Section 1: Epidemiology and aetiology
A vestibular schwannoma, also commonly called an acoustic neuroma, is a benign primary intracranial tumour involving the myelin-forming Schwann cells of the vestibulocochlear nerve (cranial nerve VIII).
It usually begins growing in the internal auditory canal and extends into the cerebellopontine angle of the posterior cranial fossa with time.
Vestibular schwannomas account for 80% of all tumours arising within the cerebellopontine angle.
The incidence is nearly 2 per 100,000 per year. The incidence has risen, due to the increased use of MRI.1 Many vestibular schwannomas are asymptomatic and detected as an incidental finding on scans undertaken for other purposes.
The aetiology of vestibular schwannoma is unknown. Most patients have no apparent risk factors. Epidemiological studies have shown no causal relationship between wireless phone use and the incidence of vestibular schwannoma.
Other studies have associated a history of chickenpox and exposure to more than one cranial X-ray procedure as potential risk factors.
Neurofibromatosis type II
Neurofibromatosis type II occurs in patients who have a defective tumour suppressor gene located on chromosome 22q12.2. The defective protein produced by the gene is called merlin or schwannomin.
Bilateral acoustic tumours are a principal clinical feature of neurofibromatosis type II.
Other manifestations include peripheral neurofibromata, meningioma, glioma and juvenile posterior subcapsular lenticular opacities.
These patients typically present in late adolescence or early adulthood but occasionally may present later in the fifth to seventh decade with slowly growing tumours.
Section 2: Making the diagnosis
Most (95%) of these tumours are sporadic and occur in one ear. Symptoms do not correlate well with size.
The growth pattern is variable and incompletely understood. Some patients with relatively small tumours may have overt symptoms, while some with large tumours may be asymptomatic.
The most common presenting symptom is asymmetrical sensorineural hearing loss. Typically, the loss is gradual, but sudden onset has been found in 12-16% of affected patients.
Patients may also have unilateral tinnitus, vertigo and balance disturbance. Facial and trigeminal nerve function may be altered, but these are uncommon.
Large tumours may compress the brainstem and result in headaches and other symptoms such as vomiting and altered consciousness. Large tumours that compress the adjacent brainstem may affect other local cranial nerves.
The glossopharyngeal and vagus nerves are rarely involved, but their involvement may lead to altered gag or swallowing reflexes, respectively.
The diagnosis is made by history, hearing tests and MRI scan. Pure-tone audiometry may demonstrate unilateral asymmetric sensorineural hearing loss.
Patients attending specialist skull base clinics may go on to have a speech discrimination test. Patients with vestibular schwannoma normally have worse speech discrimination than can be expected from the pure-tone audiogram (figure 1).
The current standard radiological investigation is MRI of the internal auditory meatus (figure 2). MRI has been shown to be a cost-effective and accurate investigation for vestibular schwannoma compared to audiovestibular modalities.
Section 3: Managing the condidition
Management depends on tumour size, patient symptoms, preference, comorbidities and availability of treatment facilities and expertise. Options include observation, radiation or surgery.
Patients with a vestibular schwannoma should be managed in a skull base multidisciplinary team (MDT). Close observation with serial MRI can be an option for small tumours or patients with significant medical comorbidities.
In Liverpool, these patients go on to have initial six-month then yearly interval scan, which is reviewed by the MDT. Treatment may be necessary if there is growth or increasing symptoms.
An audit was undertaken by the Liverpool skull base team to assess the clinical, audiological and radiological outcomes of conservative management for 15mm or larger vestibular schwannomas.
It was noted that 66.7% of tumours remained stable. Only 24.4% grew, while the remaining 8.9% regressed. The median follow-up duration was three years. Clinical features worsened in six patients (13.3%) and 50% of these occurred in patients with growing vestibular schwannomas.
Mean hearing thresholds deteriorated from 73.4dB to 80.9dB. Hearing deterioration was significantly greater in growing tumours (8.9dB per year) compared to non-growing ones (1.1dB per year).
It was concluded that conservative management was an appropriate option for many patients and given that hearing thresholds were already poor, the decision for intervention was based on tumour growth.
This corroborates the medical literature, which reports that as many as 75% of tumours show no growth, supporting a 'wait and rescan' policy in many patients.2 There are no reliable predictors of tumour behaviour.
Microsurgical excision of the tumour is still regarded as the gold standard.3 The translabyrinthine approach may be appropriate in large tumours or where there is poor preoperative hearing. This surgical approach is associated with complete hearing loss.
Hearing preservation approaches (middle fossa and retrosigmoid) may be used in smaller tumours with good presenting hearing.
The middle cranial fossa approach seems safest for hearing preservation in patients with smaller tumours. The retrosigmoid approach seems to be the most versatile for facial nerve preservation for most tumour sizes, but is associated with a higher risk of postoperative pain and CSF fistula.
