The seventh and eighth cranial nerves enter the internal acoustic meatus together. The eighth nerve terminates at the membranous labyrinth in a cochlear and vestibular division. The membranous labyrinth is located in the petrous portion of the temporal bone.
The divisions of the acoustic nerve at the membranous labyrinth are shown. Acoustic neuromas usually arise from the superior division of the vestibular portion of the nerve. The neuroma expands centrally out the internal acoustic meatus, compressing or enmeshing the cochlear portion of the nerve.
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