Internal acoustic canal
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View Frank Gaillard's current disclosures- Internal acoustic meatus (IAM)
- Internal auditory meatus (IAM)
- Internal auditory canal (IAC)
- Internal acoustic canal (IAC)
- Internal acoustic meatus
The internal acoustic canal (IAC), also known as the internal auditory canal or meatus (IAM), is a bony canal within the petrous portion of the temporal bone that transmits nerves and vessels from within the posterior cranial fossa to the auditory and vestibular apparatus.
On this page:
Gross anatomy
The opening of the IAC, the porus acusticus internus, is located within the cranial cavity, near the posterior surface of the temporal bone. The margins of the opening are smooth and rounded, and the canal is short (1 cm), running laterally to the bone. The canal narrows laterally, and the lateral boundary is the fundus, where the canal splits into three distinct openings, one of which is the facial nerve canal.
Contents
labyrinthine artery (usually a branch of the AICA or basilar artery)
Nerves
There are five nerves that run through the IAC:
nervus intermedius (sensory component of CN VII)
facial motor root (motor component of CN VII)
cochlear nerve (component of CN VIII)
inferior vestibular nerve (component of CN VIII)
superior vestibular nerve (component of CN VIII)
Their position is most constant in the lateral portion of the meatus which is anatomically divided by the falciform crest. This horizontal ridge divides the canal into superior and inferior portions:
superior: facial nerve and superior vestibular nerve (SVN); the facial nerve is anterior to the SVN and is separated from it laterally by Bill's bar, a vertical ridge of bone
inferior: cochlear nerve and inferior vestibular nerve (IVN); the cochlear nerve is situated anteriorly
See mnemonic for the position of the nerves in the IAC.
Ganglion
In addition to the three nerves which enter it, it also contains the vestibular ganglion (ganglion of Scarpa). From here three bundles emerge: superior and inferior division of the vestibular nerve and the nerve from the posterior semicircular canal (see article: vestibulocochlear nerve (CN VIII) for further details).
Variant anatomy
narrow duplicated internal acoustic canal 2
Radiographic features
MRI
The anatomy of the IAC is best seen on high-resolution T2-weighted image sequences. Structures that can be seen are facial and vestibulocochlear nerves.
References
- 1. Gray's Anatomy. Churchill Livingstone. (2011) ISBN:0443066841. Read it at Google Books - Find it at Amazon
- 2. Vincenti V, Ormitti F, Ventura E. Partitioned versus duplicated internal auditory canal: when appropriate terminology matters. Otology & neurotology : official publication of the American Otological Society, American Neurotology Society [and] European Academy of Otology and Neurotology. 35 (7): 1140-4. doi:10.1097/MAO.0000000000000458 - Pubmed
Incoming Links
- Sensorineural hearing loss
- Anterior inferior cerebellar artery loop
- Perilymphatic duct
- Vestibular schwannoma
- Internal auditory canal atresia
- Porus acusticus externus
- Möbius syndrome
- Temporal bone (modified Stenvers view)
- Nervus intermedius schwannoma
- Cochlear aqueduct
- Deafness
- Cochlear hypoplasia
- Internal auditory canal nerves (mnemonic)
- Petrous part of temporal bone
- Petrous apex
- Paget disease (bone)
- Cranial foramina
- Anterior inferior cerebellar artery
- Vestibular ganglion
- Porus acusticus internus
- Anterior inferior cerebellar artery loop - type III
- Vestibular schwannoma
- Anterior inferior cerebellar artery loop (Type III)
- Internal auditory canal stenosis
- Skull base hyperpneumatisation
- Intracanalicular vestibular schwannoma
- Trigeminal schwannoma
- Vestibular schwannoma - intracanalicular
- Corpus callosum dysgenesis
- Cerebellopontine angle meningioma
- Epidermoid cyst of the cerebellopontine cistern
- En plaque meningioma with associated CPA / frontal convexity meningiomas
- Meningioma of the cerebellopontine angle
- Meningioma - cerebellopontine angle
- Epidermoid cyst compressing the trigeminal nerve
- Anterior inferior cerebellar artery vascular loop - type 1
- Anterior inferior cerebellar artery vascular loop - type II
- Epidermoid cyst compressing the trigeminal nerve
- Arachnoid cyst: extremely large
- Lipoma-cerebellopontine angle
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