Thursday
Dec302010

Cochlear Implants

   
 

Insight into an implantable device to help you hear

Provided by your physician and the American Academy of Otolaryngology - Head and Neck Surgery, Inc.

A cochlear implant is an electronic device that restores partial hearing to the deaf. It is surgically implanted in the inner ear and activated by a device worn outside the ear. Unlike a hearing aid, it does not make sound louder or clearer. Instead, the device bypasses damaged parts of the auditory system and directly stimulates the nerve of hearing, allowing individuals who are profoundly hearing impaired to receive sound.

What is normal hearing?

Your ear consists of three parts that play a vital role in hearing – the external ear, middle ear, and inner ear.

Conductive hearing: Sound travels along the ear canal of the external ear causing the ear drum to vibrate. Three small bones of the middle ear conduct this vibration from the ear drum to the cochlea (auditory chamber) of the inner ear.

Sensorineural hearing: When the three small bones move, they start waves of fluid in the cochlea, and these waves stimulate more than 16,000 delicate hearing cells (hair cells). As these hair cells move, they generate an electrical current in the auditory nerve. It travels through inner-connections to the brain area that recognizes it as sound.

How is hearing impaired?

If you have disease or obstruction in your external or middle ear, your conductive hearing may be impaired. Medical or surgical treatment can probably correct this.

An inner ear problem, however, can result in a sensorineural impairment or nerve deafness. In most cases, the hair cells are damaged and do not function. Although many auditory nerve fibers may be intact and can transmit electrical impulses to the brain, these nerve fibers are unresponsive because of hair cell damage. Since severe sensorineural hearing loss cannot be corrected with medicine, it can be treated only with a cochlear implant.

How do cochlear implants work?

Cochlear implants bypass damaged hair cells and convert speech and environmental sounds into electrical signals and send these signals to the hearing nerve.

The implant consists of a small electronic device, which is surgically implanted under the skin behind the ear and an external speech processor, which is usually worn on a belt or in a pocket. A microphone is also worn outside the body as a headpiece behind the ear to capture incoming sound. The speech processor translates the sound into distinctive electrical signals. These ‘codes’ travel up a thin cable to the headpiece and are transmitted across the skin via radio waves to the implanted electrodes in the cochlea. The electrodes’ signals stimulate the auditory nerve fibers to send information to the brain where it is interpreted as meaningful sound.

Who can benefit from an implant?

Implants are designed only for individuals who attain almost no benefit from a hearing aid. They must be two years of age or older (unless childhood meningitis is responsible for deafness).

Otolaryngologists (ear, nose, and throat specialists) perform implant surgery, though not all of them do this procedure. Your local doctor can refer you to an implant clinic for an evaluation. The evaluation will be done by an implant team (an otolaryngologist, audiologist, nurse, and others) that will give you a series of tests:

Ear (otologic) evaluation: The otolaryngologist examines the middle and inner ear to ensure that no active infection or other abnormality precludes the implant surgery.

Hearing (audiologic) evaluation: The audiologist performs an extensive hearing test to find out how much you can hear with and without a hearing aid.

X-ray (radiographic) evaluation: Special X-rays are taken, usually computerized tomography (CT) or magnetic resonance imaging (MRI) scans, to evaluate your inner ear bone.

Psychological evaluation: Some patients may need a psychological evaluation to learn if they can cope with the implant.

Physical examination: Your otolaryngologist also gives a physical examination to identify any potential problems with the general anesthesia needed for the implant procedure.

What about surgery?

Implant surgery is performed under general anesthesia and lasts from two to three hours. An incision is made behind the ear to open the mastoid bone leading to the middle ear. The procedure may be done as an outpatient, or may require a stay in the hospital, overnight or for several days, depending on the device used and the anatomy of the inner ear.

Training, Expectation, and Cost

Is there care and training after the operation?

About one month after surgery, your team places the signal processor, microphone, and implant transmitter outside your ear and adjusts them. They teach you how to look after the system and how to listen to sound through the implant. Some implants take longer to fit and require more training. Your team will probably ask you to come back to the clinic for regular checkups and readjustment of the speech processor as needed.

What can I expect from an implant?

Cochlear implants do not restore normal hearing, and benefits vary from one individual to another. Most users find that cochlear implants help them communicate better through improved lip-reading, and over half are able to discriminate speech without the use of visual cues. There are many factors that contribute to the degree of benefit a user receives from a cochlear implant, including:

how long a person has been deaf,

the number of surviving auditory nerve fibers, and

a patient’s motivation to learn to hear.

Your team will explain what you can reasonably expect. Before deciding whether your implant is working well, you need to understand clearly how much time you must commit. A few patients do not benefit from implants.

How are new implant devices approved?

The Food and Drug Administration (FDA) regulates cochlear implant devices for both adults and children and approves them only after thorough clinical investigation.

Be sure to ask your otolaryngologist for written information, including brochures provided by the implant manufacturers. You need to be fully informed about the benefits and risks of cochlear implants, including how much is known about how safe, reliable, and effective a device is, how often) you must come back to the clinic for checkups, and whether your insurance company pays for the procedure.

How much does an implant cost?

