What Are Microtia and Atresia?
Microtia pertains to the abnormal development of the pinna. The abnormalities may be in the form of a smaller than usual ear or even severe forms where the pinna is totally absent. This is usually associated with atresia of the external auditory meatus. Atresia, therefore, means that the ear canal is partly or totally absent. Most of these anomalies go hand-in-hand because the outer ear and the ear canal grow simultaneously during pregnancy. Thus, in some cases, the ear canal may appear completely normal externally and end in a blind alley internally.
Microtia is an anomaly more common in boys than girls and usually unilateral. It always seems to include the right ear more frequently than the left. About 1 in 10 children with microtia have bilateral microtia, which means that both ears are affected. It occurs in about 1 in every 8,000 to 10,000 births. If the family already includes a member with microtia or atresia, the incidence in future children is about 1 in 20. Most children with the problem of microtia or atresia alone do not have any other medial conditions, although in some it is part of syndrome—an associated collection of symptoms recognized by doctors.
Causes of Microtia and Atresia
The exact cause of microtia and atresia is still unknown. Usually, these conditions occur in an isolated, nonsyndromic form, without any recognizable trigger associated with the mother's behavior in the period before or during pregnancy. Current medical research indicates that some sporadic cases may be influenced by genetic and/or environmental factors or by certain drugs taken during pregnancy. Their association will be discussed with a multidisciplinary team in the initial consultations.
Steps to Take If Your Child Has Microtia
If your child is diagnosed with microtia, he will be recommended for audiometry testing, which is typically done a few days after birth. However, if this is not done routinely in your country, you can seek referral via your GP, health visitor or your pediatrician to an audiologist. In Australia, government-financed audiological care for under 26 years old children is provided by Hearing Australia. This includes regular hearing assessment and hearing aid maintenance if needed.
Also, you should seek referral to a specialist microtia/atresia clinic or persons who have experience with these conditions. Clinics are available in Sydney and Melbourne, and your local team will liase with them. A multidisciplinary team that comprises ENT surgeons, plastic surgeons, audiologists, speech pathologists, geneticists, and other relevant specialists will review your child's condition in these designated clinics. They may involve also geneticists and other relevant specialists as indicated.
Your baby is likely to be seen fairly small by the specialist team. They will discuss with you the options for treatment and come up with a long-term management plan that addresses cosmetic and hearing concerns. They will show you examples of previous cases, and they may use computer-aided software in order to illustrate potential reconstructive surgery outcomes. They will also liase with Hearing Australia for hearing tests and the fitting of hearing aids if necessary. Early consultation can enable any loss to be managed and provide information on options for the future.
As microtia is associated with many syndromes that involve other organs, your child will probably need further medical testing. These may include blood and urine tests and renal ultrasound, as well as CT scans of the inner ear to identify any other conditions and provide a general health profile.
Treatment of Atresia-Associated Deafness with Microtia
There are three types of atresia-associated deafness occurring with microtia:
Conductive Deafness: This occurs when there is a bad transmission of sound through the outer and middle ear into the inner ear. Conductive deafness might be because of abnormalities in the structures of the ear like abnormalities in the pinna, ear canal, or even the middle ear bones. This might cause conductive deafness due to these deformities of microtia.
Sensorineural Deafness: This type is caused by issues with the inner ear or in the auditory nerve. While it has been rarely found in microtia, sensorineural deafness can occur due to associated abnormalities or even syndromes.
Mixed Deafness: A combination of conductive and sensorineural deafness. In this category, both types of hearing losses can co-exist.
Types of Microtia
Grade I: A smaller ear with visible anatomical structures and a tiny but present ear canal. Grade I microtia generally does not cause deafness.
Grade II: A misshapen pinna with a tiny, closed ear canal. This grade usually causes conductive deafness.
Grade III: The most common and serious degree is the absence of the pinna, ear canal, and eardrum, with only a small peanut-shaped lobe in lieu of the pinna. There is generally conductive deafness with this grade.
Grade IV (Anotia): The ear is completely absent.
The vast majority of children with microtia and atresia have moderate deafness, except those from 40 to 70 dB in the affected ear. The aberration of the bones that belongs to the middle ear and the poor evolution of the mastoid bone may add to depreciated hearing.
Surgical and Non-Surgical Treatment Options
Hearing Aids: These devices amplify sound and are suitable for many various degrees of hearing loss. However, conventional behind-the-ear hearing aids can be impossible to fit on a child with microtia due to smaller ear canals. Bone conduction and bone-anchored hearing aids are other options for those people who have more extensive deformities.
Bone Conduction Hearing Aids: These use vibrations to pass the sound through the skull bone onto the inner ear; usually worn on a headband for very small children.
Bone-Anchored Hearing Aids: A small titanium screw is fitted into the skull, with the sound processor fixed to the screw. This method, suitable for children above the age of five years, directly transmits the sound to the inner ear.
Surgical Options: There are several surgical options which can enhance the hearing and cosmetic appearance. They include:
Autogenous reconstruction: This involves reconstructing an ear using the child's rib cartilage. There is normally only one, or occasionally more, surgeries. The age at which this method is performed is usually when the child is about six years old.
Reconstruction with an Artificial Framework: This is an earmade with an artificial framework covered with the tissue of the child. This might be carried out much earlier than the autogenous reconstruction and slightly oversized to allow for growth.
Prosthetic Ears: Silicone-made and matched to the skin tone, prosthetic ears can be attached using adhesive or titanium fixtures. This may be used in cases where reconstructive surgery cannot be done or temporarily.
Associated Syndromes
Microtia has been associated with several syndromes, including the following:
Treacher Collins Syndrome: The condition is characterized by underdeveloped bones of the face and abnormalities in the external and middle ear. This usually presents as bilateral conductive deafness.
Hemifacial Microsomia: The face half, including the ears and jaw, is underdeveloped. Some cases show conductive or mixed deafness.
Goldenhar Syndrome: Characterized by incomplete development of the ear, nose, and other facial structures; some involvement of other organs is possible.
Other Resources and Organizations
Work with your child's audiologist and multidisciplinary team. They will help you seek answers and advice on how to manage the hearing loss, access support services, and discuss treatment options. Because unilateral microtia puts a child at higher risk for future hearing loss, regular monitoring is important. Ongoing support from hearing professionals can best ensure a positive outcome for your child's hearing and their overall development.
