First, a narrow IAC may contain a rudimentary or absent cochlear nerve. Ī narrow IAC can lead to an inferior CI outcome due to various reasons. Furthermore, IAC hypoplasia may be associated with an aberrant facial nerve, which renders the surgical approach to the cochlea more challenging and the risk for intraoperative facial nerve injury is increased. Among other factors, a narrow bony internal auditory canal (IAC) may be associated with poorer hearing performances after cochlear implantation as a narrow IAC commonly contains a hypoplastic cochlear nerve. Since a hypoplastic IAC can be associated with a hypoplastic cochlear nerve and sensorineural hearing loss, radiologic assessment of the IAC is crucial in patients with severe sensorineural hearing loss undergoing cochlear implantation.Ĭochlear implant (CI) surgery is the current gold-standard treatment in profound sensorineural hearing loss. Volumetric measurement of IAC in cases of IEMs reduces measurement variability and may add to classifying IEMs. Inter-rater reliability was higher in IAC volume than in IAC diameter (intraclass correlation coefficient 0.92 vs. In controls, the mean IAC diameter was 5.5 mm (SD 1.1 mm) and the mean IAC volume was 175.3 mm 3 (SD 52.6 mm 3). The IAC diameter was measured in the axial plane and the IAC volume was measured by semi-automatic segmentation and three-dimensional reconstruction. In this multicentric study, we included high-resolution CT (HRCT) scans of 128 temporal bones (85 with IEMs: cochlear aplasia, n = 11 common cavity, n = 2 cochlear hypoplasia type, n = 19 incomplete partition type I/III, n = 8/8 Mondini malformation, n = 16 enlarged vestibular aqueduct syndrome, n = 19 45 controls). We aimed to refine the definition of a narrow IAC by determining IAC volume in both control patients and patients with inner ear malformations (IEMs). However, definitions for a narrow IAC vary widely and commonly, qualitative grading or two-dimensional measures are used to characterize a narrow IAC. Facial nerve cannot be detected within the parotid gland with conventional imaging.A narrow bony internal auditory canal (IAC) may be associated with a hypoplastic cochlear nerve and poorer hearing performances after cochlear implantation.CT is preferable for imaging the lateral course of the facial nerve from the porus acusticus to the stylomastoid foramen.The facial nerve is the only cranial nerve that may show normal post-contrast enhancement (in the majority of the cases is asymmetric left-to-right).The facial nerve subdivides into 5 terminal branches: Which represents a convenient surgical landmark. Where it follows a virtual plane between the deep and superficial lobes of the parotid gland and splits into a nerve plexus called the pes anserinus (“goosefoot”), Which are typically below the resolution of MRI.Īfter the facial nerve crosses lateral to the styloid process, It gives off the posterior auricular nerve and then gives off two small motor nerves to the stylohyoid muscle and the posterior belly of the digastrics muscle, The nerve exits the temporal bone at the stylomastoid foramen. The extratemporal/extracranial segment (from stylomastoid foramen to post parotid branches). References: Department of Radiology, KAT General Hospital, Athens, Greece Which sends sympathetic fibers to the middle meningeal artery Which carry parasympathetic fibers to the lacrimal and parotid glands the greater superficial petrosal and lesser petrosal nerves,.Three branches arise from the geniculate ganglion: The labyrinthine segment courses superior to the cochlea and anterior to the vestibule and then bends posteriorly at the geniculate ganglion. The facial nerve enters the facial (Fallopian) canal (bony canal from the IAC to the stylomastoid foramen)(Figure 6) on the anterior aspect of the Bill bar (tiny triangular bone separating the facial nerve from the superior vestibular nerve). It is both the narrowest (<0.7mm diameter) and shortest (3–5mm length) segment. The labyrinthine segment (IAC to geniculate ganglion). References: Radiopaedia (Case courtesy of A.Prof Frank Gaillard,, rID: 36049), Department of Radiology, KAT General Hospital, Athens, Greece (VII = facial nerve, NI = nervus intermedius, VIIIc = cochlear nerve, VIIIvs = superior division of vestibular nerve, VIIIvi = inferior division of vestibular nerve) (B) The annotated sagitally T2-weighted, thin-slice MR image of the internal auditory canal showing the facial nerve situated at the anterior superior quadrant of the internal auditory canal. (A) The diagram for the orientation of the nerves of the internal acoustic meatus. 4: Orientation of the meatal facial nerve.
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