[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [Anatomy](https://durgical.com/en/anatomy/) › [Head and neck](https://durgical.com/en/anatomy/region/head-and-neck/) › Internal acoustic meatus [Skeletal system](https://durgical.com/en/anatomy/system/skeletal-system/) · [Head and neck](https://durgical.com/en/anatomy/region/head-and-neck/) # Internal acoustic meatus The internal acoustic meatus is a canal on the inner side of the temporal bone; it carries the facial nerve and the nerve for hearing and balance. [See in 3D →](https://durgical.app/?from=durgipedia&lang=en#region=head_neck&select=internal_acoustic_meatus&side=r) Opens in the Durgical app, no sign-up needed. ## What it is A canal in the inner surface of the petrous temporal bone. ## What it does Carries the facial and vestibulocochlear nerves. ## Key points - Vestibular schwannoma (acoustic neuroma) grows from the vestibular nerve inside the meatus and widens it; the usual first sign is one-sided hearing loss with tinnitus - At the fundus, a horizontal crest and a small vertical crest (Bill bar) split it into four areas: facial nerve upper front, cochlear nerve lower front, the two vestibular nerves behind - Its inner opening faces the cerebellopontine angle, so a tumour here can grow out of the canal and press on the brainstem, the cerebellum and the [trigeminal nerve](https://durgical.com/en/anatomy/trigeminal-nerve/) ## Key facts **Where** Posterior surface of the petrous temporal bone **Function** Transmits the facial (VII) and vestibulocochlear (VIII) nerves and the labyrinthine artery ## Relations **Contents** [Facial nerve (VII)](https://durgical.com/en/anatomy/facial-nerve/) with its sensory root (nervus intermedius), the [vestibulocochlear nerve (VIII)](https://durgical.com/en/anatomy/vestibulocochlear-nerve/) as cochlear and superior and inferior vestibular nerves, and the labyrinthine artery and vein **Course** From its opening (porus) on the posterior surface of the petrous [temporal bone](https://durgical.com/en/anatomy/temporal-bone/) it runs laterally for about a centimetre to a blind end (fundus), a thin plate pierced by the nerves to the inner ear **Lateral** At the fundus, the [cochlea](https://durgical.com/en/anatomy/cochlea/) in front and the vestibule and [semicircular canals](https://durgical.com/en/anatomy/semicircular-canals/) behind; the facial nerve leaves the upper front corner to enter the facial canal **Medial** Cerebellopontine angle: the [pons](https://durgical.com/en/anatomy/pons/), the flocculus of the [cerebellum](https://durgical.com/en/anatomy/anterior-quadrangular-lobule/) and the anterior inferior cerebellar artery, which often loops into the opening ## How to find it It cannot be felt. In a dry skull it is the oval opening on the posterior surface of the petrous ridge, seen from inside the posterior cranial fossa above the [jugular foramen](https://durgical.com/en/anatomy/jugular-foramen/). On axial CT or MRI it lies at the level of the inner ear, roughly in line with the [external acoustic meatus](https://durgical.com/en/anatomy/external-acoustic-meatus/). ## Examination - Tuning fork tests: with a lesion here the loss is sensorineural, so Rinne stays positive (air better than bone) and Weber lateralises to the better ear - Pure-tone and speech audiometry: one-sided sensorineural loss, with speech understanding worse than the tone loss would predict, suggests a lesion beyond the cochlea - Corneal reflex: reduced on the side of a large tumour that has reached the trigeminal nerve, often before facial weakness appears ## On imaging MRI with gadolinium, or thin heavily T2-weighted slices, is the standard to find a vestibular schwannoma: an enhancing mass in the canal that may bulge into the angle like an «ice cream cone». CT with bone windows shows the canal widened or eroded. ## Clinical notes - Facial weakness is late and uncommon in vestibular schwannoma even when VII is stretched; early facial palsy suggests another lesion, such as a facial nerve schwannoma or a meningioma - Schwannomas of the vestibular nerve on both sides are the hallmark of neurofibromatosis type 2 - The labyrinthine artery, usually from the anterior inferior cerebellar artery, is an end artery: its occlusion can cause sudden deafness and vertigo - Surgery for tumours in the canal (translabyrinthine, retrosigmoid or middle fossa approaches) is planned around preserving hearing and facial function ## Memory aid At the fundus the meatus splits into four areas: facial nerve (VII) upper front, cochlear nerve lower front, the two vestibular nerves behind. ## Related conditions - [Vestibular schwannoma (acoustic neuroma)](https://durgical.com/en/conditions/vestibular-schwannoma/) ## Test yourself Think of the answer, then tap the question to see it. ## Which structures pass through the internal acoustic meatus? The facial nerve (VII) with the nervus intermedius, the vestibulocochlear nerve (VIII) and the labyrinthine artery and vein. ## What tumour widens the internal acoustic meatus, and what is its usual first sign? Vestibular schwannoma (acoustic neuroma), from the vestibular nerve; the usual first sign is one-sided hearing loss with tinnitus. ## How are the nerves arranged at the fundus of the internal acoustic meatus? Facial nerve upper front, cochlear nerve lower front, the two vestibular nerves behind; split by the horizontal crest and Bill bar. ## What do the Rinne and Weber tests show with a lesion in the internal acoustic meatus? Sensorineural loss: Rinne stays positive (air better than bone) and Weber lateralises to the better ear. ## What do bilateral vestibular schwannomas in the internal acoustic meatus indicate? Neurofibromatosis type 2; they are its hallmark. [Add to my cards (5)](https://durgical.app/estudiar/?add=/en/anatomy/internal-acoustic-meatus/) Educational information, not medical advice. For any symptom, see a health professional. ## Its names **Official Latin (TA2)** meatus acusticus internus TA2 671 **Official Spanish (DeCS)** Meato acústico interno **English (TA2)** Internal acoustic meatus **Also called** internal auditory canal ## Related - [Vestibulocochlear nerve (VIII)](https://durgical.com/en/anatomy/vestibulocochlear-nerve/) - [Facial nerve (VII)](https://durgical.com/en/anatomy/facial-nerve/) Sources: Terminologia Anatomica (TA2); [Anatomy, Head and Neck, Skull Foramen](https://www.ncbi.nlm.nih.gov/books/NBK546621/); [Neuroanatomy, Cranial Nerve 8 (Vestibulocochlear)](https://www.ncbi.nlm.nih.gov/books/NBK537359/). ## **Spotted a mistake?** We are always improving for the community. Tell us what is wrong and our team will review it. 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