An acoustic neuroma is a benign (non-cancerous) growth, or tumour, in the brain. It's also known as a vestibular schwannoma.
An acoustic neuroma grows on the vestibulocochlear nerve, which helps control hearing and balance. This nerve runs alongside the facial nerve, which carries information from the brain to the face muscles.
The symptoms of an acoustic neuroma tend to develop gradually and can vary in severity. This can make the condition difficult to diagnose (see below).
A small acoustic neuroma can lead to problems with:
hearing – causing hearing loss or tinnitus (a noise perceived inside the ear but with no outside source)
balance – causing vertigo (the sensation that you're spinning)
A large acoustic neuroma can cause a number of symptoms, including:
headaches with blurred vision
numbness or pain on one side of the face
problems with limb co-ordination on one side of the body
Occasionally, large neuromas can also result in muscle weakness on one side of the face. In rare cases, it may also cause changes to the voice or difficulty swallowing (dysphagia).
What causes an acoustic neuroma?
The cause of most acoustic neuromas is unknown, but a small number of cases (about 5%) are caused by a rare, inherited condition called neurofibromatosis type 2.
Acoustic neuromas grow from the cells that cover the vestibulocochlear nerve, called Schwann cells.
Diagnosing an acoustic neuroma
If your GP thinks you have an acoustic neuroma, you'll be referred to hospital for tests.
The three types of test you may have are:
magnetic resonance imaging (MRI) scan
computerised tomography (CT) scan
Treating an acoustic neuroma
Acoustic neuromas tend to grow slowly and don't spread to other parts of the brain.
They can be so small and grow so slowly that they may not cause any symptoms or problems. In such cases, the acoustic neuroma may just be monitored to avoid risks associated with surgery.
In rare cases, the tumour can grow large enough to press on the brain. However, most acoustic neuromas can be treated before they reach this stage, either with surgery to remove the tumour or radiotherapy to destroy it.
Complications of an acoustic neuroma
Acoustic neuromas aren't usually life-threatening but the symptoms can be disruptive. For example, the loss of hearing may affect your ability to communicate with others.
Speak to your GP or specialist if you feel the symptoms are having an impact on your day-to-day life. There may be ways of easing your symptoms, such as using a hearing aid or taking painkilling medication.
Symptoms of an acoustic neuroma
A small acoustic neuroma may not cause any symptoms, or your symptoms may develop gradually as acoustic neuromas tend to grow slowly.
Acoustic neuromas may grow about 1-2mm every year. However, there could be long periods when the tumour doesn't grow at all.
The possible symptoms of an acoustic neuroma are described below.
Hearing loss – is the most common symptom and usually develops gradually in one ear, although in some cases it can develop suddenly.
Tinnitus – the perception of noise in one or both ears that comes from inside the body rather than from an outside source. For example, you may hear ringing in one ear.
Vertigo – the sensation that you or the environment around you is moving or spinning. You may feel the sensation of movement even when you're standing completely still.
Facial numbness, tingling or pain –are relatively rare symptoms which can occur if the tumour begins to press on the nerve that controls feeling and sensation in your face (known as the trigeminal nerve).
Headaches – also a relatively rare symptom, although it can happen if the tumour blocks the flow of cerebrospinal fluid surrounding your brain.
Temporary vision problems – this is rare and is also caused by a cerebrospinal fluid blockage.
Ataxia –a loss of physical co-ordination that affects your ability to do activities, such as walking or writing. Ataxia caused by an acoustic neuroma usually only affects one side of the body (the same side as any hearing loss).
Hearing loss and tinnitus are the most common symptoms of acoustic neuroma. They usually only affect one ear. However, acoustic neuroma caused by neurofibromatosis type 2 (a rare inherited condition) can affect both ears.
The severity of hearing loss isn't necessarily linked to tumour size.
Causes of an acoustic neuroma
In most cases, the cause of an acoustic neuroma is unknown.
The only known risk factor for developing an acoustic neuroma is having a rare genetic condition called neurofibromatosis type 2 (see below).
Acoustic neuromas grow from the Schwann cells lining the vestibulocochlear nerve, which is why they are sometimes called vestibular schwannomas. Schwann cells form a sheath around nerves, helping electrical signals to travel through the body.
It's also not known what causes some acoustic neuromas to start growing or continue growing while others remain the same size.
Neurofibromatosis type 2
A small number of acoustic neuroma cases (about 5%) are caused by a rare, inherited condition called neurofibromatosis type 2.
Neurofibromatosis type 2 causes benign (non-cancerous) tumours to grow on the nerve tissue in the body, in particular within the head cavity and spine. The condition is generally characterised by an acoustic neuroma on each side that's growing from both the left and right acoustic nerves.
