Cochlear Implants

Definition
Purpose
Description
Aftercare
Risks
Normal results

Definition

A cochlear implant is a small, complex electronic device used to treat severe to profound hearing loss. It is surgically implanted underneath the skin behind the patient’s ear.

Purpose

A cochlear implant delivers useful auditory signals from the environment to the patient by electronically bypassing nonfunctional parts of the ear and directly stimulating the auditory nerve. Unlike a hearing aid, it does not merely amplify sound. Instead, an implant increases the amount of nervous response to sound. Although it does not restore normal hearing, the additional input provided by the implant often improves sound detection and increases speech understanding.

Description

Normal hearing occurs because sound travels from the outer ear into the ear canal and vibrates the eardrum. The vibration is carried through the middle ear by three small bones attached to the eardrum and on to a fluid-filled part of the inner ear called the cochlea. Movement in the cochlear fluid is transferred to hair fibers within the cochlea. The movement of these hair cells stimulates nerve cells called ganglion cells, which send an electrical current to the auditory nerve. In turn, the nerve carries the current to the brain, where the electrical stimulation is recognized as sound.

A common cause of hearing loss is damage to the hair cells within the cochlea. This kind of deafness, called sensorineural deafness, can often be treated with cochlear implants. This is particularly true if damage to the hair cells is not accompanied by damage to the auditory nerve itself. It has been estimated that more than 100,000 individuals have received cochlear implants.

Cochlear implants consist of internal and external parts. The external parts include a microphone, a speech processor, and a transmitter. The internal parts include a receiver-stimulator and an electrode. Some models include a small headpiece that is worn just behind the ear and contains all the external parts, while other models also use body-worn modules that are placed in a shoulder pouch, in a pocket, or worn on a belt. The convenience of the all-in-one headpiece is balanced by shorter life for the batteries used in the smaller units, although systems using rechargeable batteries do solve some of these issues.

Within the headpiece, the microphone picks up sound in the environment. The speech processor converts these sounds into a digital signal. The content of the generated digital signal is determined by the programming of the processor and is complex. It includes information about the pitch, loudness, and timing of sound signals, and attempts to filter out extraneous noise. The transmitter converts the digital signals into FM radio signals and sends them through the skin to the internal parts of the implant. The transmitter and

KEY TERMS

Auditory nerve— The nerve that carries electrical signals from the cochlea to the brain.

Cochlea— The hearing part of the inner ear. This snail-shaped structure contains fluid and thousands of microscopic hair cells tuned to various frequencies.

Hair cells— Sensory receptors in the inner ear that transform sound vibrations into messages that travel to the brain.

Inner ear— The interior section of the ear, where sound vibrations and information about balance are translated into nerve impulses.

Middle ear— The small cavity between the eardrum and the oval window that houses the three tiny bones of hearing.

Sensorineural deafness— Hearing loss due to the inability to convert sound from vibration to electrical signals. Often involves defects in the function of cochlear hair cells.

the internal parts are kept in correct alignment by using magnets present in both the internal and external parts of the device.

The internal parts are those that are surgically implanted into the patient. The receiver-stimulator is disk-shaped and is about the size of a quarter. It receives the digital signals from the transmitter and converts them into electrical signals. A wire connects the receiver to a group of electrodes that are threaded into the cochlea when the implant is placed. As many as 24 electrodes, depending on the type of the implant, stimulate the ganglion cells in the cochlea. These cells transmit the signals to the brain through the auditory nerve. The brain then interprets the signals as sound.

The sounds heard through an implant are different from the normal hearing sounds and have been described as artificial or robot-like. This is because the implant’s handful of electrodes cannot hope to match the complexity of a person’s 15,000 hair cells. However, as more electrodes are added, electrode placement issues are solved, and the software for the implant speech processor takes into account more and more aspects of sound, the perceived results are moving closer to how speech and other sounds are naturally perceived.

Despite the benefits that the implant appears to offer, some hearing specialists and members of the deaf community believe that the benefits may not outweigh the risks and limitations of the device. Because the device must be surgically implanted, it carries some surgical risk. Manufacturers cannot promise how well a person will hear with an implant. Moreover, after getting an implant, some people say they feel alienated from the deaf community, while at the same time not feeling fully a part of the hearing world. The decision to undergo cochlear implant surgery is a complex one, and a person should take into account the risks and realistic rewards of the device.

