Understanding Acoustic Neuroma
An acoustic neuroma — more accurately called a vestibular schwannoma — is a benign (non-cancerous) tumour that develops on the vestibulocochlear nerve, the eighth cranial nerve responsible for transmitting hearing and balance signals from the inner ear to the brain. The tumour grows from Schwann cells, which form the insulating myelin sheath around the nerve fibres. Although the name "acoustic neuroma" is still widely used by patients and many clinicians, the term vestibular schwannoma is technically more precise, since the tumour most commonly originates on the vestibular (balance) portion of the nerve rather than the acoustic (hearing) portion.
Acoustic neuromas are relatively rare. Approximately 1,200 new cases are diagnosed in the UK each year, according to the British Acoustic Neuroma Association (BANA), accounting for roughly 6-8% of all primary intracranial tumours. They are most commonly diagnosed in adults aged 40 to 60, though they can occur at any age. The condition affects men and women approximately equally. Despite being classified as benign — meaning they do not spread to other parts of the body — acoustic neuromas can cause significant symptoms as they grow, due to their location in the narrow bony channel (the internal auditory canal) between the inner ear and the brain.
The good news is that acoustic neuromas are almost always slow-growing, and the overall prognosis is generally very good. With modern diagnostic techniques and treatment options, most people with an acoustic neuroma can expect an excellent long-term outcome, though the impact on hearing and the treatment journey can be challenging.
How Acoustic Neuromas Grow
Acoustic neuromas typically grow very slowly, at an average rate of 1-2 millimetres per year, though growth rates vary considerably between individuals. Some tumours remain stable for years or even decades without any measurable change, while others grow more rapidly. In rare cases, a tumour may spontaneously shrink slightly.
The tumour begins within the internal auditory canal — a narrow, bony passage approximately 1cm long that runs from the inner ear to the brainstem. As the tumour enlarges, it can:
- Compress the hearing nerve fibres — causing progressive sensorineural hearing loss on the affected side, typically developing gradually over months or years
- Affect the balance nerve — leading to unsteadiness, though the brain often compensates gradually, meaning that many people with acoustic neuromas do not experience severe vertigo
- Extend into the cerebellopontine angle (CPA) — the space between the brainstem and the cerebellum. At this stage, the tumour may begin to press on adjacent cranial nerves
- Compress the facial nerve (cranial nerve VII) — which runs in close proximity to the vestibulocochlear nerve. This can cause facial numbness (via the trigeminal nerve) or, in rare cases with very large tumours, facial weakness
- Press on the brainstem — in rare cases where the tumour grows very large, brainstem compression can occur, which is a more serious situation requiring intervention
The slow growth rate of most acoustic neuromas means that symptoms typically develop gradually, giving the brain time to compensate for some of the vestibular (balance) changes. This is why many people with acoustic neuromas report unsteadiness rather than the sudden, spinning vertigo seen in conditions like labyrinthitis or Meniere`s disease.
Symptoms of Acoustic Neuroma
The symptoms of an acoustic neuroma depend on its size, location, and growth rate. The most common symptoms include:
Asymmetric Hearing Loss
The hallmark symptom of acoustic neuroma is unilateral or asymmetric sensorineural hearing loss — hearing loss that is noticeably worse in one ear compared to the other. This is the presenting symptom in approximately 90% of cases. The hearing loss typically develops gradually over months or years and often affects high frequencies first, making it difficult to understand speech clearly, particularly in noisy environments. Some people first notice the problem when using the phone on the affected side. In around 10-20% of cases, the hearing loss presents suddenly — as sudden sensorineural hearing loss (SSHL) — which is why MRI scanning is recommended for all patients with SSHL.
Tinnitus
Tinnitus in the affected ear is present in approximately 70% of cases. It is often described as a high-pitched ringing, hissing, or buzzing. Unilateral tinnitus — tinnitus in only one ear — is an important symptom that should always be investigated, as it can be an early indicator of acoustic neuroma.
Balance Problems
Unsteadiness, a sense of imbalance, and difficulty walking in the dark or on uneven surfaces are common. True spinning vertigo is less typical because the slow growth of the tumour allows the brain to compensate gradually. However, some patients do experience episodes of vertigo, particularly early in the condition or if the tumour grows more rapidly.
