Synonyms: acoustic neurilemoma, acoustic neurinoma, vestibular schwannoma
Acoustic neuromas are tumours of the vestibulocochlear nerve (eighth cranial nerve), arising from the Schwann cells of the nerve sheath. Most arise from the vestibular portion and only a few arise from the cochlear (auditory) division. They are typically benign and slow-growing, but can cause symptoms through mass effect and pressure on local structures, eventually becoming life-threatening. Patterns of growth can vary and a small number may grow rapidly (doubling size in six months). Considering the possibility can enable earlier diagnosis, increase management options and may decrease morbidity.
Within the cerebellopontine angle (CPA), tumours can grow as big as 4 cm in diameter and slow growth allows stretching and accommodation of growth without affecting function. However, tumours within the internal auditory canal produce symptoms much earlier with hearing loss (the most common presenting symptom) or vestibular disturbance.
Acoustic neuroma represents 8% of all intracranial tumours and 80% of those arising at the CPA.
Confirmed risk factors include:
- High-dose ionising radiation (children who received radiation for benign conditions of their head and neck - for example, to decrease the size of their tonsils and adenoids - were at increased risk of developing an acoustic neuroma much later in life).However, the medical use of low-dose ionising radiation, such as used in imaging, has not been established as a risk.
Consider the diagnosis of acoustic neuroma in patients with:
- Unilateral or asymmetrical hearing loss or tinnitus, whether progressive or acute in onset.
- Impaired facial sensation.
- Balance problems without other explanation.
Classic presentation of acoustic neuroma confined to the internal auditory canal, involves unilateral progressive hearing loss, vestibular dysfunction and tinnitus.
- A small minority of patients will experience sudden and complete unilateral hearing loss.
- Hearing may also fluctuate.
- A few patients will have normal hearing at presentation.
- Most patients have quite subtle balance disturbance at presentation.
- The severity of tinnitus has been shown to correlate with tumour size.
As the tumour spreads, there is an increase in hearing loss and disequilibrium, and symptoms due to compression of other structures may occur:
- Facial pain or numbness due to involvement of the trigeminal nerve.
- Facial weakness is uncommon despite the tumour pressing on the facial nerve.
- Ataxia due to cerebellar compression.
- Severe brainstem compression can produce hydrocephalus with visual loss and persistent headache and even decreased level of consciousness.
Acoustic neuroma may be diagnosed incidentally and earlier as a result of investigations for unrelated problems.
Bilateral acoustic neuroma occurs in neurofibromatosis-type 2 (NF2). NF2 is an autosomal dominant disorder (ie has a 50% risk of transmission from a parent) but also shows high levels of mosaicism. 7% of patients with acoustic neuroma also have NF2.Acoustic neuroma due to NF2 tends to present earlier, typically around 30 years old. Genetic screening for NF2 in patients presenting with sporadic, unilateral acoustic neuroma is usually only productive in cases of very early onset (younger than 20 years). NF2 patients are predisposed not only to developing acoustic neuroma but also schwannomas of other cranial nerves.
Increasing symptoms associated with acoustic neuroma increases the likelihood of clinically significant anxiety and depression.
Other CPA tumours include meningiomas, epidermoids, lower cranial nerve schwannomas and arachnoid cysts.
All patients with unilateral or asymmetric hearing loss should be referred for audiological assessment to quantify and clarify the loss as sensorineural. See reference (below) for examples of audiograms and MRI scans from patients with acoustic neuroma.
MRI has largely superseded CT scanning as the investigation of choice for suspected acoustic neuroma.
The growth pattern of acoustic neuromas is variable. As many as 75% of tumours have been reported to show no growth. However, there are no reliable predictors of tumour behaviour.There are three treatment options: microsurgery (the technique of choice), stereotactic radiosurgery and observation.When assessing the most appropriate management for each individual patient, consideration needs to be given to future quality of life and symptom relief as well as tumour control, facial nerve function and hearing preservation.
For patients with small neuromas and good preserved hearing, the most appropriate course of action may be to watch and wait with serial scans (usually annually) to monitor growth. Where growth is detected, more active treatment is usually advocated since risk of complications with surgery and ability to preserve hearing are related, in part, to tumour size. There is some evidence that quality of life is reduced in untreated patients. There is no agreed size of tumour triggering active treatment across centres.
