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|Vestibulocochlear Nerve
🧠 Acoustic neuroma (vestibular schwannoma) is a benign tumour of Schwann cells affecting cranial nerve VIII.
📈 Accounts for ~8% of primary intracranial tumours and is the most common mass in the cerebellopontine angle.
💡 Always suspect in patients with unilateral sensorineural hearing loss (USNHL) until proven otherwise.
📖 About
- Benign schwannoma of the vestibulocochlear nerve (CN VIII).
- ~8% of intracranial tumours; ~80% of CPA lesions.
- Associated with NF2 → bilateral tumours (merlin gene mutation).
- Slow-growing but cause morbidity through local compression.
🧬 Aetiology
- Schwann cell proliferation (myelinating cells of peripheral nerves).
- Sporadic (majority) or inherited (NF2, autosomal dominant).
- Rare link with prior childhood cranial irradiation.
⚠️ Risk Factors
- Age 40–60 years.
- NF2 or strong family history.
- High-dose cranial irradiation in childhood.
📉 Effects of Tumour Expansion
- CN VIII → unilateral SNHL, tinnitus, imbalance 🎧.
- CN V → facial numbness, loss of corneal reflex.
- CN VII → LMN facial palsy, taste disturbance.
- Cerebellum → ipsilateral ataxia, unsteady gait 🚶.
- Brainstem → compression, hydrocephalus, raised ICP.
- Raised ICP → headache, nausea, papilloedema.
🩺 Clinical Features
- Unilateral SNHL (~95%).
- Tinnitus (buzzing/ringing).
- Vertigo, imbalance, disequilibrium.
- Facial numbness, paraesthesia.
- Facial weakness (late feature).
- Headache, vomiting (raised ICP).
- Ataxia, poor coordination.
- Think NF2 if bilateral lesions.
💡 Exam Pearl: Any patient with USNHL ± unilateral tinnitus → arrange MRI internal auditory meatus (IAM) to exclude vestibular schwannoma.
🔎 Investigations
- Pure tone audiometry → confirms SNHL.
- MRI IAM with gadolinium (gold standard) → “ice-cream cone” lesion 🍦.
- CT if MRI contraindicated → bone erosion, large lesions.
- BAEP (brainstem auditory evoked potentials) → pathway integrity.
- CSF protein ↑ (nonspecific).
- Genetic testing if NF2 suspected.
🧾 Differential Diagnosis
- Cerebellopontine angle meningioma.
- Epidermoid cyst.
- Other schwannomas (rare).
- Metastases.
- Multiple sclerosis (SNHL mimic).
🛠️ Management
- 👀 Observation: small, incidental lesions; elderly/frail patients → serial MRI.
- 🔪 Microsurgery: translabyrinthine, retrosigmoid, or middle fossa approach depending on tumour size/location.
- 🎯 Stereotactic radiosurgery (Gamma Knife / CyberKnife): for small-medium tumours or poor surgical candidates.
- 📡 Fractionated radiotherapy: selected cases.
- 🎧 Rehabilitation: hearing aids, vestibular rehab, facial nerve physiotherapy.
- MDT: neurosurgery, ENT, audiology, neuroradiology, genetics (NF2).
📊 Prognosis
- Good outcome if detected early.
- Hearing preservation depends on tumour size and surgical approach.
- Recurrence risk ~5% → long-term follow-up essential.
- Untreated → progressive compression, hydrocephalus, death.
🔒 Prevention & Screening
- No prevention for sporadic cases.
- NF2 → genetic counselling, baseline + interval MRI scans.
📚 References
