These spiral ganglia are bipolar, with one axon arising from the cochlear organ of Corti that receives auditory information and one axon that transmits this information to the brainstem. The cell bodies of the cochlear nerve are located in the modiolus, the spongy bone at the center of the cochlea. Finally, lesions of the petrous apex are discussed, both as potential causes of hearing loss and as they may be unexpectedly discovered at the time of temporal bone imaging for SNHL or conductive hearing loss (CHL). The congenital and acquired pathologic conditions that may be found along the central acoustic pathway from the IAC to the auditory cortex are then discussed, with an emphasis on the most commonly found lesion causing adult SNHL, the vestibular schwannoma. Magnetic resonance imaging (MRI) plays an important role in the evaluation of patients with SNHL, and a discussion of the currently available techniques for high-resolution imaging of the inner ear, IAC, and CPA follows. This chapter begins with a discussion of the anatomy of the retrocochlear auditory pathway from the cochlear modiolus to the primary auditory cortex of the superior temporal gyrus. Bilateral SNHL or complex auditory dysfunction, such as auditory agnosia, suggests a process that is more centrally located along the auditory pathway. SNHL in association with cerebellar-type neurological findings such as ataxia and weakness suggests the presence of a posterior fossa and/or brainstem abnormality. If additional cranial neuropathies are present in association with the SNHL, such as trigeminal neuralgia or facial nerve palsy, then a large CPA mass, a leptomeningeal process, or a brainstem abnormality such as multiple sclerosis must be considered. When presented with a request to image a patient with a history of SNHL, dedicated imaging is required of the cochlea, IAC, and the CPA. The most common abnormality when imaging a child with SNHL is a congenital inner ear malformation, 1 whereas the most common cause of unilateral or asymmetric SNHL in an adult is a schwannoma of the vestibulocochlear nerve. Dysfunction in this pathway results in sensorineural hearing loss (SNHL). The vestibulocochlear nerve passes through the internal auditory canal (IAC) and cerebellopontine angle (CPA), forming the extraaxial component of the central auditory pathway. The vestibulocochlear nerve is the eighth cranial nerve (CN VIII) and is responsible for the transmission of electrical impulses from cochlear hair cells of the inner ear to the cochlear nuclear complex in the brainstem. 8 The Vestibulocochlear Nerve, with an Emphasis on the Normal and Diseased Internal Auditory Canal and Cerebellopontine Angle
0 Comments
Leave a Reply. |
Details
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |