Vestibular Schwannoma
Vestibular schwannoma, formerly known as acoustic neuroma, is a benign intracranial tumour arising from cranial nerve VIII (vestibulocochlear nerve).
This updated UKMLA guide to vestibular schwannoma is based on EANO guideline, which covers causes, risk factors, symptoms, diagnosis, and management.
Relevant Anatomy
Vestibular schwannomas arise from the cranial nerve VIII (vestibulocochlear nerve)
- ~80% arise from the vestibular portion
- ~20% arise from the cochlear portion
Anatomical location:
- The tumour is located inside the internal acoustic canal
- As the tumour grows larger, it can protrude out of the internal acoustic canal, extending into the cerebellopontine angle (a fluid-filled space located at the junction of the cerebellum and the pons of the brainstem)
Vestibular schwannomas make up >80% of all tumours found in the cerebellopontine angle, making them the most common extra-axial posterior fossa tumours in adults
Epidemiology
Incidence increases with age (peak at 65-74 y/o)
Racial variations:
- Highest among Caucasian population
- Lowest among Black and Hispanic populations
Causes and Risk Factors
Vestibular schwannoma is primarily driven by genetic alterations (even in non-inherited cases):
- NF2 tumour suppressor gene inactivation (seen in ~77% cases)
- Neurofibromatosis type 2
- Associated with 4-6% of vestibular schwannoma cases
- Autosomal dominant monogenic condition that causes bilateral tumours (→ bilateral vestibular schwannoma)
Specific environmental or lifestyle risk factors for vestibular schwannoma are not well established
- Risk is higher in parous women (compared to nulliparous)
- Risk is lower in current smokers (but not ex-smokers)
Clinical Features
Typically presents as unilateral:
- Progressive sensorineural hearing loss (most common feature – seen in ~94% cases)
- Tinnitus
- Vestibular symptoms (e.g. vertigo, imbalance)
Larger tumours can compress nearby structures:
- CN V (trigeminal nerve) palsy → facial numbness, reduced corneal reflex
- CN VII (facial nerve) palsy → facial weakness, inability to close the eyelids completely (can cause exposure keratopathy)
- Possible life-threatening complications like brainstem compression and hydrocephalus (in extremely large tumours)
In most cases, clinical features of vestibular schwannoma present unilaterally.
Bilateral vestibular schwannoma is a hallmark clinical sign of neurofibromatosis type 2.
Investigation and Diagnosis
| Neuroimaging (diagnostic) | Gold standard and 1st line: MRI of the internal auditory meatus with contrast
CT is used for pre-operative planning and to assess bony surgical anatomy of the skull base |
| Hearing test | Objective audiometric assessment (pure tone audiogram and speech discrimination)
Hearing function influences treatment decisions (e.g. whether to attempt to preserve hearing or not) |
| Biopsy | Biopsy and histological diagnosis is NOT always required to make a diagnosis, especially if MRI findings are definitive
However, histological analysis is still performed post-surgical resection to assess morphology and immunohistochemistry |
| NF2 Screening | Consider genetic screening for neurofibromatosis type 2 if a patient <30 y/o presents with a unilateral vestibular schwannoma |
Management
Key management options are:
- Active observation (annual MRI follow-up for 5 years)
- Stereotactic radiosurgery
- Surgery
Decision algorithm (simplified, unlikely to be examined in detail):
| Scenario | Recommended management |
|---|---|
| Small, asymptomatic tumour |
|
| Small, symptomatic tumour |
|
| Medium-sized tumours |
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| Large tumour with brainstem compression |
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| Neurofibromatosis type 2 |
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Hearing aids should be offered as a standard supportive care measure to those with reduced hearing (see the Hearing Loss article for more information).