When Roberto’s parents learned that he was born deaf, they knew that they had much to learn about the best way to raise their son. In the end, they decided to follow their county school system’s advice: use hearing aids along with signed language. But when Roberto was eight and couldn’t read, speak, or communicate well with sign language, they decided to check with a local cochlear implant team. Roberto’s parents found that it was too late to receive normal benefit with a cochlear implant. In order to hear and speak normally, he would have needed to be implanted by one to two years of age. Now Roberto was stuck in the middle; he was considered an outsider by the Deaf kids and would never catch up with the hearing or cochlear implant kids. Talk about angry parents . . .
Cochlear implants (CI) are computer-based devices that provide hearing to children and adults with nerve deafness. By changing sound waves into tiny electrical signals that stimulate the sense of hearing in the brain cochlear implants replace the function of the cochlea.
How Cochlear Implants Work
In people with normal hearing, the hair cells of the cochlea convert sound waves to electrical/nerve signals that travel the auditory nerves to the brain. But in people who have moderate to profound nerve deafness, many or most hair cells don’t work, and the hearing process is blocked. Cochlear implants bypass the hair cells. The electrical signals are delivered directly to the auditory nerves.
Figure 9.1
Hearing aids make sound waves louder and send them to the hair cells in the cochlea. Cochlear implants turn sound waves into electrical signals and send them on the nerve path to the brain, bypassing hair cells.
How Does It Differ from a Hearing Aid?
Hearing aids make sounds louder but if the hair cells are not working (as in nerve deafness) no matter how loud speech is, it cannot be understood. In that case, cochlear implants are recommended because a cochlear implant does not stimulate using sound, just tiny electrical signals.
If a person has enough remaining hair cells to hear adequately with a hearing aid, then a hearing aid is recommended. If not, then a cochlear implant is indicated. It is usually necessary to try a high-power hearing aid for a period of months to see if it can deliver speech understanding before considering a cochlear implant.
Inner and Outer Components
There are two parts of a cochlear implant. The outer part looks somewhat like a hearing aid and is completely removable. The inner part is implanted entirely under the scalp. The two parts communicate through radio frequency waves. Experimental use of cochlear implants that are completely implanted (have no outside part) have so far produced inadequate performance.
External part of the cochlear implant. The external part of a CI contains a microphone, speech processor, antenna, and battery. The microphone changes sound waves to electrical signals. The speech processor (a tiny, programmable computer), processes the electrical waves into signals that are coded for speech understanding.
Both power and the coded signals for hearing are transmitted by radio frequency waves from the external antenna to a matching internal antenna. The two antennas are held in place by a magnet that will last for more than a lifetime. Some external devices are waterproof to allow users to hear while swimming or playing in a pool. Other external devices are not waterproof and must be removed and placed in plastic bags to protect them when used near water.
Internal part of the cochlear implant. The internal part of the CI consists of the antenna, internal microprocessor, a magnet to hold the external antenna in position, and the delicate electrode array that is placed into the cochlea. The internal microprocessor receives radio frequency signals and sends them on to the electrodes. They are placed under the scalp just above and behind the outer ear. There are no internal batteries; power is transmitted from the outside.
Figure 9.2
This is an image of the right ear as if the head were facing toward you. The external part of the cochlear implant looks like a hearing aid with a trans- mitting antenna seen overlying the receiving implant that is seen just under the scalp. Just under the intact scalp, the inner part of the implant is seen with the electrode passing through the middle ear into the cochlea.
Candidates for Cochlear Implantation
About 400,000 people have received cochlear implants worldwide, including more than 200,000 Americans. But cochlear implantation is not for everyone. Many people have too much hearing left to qualify and others prefer to live without hearing. Still others may have anatomical or general health conditions that prevent implantation. Communication through signed language (American Sign Language in the United States) is an important alternative to hearing and speaking with a cochlear implant.
The decision to undergo cochlear implantation is made by the patient or family and the cochlear implant surgeon. The surgeon receives input from a team of professionals including audiologists, radiologists, language therapists, psychologists, and others. The family may also receive input from family, friends, other patients, or parents of children who have received implants, and members of the Deaf community.
The cochlear implant team considers type and degree of hearing loss, duration of hearing loss, age of the patient, success or failure of a hearing aid trial, anatomy, health conditions, and commitment to aural communication. Their recommendation is meant to serve the best interest of the patient.
Children
The Food and Drug Administration (FDA) recommends implanting a CI in children born deaf no earlier than twelve months of age. In clinical practice, however, implantation is often performed as early as six months of age. Earlier implantation takes advantage of this important period in a baby’s life when he or she normally develops language. Your CI surgeon will consider the child’s general health and size when making a recommendation as to the age at which to have the surgery.