Surgical procedure

The procedure can be preformed on an outpatient basis for adult and adolescent patients. With children, it is often performed with a one-night stay in the hospital.

The internal parts of the implant are placed under the skin behind the patient’s ear. The area is shaved, although newer procedures allow for sterilization of the hair in the area so less shaving has to occur. Once the sterile field is established, the surgeon makes an 2–3 in (5-7.6 cm) incision behind the ear and opens the mastoid bone (the ridge on the skull behind the ear) leading into the middle ear. A depression is made in the bone next to the opening to allow the receiver-stimulator to sit flush with the skull surface. After seating, the receiver-stimulator is held in place with a long-lasting suture.

The surgeon then goes through the opening in the mastoid bone to create a new opening in the cochlea for the implant electrodes. The electrode is then very slowly and carefully threaded through this new opening. The electrode structure itself is designed to align the electrodes as closely as possible to the ganglion cells, as this allows the electrical signals that function to be less powerful. Once in place, the device is tested to be certain it is working. If all is well, the surgeon then closes up the incision with absorbable sutures, so the area does not need to be revisited to remove the stitches.

The entire operation takes between one and two hours, although the procedure is more complex for younger patients due to the smaller size of their middle ear structures and tends to take longer.

Aftercare

For a short period of time after the surgery, a special bandage is worn on the head during sleep. After about one month, the surgical wounds heal. The patient then returns to the implant clinic to be fitted with the external parts of the device and to have

WHO PERFORMS THE PROCEDURE AND WHERE IS IT PERFORMED?

Cochlear implants are inserted during a surgery performed by a specialist in otolaryngology (ear, nose, and throat medicine). The surgery is performed in a larger hospital, usually on an outpatient basis, but sometimes with an overnight hospital stay.

it turned on and mapped. Mapping involves fine tuning the speech processor and setting levels of stimulation for each electrode, from soft to loud.

The patient is then trained in how to interpret the sounds heard through the device. The length of the training varies from days to years, depending on how well the person can interpret the sounds heard through the device.

Risks

As with all operations, there are risks with this surgery, including:

• infection at the incision site
• bleeding
• complications related to anesthesia
• transient dizziness
• facial paralysis (rarely)
• temporary taste disturbances
• additional hearing loss
• device failure

However, it should be noted that serious surgical complications have been observed in only one in 10,000 procedures of this type.

Some long-term risks of the implant include the unknown effects of electrical stimulation on the nervous system. It is also possible to damage the implant’s internal components by a blow to the head, which will render the device unworkable.

A further consideration is that the use of magnetic resonance imaging (MRI) for patients with cochlear implants is not recommended because of the magnets present in the devices. Several companies have developed implants that do not use magnets, or have altered the receiver-stimulator to make it easier to remove the magnets before testing. One fact that reduces the concern about MRI testing is that for many medical indications, MRI can be replaced with a computer assisted

QUESTIONS TO ASK THE DOCTOR

• How “normal” will the implant make the patient’s hearing?
• What kind of training does the patient undergo to learn how to use the device?
• How does the patient care for the device?

tomography (CAT, CT) scan, which is not a problem for persons with cochlear implants.

Additionally, in July 2002, the Food and Drug Administration (FDA) issued a warning about a possible connection between increased incidence of meningitis and the presence of a cochlear implant. This warning included special vaccine recommendations for those with implants, as well as the voluntary removal from the market of certain devices. Specifically, those implants that included a positioner to hold the electrodes in place in the cochlea appear to be associated with an increased risk of the disease.

Normal results

Most profoundly deaf patients who receive an implant are able to discern medium and loud sounds, including speech, at comfortable listening levels. Many use sound clues from the implant, together with speech reading and other facial cues, to achieve understanding. Almost all adults improve their communication skills when combining the implant with speech reading (lip reading), and some can understand spoken words without speech reading. More than half of adults who lost hearing after they learned to speak can understand some speech without speech reading. Especially with the use of accessory devices, the great majority can utilize the telephone with their implants.