Stereotactic radiation therapy (figure 3) can be used for tumours of up to 3cm maximum dimension, particularly in the elderly and the infirm.
The aim of surgery is total tumour removal while minimising morbidity. Radiation is used to halt tumour growth. All treatment is aimed at limiting morbidity caused by tumour growth. Success rates range from 90-99% for either modality.
Section 4: Prognosis
Patients with residual tumour after surgery and those who have radiotherapy require long-term follow-up, including regular MRI scans.
Patients with a severe or profound unilateral hearing loss are significantly disabled in a number of situations, such as hearing sounds from the deaf side, hearing above background noise and localising sounds.
It is recommended that hearing difficulties (including tinnitus) after tumour removal should be thoroughly examined by an audiologist, so rehabilitation can be discussed.4 Options include a hearing aid in the ear that was not operated on, a contralateral routing of signals (CROS) hearing aid or bone- anchored hearing aid.
Patients may experience disequilibrium following treatment. After surgery, patients may also require intensive vestibular rehabilitation by an experienced physiotherapist, if they had good preoperative peripheral vestibular function.
Patients should be encouraged to join support groups, an important part of the support network where patients can make personal contact with others who have gone through a similar experience.
Facial palsy is an uncommon yet devastating consequence of vestibular schwannoma treatment. The paralysis can be either temporary or permanent. These patients would benefit from physiotherapy, eutrophic electrical stimulation and even surgery to rehabilitate the paralysed face.5 Further information can be obtained from Facial Palsy UK (www.facialpalsy.org.uk/).
Ssection 5: Case study
A 42-year-old woman was referred to her local ENT department with unilateral hearing loss.
The left-sided hearing loss had been present for years, but was noted to be progressively worse over the past six months.
There was associated high-pitched, non-pulsatile tinnitus, but facial nerve function was normal. There was no previous history of excessive noise exposure, skull base fracture or family history of early-onset hearing loss.
Clinical examination was unremarkable but pure-tone audiogram showed moderate sensorineural hearing loss.
An MRI scan showed a 1.5cm gadolinium enhancing lesion in the cerebropontine angle with brain stem compression (figure 4). She was referred to the regional skull base department for further management.
The case was discussed at the skull base MDT and given the position and size of the tumour, it was decided to offer the patient stereotactic radiotherapy. She agreed to this and received one treatment course at the regional oncology centre.
At the two-year follow-up, sequential MRI scans showed reduction in the size of the tumour. However, the patient complained that her hearing had deteriorated after treatment.
She tried a hearing aid but felt this was not beneficial. In addition, the tinnitus had worsened, but she had learnt to cope with it after rehabilitation with the audiologist. The patient remained on low-dose oral gabapentin for mild neuropathic facial pain. The facial nerve was unaffected. She remains on long-term follow-up.
Section 6: Evidence base
Theodosopoulos PV, Pensak ML. Contemporary management of acoustic neuromas. Laryngoscope 2011; 121(6): 1133-7.
Nikolopoulos TP, Fortnum H, O'Donoghue G et al. Acoustic neuroma growth: a systematic review of the evidence. Otol Neurotol 2010; 31(3): 478-85.
British Acoustic Neuroma Association. The British Acoustic Neuroma Association website is supported by people affected by vestibular schwannoma, using information and data gathered from traceable sources.
The Acoustic Neuroma and Meningioma Network (AMNET) AMNET is the support group for acoustic neuroma or meningioma patients at Addenbrooke's Hospital in Cambridge.
The British Skull Base Society http://www.skullbase.co.uk/ The British Skull Base Society is a professional body that represents the major UK and Irish centres involved in the care of patients with skull base pathologies. The membership includes clinicians from a number of disciplines including otolaryngology, neurosurgery and oncology. This website has good resources on skull base units and surgery for vestibular schwannomas.
- Mr Samuel Leong is clinical lead for facial palsy service and Mr. Ahmed Youssef is consultant ENT and skull base surgeon at Liverpool Skull Base Unit, Aintree University Hospital NHS Foundation Trust, Liverpool
This is an updated version of an article that was first published in November 2012.
- Stangerup SE, Tos M, Thomsen J, Caye-Thomasen P. True incidence of vestibular schwannoma? Neurosurgery. 2010; 67(5):1335-40.
- Nikolopoulos TP, Fortnum H, O'Donoghue G et al. Acoustic neuroma growth: a systematic review of the evidence. Otol Neurotol 2010; 31(3): 478-85.
- Theodosopoulos PV, Pensak ML. Contemporary management of acoustic neuromas. Laryngoscope 2011; 121(6): 1133-7.
- Snapp HA, Schubert MC. Habilitation of auditory and vestibular dysfunction. Otolaryngol Clin North Am 2012; 45(2): 487-511.
- Rudman KL, Rhee JS. Habilitation of facial nerve dysfunction after resection of a vestibular schwannoma. Otolaryngol Clin North Am 2012; 45(2): 513-30.
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