More expensive than a hearing aid, the total cost of a cochlear implant including evaluation, surgery, the device, and rehabilitation is around $30,000. Most insurance companies provide benefits that cover the cost. (This is true whether or not the device has received FDA clearance or is still in trial.)

National Institutes of Health Consensus Development Conference Statement
May 15-17, 1995

COCHLEAR IMPLANTS IN ADULTS AND CHILDREN

This statement is published as:
     Cochlear Implants in Adults and Children. NIH Consens Statement
     1995 May 15-17; 13(2):1-30.
For making bibliographic reference to consensus statement no. 100 in the
electronic form displayed here, it is recommended that the following format
be used:
     Cochlear Implants in Adults and Children. NIH Consens Statement
     Online 1995 May 15-17 [cited year month day]; 13(2):1-30.
Introduction
Cochlear implants are now firmly established as effective options in the
habilitation and rehabilitation of individuals with profound hearing
impairment. Worldwide, more than 12,000 people have attained some degree of
sound perception with cochlear implants, and the multichannel cochlear
implant has become a widely accepted auditory prosthesis for both adults
and children. The vast majority of adults who are deaf and have cochlear
implants derive substantial benefit from them when they are used in
conjunction with speech reading. Many of these individuals are able to
understand some speech without speech reading, and some of these individuals
are able to communicate by telephone. Benefits have also been observed in
children, including those who lost their hearing prelingually; moreover,
there is evidence that the benefits derived improve with continued use. New
speech-sound processing techniques have improved the effectiveness of
cochlear implants, increasing user performance levels to ones previously
unseen.
The NIH sponsored a Consensus Development Conference on Cochlear Implants
in 1988. Since then, implant technology has been continually improved.
Questions unanswered at that time have now been resolved. New issues have
emerged that must be addressed.
For example, the performance of some severely to profoundly
hearing-impaired adults using hearing aids is poorer than that of even more
severely hearing-impaired individuals using cochlear implants with advanced
speech- processing strategies. It is possible that cochlear implants could
be beneficial for some of these individuals. Therefore, the criteria for
implantation should be re-examined. The ability to predict preoperatively
the level of performance at which an individual implant recipient will
function is highly desirable. Currently, the limited prediction of implant
efficacy in a specific individual remains a pressing problem. Agreement
does not exist on the definition of a successful implant user. What are the
appropriate expectations for individuals using cochlear implants? How is
benefit defined and measured? What are the audiological, educational, and
psychosocial impacts of this intervention and is it cost-effective?
Advancing technology will allow for the modification of existing devices or
the development of new devices. It is therefore important to know what
risks and benefits are associated with device explantation/reimplantation.
Surgical and other risks and possible long-term effects of cochlear
implants require evaluation.
Implantation of individuals with multiple disabilities, the elderly, and
children, particularly children who are prelingually deaf, engenders
special questions. Longitudinal studies are providing information on the
development of auditory speech perception and production and language
skills in children who are deaf and have a cochlear implant. What
educational setting is best for the development of speech and language in
these children? Are cochlear implants efficacious in children who are
prelingually deaf?
To address these new issues since the 1988 Consensus Development Conference
(CDC) on Cochlear Implants, the National Institute on Deafness and Other
Communication Disorders, together with the NIH Office of Medical
Applications of Research, convened a Consensus Development Conference on
Cochlear Implants in Adults and Children, May 15-17, 1995. The conference
was cosponsored by the National Institute on Aging, the National Institute
of Child Health and Human Development, the National Institute of
Neurological Disorders and Stroke, and the Department of Veterans Affairs.
The conference was convened to summarize current knowledge about the range
of benefits and limitations of cochlear implantation that have accrued to
date. Such knowledge is an important basis for informed choices for
individuals and their families whose philosophy of communication is
dedicated to spoken discourse. Issues related to the acquisition of sign
language were not directly addressed by the panel, because the focus of the
conference was to synthesize thoughtfully the new information on cochlear
implant technology and its use. The panel acknowledges the value and
contributions of bilingual-bicultural approaches to deafness.
This conference brought together specialists in auditory anatomy and
physiology, otolaryngology, audiology, aural rehabilitation, education,
speech-language pathology, bioengineering, and other related disciplines as
well as representatives from the public. After 1-1/2 days of presentations
and audience discussion, an independent, non- Federal consensus panel
weighed the scientific evidence and developed a draft statement that
addressed the following five questions:
1. What Factors Affect the Auditory Performance of Cochlear Implant
Recipients?
Subject Factors
Auditory performance, defined as the ability to detect, discriminate,
recognize, or identify acoustic signals, including speech, is highly
variable among individuals using cochlear implants. Since the 1988 CDC on
Cochlear Implants, however, some factors associated with outcome
variability are now better understood.
Etiology
Because of a larger subject sample, the effects of etiology can now be
distinguished from other factors such as the duration of deafness and the
age of onset. Meningitic deafness does not necessarily limit the benefit of
cochlear implantation in the absence of central nervous system
complications, cochlear ossification, or cochlear occlusion. Children with
congenital deafness and children with prelingually acquired meningitic