In children who are born deaf, implantation after the age of eighteen months results in poorer outcomes in terms of hearing, comprehending language and music, and speaking. After the age of five years, implants may fail to provide hearing that is adequate for spoken language. However, in children who had hearing at birth and lost it later in childhood, implantation anytime in childhood can be very effective.
Adults and Adolescents
Most adult candidates for CI have had hearing and language prior to being deafened. This is called post-lingual deafness, and results are generally good. However, if an adult has been severely to profoundly deaf from birth and has communicated primarily in manual (signed) language, the success rate for implantation is lower. This may be because the language areas (temporal and frontal lobes) of the brain may be taken over by visual areas in congenitally deaf signers.
There is no upper age limit on the use of cochlear implants. Many people now lead active vigorous lives into their eighth and ninth decades. Loss of hearing in older adults is associated with social isolation, psychological involution, and dementia. Cochlear implantation is routinely performed for healthy people in their eighties and occasionally in people who are older than ninety. Being able to speak with family members by telephone and to communicate with friends and workers at care facilities is important at this stage of life.
Adolescents who have been deaf from birth frequently have poor cochlear implant outcomes. This may be in part a result of psychological and social pressures. An adolescent may be uncertain of his or her identity as a deaf or hearing person and may be ostracized by friends if the decision is to go ahead with the implant.
Degree of Hearing Loss
Guidelines for implantation have always been prescriptive for the individual patient (that is, one size does not fit all) and continue to be modified based on technological advances. Your cochlear implant team will be able to tell you the most current guidelines.
The criteria for implanting adults once required profound hearing loss (90 dB) in both ears. In contrast, criteria are now more liberal and have expanded to include moderate hearing loss (40 dB) in the low frequencies. Figure 9.3 shows the criteria changes in the level of hearing loss over the past three decades.
However, speech understanding, not threshold (see chapter 5), is the main criterion for adult implantation. Speech understanding results using hearing aids should be less than 60 percent in the ear to be operated on. Nonetheless, Medicare places further limits on care for seniors and will not routinely cover implantation unless speech understanding is 40 percent or less.
Figure 9.3. Changing criteria for using cochlear implants in adults, 1970s–2017. The amount of hearing loss is shown in the left column. The frequency of the hearing loss is noted at the top. In the 1970s and 1980s, candidates were required to have profound hearing loss in order to qualify for a cochlear implant (bottom box). In the 1990s, people with severe hearing loss in the low and middle frequencies were included (middle box). In 2017, people with normal hearing loss in the lowest frequencies (top box) were added (with emphasis on speech recognition rather than threshold).
Pediatric criteria are more conservative. Current FDA recommendations include profound hearing loss (90 dB) for children under twenty-four months and severe hearing loss (70 dB) for children over twenty-four months as well as evidence of limited benefit from a hearing aid trial. Threshold is used, rather than speech understanding, for most children with deafness because they do not have adequate language to be tested for speech understanding.
Other Considerations
There should be a strong commitment to living in the hearing world with the enthusiastic support of family and friends. The patient, if the patient is old enough, and his or her family should understand the risks, advantages, and alternatives and have realistic expectations about the probable benefit of the cochlear implant.
Not So Fast
If the cochlea or cochlear nerve is absent, it is not possible to have a cochlear implant. If your child is five years old or more and was born deaf, cochlear implant hearing outcomes are generally not as good as outcomes of younger children. This is especially true if the child communicates in signed language or has no language at all. Poorer results are also common in adolescents, if the cochlea or auditory nerves are not normal or with diminished memory or cognitive function.
Cochlear Implants and Signed Language
By the age of five years, a normal hearing child will have a vocabulary of around 5,000 to 26,000 words. A deaf signing five-year-old will have a vocabulary of only about 200 spoken and/or signed words.
Unfortunately, American Sign Language (ASL) does not have a written form. This is one reason that deaf children who communicate in ASL and attend state residential schools for the Deaf graduate from high school at an average age of twenty+ years with a reading level of a third or fourth grader. Because so many jobs are now in technology sectors and require a high level of literacy, many young Deaf adults may not be able to compete and are often under-employed.
ASL provides many opportunities for communication, education, and socialization. It is at the core of Deaf culture and is a viable alternative to cochlear implantation. Deaf children born to Deaf parents (about 5 percent of all children who are born deaf) do especially well with ASL because they are immediately integrated as members of Deaf culture and are often educated at state schools for the deaf. Cochlear implant teams recognize the value of ASL and respect members of Deaf culture.
