acoustic neuroma, listed earlier. Long-term pressure can cause permanent damage. 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. The brainstem is the lower part of your brain that connects to the spinal cord. It controls vital bodily functions. If the brainstem is affected (very rare) then it is possible to have problems with breathing, consciousness, the circulation, co-ordination and balance, and your arm and leg function. Again, 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.
Possible complications due to 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.
Return (recurrence) of acoustic neuroma
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 a recurrence.
What is the outlook (prognosis) with an acoustic neuroma?
The outlook is generally very good, particularly as it is a non-cancerous (benign) tumour. It is generally very suitable for treatment and complications are uncommon. There is usually a degree of hearing loss in the affected ear after treatment.
Further help & information
Dr Katrina Ford
Dr Colin Tidy
Dr Helen Huins