Children who were born deaf or who lost their hearing before they could speak have the most difficulty in learning to use the implant. Research suggests, however, that most of these children are able to learn spoken language and understand speech using the implant. In general, the earlier the implant occurs, the greater the chance of the implant providing sufficient sound input to provide speech understanding. As with the use of the telephone in adults, accessory devices such as special microphones often help the function of the implant in classroom settings.

Resources

BOOKS

Cummings, C. W., et al. Otolayrngology: Head and Neck Surgery. 4th ed. St. Louis: Mosby, 2005.

Niparko, John K., ed. Cochlear Implants: Principles and Practices. Philadelphia: Lippincott, Williams & Wilkins, 2000.

PERIODICALS

Roland, J. T. Jr., et al. “Revision cochlear implantation.” Otolaryngol Clin North Am 39, no. 4 (August 1, 2006): 833–839.

ORGANIZATIONS

Alexander Graham Bell Association for the Deaf. 3417 Volta Place NW, Washington, DC 20007. (202) 337-5220. http://www.agbell.org (accessed March 11, 2008).

The UCSF Cochlear Implant Center. http://cochlearimplant.ucsf.edu/page.asp?bodyid=resources (accessed March 11, 2008

Hearing Loss Link. 2600 W. Peterson Ave., Ste. 202, Chicago, IL 60659. (312) 743-1032, (312) 743-1007 (TDD).

National Association for the Deaf. 814 Thayer Ave., Silver Spring, MD 20910. (301) 587-1788, (301) 587-1789 (TDD). http://www.nad.org (accessed March 11, 2008).

OTHER

Cochlear Implant Recipients may be at Greater Risk for Meningitis. FDA Public Health Web Notification. October 17, 2002 [cited February 23, 2003]. http://www.fda.gov/cdrh/safety/cochlear.html (accessed March 11, 2008).

Carol A. Turkington

Michelle L. Johnson

Rosalyn Carson-DeWitt, MD

Colectomy seeBowel resection; Bowel resection, small intestine

Cochlear implants

Definition

A cochlear implant is a small, complex electronic device used to treat severe to profound hearing loss. It is surgically implanted underneath the skin behind the patient's ear.

Purpose

A cochlear implant delivers useful auditory signals from the environment to the patient by electronically bypassing nonfunctional parts of the ear and directly stimulating the auditory nerve. Unlike a hearing aid, it does not merely amplify sound. Instead, an implant increases the amount of nervous response to sound. Although it does not restore normal hearing, the additional input provided by the implant often improves sound detection and increases speech understanding.

Description

Normal hearing occurs because sound travels from the outer ear into the ear canal and vibrates the eardrum. The vibration is carried through the middle ear by three small bones attached to the eardrum and on to a fluid-filled part of the inner ear called the cochlea. Movement in the cochlear fluid is transferred to hair fibers within the cochlea. The movement of these hair cells stimulates nerve cells called ganglion cells that send an electrical current to the auditory nerve. In turn, the nerve carries the current to the brain, where the electrical stimulation is recognized as sound.

A common cause of hearing loss is damage to the hair cells within the cochlea. This kind of deafness, called sensorineural deafness, can often be treated with cochlear implants. This is particularly true if damage to the hair cells is not accompanied by damage to the auditory nerve itself. As of 2002, it is estimated that over 35,000 individuals have received cochlear implants.

Cochlear implants consist of internal and external parts. The external parts include a microphone, a speech processor, and a transmitter. The internal parts include a receiver-stimulator and an electrode. Some models include a small headpiece that is worn just behind the ear and contains all the external parts while other models also use body-worn modules that are placed in a shoulder pouch, in a pocket, or worn on a belt. The convenience of the all-in-one headpiece is balanced by shorter life for the batteries used in the smaller units, although systems using rechargeable batteries do solve some of these issues.

Within the headpiece, the microphone picks up sound in the environment. The speech processor converts these sounds into a digital signal. The content of the generated digital signal is determined by the programming of the processor and is complex. It includes information about the pitch, loudness, and timing of sound signals and attempts to filter out extraneous noise. The transmitter converts the digital signals into FM radio signals and sends them through the skin to the internal parts of the implant. The transmitter and the internal parts are kept in correct alignment by using magnets present in both the internal and external parts of the device.

