The cochlear nerve is the auditory division of the vestibulocochlear nerve (CN VIII), carrying special sensory fibres from the spiral ganglion of the cochlea to the cochlear nuclei of the brainstem. Its bipolar neurons have peripheral processes in contact with inner and outer hair cells of the organ of Corti and central processes that form the cochlear nerve proper, which travels in the internal auditory meatus with the facial nerve and vestibular nerve.
The cochlear nerve is the target of cochlear implant electrode arrays, which bypass damaged hair cells and directly stimulate the spiral ganglion neurons electrically, restoring functional hearing in severe-to-profound sensorineural hearing loss. Acoustic neuroma (vestibular schwannoma) arises from the vestibular nerve but compresses the cochlear nerve, producing progressive sensorineural hearing loss as the first symptom in 90% of cases. Auditory brainstem response (ABR) testing assesses cochlear nerve and brainstem auditory pathway integrity without requiring patient cooperation.
A vestibular schwannoma expanding in the internal auditory canal compresses the cochlear nerve, producing unilateral sensorineural hearing loss often with tinnitus; diagnosis by gadolinium MRI showing internal auditory canal enhancement, managed by microsurgical excision, stereotactic radiosurgery, or observation.
Translabyrinthine removal of acoustic neuroma sacrifices the cochlear nerve intentionally, producing complete ipsilateral deafness; hearing preservation approaches (retrosigmoid, middle fossa) attempt to spare the nerve but succeed in only 30-50% of cases depending on tumour size.