deafness, for example, achieve similar auditory performance if the cochlear
implant is received before age 6 years. In general, etiology does not
appear to impact auditory performance in either children or adults.
Age of Onset of Deafness
The age of onset continues to have important implications for cochlear
implantation, depending on whether the hearing impairment occurred before
(prelingual), during (perilingual), or after (postlingual) learning speech
and language. At the time of the last CDC, data on cochlear implantation
suggested that children or adults with postlingual onset of deafness had
better auditory performance than children or adults with prelingual or
perilingual onsets. On average, current data following auditory performance
in children over a longer period of time support this finding. However, the
difference between children with postlingual and prelingual-perilingual
onsets appears to lessen with time. Large individual differences remain
within each group.
Age at Implantation
Previous data suggested that prelingually or perilingually deafened persons
who were implanted in adolescence or adulthood did not achieve as good
auditory performance as those implanted during childhood, although
individual differences were recognized. Current data continue to support
the importance of early detection of hearing loss and implantation for
maximal auditory performance. However, it is still unclear whether
implantation at age 2, for example, ultimately results in better auditory
performance than implantation at age 3.
Duration of Deafness
As deafness endures, even in postlingually deafened individuals, some
acquired skills and knowledge may decline and some behaviors that work
against successful adaptation to a sensory device may develop. Individuals
with shorter durations of auditory deprivation tend to achieve better
auditory performance from any type of sensory aid, including cochlear
implants, than individuals with longer durations of auditory deprivation.
Residual Hearing
Cochlear implants tend to give people with profound deafness a level of
auditory performance that is similar to, or better than, the performance of
people with severe hearing impairment who use hearing aids. These data
raise the issue of whether cochlear implants might give persons with severe
hearing impairment and some residual hearing even better auditory
performance than they can attain with a hearing aid. No residual hearing is
typically defined as profound hearing loss and no open-set speech
recognition. However, the degree of preimplantation residual hearing does
not predict postimplantation auditory performance. Research is now
addressing the critical distinction between the importance of residual pure
tone sensitivity compared with that of overall residual auditory capacities
and functional communication status.
Electrophysiological Factors
Some surviving spiral ganglion cells are necessary for auditory performance
with a cochlear implant. Degenerative changes occur in both ganglion cells
and central auditory neurons following sensorineural deafening. Although a
relationship between the number of surviving ganglion cells and
psychophysical performance has been demonstrated in animals, a direct
relationship between ganglion cell survival and level of auditory
performance in humans has not been shown. Animal studies also suggest that
electrical stimulation increases ganglion cell survival and also modifies
the functional organization of the central auditory system. The
implications of these new findings remain to be determined.
Device Factors
The task of representing speech stimuli as electrical stimuli is central to
the design of cochlear implants. Designs vary according to (1) the
placement, number, and relationship among the electrodes; (2) the way in
which stimulus information is conveyed from an external processor to the
electrodes; and (3) how the electrical stimuli are derived from the speech
input (and other signals). Changes in cochlear implant design/processing
strategies and their effects on auditory performance are discussed in
Section 3.
2. What Are the Benefits and Limitations of Cochlear Implantation?
Impact on Speech Perception in Adults
Cochlear implantation has a profound impact on hearing and speech reception
in postlingually deafened adults. Most individuals demonstrate
significantly enhanced speech-reading capabilities, attaining scores of
90-100 percent correct on everyday sentence materials. Speech recognition
afforded by the cochlear implant effectively supplements the information
least favorably cued through speech-reading. A majority of those
individuals with the latest speech processors for their implants will score
above 80-percent correct on high-context sentences without visual cues.
Performance on single-word testing in these individuals is notably poorer,
although even these scores have been significantly improved with newer
speech-processing strategies. Recognition of environmental sounds and even
appreciation of music have been repeatedly observed in adult implant
recipients. Noisy environments remain a problem for cochlear-implanted
adults, significantly detracting from speech-perception abilities.
Prelingually deafened adults have generally shown little improvement in
speech perception scores after cochlear implantation, but many of these
individuals derive satisfaction from hearing environmental sounds and
continue to use their implants.
Speech Perception, Speech Production, and Language Acquisition in Children
Improvements in the speech perception and speech production of children
following cochlear implantation are often reported as primary benefits.
Variability across children is substantial. Factors such as age of onset,
age of implantation, the nature and intensity of (re)habilitation, and mode
of communication contribute to this variability. Using tests commonly
applied to children and adults with hearing impairments (e.g., pattern
perception, closed-set word identification, and open-set perception),
perceptual performance increases on average with each succeeding year post
implantation. Shortly after implantation, performance may be broadly
comparable to that of some children with hearing aids and over time may
improve to match that of children who are highly successful hearing aid
users. Children implanted at younger ages are on average more accurate in
their production of consonants, vowels, intonation, and rhythm. Speech
produced by children with implants is more accurate than speech produced by
