The only difference between the anatomy of the facial nerve in infants compared with adults is in the region of the stylomastoid foramen. The bony facial canal develops until birth, enclosing the facial nerve in bone throughout its course except at the facial hiatus (the site of the geniculate ganglion) in the floor of the middle cranial fossa. By the 16th week, the neural connections are completely developed. Complete separation of the facial and acoustic nerves and development of the nervus intermedius (or nerve of Wrisberg) occurs by 6 weeks of gestation. The facial nerve is composed of motor, sensory, and parasympathetic fibers. Development and Anatomy of the Facial Nerve In this paper we describe the development and anatomy of the facial nerve, then radiographic techniques used in facial nerve evaluation, and finally the pathologic entities that affect the facial nerve.ΔΆ. In all cases, choice of the imaging modality utilized should be determined by specifics of the patient's symptoms and the differential diagnosis. This technique has been shown to be potentially useful in the identification displacement of cranial nerve fibers by vestibular schwannomas. Diffusion tensor (DT) tractography, which uses MRI to make three-dimensional (3D) reconstructions of the facial nerve, has recently been developed. Facial nerve ultrasound has been used in a recent study to predict functional outcomes in Bell's palsy. Magnetic resonance imaging (MRI) is useful for identifying soft tissue abnormalities around the facial nerve, as seen in inflammatory disorders, neoplasms, and hemifacial spasm. Computed tomography is useful for identifying bony abnormalities of the intratemporal facial nerve, which can occur with congenital malformations, trauma, and cholesteatoma. The facial nerve has a complex anatomical course, and dysfunction can be due to congenital, inflammatory, infectious, traumatic, and neoplastic etiologies. Pneumo-CT is an effective means of diagnosing vascular loops and differentiating them from other lesions of the cerebellopontine angle.Imaging plays an important role in the evaluation of facial nerve disorders. 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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