The internal parts are those that are surgically implanted into the patient. The receiver-stimulator is disk-shaped and is about the size of a quarter. It receives the digital signals from the transmitter and converts them into electrical signals. A wire connects the receiver to a group of electrodes that are threaded into the cochlea when the implant is placed. As many as 24 electrodes, depending on the type of the implant, stimulate the ganglion cells in the cochlea. These cells transmit the signals to the brain through the auditory nerve. The brain then interprets the signals as sound.

The sounds heard through an implant are different from the normal hearing sounds and have been described as artificial or robot-like. This is because the implant's handful of electrodes cannot hope to match the complexity of a person's 15,000 hair cells. However, as more electrodes are added, electrode placement issues are solved, and the software for the implant speech processor takes into account more and more aspects of sound, the perceived results are moving closer to how speech and other sounds are naturally perceived.

Despite the benefits that the implant appears to offer, some hearing specialists and members of the deaf community believe that the benefits may not outweigh the risks and limitations of the device. Because the device must be surgically implanted, it carries some surgical risk. Manufacturers can not promise how well a person will hear with an implant. Moreover, after getting an implant, some people say they feel alienated from the deaf community, while at the same time not feeling fully a part of the hearing world. The decision to undergo cochlear implant surgery is a complex one and a person should take into account the risks and realistic rewards of the device.

Surgical procedure

The procedure can be preformed on an outpatient basis for adult and adolescent patients. With children, it is often performed with a one-night stay in the hospital.

The internal parts of the implant are placed under the skin behind the patient's ear. The area is shaved, although newer procedures allow for sterilization of the hair in the area so less shaving has to occur. Once the sterile field is established, the surgeon makes an 2–3 in (5–7.6 cm) incision behind the ear and opens the mastoid bone (the ridge on the skull behind the ear) leading into the middle ear. A depression is made in the bone next to the opening to allow the receiver-stimulator to sit flush with the skull surface. After seating, the receiver-stimulator is held in place with a long-lasting suture.

The surgeon then goes through the opening in the mastoid bone to create a new opening in the cochlea for the implant electrodes. The electrode is then very slowly and careful threaded through this new opening. Care is taken during the procedure, and the electrode structure itself is designed to align the electrodes as closely as possible to the ganglion cells, as this allows the electrical signals that function to be less powerful. Once in place, the device is tested to be certain it is working. If all is well, the surgeon then closes up the incision with absorbable sutures, so the area does not need to be revisited to remove the stitches.

The entire operation takes between one and two hours, although the procedure is more complex for younger patients due to the smaller size of their middle ear structures and tends to take longer.

Aftercare

For a short period of time after the surgery, a special bandage is worn on the head during sleep. After about one month, the surgical wounds are healed and the patient returns to the implant clinic to be fitted with the external parts of the device and to have the device turned on and mapped. Mapping involves fine tuning the speech processor and setting levels of stimulation for each electrode, from soft to loud.

The patient is then trained in how to interpret the sounds heard through the device. The length of the training varies from days to years, depending on how well the person can interpret the sounds heard through the device.

Risks

As with all operations, there are risks with this surgery. These include:

• infection at the incision site
• bleeding
• complications related to anesthesia
• transient dizziness
• facial paralysis (rarely)
• temporary taste disturbances
• additional hearing loss
• device failure

However, it should be noted that serious surgical complications have been observed at only one in 10,000 procedures of this type.

Some long-term risks of the implant include the unknown effects of electrical stimulation on the nervous system. It is also possible to damage the implant's internal components by a blow to the head, which will render the device unworkable.

A further consideration is that the use of magnetic resonance imaging (MRI) for patients with cochlear implants is not recommended because of the magnets present in the devices. Several companies have developed implants that do not use magnets or have altered the receiver-stimulator make up to make it easier to remove the magnets before testing. One fact that reduces the concern about MRI testing is that for many medical indications, MRI can be replaced with a computer assisted tomography scan (CAT or CT scan), which is not a problem for persons with cochlear implants.