children with comparable hearing losses using vibro-tactile or hearing
aids. One year after implantation, speech intelligibility is twice that
typically reported for children with profound hearing impairments and
continues to improve. Oral-aural communication training appears to result
in substantially greater speech intelligibility than manually based total
communication.
The language outcomes in children with cochlear implants have received less
attention. Reports involving small numbers of children suggest that
implantation in conjunction with education plus habilitation leads to
advances in oral language acquisition. The nature and pace of language
acquisition may be influenced by the age of onset, age at implantation,
nature and intensity of habilitation, and mode of communication.
One current limitation is that children are typically implanted at no
earlier than age 2 years, which is beyond what may be critical periods of
auditory input for the acquisition of oral language. Benefits are not
realized immediately, but rather are manifested over time, with some
children continuing to show improvement over several years.
Few studies have used language as an outcome measure. The assessment of
speech perception, language production, and language comprehension in young
children is particularly challenging. Furthermore, all results in children
have been reported for single-channel or feature-based devices only,
despite the relatively rapid evolution of alternatives in speech-coding
strategies. Oral language development in deaf children, including those
with cochlear implants, remains a slow, training-intensive process, and
results will typically be delayed in comparison with normally hearing
peers.
Psychologic and Social Issues in Adults and Children
Although psychological evaluation has previously been a part of the
preimplant evaluation process, comparatively little research has been
conducted on the long-term psychological and social effects of electing for
implantation. Still, the psychological and social impact for adults is
generally quite positive, and there appears to be agreement between
preimplantation expectations and later benefit. This benefit is expressed
as a decline in loneliness, depression and social isolation and an increase
in self-esteem, independence, social integration, and vocational prospects.
Many adults report being able to function socially or vocationally in ways
comparable to those with moderate hearing loss. Furthermore, they describe
a new or renewed curiosity about the experience of hearing and the
phenomena of sound. In some cases the experience of implantation becomes an
integral part of the individual's identity, leading implant users to
participate and share experiences in self-interest and advocacy groups.
Negative psychological and social impact is less frequently observed and is
often related to concerns about the maintenance and/or malfunction of the
implant and external hardware. Other social insecurities may result from
the difficulty of hearing amidst background noise, and from unreasonable
expectations of aural-only benefit on the part of the implant user or
his/her family and friends.
The assessment of psychological impact in children with implants lags
behind that for the adult population, in part because psychological outcome
is a factor of audiological benefit, which is realized more slowly in
children. Additionally, such assessment must consider the child's family
setting. Because language acquisition is closely associated with identity,
social development, and social integration, the impact of implantation on a
child's development in these areas deserves more study in order to produce
useful indicators that can bear upon parental decision-making processes.
Rehabilitation and Educational Issues
Although a cochlear implant can provide dramatic augmentation of the
auditory information perceived by deaf children and adults, it is clear
that training and educational intervention play a fundamental role in
optimizing postimplant benefit. Access to postimplant rehabilitation
involving professionals familiar with cochlear implants must be provided to
ensure successful outcomes for implant recipients.
Rehabilitation efforts must be tailored to meet individual needs, and
protocols should be developed to reflect therapies effective for various
types of individuals receiving implants. Therapeutic intervention with
prelingually deaf adults may differ significantly in both time and content
from that of postlingually deaf recipients.
Pediatric cochlear implantation requires a multidisciplinary team composed
of physicians, audiologists, speech-language pathologists, rehabilitation
specialists, and educators familiar with cochlear implants. These
professionals must work together in a long-term relationship to support the
child's auditory and oral development. Although the effects of
communication mode in implantation habilitation have not been sufficiently
documented, it is clear that the educational programs for children with
cochlear implants must include auditory and speech instruction using the
auditory information offered by the implant.
Cost-Utility
The cost-benefit or cost-utility of cochlear implantation must be
calculated for children and adults separately. For adults, the cost of
cochlear implantation includes the initial costs of assessment, the device,
implantation, rehabilitation, system overhead, and maintenance. The benefit
or utility is estimated as a function of quality of life over time. On this
basis, cochlear implantation whether at age 45 years or 70 years compares
quite favorably to many medical procedures now commonly in use (e.g.,
implantable defibrillator insertion).
Although it appears that the cost-utility estimates for children are also
quite favorable, we are still in the early stages of cochlear implant
application and cannot yet estimate the cost or potential cost savings that
will accrue in the area of (re)habilitation and education.
3. What Are the Technical and Safety Considerations of Cochlear
Implantation?
Cochlear Implant Design Issues
A cochlear implant works by providing direct electrical stimulation to the
auditory nerve, bypassing the usual transducer cells that are absent or
nonfunctional in a deaf cochlea. Over the past 10 years, significant
improvements have been made in the technology used to accomplish auditory
stimulation.
