|ECR 2019 / C-1911||
|Congenital inner ear abnormalities: a practical review.|
Sensorineural hearing loss in children is a major cause of disability. Its early diagnosis is very important since delayed diagnoses may affect the development of language, the academic skills and social and emotional development. It can be due to congenital or acquired anomalies; at least half of them have a genetic origin and among the acquired ones the infection due to cytomegalovirus is the most common cause.
Congenital sensorineural hearing loss can be divided into two categories. The majority of which are membranous malformations. Here, the pathology involves inner ear hair cells. There is no gross bony abnormality .Hence, high-resolution computed tomography (CT) and magnetic resonance (MR) of the temporal bone reveal normal findings. The remaining have abnormalities involving the bony labyrinth and, therefore, can be demonstrated by CT and MRI.
Imaging plays an important role in the evaluation of congenital sensorineural hearing loss. High-resolution CT and MR imaging provide excellent delineation of the intricate anatomy of the inner ear: CT depicts the minute details of osseous structures, and MR imaging allows visualization of the fluid-filled spaces and the vestibulocochlear nerve. Together, these complementary modalities can aid decision making about the best management strategy by facilitating the identification and characterization of inner ear malformations and any associated neurologic abnormalities.
A broad spectrum of inner ear malformations have been described and linked to developmental insults at different stages of embryogenesis, and various systems have been proposed for classifying them.
Development of the inner ear:
The inner ear arises from the otic placode in a process that begins early in the 3rd week of gestation. By the 8th week, the development of the cochlea is complete. The vestibule is completely developed by the 11th week, and the semicircular canals, between the 19th and 22nd weeks; the lateral canal or duct is the last to form. Ossification of the labyrinth is complete by the 23rd week, and the development of the inner ear is complete by the 26th week. Various inner ear malformations may result from developmental arrest at any prior stage, with the type of malformation depending on the gestational age at which the arrest occurs(Table 1).
Many syndromes with associated inner ear malformations have been described. Specific types of inner ear malformation have been described by Jackler et al and Sennaroglu and Saatci .
Conveniently starting at 3rd week till the end of 7th week of gestation, an insult during each subsequent week results in a distinct inner ear abnormality:
- complete labyrinthine aplasia or Michel deformity: 3rd week
- cochlear aplasia: 4th week
- common cavity malformation to the cochlea and vestibule: early 5th week
- cochlear incomplete partition type I including cystic cochleovestibular anomaly: late 5th week
- cochlear hypoplasia: 6th week
- cochlear incomplete partition type II including Mondini dysplasia: 7th week.
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