Additionally, in July 2002, the Food and Drug Administration (FDA) issued a warning about a possible connection between increased incidence of meningitis and the presence of a cochlear implant. This warning included special vaccine recommendations for those with implants, as well as the voluntary removal from the market of certain devices. Specifically, those implants that included a positioner to hold the electrodes in place in the cochlea appear to be associated with an increased risk of the disease.

Normal results

Most profoundly deaf patients who receive an implant are able to discern medium and loud sounds, including speech, at comfortable listening levels. Many use sound clues from the implant, together with speech reading and other facial cues, to achieve understanding. Almost all adults improve their communication skills when combining the implant with speech reading (lip reading), and some can understand spoken words without speech reading. More than half of adults who lost hearing after they learned to speak can understand some speech without speech reading. Especially with the use of accessory devices, the great majority can utilize the telephone with their implants.

Children who were born deaf or who lost their hearing before they could speak have the most difficulty in learning to use the implant. Research suggests, however, that most of these children are able to learn spoken language and understand speech using the implant. In general, the earlier the implant occurs the greater the chance of the implant providing sufficient sound input to provide speech understanding. As with the use of the telephone in adults, accessory devices such as special microphones often help the function of the implant in classroom settings.

Resources

books

Christiansen, John B. and Irene W. Leigh. Cochlear Implants in Children: Ethics and Choices. Washington, DC: Galladet University Press, 2002.

Niparko, John K., ed. Cochlear Implants: Principles and Practices. Philadelphia: Lippincott, Williams & Wilkins, 2000.

periodicals

Cheng, Andre K., et al. "Cost-Utility Analysis of the Cochlear Implant in Children." Journal of the American Medical Association 284, no. 7 (August 16, 2000): 850–856.

"The Earlier the Implant, the Greater the Benefit." The Hearing Journal (February 2001).

Mraz, Stephen J. "Breaking the Wall of Silence." Machine Design (December 9, 1999).

organizations

Alexander Graham Bell Association for the Deaf. 3417 Volta Place NW, Washington, DC 20007. (202) 337-5220. <http://www.agbell.org>.

Cochlear Implant Club International. 5335 Wisconsin Ave. NW, Suite 440, Washington, D.C. 20015-2052. (202) 895-2781. <http://www.cici.org>.

Hearing Loss Link. 2600 W. Peterson Ave., Ste. 202, Chicago, IL 60659. (312) 743-1032, (312) 743-1007 (TDD).

National Association for the Deaf. 814 Thayer Ave., Silver Spring, MD 20910. (301) 587-1788, (301) 587-1789 (TDD). <http://www.nad.org>.

other

Cochlear Implant Recipients may be at Greater Risk for Meningitis. FDA Public Health Web Notification. October 17, 2002 [cited February 23, 2003]. <http://www.fda.gov/cdrh/safety/cochlear.html>.

Carol A. Turkington Michelle L. Johnson

WHO PERFORMS THE PROCEDURE AND WHERE IS IT PERFORMED?

Cochlear implants are inserted during a surgery performed by a specialist in otolaryngology (ear, nose, and throat medicine). The surgery is performed in a larger hospital, usually as on an outpatient basis, but sometimes with an overnight hospital stay.

QUESTIONS TO ASK THE DOCTOR

• How "normal" will the implant make my/my child's hearing?
• What kind of training does the patient undergo to learn how to use the device?
• How do I care for the device?

Cochlear Implants

Definition

A cochlear implant is a surgical treatment for hearing loss that works like an artificial human cochlea in the inner ear, helping to send sound from the ear to the brain. It is different from a hearing aid, which simply amplifies sound.

Purpose

A cochlear implant bypasses damaged hair cells and helps establish some degree of hearing by stimulating the hearing (auditory) nerve directly.

Precautions

Because the implants are controversial, very expensive, and have uncertain results, the U.S. Food and Drug Administration (FDA) has limited the implants to people:

• who get no significant benefit from hearing aids
• who are at least two years old (the age at which specialists can verify severity of deafness)
• with severe to profound hearing loss

Description

Hearing loss is caused by a number of different problems that occur either in the hearing nerve or parts of the middle or inner ear. The most common type of deafness is caused by damaged hair cells in the cochlea, the hearing part of the inner ear. Normally, hair cells stimulate the hearing nerve, which transmits sound signals to the brain. When hair cells stop functioning, the hearing nerve remains unstimulated, and the person cannot hear. Hair cells can be destroyed by many things, including infection, trauma, loud noise, aging, or birth defects.

