National Center For Ocular & Facial Prosthesis: India

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Incidence and possible causes of Microtia

Microtia occurs more commonly in males and on the right side (unilateral). Approximately 10% may occur on both sides (bilateral).

Microtia usually occurs as an isolated deformity although it can present itself as part of a spectrum of other deformities, either minor or major such as hemifacial microsomia, Goldenhar syndrome and Treacher-Collins syndrome. Most patients with the most severe form of microtia also lack an external auditory canal, also known as “atresia”.

Although causes of microtia and other ear deformities are difficult to define, some theories include a decreased blood supply to the developing ear in-utero. Others have theorized certain medication taken by the mother during pregnancy such as Accutane, Thalidomide and retinoic acid. Environmental factors have also been questioned.

Bilateral Microtia

Children born with bilateral microtia (both sides affected) are managed differently than those with unilateral (one-sided) microtia.

Luckily, children with unilateral microtia have the other normal side to hear good, crisp, clean sounds. Children with bilateral microtia don’t have that luxury. Their hearing loss requires amplification with a bone-conduction hearing aid. There are usually three specialists involved in obtaining a bone-conduction hearing aid. The primary care doctor usually refers the child to an ear, nose and throat specialist. A hearing test is performed by an audiologist and this person is usually the one that dispenses and tests the hearing aid.

If one wants to know what a child with bilateral microtia hears, it is rather simple to reproduce this hearing loss. If one places a finger in each ear in order to totally occlude the ear canal, that is what a child with bilateral microtia and atresia hears. One may ask, then how can the child hear if both ear canals are occluded. The answer is simple: Bone Conduction. Because the vast majority of children with microtia have normal inner ears (where the hearing nerve is located), sound travels via the skull via vibrations. In other words, a sound will strike the skull, nose, jaw, etc. and a vibration gets transmitted straight to the inner ears, totally bypassing the ear canals.

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