Neurofibromatosis type 2 shouldn't be confused with neurofibromatosis type 1, which is much more common and can also cause benign spinal tumours. Neurofibromatosis type 1 affects the skin and doesn't cause acoustic neuromas.
In neurofibromatosis type 2 both acoustic nerves are usually affected. This means that you're more likely to have hearing loss in both ears. Therefore, it's important to address issues such as lip reading and sign language early on in case you lose hearing in both ears.
Diagnosing an acoustic neuroma
An acoustic neuroma can be difficult to diagnose because the symptoms often develop gradually and can be hard to spot.
Symptoms, such as dizziness and hearing loss, can also be attributed to a number of other conditions, such as Ménière's disease (a rare disorder that affects the inner ear).
If your GP thinks that you may have an acoustic neuroma, you'll be referred to a hospital or clinic for further testing.
You may need to have a series of tests to check whether your nervous system (brain, nerves and spinal cord) is being affected by an acoustic neuroma.
Part of the neurological testing process involves checking your hearing.
You may have a number of hearing tests including a pure tone audiometry test and a speech recognition audiometry test.
During a pure tone audiometry test a machine called an audiometer is used to produce sounds at various volumes and frequencies. You listen through headphones and press a button when you hear a sound.
A speech recognition audiometry test tests your ability to recognise words spoken at different volumes.
Magnetic resonance imaging (MRI) scan
A magnetic resonance imaging (MRI) scan is one of the most accurate ways of diagnosing an acoustic neuroma. This type of scan allows your doctor to see the size and position of your tumour (growth).
An MRI scan uses a strong magnetic field and radio waves to produce a detailed picture of the inside of your head. It's a painless procedure that takes 15-60 minutes to complete. However, it can be noisy and you may feel slightly claustrophobic because you have to lie in a tunnel inside the scanner.
MRI scans don't use X-rays (high frequency radiation). However, if you're pregnant and in your first trimester (up to week 13 of the pregnancy) your MRI scan is likely to be delayed. After the first trimester, MRI scans can be used safely.
MRI scans are the most common way of looking for an acoustic neuroma.
Computerised tomography (CT) scan
Computerised tomography (CT) scans use X-rays and a computer to create detailed images of the structures inside the body, including internal organs, blood vessels, bones and tumours.
CT scans can't always locate small acoustic neuromas, but they're often useful in providing additional information, such as picking up a bone anomaly, which can help the doctor in charge of your care.
During a CT scan, you'll usually lie on your back on a flat bed. The CT scanner has an X-ray tube that rotates around your body. You'll usually be moved continuously through this rotating beam. The rays will be analysed by a detector on the opposite side of your body.
Unlike an MRI scan, where you're placed inside a tunnel, you shouldn't feel claustrophobic. The scan is painless and usually takes 10-30 minutes, depending on the part of your body being scanned.
Treating an acoustic neuroma
There are several different treatment options for an acoustic neuroma depending on your age, overall health, and the size and position of your tumour.
The results of any tests or scans you've had will also help determine the best course of treatment. You could be treated by a few different specialists including:
a neurosurgeon – a surgeon who specialises in operating on the nervous system (brain, nerves and spinal cord)
an ear, nose and throat (ENT) surgeon – a surgeon who specialises in treating conditions that affect the ears, nose or throat
a radiotherapist – a doctor who specialises in treatment with radiotherapy
If you have an acoustic neuroma that's very small or growing very slowly, you may not need to have any immediate treatment. Instead, your condition will be carefully monitored.
Research suggests that up to three-quarters of acoustic neuromas don't appear to be growing, so monitoring the tumour is all that's needed.
Simply monitoring an acoustic neuroma is often the best option because the risks associated with surgery or radiosurgery (see below) outweigh the risk of the tumour having an adverse effect on your health.
To help monitor your condition, you'll need to have regular magnetic resonance imaging (MRI) scans (where a magnetic field and radio waves are used to create an image of the inside of your body). The MRI scan will be used to check the size and growth of your acoustic neuroma.
Other treatments may be considered if the tumour shows any signs of growing or if there's a risk of it significantly affecting your health.
You may need to have an MRI scan every one to two years, although this will depend on your general health and the size of your tumour.
Microsurgery can be used to remove an acoustic neuroma. The surgery will be carried out under general anaesthetic, and the acoustic neuroma will be removed through an incision made in your skull.
Small acoustic neuromas can usually be completely removed. If you have a large tumour, a small part will occasionally be left behind to minimise the risk of damaging the facial nerve, which runs next to the acoustic nerve.
If a small part of the tumour remains, it can either be monitored with MRI scans or effectively treated using radiosurgery (see below).