Other Symptoms (Usually with Larger Tumours)
- Facial numbness or tingling — caused by pressure on the trigeminal nerve (cranial nerve V), occurring in around 25% of patients with larger tumours
- A feeling of fullness or pressure in the affected ear
- Headache — uncommon and usually associated with larger tumours
- Facial weakness — rare, and usually only seen with very large tumours or as a surgical risk
Neurofibromatosis Type 2 (NF2)
While the vast majority of acoustic neuromas are sporadic (arising from a random genetic mutation in a single Schwann cell, with no known cause or inherited component), a small proportion are associated with neurofibromatosis type 2 (NF2), a rare genetic condition. NF2 causes bilateral acoustic neuromas — tumours on both hearing nerves — which is the defining feature of the condition. NF2 affects approximately 1 in 33,000 people in the UK.
NF2-related acoustic neuromas typically present at a younger age (teens or twenties) and may grow more aggressively than sporadic tumours. The management of NF2-related acoustic neuromas is more complex, as preserving hearing in at least one ear is a critical priority. Patients with NF2 are managed by specialist multidisciplinary teams at designated NF2 centres in the UK, with lifelong follow-up. If you have a family history of NF2 or bilateral hearing difficulties, speak to your GP about referral for genetic counselling and specialist assessment.
Diagnosis of Acoustic Neuroma
Early diagnosis is important for ensuring the widest range of management options and the best chance of preserving hearing. The diagnostic pathway typically involves several steps:
Audiogram
A standard hearing test (audiogram) will usually show unilateral or asymmetric sensorineural hearing loss, often with a characteristic pattern of poor speech discrimination scores — meaning the person struggles to understand words clearly even when they are loud enough to hear. This poor speech discrimination, out of proportion to the degree of hearing loss on the audiogram, is a red flag that raises suspicion of a retrocochlear (behind the cochlea) cause such as acoustic neuroma.
MRI Scan — The Gold Standard
The gold standard investigation for diagnosing acoustic neuroma is an MRI scan with gadolinium contrast. Gadolinium is a contrast agent injected into a vein during the scan that makes the tumour light up clearly on the images, allowing even very small tumours (a few millimetres in size) to be detected. According to NICE guidelines, any patient presenting with asymmetric sensorineural hearing loss, unilateral tinnitus, or unexplained unilateral balance disturbance should be considered for MRI to rule out acoustic neuroma.
Auditory Brainstem Response (ABR)
An auditory brainstem response (ABR) test measures the electrical activity in the hearing nerve and brainstem in response to sounds. While MRI is more sensitive, ABR can be a useful screening tool and is sometimes used when MRI is not immediately available or is contraindicated (for example, in patients with certain metallic implants).
Other Investigations
Tympanometry and otoacoustic emissions (OAE) testing may be performed as part of the initial audiological assessment to help distinguish between cochlear and retrocochlear causes of hearing loss. A balance assessment may also be carried out to evaluate vestibular function.
The Three Management Options
Management of acoustic neuroma depends on several factors: the size and growth rate of the tumour, the patient`s symptoms, age, general health, and — crucially — the hearing status in both ears. In the UK, treatment decisions are made by a specialist multidisciplinary team (MDT) that typically includes a neurosurgeon, an ENT/skull base surgeon, an audiologist, and a specialist nurse. There are three main approaches:
1. Watch and Wait (Conservative Management)
For many patients — particularly those with small, stable tumours — active monitoring without immediate intervention is the recommended approach. This involves:
- Regular MRI scans, typically every 6 to 12 months initially, then annually or less frequently if the tumour remains stable
- Serial audiograms to monitor any changes in hearing
- Clinical review of symptoms at each visit
Watch and wait is particularly appropriate for older patients, those with small tumours (under 1-1.5cm), and those whose tumour shows no growth on serial imaging. Research shows that a significant proportion of acoustic neuromas — particularly in older adults — do not grow at all over many years of follow-up. The advantage of this approach is that it avoids the risks associated with surgery or radiation while the tumour poses no immediate threat. If growth is detected on follow-up scanning, active treatment can be initiated at that point.
2. Stereotactic Radiosurgery (Gamma Knife)
Stereotactic radiosurgery — most commonly delivered using the Gamma Knife system, though other platforms such as CyberKnife and linear accelerator-based systems are also used — is a non-invasive treatment that delivers a precisely focused, high dose of radiation to the tumour in a single session (or occasionally a small number of sessions, known as fractionated stereotactic radiotherapy).
