An acoustic neuroma is a rare non-cancerous 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 symptoms
A small acoustic neuroma may cause no symptoms. If symptoms do arise from an acoustic neuroma, these usually develop gradually, as the tumour is usually very slow-growing.
The symptoms that an acoustic neuroma can cause are very common. Remember that acoustic neuromas are very rare. People who develop these symptoms should see their doctor, but they are more likely to be due to conditions other than an acoustic neuroma.
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, meaning that the nerve for hearing 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 hearing loss due to other causes.
Other symptoms of acoustic neuroma can include:
- Vertigo. This is a false sensation of movement, commonly spinning. It is not a fear of heights as some people incorrectly think. This feeling of movement can occur even when standing still. It can come and go. Vertigo can also be caused by other conditions affecting the inner ear.
- Loss of feeling (numbness or altered sensation), tingling or pain in the face. These symptoms are due to pressure from the acoustic neuroma on other nerves. The nerve that is most commonly affected 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 often goes unnoticed. 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, this is a rare symptom. If it does occur, it is usually 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.
Acoustic neuroma causes
The cause of most acoustic neuromas is unknown. In fewer 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 affects about 1 in 25,000 people.
Acoustic neuromas are not cancerous and so they are known as benign tumours.
The tumour grows along a nerve in the brain (these nerves are called cranial nerves). The term 'acoustic neuroma' was used first because the tumour grows on what was previously called the acoustic nerve. However, technically a neuroma is a tumour of nerve cells, whereas these growths originate from the Schwann cells around the nerves. So the term 'vestibular schwannoma' is more technically correct.
How fast do acoustic neuromas grow?
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. An acoustic neuroma that is causing no symptoms may occasionally be found incidentally (by chance) on a MRI scan. Bigger acoustic neuromas can interfere with how the vestibulocochlear nerve works and cause tinnitus or hearing loss most commonly.
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).
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 an acoustic neuroma?
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 8 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.
How is an acoustic neuroma diagnosed?
Acoustic neuromas can be difficult to diagnose. If symptoms of an acoustic neuroma develop, referral to a hospital ear, nose and throat (ENT) specialist would probably be advised.
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, additional tests may also be necessary 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 the brain, and of the structures inside it. It is painless but it can be noisy and can make people 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. Vestibular (balance) tests may also be performed, particularly if one of the symptoms is unsteadiness.
Acoustic neuroma treatment
If the acoustic neuroma is very small, doctors might decide that the best way to treat 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, the situation will be monitored with regular scans.
The main treatment options for acoustic neuroma are surgical removal or stereotactic radiosurgery. The treatment offered will depend on:
- Suitability for surgery or radiotherapy. Factors such as age and general health determine fitness for different treatments.
- The growth (tumour). The size and position of the acoustic neuroma will influence the type of treatment offered.
The results of the tests and scans can also help to determine which type of treatment is best for each individual.
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. Although the aim is to remove the tumour completely, sometimes 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. Following surgery for an acoustic neuroma, admission to hospital for a few days for monitoring is usually advised. Full recovery typically takes 6-12 weeks, and if the tumour was completely removed, no further treatment is needed usually.
This is another 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 the 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 the 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 small tumours.
Proton beam therapy (a form of radiation therapy) and also biological treatments (so called because they interfere with the biological function of the tumour) such as bevacizumab, everolimus, and lapatinib are currently being tried out. Aspirin may also be a useful treatment for controlling the growth of the tumour. However, these treatments are not yet offered routinely in the UK.
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. Monitoring devices are typically used during surgery to try to prevent this nerve damage.
- Damage to the vestibulocochlear nerve, leading to deafness. As mentioned, a degree of hearing loss is normal after treatment for acoustic neuroma. Following surgery for bilateral tumours in those with NF2, there is a strong chance of complete loss of hearing in both 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.
Complications of an acoustic neuroma
Possible complications due to the acoustic neuroma include:
- Hearing loss:
- The most common symptom of an acoustic neuroma is hearing loss.
- The degree of hearing loss varies from person to person.
- 'Water on the brain' (hydrocephalus):
- If an 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 this is 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 an acoustic neuroma is treated.
- 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 an acoustic neuroma is treated 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. There is often some permanent hearing loss in the affected ear after treatment but this can be managed successfully with hearing devices.
Fewer than 5 in every 100 acoustic neuromas come back. So it is uncommon, but possible. Recurrence (re-growth of the tumour) is more likely in those affected by NF2. It could cause any of the symptoms mentioned earlier, or any of the complications. After treatment for acoustic neuroma, follow up takes place in an outpatient clinic to check for any symptoms or signs of it coming back.
Further reading and references
Gupta VK, Thakker A, Gupta KK; Vestibular Schwannoma: What We Know and Where We are Heading. Head Neck Pathol. 2020 Dec14(4):1058-1066. doi: 10.1007/s12105-020-01155-x. Epub 2020 Mar 30.
Yao L, Alahmari M, Temel Y, et al; Therapy of Sporadic and NF2-Related Vestibular Schwannoma. Cancers (Basel). 2020 Mar 3112(4). pii: cancers12040835. doi: 10.3390/cancers12040835.
Santacroce A, Trandafirescu MF, Levivier M, et al; Proton beam radiation therapy for vestibular schwannomas-tumor control and hearing preservation rates: a systematic review and meta-analysis. Neurosurg Rev. 2023 Jul 446(1):163. doi: 10.1007/s10143-023-02060-x.
Jakubeit T, Sturtz S, Sow D, et al; Single-fraction stereotactic radiosurgery versus microsurgical resection for the treatment of vestibular schwannoma: a systematic review and meta-analysis. Syst Rev. 2022 Dec 1211(1):265. doi: 10.1186/s13643-022-02118-9.
Rosahl S, Bohr C, Lell M, et al; Diagnostics and therapy of vestibular schwannomas - an interdisciplinary challenge. GMS Curr Top Otorhinolaryngol Head Neck Surg. 2017 Dec 1816:Doc03. doi: 10.3205/cto000142. eCollection 2017.