The best performance in speech recognition occurs with intracochlear
electrodes that are close to the nerve fibers to be stimulated, thus
minimizing undesirable side effects.
Early implants used only a single electrode; it has been found that these
single-channel implants rarely provide open-set speech perception. Most
recent implants have used multielectrode arrays that provide a number of
independent channels of stimulation. Such devices provide more information
about the acoustic signal and give better performance on speech
recognition. No agreement exists on the optimum number of channels,
although at least 4-6 channels seem to be necessary.
Much of the recent progress in implant performance has involved
improvements in the speech processors, which convert sound into the
electrical stimulus. The best performance comes with speech processors that
attempt to preserve the normal frequency code or spectral representation of
the cochlea. These are distinguished from feature-based processors, which
attempt to analyze certain features known to be important to speech
perception and present only those features through the electrodes. A major
problem in multichannel implants is channel interaction, in which two
electrodes stimulate overlapping populations of nerves. Channel interaction
has now been minimized with speech processors that activate the electrodes
in a nonsimultaneous or interleaved fashion, which has been shown to
improve speech recognition significantly.
A final design issue is the means by which the stimulus information is
passed through the skin from the speech processor to the electrodes. In a
transcutaneous system, the skin is intact and the coupling is done
electromagnetically to an implanted antenna. In a percutaneous system, the
leads are passed directly through the skin. The two systems have slightly
different surgical complications, which are discussed below. The
percutaneous system (1) provides a more flexible connection to the
electrodes in case a change in speech processor is desired, (2) is easier
to troubleshoot in case of electrode problems, and (3) is magnetic
resonance imaging (MRI) compatible. Currently, percutaneous systems are not
commercially available.
Issues Related to Magnetic Resonance Imaging
Magnetic Resonance Imaging (MRI) is increasingly the diagnostic tool of
choice for a variety of medical conditions. Implants that use
transcutaneous connectors contain an implanted magnet and some ferrous
materials that are incompatible with the high magnetic fields of an MRI
scanner. Implant manufacturers are redesigning their devices to circumvent
this problem. Potential MRI risks should be part of the informed consent
procedure for persons considering an implant. The external speech processor
cannot be made MRI compatible and should not be taken into the scanner.
Surgical Issues
Cochlear implantation entails risks common to most surgical procedures,
e.g., general anesthetic exposure, as well as unique risks that are
influenced by device design, individual anatomy and pathology, and surgical
technique. Comparative data of major complications incurred in adult
implantation show a halving of the complication rate to approximately 5
percent in 1993. The complication rate in pediatric implantation is less
than that currently seen in adults. Overall, the complication rate compares
favorably to the 10 percent rate seen with pacemaker/defibrillator
implantation.
Major complications, i.e., those requiring revision surgery, include flap
problems, device migration or extrusion, and device failure. Facial palsy
is also considered a major complication but is distinctly uncommon and
rarely permanent. Notably, no mortalities have been attributed to cochlear
implantation.
Alterations in surgical technique, especially flap design, have led to a
considerable reduction in the flap complication rate, which is particularly
relevant to transcutaneous devices. Alterations in surgical technique,
particularly in methods used to anchor the device, have contributed to a
decrease in device migration/extrusion.
All implants are potentially prone to failure--either because of
manufacturing defects or use- related trauma. Pedestal fracture is a
problem unique to the percutaneous device, but occurs rarely. Manufacturer
redesign has produced electrode arrays that are smaller but sturdier. For
the most commonly implanted device, 95 percent of implants are still
functioning after 9 years. Most current implants with transcutaneous
connectors do not provide self-test capability for the implanted portion,
making it cumbersome to test for simple electrode failure, such as open and
short circuits. Failure detection is particularly problematic in young
children. Device manufacturers should include self-test circuity in future
implant designs.
Minor complications are those that resolve without surgical intervention.
The most common is unwanted facial nerve stimulation with electrode
activation, which is readily rectified by device reprogramming. In
percutaneous devices, pedestal infections are uncommon and can be treated
successfully with antibiotics, but on rare occasions may require
explantation.
Reimplantation is necessary in approximately 5 percent of cases because of
improper electrode insertion or migration, device failure, serious flap
complication, or loss of manufacturer support. In general, reimplantation
in the same ear is usually possible, and thus far individual auditory
performance after reimplantation equals or exceeds that seen with the
original implant.
Long-term complications of implantation relate to flap breakdown, electrode
migration and receiver/stimulator migration. Particularly in the child, the
potential consequences of otitis media have been of concern, but as the
implanted electrode becomes ensheathed in a fibrous envelope, it appears
protected from the consequences of local infection.
4. Who Is a Candidate for Cochlear Implantation?
Adults
Cochlear implants are often highly successful in postlingually deafened
adults with severe/profound hearing loss with no speech perception benefit
from hearing aids. Previously, individuals receiving marginal benefit from
hearing aids were not considered implant candidates. Ironically, such
individuals often have less speech perception than more severely deafened
persons who receive implants. Recent data show that most marginally
successful hearing aid users implanted with a cochlear implant will have
improved speech perception performance. It is therefore reasonable to
