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Chapter 2: What’s Missing in CAAM?


Children with CAAM don’t have normal hearing systems. No outer ear exists to focus sound down the ear canal. There is no eardrum. Bone completely fills the area where the ear canal normally should have developed and blocks sound from reaching the middle ear bones. This means children with CAAM can’t hear normal sounds, like conversations, at a normal volume.

An example of anatomy in an CAAM ear. Note the absent ear
canal, eardrum, and outer ear.

You may notice your child can hear louder sounds. This is possible when vibrations are loud enough to be transmitted through the bone of the skull, directly to the cochlea. Such loud sounds make it possible to test the function of a child’s hearing nerves before CAAM surgery. At normal volumes, however, virtually no sound is received by or transmitted with CAAM.

Types of Hearing Loss

To understand this subject, I need to teach you a bit about hearing loss. Hearing impairment generally falls into three categories.


  • Sensorineural hearing loss results from a hearing nerve abnormality.
  • Conductive hearing loss indicates that either the outer ear, ear canal, eardrum, or middle ear bones are dysfunctional. In other words, some problem with the outer or middle ear prevents sound waves from being conducted successfully into the inner ear.
  • Mixed hearing loss incorporates both sensorineural and conductive components.

Types of CAAM

The kind of CAAM your child has will influence the best treatment.


  • Single-sided CAAM: About 90% of CAAM cases affect only one ear. Ear abnormalities are more common on the right side than left. Infant boys also have the condition more often than girls.
  • Bilateral CAAM: About 10% of CAAM cases affect both ears. In this situation, early exposure to sound via bone conduction hearing devices is a must. Without them, the hearing nerves and brain are not stimulated by sound, which prevents the development of normal speech and language and can severely and permanently impact the child’s function over the lifespan.
  • Partial CAAM: A partially formed ear canal and eardrum on one or both sides of the head occurs in a small percentage of cases. It’s as if the ear canal and outer ear started to develop but stopped prior to completion.
  • Atresia only: It is rare but possible for children to be born with normal outer ears but an abnormal or absent ear canal. When this specific condition does occur, it’s likely due to a genetic disease.

Causes of CAAM

Almost every mother who has a child with CAAM asks herself if she did something during her pregnancy to cause the condition. Don’t blame yourself or your spouse.

As far as doctors can tell, CAAM is almost never related to parents’ actions or lack thereof.

We still have much to learn regarding the cause of CAAM. As we continue to learn more, I believe we will discover that genetics is responsible for most cases. The condition is, however, affected by more than just one abnormal gene. For example, I have treated nearly two dozen sets of identical twins, where only one infant has CAAM even though the twins share identical genetics. It is rare for both identical twins to have the same CAAM defect. If this condition was due to a single gene, both identical twins would always have the same CAAM defect since identical twins have an identical genetic makeup. In still other examples, in a small percentage of patients, we know CAAM is part of a larger genetic condition (medically called a genetic syndrome) that includes abnormalities of other body systems. Based on our current understanding of CAAM, genes are seemingly largely responsible for the condition, and some of these genes have been identified already.

By the time your children are having their own children, I believe we will be able to answer everyone’s question: “What caused this and what’s the chance my future children will have it?” Though doctors are making great strides in understanding leading indicators for CAAM, still much is unknown about the causes of the condition. Right now, we know the following:


  • CAAM is often independent of family history. In the great majority of cases, CAAM affects families that lack any family history of ear abnormalities.
  • CAAM is sometimes associated with syndromes. In a small percentage of cases, a genetic syndrome may cause the condition. We review such syndromes in Chapter 3.
  • CAAM does not tend to affect the same family twice. Parents who have one child with CAAM rarely have a second. The rate of CAAM for later children goes up only slightly unless your family tree carries a gene that causes a syndrome specifically associated with CAAM.
  • CAAM is not usually hereditary. Individuals with CAAM are only slightly more likely to pass the condition on to their children. The only exception is if a parent with CAAM also has a genetic syndrome; in that case, the incidence of CAAM is higher.
  • CAAM appears to be caused by a genetic susceptibility. It may also be caused by another factor from the environment working together with a genetic susceptibility. A recent area of development called epigenetics may help unravel these questions.

How Hearing Systems are Impacted in Children with Single-Sided CAAM

In children with CAAM, the ear canal and the outer ear fail to develop normally. Whether present in only one or both ears, this abnormal development doesn’t just impact the child’s hearing system. His or her language and speech skills also suffer[iii], as well as a variety of other factors that we will explore momentarily. Children with single-sided CAAM seem to function normally in quiet environments but have significant issues listening in normal environments.

CAAM’s Impact on Language

Have you ever wondered why we have two ears? It’s a good question to consider, especially if your child was born with single-sided CAAM and your family is trying to determine if one hearing ear is enough.

Our ears work as a pair.

Children and adults suffer limitations when they only have one working ear. Their learning and language are delayed. They may have trouble with social confidence because it is hard to hear in social settings. In this section, we’ll explore why one ear is not enough—and how you need to understand that humans need two ears—before you make critical treatment decisions for your child with CAAM.

