What Is Acoustic Neuroma?

Overview

Acoustic neuromas are rare, benign (non-cancerous) brain tumours that form on the vestibulocochlear nerve.¹ The vestibulocochlear nerve runs between the brain and the ear and controls hearing and balance.²

An acoustic neuroma may also be referred to as a vestibular schwannoma.¹ This name is given because these tumours arise on the vestibulocochlear nerve (hence, vestibular) in specialised Schwann cells (hence, schwannoma). Schwann cells are fatty cells that surround, protect and maintain our nerves.³ The term “vestibular schwannoma” is now generally the preferred term amongst the medical community.¹ 

If you have been diagnosed with an acoustic neuroma or know someone who has, this article can help you make sense of the diagnosis and understand what treatment options may be available to you. 

Causes of and risk factors for acoustic neuroma

The majority of acoustic neuromas arise sporadically. Sporadic tumours occur randomly in the population without a known underlying cause. The majority of sporadic cases of acoustic neuroma occur unilaterally (one side), meaning that only one of our two vestibulocochlear nerves are affected. Assigned birth gender is not believed to influence risk.⁴ 

People with neurofibromatosis type 2 (NF-2) are at increased risk of acoustic neuroma and other benign nerve tumours. Around 5% of acoustic neuromas are linked to NF-2 and are more likely to occur bilaterally (on both the left and right vestibulocochlear nerve).⁴ It has been observed that some families without NF-2 appear to be at increased risk for acoustic neuroma although the underlying reasons are not well understood.⁵ 

Tumours arise when genetic changes occur within affected cells that allow the cells to grow in an uncontrolled way. The most common genetic change in sporadic acoustic neuroma is the inactivation of a gene which is important in regulating cell division and preventing the  development of tumours. This gene is NF2 - the same gene which contains changes in those with neurofibromatosis type 2. This explains why people with NF-2 are at increased risk of acoustic neuroma compared with the general population.⁶ 

Signs and symptoms of acoustic neuroma

Acoustic neuromas most commonly present with symptoms of hearing loss and tinnitus (a buzzing or ringing sound in the ear). Since most cases of acoustic neuroma occur on one side of the body, symptoms usually affect one side, too. Hearing loss affects 94% of patients and generally gets worse over time.⁶

Other symptoms include:^{6, 7}

• Headache
• Visual changes
• Earache
• Vertigo (a sensation that you are spinning) and unsteadiness
• Facial numbness, weakness and pain occur when a larger tumour compresses nerves that run near to the vestibulocochlear nerves. These symptoms usually occur on one side of the face given that in most cases acoustic neuromas affect only one of our two vestibulocochlear nerves
• Problems with coordination

The size of acoustic neuroma does not seem to correlate well with the severity of symptoms a person has. Large tumours may cause no symptoms.⁷ 

If you have any of the above symptoms and are worried that you could have an acoustic neuroma, speak to your healthcare provider. It is important to remember that many different conditions can cause similar symptoms, so the ones outlined above do not necessarily mean that you have developed an acoustic neuroma. 

Diagnosis of acoustic neuroma

The most accurate way to diagnose acoustic neuroma is through MRI scanning. MRI scans can detect very small acoustic neuromas measuring as little as 2 mm in diameter. In most cases, the diagnosis can be made on the basis of MRI images alone. It is not usually necessary to take a biopsy to confirm the diagnosis.⁷

Acoustic neuromas can be picked up incidentally. This typically occurs during hearing tests carried out for another reason (for example, in relation to work or school) or when an MRI scan is carried out for a different indication. Between one and five percent of people without symptoms who undergo an MRI scan for another reason are found to have an acoustic neuroma.⁷

Management and treatment for acoustic neuroma

The management options for acoustic neuroma depend on a number of factors, such as the size of the tumour, the severity of symptoms and the wishes of the patient.¹

Observational management

Since many neuromas generally grow slowly, the first option is to simply monitor the tumour.⁴ Usually this will be done by offering MRI scans and hearing tests at regular intervals. This option is usually best for those with small tumours that aren’t causing many symptoms.⁶ Observational management is increasing in popularity amongst physicians as it ultimately allows some patients with slow-growing tumours to avoid invasive treatments.⁷ 