However 90 to 95 percent of deaf children are born to at least one parent with hearing. As hearing parents become aware of low reading levels associated with ASL, limited career prospects, and the reality that fewer than 2 percent of neighbors, plumbers, mail carriers, and store clerks will be able to sign with their child, many choose to provide the child with hearing. Fortunately, the Deaf culture is beginning to accept children with cochlear implants as examples of another way to be deaf within their diverse community.
Meningitis
Meningitis is a serious infection of the tissues that surround the brain. It is thought to be more common in children who receive cochlear implants based on studies by the Centers for Disease Control and Prevention (CDC). However, more recent research in the United Kingdom has shown that the risk of meningitis for children who are deaf who have cochlear implants is about the same as children who are deaf who do not have CI. The most common cause of meningitis in implantees is the bacterium Streptococcus pneumoniae (pneumococcus). Vaccination reduces the chances of meningitis but does not prevent it.
All children should now be vaccinated against meningitis-causing organisms as part of the normal healthy child immunization program (see table 9.1). Your pediatrician will be certain that all immunizations are up to date. Children are protected if they are up to date on vaccination, even if they will require further vaccination in the near future. Adults receiving cochlear implants are also immunized.
Meningitis is rare but life threatening, and successful treatment depends on early diagnosis. The signs and symptoms to be aware of include fever, headache, stiff neck, pain caused by bright lights, nausea, and vomiting. Early diagnosis in infants is more difficult because only irritability, sleepiness, and appetite loss may be present.
Table 9.1
Recommended Meningitis Vaccinations for All Children and for Adults with Cochlear Implants (CI)
Cochlear Implant Surgery
Cochlear implantation is usually performed under general anesthesia as an outpatient. It usually requires one to two hours, not including preparation, administration of anesthesia, and time in the recovery room. Current techniques require only a small shave and an incision less than 2 inches long. Preventative antibiotics and a dose of intravenous steroids are often used to avoid infection and reduce inflammation in the cochlea.
After the incision is made, a pocket (or seat) is created under the scalp to securely hold the implanted portion. Various types of seats for the implant are sometimes drilled into the skull. The bone over the mastoid cavity is removed; the facial nerve is located and preserved under a layer of bone. The middle ear is then entered, an opening made in the cochlea, and the electrode inserted into the cochlea. The implantable cochlear stimulator is secured in the pocket and may be held in place by a permanent suture. The area is rinsed with saline, the incision closed, and a light pressure dressing is applied. The device is not activated for a period of days up to a month in order to allow healing.
Outcomes
Cochlear implants improve hearing in over 90 percent of the people who receive them. That is not to say the hearing becomes normal, but the average person understands over 80 percent of what is said in quiet surroundings (normal is 90 to 100 percent).
As noted above, certain patients will have less successful outcomes due to underlying conditions. Children with abnormal anatomy, multiple developmental disabilities, and those over five years of age at the time of the surgery who were born deaf have generally poorer results. Adults who have been deaf for more than twenty years and seniors with memory loss or early dementia should also have lower expectations.
Complications
Some cochlear implant complications are common to any operation, including the risks related to anesthesia and the possibility of infection. Specific cochlear implant complications include slippage of the device, taste disturbance, dizziness, facial nerve injury, and tinnitus.
Infections of the implant are uncommon. Any evidence of redness, swelling, tenderness to touch, or pain can be signs of infection. See your surgeon immediately. Rejection of the cochlear implant is rare (cochlear implants are made of the same biocompatible materials as pacemakers, heart valves, and other implanted devices). The symptoms of rejection can be very similar to those of infection, and sometimes cannot be distinguished without electron microscopic analysis of a removed device.
Rarely, the implanted part of a cochlear implant will migrate out of position. Minor degrees of implant migration do not usually require revision surgery. However, if the electrode begins to slip out of the cochlea, it will probably need to be replaced and re-secured.
Taste disturbance occurs when the nerve of taste obstructs access to the cochlea (about 10 percent of the time) and must be cut. Over a period of months the other taste nerves usually take over, restoring taste.
Dizziness or imbalance problems following implantation are rare and are more often seen in the elderly. If balance symptoms do occur after cochlear implant, they usually last only a few hours or days, but in some cases they may persist for longer periods of time.
This operation requires working adjacent to the facial nerve, which puts the nerve at some risk. Reversible injury occurs in about 2 percent of cases and results in weakness or paralysis of one side of the face. Unless the nerve is severely damaged, it will return to normal function within a month or so. Severe injury to the facial nerve during cochlear implantation is uncommon and may require surgical repair.
Tinnitus may become worse after cochlear implantation in 10 to 15 percent of patients, but it is improved in about 50 to 92 percent of patients who experienced tinnitus before implantation.