All cochlear implants consist of a microphone worn behind the ear that picks up sound and sends it along a wire to a speech processor, which is worn in a small shoulder pouch, pocket, or belt. The processor boosts the sound, filters out background noise, and turns sound into digital signals before sending it to a transmitter worn behind the ear. A magnet holds the transmitter in place through its attraction to the receiver-stimulator, a part of the device that is surgically attached beneath the skin in the skull. The receiver picks up digital signs forwarded by the transmitter, and converts them into electrical impulses. These electrical impulses flow through electrodes contained in a narrow, flexible tube that has been threaded into the cochlea.

As many as 24 electrodes (depending on the type of implant) carry the impulses that stimulate the hearing nerve. The brain then interprets the signals as specific sounds.

Despite the benefits that the implant appears to offer, some hearing specialists and members of the deaf community still believe that the benefits may not outweigh the risks and limitations of the device. Because the device must be surgically implanted, it carries some surgical risk. Also, manufacturers cannot promise how well a person will hear with an implant. Moreover, after getting an implant, some people say they feel alienated from the deaf community, while at the same time not feeling fully a part of the hearing world.

The sounds heard through an implant are different from the normal hearing sounds, and have been described as artificial or "robotlike." This is because the implant's handful of electrodes cannot hope to match the complexity of a person's 15,000 hair cells.

Surgical procedure

During the procedure, the surgeon makes an incision behind the ear and opens the mastoid bone (the ridge on the skull behind the ear) leading into the middle ear. The surgeon then places the receiver-stimulator in the bone, and gently threads the electrodes into the cochlea. This operation takes between one and one-half to five hours.

Preparation

Before a person gets an implant, specialists at an implant clinic conduct a careful evaluation, including extensive hearing tests to determine how well the candidate can hear.

Unfortunately, it is not possible to predict who will benefit from an implant. In general, the later in life a person becomes deaf, and the shorter the duration of deafness, the better the person is likely to understand speech with an implant. Likewise, someone with a healthy hearing nerve will do better than someone with a damaged nerve.

First, candidates undergo a trial with a powerful hearing aid. If the aid cannot improve hearing enough, a physician then performs a physical exam and orders a scan of the inner ear (some patients with a scarred cochlea are not good candidates). A doctor may also order a psychological exam to better understand the person's expectations. Patients need to be highly motivated, and have a realistic understanding of what an implant can and cannot do.

Aftercare

The patient remains in the hospital for a day or two after the surgery. After a month, the surgical wounds will have healed and the patient returns to the implant clinic to be fitted with the external parts of the device (the speech processor, microphone, and transmitter). A clinicican tunes the speech processor and sets levels of stimulation for each electrode, from soft to loud.

The patient is then trained in how to interpret the sounds heard through the device. The length of the training varies from days to years, depending on how well the person can interpret the sounds heard through the device.

Risks

As with all operations, there are a few risks of surgery. These include:

• dizziness
• facial paralysis (rarely)
• infection at the incision site

Scientists are not sure about the long-term effects of electrical stimulation on the nervous system. It is also possible to damage the implant's internal components by a blow to the head, which will render the device unworkable.

Normal results

Most profoundly, deaf patients who receive an implant are able to discern medium and loud sounds, including speech, at comfortable listening levels. Many use sound clues from the implant, together with speech reading and other facial cues. Almost all adults improve their communication skills when combining the implant with speech reading (lip reading), and some can understand spoken words without speech reading. More than half of adults who lost hearing after they learned to speak can understand some speech without speech reading. About 30% can understand spoken sounds well enough to use the phone.

Children who were born deaf or who lost their hearing before they could speak have the most difficulty in learning to use the implant. Research suggests, however, that most of these children are able to learn spoken language and understand speech using the implant.