After surgery to remove an acoustic neuroma, hearing in the ear affected by the tumour is almost always lost.
You may wish to discuss the possibility of having a 'bone anchored hearing aid' with your ENT surgeon, which will help divert sound from your affected ear to your good ear.
Facial nerve damage
Surgery can occasionally damage the facial nerve. This is because the acoustic nerve is very close to the facial nerve and large tumours are often stuck to it. Your surgeon will try not to damage your facial nerve and with large tumours will sometimes leave a small part of the tumour on the facial nerve to try to preserve it.
If your facial nerve is damaged during surgery you may find that:
your face droops on one side (facial palsy)
you drool saliva on the weak side of your face
you have difficulty closing your eye on the weak side of your face
your speech is less clear
These symptoms may improve within six to 12 months of having surgery and be helped with physiotherapy. However, it's important to be aware that some damage to your facial nerve may be permanent.
Facial nerve damage can also affect your eyes. For example, you may find it difficult to blink or close your eye completely on the side that was operated on. As a result, your eye may dry out and you may need to use artificial tears (eye lubricant).
In cases where the tumour is small, less than one in every 100 people's facial nerve will be badly affected after treatment.
For large tumours, around three in 10 people will have permanent, severe facial nerve weakness after surgery if a complete tumour removal is attempted. This falls to around one person in over 100 if a small part of the tumour is left on the facial nerve to preserve it.
Any minor post-surgery facial nerve weakness is likely to be temporary, although it may take several months to recover.
Recovery from surgery
Following surgery, you'll usually need to spend up to a week in hospital to recuperate.
You should be able to return to work after about two months. The length of time it takes you to recover may depend on the size and position of the tumour that was removed. The healthcare professionals treating you will be able to advise you further.
If your acoustic neuroma was completely removed, you won't usually need further treatment. However, you'll continue to be monitored with MRI scans.
Stereotactic radiosurgery delivers a very focused and precise dose of radiation to your acoustic neuroma. Stereotactic means locating a point (in this case the position of the tumour in your brain) using three-dimensional co-ordinates.
During stereotactic radiosurgery, the maximum amount of radiation will be aimed at your tumour without the surrounding tissue being exposed. It may be given as a single dose or delivered over several sessions. It doesn't get rid of your tumour but aims to stop it growing further. It can only be used on small tumours or the remains of a tumour after surgery on large tumours. It's not usually used for large tumours.
Stereotactic radiosurgery is carried out under local anaesthetic, which means you'll be conscious throughout the procedure but your scalp will be numbed. A lightweight metal frame is usually attached to the scalp and a series of scans will accurately pinpoint the position of the tumour. It can then be treated using a precise beam of radiation.
Immediate side effects of stereotactic radiosurgery are rare, and you'll usually only need to take a couple of days off work to have the treatment.
In some cases, stereotactic radiosurgery can cause nerve damage, although it may not be apparent until several weeks or months after treatment.
Symptoms of nerve damage can include:
facial numbness (loss of feeling)
facial paralysis (an inability to move part of your face)
Facial paralysis affects around one in every 100 people who has stereotactic radiosurgery. It's estimated that just under a third of people may experience hearing loss after stereotactic radiosurgery.
Complications of an acoustic neuroma
The symptoms of an acoustic neuroma can affect your day-to-day life, but more serious complications are rare.
Coping with your symptoms
Some symptoms of an acoustic neuroma can be difficult to live with and may affect your quality of life. For example, hearing impairment may have an impact on your job and communication may be more difficult. Severe dizziness and loss of balance may also affect your job and limit the activities you can do.
Speak to your GP or specialist if your acoustic neuroma is being monitored but you feel the symptoms are significantly affecting your daily life. There may be ways of easing your symptoms, such as using a hearing aid or painkilling medication, or you may need treatment to remove the tumour.
Occasionally, acoustic neuromas return after being removed. The tumours reoccur in less than five in every 100 people who have surgery to remove them.
It's likely that you'll need to have magnetic resonance imaging (MRI) scans over a number of years, regardless of which treatment you have.
One of the most serious complications of acoustic neuroma is a condition called hydrocephalus.
Hydrocephalus occurs when an acoustic neuroma is very large and presses on your brainstem (the lowest part of the brain that connects to the spinal cord).
This prevents the cerebrospinal fluid (CSF) from flowing between your brain and spinal cord. The blockage can cause pressure to build up inside your skull, which in turn puts pressure on the delicate tissues in your brain.
Hydrocephalus can be treated by draining away the excess CSF. It's important that it's treated quickly because in severe cases it can cause brain damage. In rare cases, hydrocephalus can be fatal.