- Best suited for: small to medium tumours, typically up to 2.5-3cm in diameter
- Tumour control rate: approximately 93-97%, meaning the tumour stops growing or shrinks in the vast majority of cases
- Hearing preservation: serviceable hearing is preserved in approximately 50-70% of patients at five years, though this declines over longer follow-up periods
- Procedure: the treatment is delivered as a day case. A stereotactic frame may be fixed to the head (under local anaesthesia) to ensure millimetre-accurate targeting. The radiation itself is painless and takes 30-90 minutes. Most patients go home the same day and return to normal activities within a few days
- Risks: the main risks include gradual hearing loss over time (despite initial preservation), facial numbness (approximately 3-5%), and very rarely facial weakness. The risk of serious complications is significantly lower than with microsurgery
Gamma Knife radiosurgery is available at several specialist centres across the UK, including in London, Sheffield, and other designated treatment sites.
3. Microsurgery
Microsurgery involves the physical removal of the tumour through an operation. It is typically recommended for:
- Larger tumours (generally over 2.5-3cm) where radiosurgery is less effective
- Tumours causing significant brainstem compression
- Tumours that have continued to grow despite radiosurgery
- Younger patients with larger tumours where long-term tumour control is the priority
The surgery is performed at specialist neurosurgical centres in the UK and typically involves a team of neurosurgeons and ENT/skull base surgeons. Several surgical approaches are used, including the translabyrinthine, retrosigmoid, and middle fossa approaches. The choice depends on the tumour size, location, and whether hearing preservation is a realistic goal.
- Total removal is achieved in approximately 95% of cases
- Facial nerve preservation is a key surgical goal. In experienced hands, the facial nerve is anatomically preserved in over 95% of operations, though temporary facial weakness is common and permanent weakness occurs in a small percentage of cases
- Hearing preservation is possible with certain surgical approaches (retrosigmoid and middle fossa) for smaller tumours, but in many cases — particularly with the translabyrinthine approach or larger tumours — hearing on the operated side is lost
- Recovery: hospital stays typically range from 3-7 days, with full recovery taking several weeks to months. Vestibular rehabilitation may be needed to help with balance during the recovery period
Hearing Preservation and Rehabilitation
For many people with acoustic neuroma, the impact on hearing is one of the most significant concerns. Whether hearing is lost due to the tumour itself or as a consequence of treatment, there are effective rehabilitation options:
- Conventional hearing aids — if there is residual hearing in the affected ear, a hearing aid can provide useful amplification. This is most appropriate when hearing loss is mild to moderate
- CROS hearing aids — for single-sided deafness, a CROS (Contralateral Routing of Signal) system places a microphone on the deaf side and wirelessly transmits sound to the hearing ear, helping to overcome the "head shadow" effect. Available through NHS and private providers including Boots Hearingcare and Specsavers Audiology
- Bone-anchored hearing aids (BAHA/Osia) — a surgically implanted device that transmits sound through the skull bone to the functioning cochlea on the other side. BAHAs are available on the NHS for qualifying patients and are particularly effective for single-sided deafness
- Cochlear implants — in selected cases where the hearing nerve is intact, cochlear implantation on the affected side may be possible, though this is not suitable for all patients
Your audiologist and ENT team will discuss the most appropriate options based on your individual hearing profile and treatment history. Our guide on choosing hearing aids provides further information on the different technologies available.
Support, Follow-up, and When to Seek Help
Receiving a diagnosis of acoustic neuroma can be anxiety-provoking, even though the tumour is benign. It is important to know that the overall prognosis is generally very good. With modern treatment, tumour-related mortality is extremely rare, and the vast majority of patients lead full, active lives. However, the journey — from diagnosis through treatment decisions and long-term follow-up — can be emotionally and practically challenging.
Key sources of support include:
- British Acoustic Neuroma Association (BANA) — provides information, peer support, and regional support groups for patients and families
- RNID — offers advice and support on living with hearing loss and tinnitus, including assistive technology and communication tips
- Your specialist MDT — long-term follow-up with serial MRI scanning and audiological monitoring is essential, regardless of which management pathway is chosen. Follow-up continues for many years (often lifelong for younger patients) to ensure the tumour remains controlled
You should see your GP promptly if you experience any of the following symptoms, which should always be investigated:
- Gradual hearing loss or tinnitus that is worse in one ear than the other
- Sudden hearing loss in one ear
- Unexplained unsteadiness or balance problems
- Facial numbness or tingling on one side
Your GP can arrange a hearing test and, if acoustic neuroma is suspected, an urgent MRI referral. Early diagnosis ensures the widest range of treatment options and the best chance of preserving your hearing. Find an audiologist near you for an initial hearing assessment.