10 Vestibular Schwannoma • Sometimes called acoustic neuroma, but is not on the cochlear (acoustic) nerve, nor is it a neuroma • Male = female distribution; typically present 40 to 60 years (younger if neurofibromatosis 2 [NF2]) • Incidence 1/100,000 per year (autopsy studies show up to 0.7% population may have vestibular schwannoma at death) • 95% unilateral, sporadic • 5% bilateral—associated with NF2 • Account for 80% of cerebellopontine angle (CPA) tumours and 6% of all intracranial tumours • May originate from junction of glial and Schwann cells of vestibular nerve, within internal auditory meatus (Obersteiner–Redlich zone) • Haemorrhage can occur in reticular type leading to sudden increase in size • Cystic degeneration possible • NF2—autosomal dominant; aberration on long arm of chromosome 22 leading to defect in tumour suppressor protein merlin (aka schwannomin, neurofibromin 2) • Questioned link with cellphone usage, but evidence not conclusive • Otological phase: small tumour compresses structures in the meatus • Neurological phase: expansion into CPA: – Facial weakness—uncommon (gradual compression allows for compensation as normal number of end plates are innervated by fewer neurons) – Ataxia/unsteadiness—brainstem/cerebellar involvement – Diplopia (VI n)—rare – Hoarseness and dysphagia (IX n, X n)—rare • Magnetic resonance imaging (MRI) scan: non-contrast screening protocols; usually iso/hypointense to brain, hyperintense to CSF on T1 and isointense to slightly hyperintense on T2; best shown with T1 contrast (gadolinium) or FIESTA or CISS (T2-weighted) sequences • (CT with contrast if MRI contraindicated) • Pure tone audiogram: 65% have high-frequency loss • Brainstem evoked response (interaural latency of wave V)—accuracy better for larger tumours (>1.5 cm) • Speech discrimination: “roll-over” seen as intensity increase and optimum discrimination score reduces • Meningioma • VII n neuroma • Cochlear nerve neuroma—rare
10.1 Terminology
10.2 Epidemiology
10.3 Pathology
10.4 Clinical Features (Fig. 10.1)
Gradual and progressive unilateral deafness (90%)—degree of hearing loss (HL) not related to size of tumour
Sudden-onset HL (10%)
Normal hearing (5%)
Associated with unilateral tinnitus (70%)—can be the only symptom
Imbalance unusual unless acutely due to bleed inside tumour (slow compression allows for gradual compensation); dysequilibrium often present with rapid head movements
Hitzelberger sign: anaesthesia of medial, posterior, or superior areas of the external auditory canal
Trigeminal nerve symptoms: facial pain, numbness, loss of corneal reflex
Headache—posterior fossa dura irritation leading to dull aching around ear
Late symptoms
Terminal symptoms (raised cerebrospinal fluid or CSF): failing vision (papilloedema), headache, reduced Glasgow coma score; coma
10.5 Investigations
10.6 Differential Diagnosis of CPA Tumours
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