KEY TERMS

Cochlea— The hearing part of the inner ear. This snail-shaped structure contains fluid and thousands of microscopic hair cells tuned to various frequencies.

Hair cells— Sensory receptors in the inner ear that transform sound vibrations into messages that travel to the brain.

Inner ear— The interior section of the ear, where sound vibrations and information about balance are translated into nerve impulses.

Middle ear— The small cavity between the eardrum and the oval window that houses the three tiny bones of hearing.

Resources

ORGANIZATIONS

Alexander Graham Bell Association for the Deaf. 3417 Volta Place NW, Washington, DC 20007. (202) 337-5220. 〈http://www.agbell.org〉.

American Speech-Language-Hearing Association. 10801 Rockville Pike, Rockville, MD 20852. (800) 638-8255. 〈http://www.asha.org〉.

Cochlear Implant Club International. 5335 Wisconsin Ave. NW, Suite 440, Washington, DC 20015-2052. (202) 895-2781. 〈http://www.cici.org〉.

Hearing Loss Link. 2600 W. Peterson Ave., Ste. 202, Chicago, IL 60659. (312) 743-1032, (312) 743-1007 (TDD).

National Association for the Deaf. 814 Thayer Ave., Silver Spring, MD 20910. (301) 587-1788, (301) 587-1789 (TDD). 〈http://www.nad.org〉.

Cochlear implants

Definition

A cochlear implant is a surgical treatment for hearing loss that works like an artificial human cochlea in the inner ear, helping to send sound from the ear to the brain. It is different from a hearing aid, which simply amplifies sound.

Purpose

A cochlear implant bypasses damaged hair cells in the child's cochlea and helps establish some degree of hearing by stimulating the hearing (auditory) nerve directly.

Description

Hearing loss is caused by a number of different problems that occur either in the auditory nerve or in parts of the middle or inner ear. The most common type of deafness is caused by damaged hair cells in the cochlea. The cochlea is a fluid-filled canal in the inner ear that is shaped like a snail shell. Inside are thousands of tiny hairs called cilia. As sound vibrates the fluid in the cochlea, the cilia move. This movement stimulates the auditory nerve and sends messages about sound to the brain. When these hair cells stop functioning, the auditory nerve is not stimulated, and the child cannot hear. Hair cells can be destroyed by many things, including infection, trauma, loud noise, aging, and birth defects.

The first piece of a cochlear implant is the microphone. It is usually worn behind the ear, and it picks up sound and sends it along a wire to a speech processor. The speech processor is usually worn in a small shoulder pouch, pocket, or on a belt. The processor boosts the sound, filters out background noise, and turns the sound into digital signals. Then it sends these digital signals to a transmitter worn behind the ear. A magnet holds the transmitter in place through its attraction to the receiver-stimulator, a part of the device that is surgically attached beneath the skin in the skull. The receiver picks up digital information forwarded by the transmitter and converts it into electrical impulses. These electrical impulses flow through electrodes contained in a narrow, flexible tube that has been threaded into the cochlea during surgery and stimulate the auditory nerve. The auditory nerve carries the electrical impulses to the brain, which interprets them as sound.

Despite the benefits that the implant appears to offer, some hearing specialists and members of the deaf community still believe that the benefits may not outweigh the risks and limitations of the device. Because the device must be surgically implanted, it carries some surgical risk. Also, it is impossible to be certain how well any individual child will respond to the implant. After getting an implant, some people say they feel alienated from the deaf community, while at the same time not feeling fully a part of the hearing world.

The sounds heard through an implant are different from those sounds heard normally, and have been described as artificial or "robot-like." This is because the implant's limited number of electrodes cannot hope to match the complexity of a human's 15,000 hair cells. Cochlear implants are, however, becoming more advanced and providing even better sound resolution.

Surgical procedure

During the procedure, the surgeon makes an incision behind the ear and opens the mastoid bone (the ridge on the skull behind the ear) leading into the middle ear. The surgeon then places the receiver-stimulator into a well made in the bone and gently threads the electrodes into the cochlea. This operation takes between an hour-and-a-half and five hours. It is performed using general anesthesia.