extend cochlear implants to postlingually deafened adult individuals
currently obtaining marginal benefit from other amplification systems.
Prelingually deafened adults may also be suitable for implantation,
although these candidates must be counseled regarding realistic
expectations. Existing data indicate that these individuals achieve minimal
improvement in speech recognition skills. However, there may be other basic
benefits such as improved sound awareness that correlate with psychological
satisfaction and safety needs.
Because of the wide variability in speech perception and recognition in
persons with similar hearing impairments, all candidates require indepth
counseling of the surgery, its risks and benefits, rehabilitation, and
alternatives to cochlear implantation. To give adequate informed consent,
adult candidates should understand that large variability in individual
audiologic performance precludes preoperative prediction of success.
Determining implant candidacy requires consideration of both objective
audiological variables as well as the subjective needs and wishes of
individual candidates. Specific characteristics of potential adult cochlear
implant recipients are provided below.
Audiologic Criteria
Indications in favor of an implant are a severe-to-profound sensorineural
hearing loss bilaterally and open-set sentence recognition scores less than
or equal to 30 percent under best aided conditions. Duration of deafness
and age of onset have been shown to influence auditory performance with
cochlear implants and should be discussed with potential candidates.
In general, when there is no residual hearing in either ear, the ear with
better closed-set performance, more sensitive electrical thresholds,
shorter period of auditory deprivation, or better radiologic
characteristics is implanted. However, when there is residual hearing, the
poorer ear should be chosen, provided that there is radiologic evidence of
cochlear patency to retain the option for continued hearing aid use and,
thus, the potential advantages of binaural sound localization.
Medical and Surgical Criteria
Traditionally, implantation candidacy was limited to healthy persons.
Although there may be specific medical contraindications to surgery and
implantation such as poor anesthetic risk, severe mental retardation,
severe psychiatric disorders, and organic brain syndromes, cochlear
implantation should be offered to a wider population of individuals. In
some circumstances, such as in individuals with low vision, implantation
may be a tool to promote independence and other quality-of-life goals.
The medical history, physical examination, and laboratory tests are
important tools in candidacy evaluation. Individuals with active ear
pathology require treatment and re-evaluation prior to implantation. The
standard evaluation includes high-resolution computed tomography (CT) scans
that serve to detect mixed fibrous and bony occlusions and anatomical
abnormalities. MRI provides better resolution of soft tissue structures and
should supplement the CT scan when indicated. These imaging techniques
should be used to identify abnormalities that may compromise or impede
implant surgery or device use.
The results of electrophysiologic tests do not predict implant success.
However, in selected individuals, such as those with cochlear obliteration
or in decisions regarding ear of implantation, the results of promontory
stimulation may be useful.
Children
Cochlear implants have also been shown to result in successful speech
perception in children. Currently, the earliest age of implantation is 24
months, but there are reasons to reassess this age threshold. A younger age
of implantation may limit the negative consequences of auditory deprivation
and may allow more efficient acquisition of speech and language.
Determining whether cochlear implant benefits are greater in children
implanted at age 2-3 years as compared to those implanted at age 4-5 years
might resolve this issue, but sufficient data are unavailable. It is also
not clear that the benefits of implantation before age 2 years would offset
potential liabilities associated with the increased difficulty in obtaining
reliable and valid characterization of hearing and functional communication
status at the younger age. A number of children under age 2 years have
received implants, both internationally and in the United States, when it
was thought that bone growth associated with meningitis would preclude
implantation at a later date. Speech/language data obtained on such
children will be helpful in determining the potential benefits of early
implantation and therefore may help to guide future policy.
Audiologic Criteria
Children age 2 years or older with profound (greater than 90 dBHL)
sensorineural hearing loss bilaterally and minimal speech perception under
best aided conditions may be considered for cochlear implantation. In the
young child, auditory brainstem response, stapedial reflex testing, and/or
otoacoustic emission testing may be useful when combined with auditory
behavioral responses to determine hearing status. Prior to implantation, a
trial period with appropriate amplification combined with intensive
auditory training should have been attempted to ensure that maximal benefit
has been achieved. When the validity of behavioral test results is
compromised by maturational factors, the above criteria should be applied
in the most stringent manner (i.e., worse hearing sensitivity, longer trial
periods, and so on). Current research may broaden audiometric criteria for
candidacy to better reflect functional auditory capacity.
Medical and Surgical Criteria
Children should undergo a complete medical evaluation to rule out the
presence of active disease, which would be a contraindication to surgery.
The child must be otologically stable and free of active middle ear disease
prior to cochlear implantation. The radiologic imaging criteria used in
adult candidates can be applied to children.
Psychosocial Criteria
Preoperative assessment should entail evaluation of the child in the
context of the home and social and educational milieu to assure that
implantation is the proper intervention. In some instances psychosocial
factors may be used as exclusionary criteria; however, in most cases it
should serve only as baseline data for tracking cochlear implant outcomes.
Informed Consent
The parents of a deaf child are responsible for deciding whether to elect