What Humans Can Do with Two Ears

When humans have two functioning ears, they have several distinct advantages over people who just have one working ear.

People with Two Ears Hear Different Signals

Each ear sends separate electrical signals to the brain. The brain uses these signals to perform important functions in our everyday lives that enable us to feel confident, stay safe, and make good decisions. Without two ears, children don’t have access to important hearing abilities.

People with Two Ears Hear Sounds Louder

The same sound is louder when heard with two ears and is called binaural summation. Imagine someone calling you from another room. Two ears turn up the volume of soft remote sounds.

People with Two Ears Develop More Language

Language development is strongly associated with normal two-ear hearing. Language development is also strongly related to job and school performance.

Hearing strongly affects vocabulary,
which is the strongest predictor of income.

People with Two Ears Tell Where Sounds Come From

Sound often reaches one ear faster than the other ear. Thanks to sound vibration inputs from both ears, our brains interpret the difference in timing to localize the sound source. This localization of sound is not possible with only one hearing ear. Normal-hearing people can tell where sounds come from without seeing the source. People with one ear have much more difficulty locating where a sound originated from.






Children and adults with single-sided CAAM cannot localize where sound comes from. Furthermore, patients who wear bone conduction hearing devices (such as the BAHA, Ponto, or BoneBridge) likewise do not have directional hearing. We’ll talk more about these devices in Chapter 4.

Being able to tell where sounds come from is an important safety skill, useful for many everyday situations, such as crossing the street or navigating a crowd.

Children without directional hearing visit the emergency room 20 times more often than other children.

In a less dire example, a child on a sports field might hear a teammate shouting, “Pass me the ball! I’m open!” Only with two ears can he or she know where the voice is coming from and respond.

People with Two Ears Hear Better in Noise

Almost always, patients who have had surgery to correct CAAM tell me they appreciate being able to understand sounds in noise the most. Why?

While individuals with single-sided CAAM hear normally in quiet environments, their understanding drops to 60% of capacity in moderate noise such as a busy meeting, restaurant, or classroom.

We spend most of our lives in a sea of sound. Our ears transmit the sounds around us to the brain, and the brain selects what we want to listen to. You can think of the ear as the receiver that sends every sound down the hearing nerve and the brain as the filter or processor. The brain requires two ears for the filter function to work. The brain also requires two ears during the critical period of development for the filter ability to develop—we are not born with it. Even people with two normal-hearing ears have more difficulty interpreting sound in loud environments, such as classrooms, crowds, grocery stores, the gym, or at coffee shops and restaurants.


On average, a person with two normal-hearing ears understands 95% of words in background noise. Someone with a single hearing ear understands only 60-65%.

The above fact explains why children with single-sided CAAM are visibly frustrated, and sometimes distracted and/or disruptive, when classroom noise increases. They can’t hear their peers or the teacher’s instructions! Unfortunately, teachers often misunderstand this and think children have concentration or behavioral issues instead.

Given these challenges, it’s no surprise that children with single-sided CAAM are 10 times more likely to repeat a grade in school, and adults with single-sided hearing loss earn only two-thirds of average income!

These situational and functional difficulties impact people with hearing loss for their entire lives.

What to Do When Doctors Say One Ear Is Enough

All over the world, I meet parents who have had a physician, plastic surgeon, pediatrician, or well-meaning advisor, say, “Your child hears normally from one ear. You don’t need to worry about hearing or development if they have single-sided CAAM.”

While one ear is definitely better than none, this reassurance is false—no matter how well-intended.

Such inaccurate advice is probably because, during training, most physicians don’t receive education about hearing and language development. Now you know more than they do, and you can protect your child’s future from irreversible developmental disabilities.

These well-intentioned professionals (and some parents) make the mistake of noting that a child’s hearing performance in a quiet atmosphere appears normal, and, as a result, they conclude that no action is necessary. It is true that a child’s performance in quiet with a single hearing ear does appear normal. The problem lies in the more difficult areas of hearing outlined above: directional hearing, soft sounds, and, most importantly, noisy situations.

It is important to understand this subtle principle: two-ear hearing must be restored to allow development of the capabilities listed above. Furthermore, hearing must be restored during the critical period of development, which occurs in the first few years of life. This period is frequently BEFORE the hearing impairments noted above are present since young children rarely demand much of their hearing in the first few years of life. If left untreated, these limitations frequently emerge in the teenage yearsat which time it may be too late to correct them, since your child is beyond the critical period of development.

Success After Surgery Is Possible

Patients who have had restorative surgery for single-sided CAAM often tell my team that they can talk to their friends in the hall between classes for the first time. They also frequently report a dramatic improvement in how easily they understand new concepts in school.

Similarly, parents report that children hear for the first time from the car backseat, even while the radio is playing. They notice that they can call their child from a different room in the house, and, for the first time, the child knows where they are calling from. Others tell us their children hardly ever use the word “huh” anymore. Still more share that their child’s grades have dramatically improved.

I shared a letter at the end of the introduction section where the writer describes struggling to hear in loud environments, and I told you I would prompt you to re-read it later. Now is the time to do that. It will give you a new understanding of how important this function is in a person’s life.

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