Fig. 18.2 Oblique sagittal T2 MR image through the porus acusticus reveals the characteristic “ball in catcher’s mitt” appearance of the facial nerve (arrow) and the vestibulocochlear nerve. The facial nerve is the “ball,” and the vestibulocochlear nerve is the “catcher’s mitt”, inferior and posterior to the facial nerve within the opening of the IAC
Fig. 18.3 Oblique sagittal T2 MR images through the mid-internal auditory canal (IAC). The four nerves which travel in the IAC are clearly identified. The common mnemonic used to remember the nerves in the IAC is 7-up (anterosuperior, facial nerve (arrow)) and coke-down (cochlear nerve anteroinferior, inferior to the facial nerve). The posterior nerves are the superior (posterior to the facial nerve) and inferior (posterior and inferior to the facial nerve) vestibular nerves
Fig. 18.4 Axial T1 noncontrasted MR image at the level of the stylomastoid foramen shows the exiting low-signal facial nerve (arrows) surrounded by high-signal fat in the “bell” of the stylomastoid foramen. The fat surrounding the facial nerve may be obscured if perineural tumor spread is present
18.2 Function
Branchial motor function (SVE): Motor fibers extend through the temporal bone through the stylomastoid foramen to supply the voluntary and involuntary muscles of facial expression.
Visceral motor function (GVE): Parasympathetic fibers travel along the greater superficial petrosal nerve to the pterygopalatine ganglion to supply innervation to the lacrimal gland and nasal mucosa. There are also parasympathetic fibers that travel with the chorda tympani to supply innervation to the submandibular and sublingual glands.
Special sensory function (SA): Sensory fibers extend through the middle ear along the chorda tympani to join the posterior division of V3 to form the lingual nerve. The chorda tympani component of the facial nerve carries taste information from the anterior two thirds of the tongue.
18.3 Pathology
Individual symptoms: Damage to the facial nerve results in the following symptoms depending on location:
Supranuclear lesions: Contralateral paresis/palsy of lower portion of the face (central paresis) with flattening of the nasolabial fold (unopposed contraction of the contralateral side of the orbicularis oris), possible drooling of saliva, and general sparing of the upper half of the face (corrugation of the forehead and voluntary eyelid closure possible).
Pontine lesions: Isolated lesions of the pons can result in a facial nerve neuropathy. Etiologies such as ischemia, neoplasm, and vascular malformations such as a cavernous malformation or demyelinating pathologies are possible.
Cisternal lesions: Masses within the cerebellopontine cistern can present with facial nerve neuropathy, such as a facial nerve schwannoma, meningioma, or metastatic disease. Neurovascular compression can result in a facial hemispasm. Lesions in the tympanic segment will cause a “peripheral” paralysis characterized by ipsilateral muscular weakness of the upper and lower face (flattening of the nasolabial fold and lagophthalmos).
Intratemporal lesions: Lesions such as facial nerve schwannomas have varied appearances when found within the temporal bone based on the surrounding anatomic landscape of the involved segments [8]. Herpetic infection of the facial nerve (Bell’s palsy) is demonstrated on imaging with normal CT osseous borders, but avid enhancement throughout the intratemporal bone and a tuft of enhancement within the lateral IAC. Traumatic fractures may injure the facial nerve within the temporal bone.Related posts:
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