cochlear implantation. The informed consent process should be used to
empower parents in their decision-making. The parents must understand that
cochlear implants do not restore normal hearing and that auditory and
speech outcomes are highly variable and unpredictable. They must be
informed of the advantages, disadvantages, and risks associated with
implantation to establish realistic expectations. Furthermore, the
importance of long-term rehabilitation to success with cochlear implants
must be stressed. As part of the process of informed consent, parents must
be told that alternative approaches to habilitation are available. All
children should be included in the informed consent process to the extent
they are able, as their active participation is crucial to (re)habilitative
success.
5. What Are the Directions for Future Research on Cochlear Implantation?
   * Research must attempt to explain the wide variation in performance
     across individual cochlear implant users. New tools, such as
     functional imaging of the brain, might be applied to unexplored
     variables such as the ability of the implant to activate the central
     auditory system. Investigations of the role of higher level cognitive
     processes in cochlear implant performance are needed.
   * The strides that have been made in improving speech perception of
     cochlear implant users should continue through improvements in
     electrode design and signal processing strategies. Noise-reduction
     technologies and enhancement of performance using binaural implants
     are promising areas.
   * Studies of the effects of cochlear stimulation on auditory neurons
     have provided clear evidence of plasticity in both the survival of
     neural elements and in receptive field organization. Comparisons of
     neural plasticity in animal experiments and of adaptation to cochlear
     implant electrical stimulation by humans provide a unique opportunity
     to study the relationships between neural activity and auditory
     perception.
   * Comparative research on language development in children with normal
     hearing, children with hearing impairment who use hearing aids, deaf
     children with cochlear implants, and deaf children using American Sign
     Language should be conducted. These studies should be longitudinal and
     reflect current theoretical and empirical advances in neurolinguistics
     and psycholinguistics.
   * Studies of the relationship between the development of speech
     perception and speech production in cochlear implant users must
     continue. Implanted deaf children provide a unique opportunity to
     examine these developmental processes and their relationship to the
     acquisition of aural/oral language. Such information is crucial to
     understanding and enhancing the performance of implanted prelingual
     children and may help define optimal age for implantation.
   * Adequate tools for the assessment of nonspeech benefits of
     implantation should be applied to gain a better understanding of the
     full effects of implantation on the quality of life of implant
     recipients. This may be particularly useful for implant recipients who
     do not realize significant speech-perception benefit. Such data will
     help in evaluating the cost-utility of cochlear implantation.
   * Identifying the components of successful (re)habilitation approaches
     will facilitate extension of these services to all children and adults
     receiving cochlear implants, as will comparison of model and routine
     service programs.
Conclusions
   * Cochlear implantation improves communication ability in most adults
     with deafness and frequently leads to positive psychological and
     social benefits as well. The greatest benefits seen to date have
     occurred in postlingually deafened adults. Cochlear implantation in
     prelingually deafened adults provides more limited improvement in
     speech perception, but offers important environmental sound awareness.
     Cochlear implantation outcomes are more variable in children.
     Nonetheless, gradual, steady improvement in speech perception, speech
     production, and language does occur. There is substantial unexplained
     variability in the performance of implant users of all ages, and
     implants are not appropriate for all individuals.
   * Currently children at least 2 years old and adults with profound
     deafness are candidates for implantation. Cochlear implant candidacy
     should be extended to adults with severe hearing impairment and poor
     open-set sentence discrimination, i.e., less than or equal to 30
     percent in the best aided condition. Although there are theoretical
     reasons to lower the age of implantation in children, data are too
     scarce to justify a change in criteria. Additional data may justify a
     change in age and audiologic criteria.
   * Auditory performance with a cochlear implant varies among individuals.
     The data indicate that performance is better in individuals who (1)
     have shorter durations of deafness, (2) were implanted before age 6
     years, and (3) acquired language before their hearing loss occurred.
     Auditory performance is not affected by etiology of hearing loss.
   * Access to optimal educational and (re)habilitation services is
     important to adults and is critical to children to maximize the
     benefits available from cochlear implantation.
   * The current generation of intracochlear, multichannel implants with
     spectrally based speech processors provides a substantial improvement
     over the previous generation of devices, especially when
     nonsimultaneous electrode activation is used.
   * The low complication rate and high reliability for cochlear implants
     compares favorably with other implanted electronic devices, and
     continues to improve.
   * Current devices are not MRI compatible, and users and physicians
     should be acutely aware of this problem. Implant manufacturers should
     include MRI compatibility and internal self-test systems in future
     devices.
   * Percutaneous connectors offer many research and clinical
     opportunities, including MRI compatibility, ease of electrode testing,
     and processor upgrades, and they should not be abandoned.
Consensus Development Panel
George A. Gates, M.D.
     Conference and Panel Chairperson
