Vestibulocochlear nerve (CN VIII)
Nerve · CN VIII Sensory
The cochlear division (spiral ganglion, from the organ of Corti) and the vestibular division (Scarpa's ganglion, from the semicircular canals, utricle and saccule) run from the inner ear through the internal acoustic meatus alongside VII to reach the pontomedullary junction at the cerebellopontine angle. Purely sensory: hearing and balance.
Traced from the start
- Pons
- Vestibulocochlear nerve (CN VIII)
Detail
- Sensory
- Hearing (cochlear nuclei → superior olive → inferior colliculus → medial geniculate → auditory cortex, bilaterally represented); head position and acceleration (vestibular nuclei → vestibulo-ocular and vestibulospinal reflexes, cerebellum)
- Bedside tests
- Rinne and Weber: sensorineural loss gives air conduction louder than bone (Rinne positive) with Weber lateralising to the better ear; conductive loss gives bone louder than air with Weber to the worse ear. Head impulse test and Dix–Hallpike for the vestibular division
- Central representation
- Because hearing is bilateral above the cochlear nuclei, unilateral deafness always means a cochlear or nerve lesion, never a cortical one
When it goes wrong
Vestibular schwannoma (acoustic neuroma) growing from the vestibular division in the internal acoustic meatus and cerebellopontine angle; bilateral in neurofibromatosis type 2
Slowly progressive unilateral sensorineural hearing loss and tinnitus with mild imbalance; later absent corneal reflex (V), facial weakness (VII) and ataxia; MRI of the internal acoustic meatus confirms it
Ototoxic drugs: aminoglycosides, cisplatin, loop diuretics, high-dose aspirin
Bilateral high-frequency sensorineural hearing loss and tinnitus, or oscillopsia and unsteadiness in the dark when the vestibular division is hit
Vestibular neuritis (viral inflammation of the vestibular division)
Days of severe constant vertigo with vomiting, unidirectional horizontal-torsional nystagmus and a positive head impulse test, hearing preserved; add hearing loss and it is labyrinthitis
Practise this structure
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