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Congenital aural atresia5/16/2023 ![]() The cartilage anlage of the first branchial arch is called the Meckel cartilage and that of the second branchial arch is called the Reichert cartilage these contribute to the formation of the mid face and mandible as well as the ossicles. The developing middle ear expands to surround the developing ossicular chain and creates “mesenteric” folds that can be abnormal, thick, and calcific in congenitally malformed ears. First, branchial arch mesenchyme differentiates into both the cartilaginous and osseous portions of the EAC. Ectodermal squamous tissue rests remaining within the middle ear account for the occasional formation of congenital middle ear cholesteatomas. Consequently, the epithelium of the external canal and outer layer of the tympanic membrane is squamous epithelium, while the middle ear is lined by respiratory epithelium. 1 The middle ear and eustachian tube are formed from the first branchial pouch arising from endoderm of the primitive foregut. The EAC arises from the first branchial groove as it accompanies the first branchial arch mesenchyme. Facial nerve development is at the interface of these two functional units of hearing, but consideration of its anomalous development is most 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 external canal, middle ear, and facial nerve, the report should emphasize the conductive part of the pathway but must also consider the remaining sensorineural pathway.Those related to possible inner ear and cochleovestibular anomalies discussed in Chapter 106.Those related to external auditory canal (EAC 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 in, essentially vibrating air, from the outside to the brain stem and then follow the facial nerve back out since the position of the latter might have a treatment impact. 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 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, syndromic relationship ( Chapter 107), or severe multicentric early process such as rubella infection during gestation. Patients suspected of having congenital defects will usually present in two distinct groups: those with external canal atresia with obvious canal stenosis and/or a deformed pinna and those with potential inner ear anomalies with sensorineural hearing loss. The structures involved in each phase of development should be evaluated in the clinical context. Reports must be logically constructed and comprehensive, anticipating all anatomic and pathologic abnormalities that might lead to altered treatment plans.ĭevelopment of the inner ear from the primitive otocyst is separate from that of the middle and external ear, which come from the first and second branchial arches.Computed tomography is critical to medical decision making in developmental abnormalities of the external and middle ear. ![]()
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