Understanding this birth defect, more common in boys, that may affect a child's hearing.

By Crayola Beauty Lips
March 09, 2014
Credit: Photo Researchers/ Getty

If you've ever seen a child with a small or abnormally shaped ear -- or even missing an ear altogether -- that's microtia, a birth defect where the outer part of a baby's ear does not form properly. This is a rare condition, seen in only 1 out of every 6,000 to 12,000 births, but it is more common in boys than in girls. Microtia tends to go hand-in-hand with another ear-related birth defect known as atresia, where a baby is born without an external ear canal. Microtia and atresia more commonly occur in only one ear, though they can occur in both.

"If a baby is born with microtia alone, his hearing may not be significantly impacted," notes Cheryl Edwards, an audiologist and interim director of diagnostic audiology at Boston Children's Hospital. "It depends on the degree of the malformation and whether the outer ear is blocked by bone or skin." But when microtia and atresia happen in tandem, children usually have a hearing loss of around 40 to 60 decibels in their affected ear.

This is because the outer ear's job is to capture and localize sound, then direct it into the ear canal, which funnels the sound down to strike the eardrum. When the eardrum vibrates, it triggers vibrations in your three middle ear bones, and this causes a wave of fluid within the inner ear to stimulate cells responsible for hearing. Those cells communicate with your hearing nerve through electrical impulses, and this sends a signal to your brain that you're hearing sound. "If you don't have an ear canal or external ear, you can't hear this way on the affected side," explains Jillian Kimberlain, Au.D., CC-A, an audiologist at Arkansas Children's Hospital. "The inner ear is usually perfectly normal, but we have a transmission problem because sound can't reach those inner ear cells." The entire chain reaction is cut off from the start.

Doctors may find it difficult to pinpoint an exact cause of your baby's microtia. You'll likely be referred to a genetics specialist to evaluate your family history. Current research suggests that it can happen when there is a decreased blood supply to a baby's developing ear prior to birth, or if expectant moms take certain medications during pregnancy. (Always discuss any medication you plan to take with your ob-gyn.) Microtia can also be associated with other birth defects such as cleft lip or palate. Unfortunately, sometimes the cause remains unknown.

But even though doctors can't always say why microtia happens, there are treatments available. Your child may be a candidate for a procedure called atresioplasty, in which a surgeon will try to restore normal hearing by opening the ear canal. "This is a very complex surgical procedure and it's important to have it done by an experienced ear specialist, known as an otologist," Kimberlain says. "The most common risk is a re-narrowing of the ear canal, but there is also a small risk of damage to the facial nerve, although this rarely happens when the procedure is performed by skilled hands." Kimberlain recommends asking for a surgeon's outcomes and to review pre- and post-surgical photos of other patients before making any decisions. If atresioplasty is not an option, your child may be a candidate for corrective plastic surgery, which can make her microtia ear more closely resemble a typically developing ear; in some cases, surgeons can even use some of your child's rib cartilage to make a brand-new ear.

Your child's hearing loss can also be improved with a bone anchored implant (BAI; they are available from Oticon Medical and Cochlear America, although they are not the same as s). BAIs consist of a high-performance sound processor that snaps on to a titanium implant located behind the affected ear, where it integrates with the skull bone. Once in place, the sound processor captures sound vibrations and directs them through the implant, where sound is conducted by the temporal bone and carried to the inner ear, where it is processed normally.

BAIs cannot be implanted until your child is at least 5 years old, but she'll be able to use the device earlier by wearing it on a soft elastic headband.

"This is a great option for children with microtia and atresia because with a BAI, sound bypasses the ear canal altogether," Edwards says. "However, you're still processing sound through a computer so it won't return hearing to normal. But we're able to make it pretty natural and most kids do very well."

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