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. The internal auditory canal (IAC) is situated at the posterior aspect of the petrous part of the temporal bone. 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, CN VIII is a sensory nerve carrying information from the spiral auditory organ (cochlear nerve) and the labyrinth (vestibular nerve) to the brain stem.Three branches arise from the geniculate ganglion: and Stenvers (long axis of the petrous segment) planes from a single. The labyrinthine segment courses superior to the cochlea and anterior to the vestibule and then bends posteriorly at the geniculate ganglion. The trigeminal nerve is the fifth (CN V) cranial nerve and its primary role is relaying sensory information from the face and head, although it does provide motor control to the muscles of mastication via the mandibular division ( TA: nervus trigeminus or nervus cranialis V). within the internal auditory canal as well as the fluid within the labyrinth. 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. It leaves the pontomedullary junction as the cisternal segment which enters the internal auditory meatus to become its meatal segment. 4: Orientation of the meatal facial nerve. Pneumo-CT is an effective means of diagnosing vascular loops and differentiating them from other lesions of the cerebellopontine angle.Fig. Eighth nerve tumors and vascular loops produce similar symptoms, but a cochlear type of hearing loss with good speech discrimination and normal caloric testing should raise suspicion of a vascular loop. The wide range of audiometric and vestibular system test results probably reflects the complex interaction between the vascular loop and eighth cranial nerve, in which the loop exerts pressure on the nerve, and the nerve compromises inner ear circulation. Only one-third of the patients had abnormal caloric tests, but spontaneous nystagmus was detected in all but one of the patients by photoelectric nystagmography. Hearing losses ranged from mild to profound, and most were of a cochlear type with excellent speech discrimination. All patients were tumor suspects before CT because of unilateral (or asymmetric) tinnitus or hearing loss. In this study, we report the results of a uniform battery of audiometric and vestibular system test results administered to fifteen patients with prominent vascular loops in the internal auditory canal diagnosed by pneumo-CT. Previous reports have described pathologic anatomy, surgical approaches, and results of treatment. These vascular loops are suspected of causing hearing loss, tinnitus, and vertigo, and surgery has been advocated to separate the vascular loop from the eighth cranial nerve. Prominent loops of the anterior inferior cerebellar artery in the cerebellopontine angle are found frequently during anatomic studies of this region.
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