Teaching Case

2-year-old boy with unilateral congenital aural atresia.

A 2-year-old boy with unilateral congenital aural atresia was admitted for CT examination of the temporal bones, in order to check the extent of the abnormalities and the possibility of surgical restoration. HRCT of the temporal bones revealed right-sided aural atresia, absence of the external auditory canal and of the tympanic membrane, which were replaced by bone. Middle ear cavity, the ossicles, bony labyrinth, internal auditory canal, facial nerve and mastoid cells were within normal limits. Left temporal bone structures were also normal.

Congenital Aural Atresia (CAA) is a birth defect that is characterized by hypoplasia of the external auditory canal. It also involves abnormalities of the tympanic membrane, the ossicles and the middle ear space. The inner ear structures develop normally in most of these patients.
The incidence of CAA is approximately 1 in 10,000 to 20,000 live births. Unilateral atresia(70 % of the cases) is more common than the bilateral form (30 % of the cases).
Although cases of autosomal dominant or recessive inheritance have been reported, CAA occurs sporadically in most of the cases. It also has been described in association with various syndromal abnormalities. The most common of these are Treacher-Collins’s (mandibulofacial dysostosis), Crouzon’s (craniofacial dysostosis), Rierre-Robin’s, DiGeorge’s, hemifacial microsomia, Nager’s (acrofacial dysostosis), Klippel-Feil’s and Goldenhar’s syndromes.
The inner ear and its components develops from the otic placode at 3rd week of gestation.
The middle ear space develops from endoderm of the first pharyngeal pouch. Its development is completed in the 30th week, except for the mastoid system.
Ossicular development starts the 4th week and by the 16th week ossicles are of adult size. The first branchial arch cartilages form the malleus head and the short procces of the incus. The second branchial arch forms the manubrium of the malleus, the long process of the incus and the stapes superstrucure.
Ectoderm of the first branchial cleft gives rise to the external auditory canal, at the 4th gestation week.
At last the auricle is being developed by a fusion of six hillocus (His) from the first and second branchial arches.
In conclusion CAA is a result of abnormal development of the first and second branchial arches.
Over time several classification systems for CAA have been proposed. But the most clinical useful classification was introduced by Jahrsdoerfer in 1992. This system predicts the possibility of a successful surgical restoration by scoring of HRCT findings. There is a score of up to 10 points. The presence of stapes gives 2 points. Presence of an open oval window, normal auricle appearance, mastoid pneumatisation, width of middle ear cleft, facial nerve position, malleus-incus complex and incudostapedial continuity give 1 point each. Scores of 6 to 10 range from marginal to excellent candidates for surgery, whereas cases with a score of 5 or less have a poor prognosis.