Active treatment

Around 50% of acoustic neuromas can be expected to increase in size over a five-year period. Growing tumours increase by 2.9 mm per year on average. Around half of those with an acoustic neuroma can be expected to lose functional hearing over 3-4 years.⁶

If a tumour is growing rapidly or it is causing significant symptoms at diagnosis or during monitoring, active treatment may be recommended. There are two main types of active treatment: 

1. Stereotactic radiotherapy and stereotactic radiosurgery

Both of these approaches deliver doses of radiation to specific target areas. The aim is to deliver radiation to the tumour cells only, avoiding normal surrounding tissue. This approach means that side-effects and complications can be reduced.⁸

Stereotactic radiosurgery involves delivering a very high, one-off dose of radiation to a specific area. It is usually used for smaller acoustic neuromas. With stereotactic radiotherapy, the radiation is divided into separate, lower doses (also known as fractions) which are spaced out over time. Stereotactic radiotherapy is used for larger acoustic neuromas.⁶ 

2. Microsurgery

For very large acoustic neuromas causing severe symptoms, microsurgery is recommended.⁶

The specific surgical approach will depend on the nature of your tumour and the expertise and preferences of your surgeon.⁶ The three main approaches are the middle fossa, translabyrinthine, and retrosigmoid approaches.⁷ If you have been recommended to have surgery, speak to your healthcare provider about the specific approach that will be used. 

Complications and rehabilitation

Stereotactic radiotherapy, stereotactic radiosurgery and microsurgery all carry the risk of complications. As a result, a period of rehabilitation may be required following active treatment.⁷ The most common complications shared by the three treatment approaches we have explored are:

1. Damage to the facial nerve: The facial nerve controls many muscles of the face. It also plays a role in taste and innervates many glands of the head and neck. It passes close to the vestibulocochlear nerve and thus is at risk of damage during treatment for acoustic neuroma.¹⁰ This can result in facial weakness, changes in taste and changes in tear production on one side of the face. Most people recover from these complications over a period of weeks to months^{1, 7} 
2. Damage to the trigeminal nerve: An important role of the trigeminal nerve is to provide sensation to many parts of the face. It also runs closely to the vestibulocochlear nerve and so can be damaged during treatment for acoustic neuroma.¹⁰ This can result in facial numbness on one side of the face. For most people, feelings of numbness improve over time^{6, 7}
3. Hearing loss: Surgical approaches aim to protect the vestibulocochlear nerve and thus hearing function. However, sometimes the nerve can be permanently damaged during surgery, leading to complete loss of hearing in that ear. Radiation treatment can also lead to hearing loss and can be either partial or complete.¹¹ For those with smaller tumours (less than 3 mm in diameter), stereotactic radiosurgery has been shown to be superior to microsurgery in terms of its ability to preserve hearing function and reduce damage to nearby nerves.⁶ It should be noted that hearing loss is also a risk in observational management, with 70% of those followed-up for small tumour being affected after five years.¹

FAQs

Can acoustic neuroma be prevented

Most cases of acoustic neuroma are sporadic, meaning that they occur randomly in the population without a known cause. No proven modifiable risk factors (risk factors under individual control) have been identified.⁴

How common is acoustic neuroma

Around 1 in 500 people can expect to be diagnosed with acoustic neuroma in their lifetime. The number of people being diagnosed has increased over time. This is thought to be due to improvements in MRI imaging and access to healthcare.¹² 

When should I see a doctor

If you have noted that you have symptoms that could indicate an acoustic neuroma, speak to your healthcare provider who will recommend the most appropriate course of investigation based on your individual signs and symptoms. 

Summary

Acoustic neuromas, also known as vestibular schwannomas, are slow-growing, benign tumours that begin in Schwann cells surrounding the vestibulocochlear nerve. We all have two vestibulocochlear nerves, with one connecting each ear to the brain. Most people diagnosed with an acoustic neuroma will be affected on one side of the body. 

Acoustic neuromas typically present with hearing loss in one ear which may be accompanied by tinnitus. An MRI scan can confirm the diagnosis. Some people experience no symptoms. 

Smaller tumours may be followed-up with a watch-and-wait approach. Larger or rapidly-growing tumours may require active treatment in the form of radiation therapy or microsurgery. Complications include further hearing loss and damage to nerves that supply the face. Some people require a period of rehabilitation after treatment.