-2 :: Case - 10506 :: - Microtia and Bilateral Atresia of the External Auditory Canals and Middle Ear Stuctures
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Discussion Author: Steven J Goldstein

The middle and external ear develops from the mesodermal first and second branchial arch and the endodermal first pharyngeal pouch between the fourth and 30th weeks. Developmental anomalies of the first pharyngeal pouch lead to disturbances of the eustachian tube and of tympanic and mastoid pneumatization. Failure of differentiation of the first branchial arch leads to malformations of the incudomalleal joint, tensor tympani muscle, and mandible. The degree of auricular anomaly is also highly correlated with dysplasias of the middle ear cavity, mastoid cells, malleus, and incus, presumably because of a common embryological origin.


Congenital aural dysplasias occur in one of 3300 to 10 000 births except in the era of thalidomide embryopathy (1959–1962), when it was diagnosed in one of 900 neonates in Europe. Microtia has been described even on Babylonian tablets and has been seen in prehistoric skulls. Microtia is often associated with abnormalities of other organs as the result of genetic disorders, chromosomal defects, and intrauterine infections.

Minor microtia is most commonly associated with external auditory canal stenosis; in those with major microtia, atresia is predominant. Middle ear malformations depend on the severity of the auricular anomalies. Ossicular dysplasias occur in almost all patients with microtia, with the stapes most commonly affected. Absence of the oval window is found in almost one third of these patients, and labyrinthine malformations is seen in about ten percent. In some cases of anterior displacement of the mastoid segment of the facial nerve and severe microtia, the facial nerve canal turns anteriorly or, less commonly, laterally, leaving the temporal bone to the temporomandibular articulation instead of continuing downward toward the stylomastoid foramen. Of great concern to the surgeon is the high frequency of facial nerve canal displacement seen in up to 75% of patients with microtia.

Although MR plays a major role in the evaluation of the patient with conductive and sensorineural hearing loss, high resolution multiplanar CT scanning is the primary imaging modality in the preoperative evaluation of patients with microtia and external auditory canal dysplasia.

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