What is hearing loss?

Hearing loss occurs when there is a problem with one or more parts of the ear and proper hearing is prevented. Hearing loss may affect one or both ears and a person may be able to hear some sounds or nothing at all. Hearing loss can be present from birth but can also develop later in childhood or adulthood. Hearing loss is the most common congenital anomaly in the newborn and occurs in 3 of every 1000 live births. Approximately 6 out of 100 school age children will develop some type of hearing loss.

Because hearing is so critical for normal speech, language and cognitive development, hearing loss can have a significant impact on the life of a child. A child with an undiagnosed hearing loss may have impairment in their ability to speak and to understand oral language. Hearing loss can also result in learning problems that affect a child’s performance at school. For this reason, the earlier a hearing loss is detected, the sooner a child can be helped.

How do we hear?

The outer ear picks up sounds, which travel through the external ear canal to reach the eardrum. The eardrum vibrates in response to sound waves. When the eardrum vibrates, three small bones in the middle ear (the hammer, anvil and stirrup) transmit the vibrations or sound signals to the inner ear (the cochlea). In the cochlea, tiny hair cells detect the incoming vibrations and change them into electric signals that move along the auditory nerves to the hearing center of the brain.

What causes hearing loss?

There are a few different types of hearing loss:

• Conductive hearing loss occurs when something interferes with sound passing through the outer or middle ear. If the outer ear canal, eardrum, hammer, anvil, stirrup or other parts of the middle ear are not functioning correctly, it can cause this type of hearing loss. Most children with conductive hearing loss have mild to moderate losses, and in many cases, the loss is temporary and can respond to medical or surgical treatment. Some examples of causes of conductive hearing loss are: wax blockage of the external ear canal, damage to the eardrum, or fluid or infection in the middle ear.
  
• Sensorineural hearing loss occurs when the hair cells of the cochlea cannot detect the incoming vibrations or when the auditory nerve cannot transmit signals to the brain. Sensorineural hearing loss can also be a result of damage to the brain’s hearing center. The degree of hearing loss from a sensorineural cause may vary from mild to profound. Sensorineural hearing loss is almost always permanent. Some examples of causes of sensorineural hearing loss are: genetic factors, infections during pregnancy such as rubella, cytomegalovirus, herpes or syphilis, head injuries, and childhood infections such as meningitis.
  
• Mixed hearing loss is a combination of conductive and sensorineural.

What are some signs of hearing loss in children?

Infants may have:

• Failure to startle at loud sounds
• Not imitate sounds after 6 months
• Lack of babbling at 9 months
• Failure to say single words by 18 months

Children may have:

• Slow vocabulary development in comparison to their peers
• Unintelligible speech
• Speak loudly
• Turn the television volume too loudly
• Ask to repeat what was said
• Have learning difficulties at school

How can hearing be tested in a child?

Hearing can be evaluated at any age. There are several methods to test a child’s hearing.

Behavioral tests are usually performed after 6 months of age. These tests require observation of a child’s behavioral response to sounds. The behavioral response might be a head turn from an infant, placement of toy in a bucket by a toddler, or a hand-raise by a school-age child.

Physiologic tests are used for children who cannot be tested behaviorally due to young age, developmental delay, or other medical conditions. There are two standard types of physiologic tests:

• In the otoacoustic emissions (OAE) test, a small microphone is placed in the child’s ear. The microphone, which is connected to a computer, delivers clicking sounds into the ear and records the cochlea’s response to sound.
  
• In the auditory brainstem response (ABR) test, clicking sounds are presented to the ear through small earphones and electrodes are placed on the child’s head. These electrodes are connected to a computer that measures and averages the activity of the auditory nerve and brain in response to sound.

A: Example of a tympanogram with a “peaked” pattern in a child with a normal eardrum and middle ear.  E: example of a “flat” tympanogram in a child with an ear infection.

Tympanometry is not a hearing test but a procedure that demonstrate how well the eardrum moves when air pressure is introduced into the ear canal. It is often performed in conjunction with the behavioral or physiologic tests described above. A “flat” line on a tympanogram suggests that the eardrum is not mobile, while a “peaked” pattern often represents normal eardrum mobility. Tympanometry is useful for identifying middle ear problems, such as fluid or infection behind the eardrum. However, an otoscopic examination of the eardrum should always be performed along with tympanometry.

How is hearing loss treated?

Surgery may be recommended if a child has a conductive hearing loss caused by chronic ear infections or malformation of the outer or middle ear.

Photograph of a behind the ear hearing aid.

An amplification device called an FM system may be recommended for use in school for some children with hearing loss. They are used in the classroom in order to improve hearing in large groups or noisy environments. The FM system can broadcasts a teacher’s voice directly to the child with hearing loss. The speaker wears a compact transmitter and microphone while the child wears a portable receiver and earphones to hear more effectively even from the back of the room.

Cochlear Implants

Some children with severe to profound hearing loss may not be able to hear enough sound to make speech audible, even with a hearing aid. These children may be candidates for cochlear implantation. The cochlear implant is a device that replaces the task of the damaged hair cells in the cochlea by working directly with the auditory nerve. A tiny electrode is surgically inserted into the cochlea and via electrical signals stimulates the nerve endings in the cochlea. More information about the Cochlear Implant Program >>

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