In the UK, most patients receiving active treatment undergo microsurgery. The surgical approach taken depends on the location of the tumour, its size and the relative importance of hearing preservation. Complete removal is possible in most cases. The risks of surgery include:
- Mortality (risk about 1%)
- CSF leak and meningitis
- Cerebellar injury
- Facial paralysis (either partial or complete)
- Hearing loss
- Balance impairment
- Persistent headache
Stereotactic radiosurgery targets a tumour with a single large dose of radiation using convergent beams of high-energy X-rays, gamma rays ('gamma knife radiosurgery') or charged particles and is an alternative, emergent treatment. The aim of treatment is to control (either slow or stop) the growth of the tumour. Stereotactic radiation may be associated with significantly better long-term hearing preservation outcome rates than microsurgery.
Salvage surgery for neuromas post-radiotherapy is technically more difficult than primary surgery. Other potential longer-term risks associated with stereotactic radiosurgery and stereotactic radiotherapy include:
Further reading and references
; International RadioSurgery Association (IRSA), March 2006
; Radiosurgery, a treatment for acoustic neuroma. Ten years' experience. Acta Otorrinolaringol Esp. 2014 May 17. pii: S0001-6519(14)00087-9. doi: 10.1016/j.otorri.2014.03.003.
; Neurofibromatosis type 2 (NF2): diagnosis and management. Handb Clin Neurol. 2013115:957-67. doi: 10.1016/B978-0-444-52902-2.00054-0.
; Acoustic neuromas following childhood radiation treatment for benign conditions of the head and neck. Neuro Oncol. 2007 Dec 13.
; Medical exposure to ionising radiation and the risk of brain tumours: Interphone study group, Germany. Eur J Cancer. 2007 Sep43(13):1990-8. Epub 2007 Aug 8.
; Acoustic neuroma observation associated with an increase in symptomatic tinnitus: results of the 2007-2008 Acoustic Neuroma Association survey. J Neurosurg. 2013 Oct119(4):864-8. doi: 10.3171/2013.5.JNS122301. Epub 2013 Jun 21.
; Incidence of vestibular schwannoma and neurofibromatosis 2 in the North West of England over a 10-year period: higher incidence than previously thought. Otol Neurotol. 2005 Jan26(1):93-7.
; Should NF2 mutation screening be undertaken in patients with an apparently isolated vestibular schwannoma? Clin Genet. 2007 Apr71(4):354-8.
; Distribution of nonvestibular cranial nerve schwannomas in neurofibromatosis 2. Otol Neurotol. 2007 Dec28(8):1083-90.
; Factors associated with anxiety and depression in the management of acoustic neuroma patients. J Clin Neurosci. 2012 Feb19(2):246-51. doi: 10.1016/j.jocn.2011.06.006. Epub 2011 Nov 2.
; Acoustic Neuroma, Dizziness-and-balance.com
; The role of magnetic resonance imaging in the identification of suspected acoustic neuroma: a systematic review of clinical and cost effectiveness and natural history. Health Technol Assess. 2009 Mar13(18):iii-iv, ix-xi, 1-154. doi: 10.3310/hta13180.
; Acoustic neuroma growth: a systematic review of the evidence. Otol Neurotol. 2010 Apr31(3):478-85. doi: 10.1097/MAO.0b013e3181d279a3.
; Treatment of vestibular schwannomas. Why, when and how? Acta Neurochir (Wien). 2007149(7):647-60
; Surgery of the ear and the lateral skull base: pitfalls and complications. GMS Curr Top Otorhinolaryngol Head Neck Surg. 2013 Dec 1312:Doc05. eCollection 2013.
; Spatial hearing disability after acoustic neuroma removal. Laryngoscope. 2007 Sep117(9):1648-51.
; Balance impairment after acoustic neuroma surgery. Otol Neurotol. 2007 Sep28(6):814-21.
; Headaches after acoustic neuroma surgery. Cephalalgia. 2007 Oct27(10):1128-35. Epub 2007 Aug 17.
; Radiation necrosis of the brain after radiosurgery for vestibular schwannoma. Am J Otolaryngol. 2007 Sep-Oct28(5):338-41.
; Glioblastoma multiforme after stereotactic radiotherapy for acoustic neuroma: case report and review of the literature. Neuro Oncol. 2007 Oct9(4):447-53. Epub 2007 Aug 17.