![]() The various degrees of dysplasia of the cochlea and vestibular system observed with imaging are simply growth arrests of these otocyst projections at various stages of development. The cochlear and vestibular aqueducts develop in conjunction with intracranial spaces, thereby completing the interconnection of the perilymphatic and endolymphatic spaces with the intracranial cerebrospinal fluid (CSF) spaces. The SCCs appear at the 6th week, and the superior SCC is completed by approximately 20 weeks, followed by the posterior SCC and finally the independently formed lateral SCC at about 22 weeks. Formation of the saccule, endolymphatic duct, and utricle is completed within 11 weeks of gestation. Cochlear development is complete at the 8th week of gestation. The anterior projection develops into the cochlear duct, the lateral projection becomes the lateral semicircular canal (SCC), and the posterosuperior projection becomes the superior and posterior SCCs. The otocyst first forms the saccule and utricle and then sends out three projections. ![]() The ectodermally derived inner ear begins as the otic pit before becoming the primitive otocyst. Facial nerve development is at the interface of these two functional units of hearing, but consideration of its anomalous development is mainly linked to disorders of the external canal and middle ear, where it can dramatically affect treatment options.ĪNATOMIC AND DEVELOPMENTAL CONSIDERATIONS Those that might impact cochlear implant candidates discussed in Chapter 136įor the patient with sensorineural hearing loss, the report should emphasize the sensorineural part of the pathway but must also consider the preceding conductive pathway.Those related to possible inner ear and cochleovestibular nerve anomalous development discussed in this chapter.Those related to external auditory canal (aural) atresia/middle ear anomalies discussed in Chapter 105.For the purposes of discussion, the suggested report content can be relatively conveniently divided into three basic categories: A reasonable approach to the general report format is to trace the sound, essentially vibrating air, from the outside to the brain stem and the facial nerve back out. Such a report must include systematic documentation of the entire auditory pathway as seen on either computed tomography (CT) or magnetic resonance imaging (MRI), and a specific statement for each structure in this linkage should appear in every report. The written report of findings in anomalies of the temporal bone and cochleovestibular nerve (cranial nerve VIII) should reflect the developmental background of these anomalies. ![]() A combined inner and external ear anomaly reflects injury to the otocyst and the branchial apparatus usually requiring a chromosomal insult, a syndromic relationship ( Chapter 107), or a severe multicentric and early acquired process such as rubella infection during gestation. Patients suspected of having congenital hearing deficits will usually present in distinct groups: sensorineural hearing loss and potential inner ear anomalies, the subject of this chapter, and those within the spectrum of aural atresia or with an otherwise unexplained conductive hearing loss ( Chapter 105). The structures involved in each phase of development should be evaluated in the clinical context.
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