Synonyms: acoustic neurilemoma, acoustic neurinoma, vestibular schwannoma
Acoustic neuromas (ANs) 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 fewer than 5% 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 6 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.
AN represents 6-10% of primary intracranial tumours but is the most common form of CPA tumour. Sporadic tumours are unilateral and account for 95% of cases, whilst those associated with neurofibromatosis are bilateral and account for the other 5%.
There are approximately 13 newly diagnosed cases per million people in the general population per annum. Danish studies showed a rise in incidence between the 1970s to 1990s from 7.8 to 12.4 per million, but this is thought to reflect better diagnosis rather than a true rise in incidence.
Estimates of prevalence are based on autopsy (8,000 cases per million) and radiological series (700 per million, based on MRI) suggest that the vast majority of AN cases go undiagnosed.
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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 much later in life but the medical use of low-dose ionising radiation, such as used in imaging, has not been established as a risk).
Hayfever has been suggested as a risk factor although not confirmed. Occupational noise exposure has not been shown to be a risk factor although some other epidemiological studies have suggested a link. Similarly, risk due to radiofrequency exposure from mobile phone use remains contentious: the large Interphone case-control study suggested no increased risk in the first decade of use but the risk of longer-term use is unknown.
Consider the diagnosis of AN in patients with:
- Unilateral or asymmetrical hearing loss or tinnitus, whether progressive or acute in onset.
- Impaired facial sensation.
- Balance problems without other explanation.
- 90% have unilateral progressive HL and 70% tinnitus.
- About 5% of patients will experience sudden and complete unilateral HL.
- Hearing may also fluctuate.
- 3% will have normal hearing at presentation.
- Most patients have quite subtle balance disturbance at presentation.
As the tumour spreads, HL and disequilibrium worsen 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 brain stem compression can produce hydrocephalus with visual loss and persistent headache and even decreased level of consciousness.
Of patients referred to ENT with asymmetric HL, 3-7.5% will have an AN.
With the increasing use of brain imaging, AN is now being diagnosed incidentally and earlier whilst undergoing investigation for unrelated problems.
Bilateral acoustic neuroma (AN) 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 AN also have NF2. AN due to NF2 tends to present earlier, typically around 30 years old. Genetic screening for NF2 in patients presenting with sporadic, unilateral AN is usually only productive in cases of very early onset (younger than 20 years). NF2 patients are predisposed not only to developing AN but also schwannomas of other cranial nerves.
Acoustic neuromas account for 85% of cerebellopontine angle (CPA) tumours. Other CPA tumours include:
- Meningiomas (3-13%)
- Epidermoids (2-6%)
- Lower cranial nerve schwannomas (1-2%)
- Arachnoid cysts (1%)
All patients with unilateral or asymmetric hearing loss (HL) should be referred for audiological assessment to quantify and clarify the loss as sensorineural.
MRI has largely superseded CT scanning as the investigation of choice for suspected acoustic neuroma (AN).
See reference (below) for examples of audiograms and MRI scans from patients with AN.
There are three basic treatment options for acoustic neuroma (AN): watch and wait, surgical removal and stereotactic radiosurgery. There are no studies systematically comparing the different treatment modalities and even evidence for the different treatments is often low-grade. In this environment of uncertainty and with each option associated with particular risks and benefits, it is critical that the patient be fully counselled and consented to their course of treatment. Consideration needs to be given to future quality of life and symptom relief as well as tumour control, facial nerve function and hearing preservation.
The natural history of ANs is not fully understood: in one study looking at small neuromas, with a mean follow-up of 40 months, 66% showed no growth, 24% showed slow growth, 4% showed rapid growth and 3% regressed. Therefore, in patients with small neuromas and good preserved hearing, the wisest course of action is often 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, the majority of patients receiving treatment for AN 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 about 95% of cases. 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. A variant, fractionated (smaller, multiple dose) stereotactic radiotherapy, is advocated by some centres. Neither of these treatments is conceived to remove neuromas but rather to control (either slow or stop) their growth.
One small prospective cohort study suggests that for unilateral, small (<3 cm) tumours, early outcomes (facial movement, hearing, general health status) for stereotactic radiosurgery were better than for surgical resection with equivalent tumour control. However, longer-term follow-up is required to indicate that tumour progression is not worse in the stereotactic radiosurgery group. Other potential longer-term risks associated with stereotactic radiosurgery and stereotactic radiotherapy include:
Further reading & references
- Medline Plus - acoustic neuroma
- Kutz JW et al; Skull Base, Acoustic Neuroma (Vestibular Schwannoma), eMedicine, Sep 2009
- BAO-HNS; Clinical effectiveness guidelines for acoustic neuroma. British Association of Otorhinolaryngologists, Head and Neck Surgeons, Spring 2002; [As PDF]
- Schneider AB, Ron E, Lubin J, et al; Acoustic neuromas following childhood radiation treatment for benign conditions of the head and neck. Neuro Oncol. 2007 Dec 13;.
- Blettner M, Schlehofer B, Samkange-Zeeb F, et al; Medical exposure to ionising radiation and the risk of brain tumours: Interphone study group, Germany. Eur J Cancer. 2007 Sep;43(13):1990-8. Epub 2007 Aug 8.
- Schlehofer B, Schlaefer K, Blettner M, et al; Environmental risk factors for sporadic acoustic neuroma (Interphone Study Group, Germany). Eur J Cancer. 2007 Jul;43(11):1741-7. Epub 2007 Jun 27.
- Edwards CG, Schwartzbaum JA, Nise G, et al; Occupational noise exposure and risk of acoustic neuroma. Am J Epidemiol. 2007 Dec 1;166(11):1252-8. Epub 2007 Sep 5.
- Schoemaker MJ, Swerdlow AJ, Ahlbom A, et al; Mobile phone use and risk of acoustic neuroma: results of the Interphone case-control study in five North European countries. Br J Cancer. 2005 Oct 3;93(7):842-8.
- Evans DG, Moran A, King A, et al; 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 Jan;26(1):93-7.
- Evans DG, Ramsden RT, Gokhale C, et al; Should NF2 mutation screening be undertaken in patients with an apparently isolated vestibular schwannoma? Clin Genet. 2007 Apr;71(4):354-8.
- Fisher LM, Doherty JK, Lev MH, et al; Distribution of nonvestibular cranial nerve schwannomas in neurofibromatosis 2. Otol Neurotol. 2007 Dec;28(8):1083-90.
- Shohet JA; Skull base, tumors, other CPA tumors, eMedicine, Feb 2009
- Hain TC, Acoustic Neuroma. Last modified Jan 2008; MRI images and audiograms from patients with AN
- Myrseth E, Pedersen PH, Moller P, et al; Treatment of vestibular schwannomas. Why, when and how? Acta Neurochir (Wien). 2007;149(7):647-60; discussion 660. Epub 2007 Jun 11.
- Aghi M, Barker FG 2nd; Benign adult brain tumors: an evidence-based medicine review. Prog Neurol Surg. 2006;19:80-96.
- Backous DD, Pham HT; Guiding patients through the choices for treating vestibular schwannomas: balancing options and ensuring informed consent. Otolaryngol Clin North Am. 2007 Jun;40(3):521-40, viii-ix.
- Al Sanosi A, Fagan PA, Biggs ND; Conservative management of acoustic neuroma. Skull Base. 2006 May;16(2):95-100.
- Douglas SA, Yeung P, Daudia A, et al; Spatial hearing disability after acoustic neuroma removal. Laryngoscope. 2007 Sep;117(9):1648-51.
- Tufarelli D, Meli A, Labini FS, et al; Balance impairment after acoustic neuroma surgery. Otol Neurotol. 2007 Sep;28(6):814-21.
- Rimaaja T, Haanpaa M, Blomstedt G, et al; Headaches after acoustic neuroma surgery. Cephalalgia. 2007 Oct;27(10):1128-35. Epub 2007 Aug 17.
- Pollock BE, Driscoll CL, Foote RL, et al; Patient outcomes after vestibular schwannoma management: a prospective comparison of microsurgical resection and stereotactic radiosurgery. Neurosurgery. 2006 Jul;59(1):77-85; discussion 77-85.
- Djalilian HR, Benson AG, Ziai K, et al; Radiation necrosis of the brain after radiosurgery for vestibular schwannoma. Am J Otolaryngol. 2007 Sep-Oct;28(5):338-41.
- Balasubramaniam A, Shannon P, Hodaie M, et al; Glioblastoma multiforme after stereotactic radiotherapy for acoustic neuroma: case report and review of the literature. Neuro Oncol. 2007 Oct;9(4):447-53. Epub 2007 Aug 17.
|Original Author: Dr Chloe Borton||Current Version: Dr Richard Draper||Peer Reviewer: Dr Helen Huins|
|Last Checked: 28/09/2011||Document ID: 1752 Version: 22||© EMIS|
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