Abnormalities of the external auditory canal

Stenosis / atresia of the EAC may be isolated or associated with malformations of the auricle (microtia) and middle ear.

Isolated EAC stenosis without microtia:

• is uncommon, accounting for <10% of individuals (6% in Jafek’s series) (1) that are evaluated for meatal atresia (over 90% of patients have associated microtia).
• No prevalence at birth studies are available to provide an estimated of the frequency of this condition.
• This abnormality is not diagnosed on ultrasound and can only be diagnosed on MRI.

Non isolated stenosis / atresia has concomitant microtia in 94% of cases (1).

Classification

Aural atresia has been classified in various ways.

Cremers (2) divided aural atresia into three types:

Type I: there is osseous or membranous atresia of the auditory canal but an almost normal medial aspect of the canal and a normal middle ear.

Type Il: accounts for most of the cases, and there is partial or totally atresia ear canal with variable involvement of the middle ear.

Type III: there is a complete bony meatal atresia, with a very small or absent middle ear cavity.

Jahrsdoerfer et al. (3) proposed a grading system for aural atresia. This system gives points for the presence of normal structures (e.g., stapes present). Higher scores predict better surgical outcome.

Imaging

External auditory canal stenosis or atresia without microtia is narrowing or absence of the external auditory canal without the presence of significant external ear malformations. In such cases the EAM atresia may be osseous (tympanic bone replaced by an atretic plate) or membranous. Osseous atresia is more common than membranous atresia.

In the series of 311 patients with aural atresia reported by Jafek et al, (1) only about 6%, had atresia without a concomitant microtia.

Associated abnormalities of the ossicles range from dysplasia to absence of the malleolus and incus (4,5).

Isolated external auditory canal atresia/stenosis can occur as a marker for deletion 18q syndrome. Any child with this atresia/stenosis who has other mild malformations, phenotypic variations, or developmental delay should be regarded as possibly having this common chromosomal syndrome (4). Auditory canal stenosis without microtia is also seen in trisomy 18, in oculo-auriculo-vertebral spectrum, and in the syndrome reported by Rasmussen et al.(7).  In the latter condition, congenital vertical talus and hypertelorism occur along with atresia of the external auditory canal. None of the kindred had external ear abnormalities.

In microtia with meatal atresia, unilaterality is much more common than bilaterality,

In aural atresia without microtia there was equal occurrence of bilateral and unilateral defects.

Because the syndromes showing isolated auditory canal atresia/ stenosis are generally different from those showing microtia with metal atresia, this defect probably reflects a unique alteration in morphogenesis. It is also of note that, in the few familial cases, the degree and frequency of ossicular chain abnormalities are less than what is usually seen in microtia with meatal atresia.

Besides the family reported by Rasmussen et al. (7) in whom the meatal atresia occurred as part of a syndrome, three other families have exhibited generation-to-generation transmission, suggesting dominant inheritance. The family in the Robinow (8) and Jahrsdoerfer (3) study showed male-to-male transmission, indicating autosomal dominant inheritance. Therefore, atresia of the auditory canal without microtia is inherited in an autosomal dominant fashion in some of the cases.

Associated syndromes (in non isolated cases)

The London Medical Databases for atretic auditory canal produce 146 syndromes (59 syndromes had associated microtia) (9). The most common syndromes include:

• Crouzon syndrome.
• Treacher-Collins syndrome.
• Goldenhar syndrome.
• Pierre-Robin syndrome.

Associated anomalies in isolated cases

• Two thirds of cases had a terminal microdeletion 18q22.3-18q23 region (10).
• Trisomy 18.

References

1. Jafek BW, Nager GT, Strife I, et al.: Congenital aural atresia: an analysis of 311 cases. Trans Am Acad Ophthalmol Otol 1975; 80:588.
2. Cremers CWRJ: Meatal atresia and hearing loss. Autosomal dominant and autosomal recessive inheritance. Int I Pediatr Otorhinolaryngol 1985; 8:211.
3. Jahrsdoerfer RA, Yeakley JWV, Aguilar EA, et al.: Grading system for the selection of patients with congenital aural atresia. Am J Otolaryngol  1992;13:6.
4. Mallo M. Formation of the middle ear:recent progress on the developmental and molecular mechanisms. Dev Biol 2001;231:410-419.
5. Robson CD, Robertson RL, Barnes PD. Imaging of pediatric temporal bone abnormalities. Neurimag Clin North Am 1999;9:133-155.
6. Stevenson RE, Hall JG. Human malformations and related anomalies. 2005. 2^nd edition. Oxford University Press.
7. Rasmussen N. Iohnsen NI. Thomsen I: Inherited congenital bilateral atresia of the external auditory canal, congenital bilateral vertical talus and increased interocular distance. Acta Otolaryngol 1979; 88:296.
8. Robinow M, lahrsdoerfer RA: Autosomal dominant atresia of the auditory canal and conductive deafness. Am J Med Genet 1979;4:89.
9. The Winter-Barrister Dysmorphology Database, London Medical Databases. http://www.Imdatabases.com.
10. Veltman JA, Jonkers Y, Nuijten I et.al. Definition of critical region on chromosome 18 for congenital aural atresia by array CGH. Am J Hum Genet 2003;72:1578-1584.

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