Precautions

Because the implants are controversial, very expensive, and have uncertain results, the United States Food and Drug Administration (FDA) has limited the implants to people for whom the following is true:

• individuals who get no significant benefit from hearing aids
• individuals who are at least 12 months old
• individuals with severe to profound hearing loss

Preparation

Before a child gets an implant, specialists at an implant clinic conduct a careful evaluation, including extensive hearing tests to determine how well the child can hear.

First, candidates undergo a trial with a powerful hearing aid. If the hearing aid cannot improve hearing enough, a physician then performs a physical examination and orders a scan of the inner ear, because some patients with a scarred cochlea are not good candidates for cochlear implants. A doctor may also order a psychological exam to better understand the person's expectations. Patients and their families need to be highly motivated and have a realistic understanding of what an implant can and cannot do.

Aftercare

The child may remain in the hospital for a day or two after the surgery, although with improving technology and techniques some children may go home the same day. After about a month, the surgical wounds will have healed, and the child returns to the implant clinic to be fitted with the external parts of the device (the speech processor, microphone, and transmitter). A clinician tunes the speech processor and sets levels of stimulation for each electrode from soft to loud.

The child is then trained in how to interpret the sounds heard through the device. The length of the training varies from days to years, depending on how well the child can interpret the sounds heard. With the new approval for using cochlear implants in children as young as 12 months of age, the toddler may not be trained specifically to interpret the sounds in the same way an older child would. The specific therapy that is recommended is highly dependent on the age of the child.

Risks

As with all operations, there are a few risks of surgery. These include the following:

• dizziness
• facial paralysis (which is rare and usually temporary)
• infection at the incision site

Scientists are not sure about the long-term effects of electrical stimulation on the nervous system. It is also possible that the implant's internal components may be damaged by a blow to the head. This may cause the device to stop working. In general the failure rate of the implants is only 1 percent after one year.

Parental concerns

There is increasing debate about the use of cochlear implants in infants. This is considered by some to be desirable because, if the implantation is done before a child has begun to significantly acquire language, there is some evidence that the child may be able to develop at a pace similar to hearing children of the same age. Making a decision about whether or not a child, especially a very young one, should have a cochlear implant can be very difficult. The child's doctor may be able to provide parents with resources or put them in contact with other parents who have had to make the same decision whom they can consult.

KEY TERMS

Cochlea —The hearing part of the inner ear. This snail-shaped structure contains fluid and thousands of microscopic hair cells tuned to various frequencies, in addition to the organ of Corti (the receptor for hearing).

Hair cells —Sensory receptors in the inner ear that transform sound vibrations into messages that travel to the brain.

Inner ear —The interior section of the ear, where sound vibrations and information about balance are translated into nerve impulses.

Middle ear —The cavity or space between the eardrum and the inner ear. It includes the eardrum, the three little bones (hammer, anvil, and stirrup) that transmit sound to the inner ear, and the eustachian tube, which connects the inner ear to the nasopharynx (the back of the nose).

See also Hearing impairment.

Resources

BOOKS

Christiansen, John B., and Irene W. Leigh. Cochlear Implants in Children: Ethics and Choices. Washington DC: Gallaudet University Press, 2002.

Chute, Patrician M., and Mary Ellen Nevins. The Parents' Guide to Cochlear Implants. Washington DC: Gallaudet University Press. 2002.

PERIODICALS

Barker, Brittan A., and Bruce J. Tomblin. "Bimodal Speech Perception in Infant Hearing Aid and Cochlear Implant Users." Archives of Otolaryngology—Head & Neck Surgery 130 (May 2004): 582–87.

Chin, Steven B. "Children's Consonant Inventories after Extended Cochlear Implant Use." Journal of Speech, Language, and Hearing Research 46 (August 2003): 849–63.

Conor, Carol McDonald, and Teresa A. Zwolan. "Examining Multiple Sources of Influence on the Reading Comprehension Skills of Children Who Use Cochlear Implants." Journal of Speech, Language, and Hearing Research 47 (June 2004): 509–27.

ORGANIZATIONS

American Society for Deaf Children. PO Box 3355 Gettysburg, PA 17325. Web site: <www.deafchildren.org>.

Tish Davidson, A.M. Carol A. Turkington