On the right (a) axial CT shows a small cyst in place of the cochleovestibular system, corresponding to labyrinthine aplasia.The internal auditory canal (IAC) is also absent. The lateral end of the IAC is termed the fundus and abuts the labyrinth. The medial opening of the IAC is termed the porus acousticus.
The anatomy of the internal auditory canal is best seen on high-resolution T2-weighted image sequences. a-d Patient 1: a 6-month-old girl presenting with congenital deafness has bilateral congenital malformations of the labyrinth on CT. The internal auditory canal (IAC) is a channel in the petrous bone that is somewhat variable in size, shape, and orientation. Narrow duplicated internal acoustic canal 2 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). In addition to the three nerves which enter it, it also contains the vestibular ganglion ( ganglion of Scarpa). See mnemonic for the position of the nerves in the IAC. Inferior: cochlear nerve and inferior vestibular nerve (IVN) the cochlear nerve is situated anteriorly 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 This horizontal ridge divides the canal into superior and inferior portions: Their position is most constant in the lateral portion of the meatus which is anatomically divided by the falciform crest. Superior vestibular nerve (component of CN VIII) Inferior vestibular nerve (component of CN VIII) PMID: 29273441 DOI: 10.1016/j.amjoto.2017.12.009 Abstract Objective: Non-contrast MRI of the internal auditory canal (IAC) using high-resolution T2WI (T2 weighted image) has been proposed as the primary screening study in patients with sudden or asymmetric sensorineural hearing loss (ASNHL). Nervus intermedius (sensory component of CN VII)įacial motor root (motor component of CN VII) There are five nerves that run through the IAM: Labyrinthine artery (usually a branch of the AICA or basilar artery) measurable parameters of internal auditory canal (IAC) magnetic resonance imaging (MRI) in patients with idiopathic sudden sensorineural hearing loss. 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. The margins of the opening are smooth and rounded, and the canal is short (1 cm), running laterally to the bone. The opening of the IAM, the porus acusticus internus, is located within the cranial cavity, near the posterior surface of the temporal bone.
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