     Professor of Otolaryngology-Head and Neck Surgery
     Director
     Virginia Merrill Bloedel Hearing Research Center
     University of Washington
     Seattle, Washington
Kathleen Daly, Ph.D.
     Assistant Professor
     Department of Otolaryngology
     University of Minnesota
     Minneapolis, Minnesota
William J. Dichtel, M.D.
     Otolaryngologist
     Roanoke, Virginia
Robert J. Dooling, Ph.D.
     Professor
     Department of Psychology
     University of Maryland
     College Park, Maryland
Aina Julianna Gulya, M.D.
     Professor
     Department of Otolaryngology
     Head and Neck Surgery
     Georgetown University
     Washington, District of Columbia
Joseph W. Hall III, Ph.D.
     Professor
     Department of Surgery
     Division of Otolaryngology
     University of North Carolina at Chapel Hill
     Chapel Hill, North Carolina
Susan W. Jerger, Ph.D.
     Professor and Director
     Children's Special Hearing Section
     Department of Otorhinolaryngology
     Baylor College of Medicine
     Houston, Texas
Jacqueline E. Jones, M.D.
     Assistant Professor
     Department of Otolaryngology
     Cornell University Medical College
     New York Hospital
     New York, New York
Margaret H. Mayer, Ed.D.
     Coordinator for Teacher Education and Research
     Northwest School for Hearing-Impaired Children
     Seattle, Washington
Michael Pierschalla
     Cambridge, Massachusetts
Lainie Friedman Ross, M.D., M.Phil.
     Assistant Professor
     Department of Pediatrics and MacLean Center for Clinical Medical
     Ethics
     University of Chicago
     Chicago, Illinois
Richard G. Schwartz, Ph.D.
     Professor
     Ph.D. Program in Speech and Hearing Sciences
     City University of New York
     New York, New York
Barbara E. Weinstein, Ph.D.
     Associate Professor of Audiology
     Director, Audiology Program
     Lehman College
     City University of New York
     New York, New York
Eric D. Young, Ph.D.
     Professor
     Department of Biomedical Engineering
     Johns Hopkins University
     Baltimore, Maryland
Speakers
Paul J. Abbas, Ph.D.
     "Factors Affecting Auditory Performance: Electrophysiologic Measures"
     Professor
     Department of Speech Pathology and Audiology
     Department of Otolaryngology
     Head and Neck Surgery
     University of Iowa
     Iowa City, Iowa
Peter Blamey, Ph.D.
     "Factors Affecting Auditory Performance of Postlinguistically Deaf
     Adults Using Cochlear Implants: Etiology, Age, and Duration of
     Deafness"
     Principal Research Fellow
     Department of Otolaryngology
     University of Melbourne
     East Melbourne, Victoria, Australia
Derald E. Brackmann, M.D., F.A.C.S.
     "Percutaneous Connectors in Cochlear Implantation"
     Clinical Professor of Otolaryngology-Head and Neck
     Surgery/Neurosurgery
     University of Southern California School of Medicine
     President
     House Ear Clinic and Institute
     Los Angeles, California
Judith A. Brimacombe, M.A.
     "Multichannel Cochlear Implants in Adults With Residual Hearing"
     Vice President
     Clinical and Regulatory Affairs
     Cochlear Corporation
     Englewood, Colorado
Patricia M. Chute, Ed.D.
     "Residual Hearing in Children"
     Director, Cochlear Implant Center
     Manhattan Eye, Ear, and Throat Hospital
     New York, New York
Noel L. Cohen, M.D.
     "Surgical Complications and Considerations"
     Professor and Chairman
     Department of Otolaryngology
     New York University School of Medicine
     New York, New York
Michael F. Dorman, Ph.D.
     "Speech Perception by Adults"
     Professor
     Department of Speech and Hearing Science
     Arizona State University
     Tempe, Arizona
     Adjunct Professor
     Division of Otolaryngology
     University of Utah
     Health Sciences Center
     Salt Lake City, Utah
Donald K. Eddington, Ph.D.
     "Introduction and Overview"
     Cochlear Implant Research Laboratory
     Massachusetts Eye and Ear Infirmary
     Boston, Massachusetts
Bruce J. Gantz, M.D., F.A.C.S.
     "Device Failure"
     Professor and Interim Head
     Department of Otolaryngology
     Head and Neck Surgery
     University of Iowa College of Medicine
     Iowa City, Iowa
James W. Heller, P.E.
     "MRI Considerations"
     Manager of Research
     Cochlear Corporation
     Englewood, Colorado
Darlene R. Ketten, Ph.D.
     "Radiologic Assessment"
     Assistant Professor
     Department of Otology and Laryngology
     Harvard Medical School
     Research Director
     Three-Dimensional Imaging Service
     Massachusetts Eye and Ear Infirmary
     Boston, Massachusetts
John F. Knutson, Ph.D.
     "Psychological and Social Issues in Cochlear Implant Use"
     Professor
     Department of Psychology
     Spence Laboratories of Psychology
     University of Iowa
     Iowa City, Iowa
Patricia A. Leake, Ph.D.
     "Long-Term Effects of Electrical Stimulation"
     Professor in Residence
     Department of Otolaryngology
     Research Director
     Epstein Hearing Research Laboratory
     University of California San Francisco
     San Francisco, California
Hugh J. McDermott, Ph.D.
     "Speech Processing Using Selected Spectral Features"
     Research Fellow
     Department of Otolaryngology
     University of Melbourne
     East Melbourne, Victoria, Australia
Richard T. Miyamoto, M.D., F.A.C.S.
     "Timing of Implantation in Children"
     Arilla Spence DeVault Professor and Chairman
     Department of Otolaryngology-Head and Neck Surgery
     Indiana University School of Medicine
     Indianapolis, Indiana
Jean S. Moog, M.S.
     "Rehabilitation and Educational Issues in Children"
     Director of Deaf Education
     Central Institute for the Deaf
     St. Louis, Missouri
Mary Joe Osberger, Ph.D.
     "Effect of Age at Onset of Deafness on Cochlear Implant Performance"
     "Speech Perception in Children"
     Director, Pediatric Clinical Research
     Advanced Bionics Corporation
     Sylmar, California
Robert V. Shannon, Ph.D.
     "Information Transmission in Cochlear Implants: Analysis Channels,
     Number of Electrodes, and Received Channels"
     Auditory Implant Research
     House Ear Institute
     Los Angeles, California
Margaret W. Skinner, Ph.D.
     "Audiologic Criteria for Cochlear Implantation in Adults and Children"
     Associate Professor
     Director of Audiology
     Director of Cochlear Implant Program
     Department of Otolaryngology-Head and Neck Surgery
     Washington University School of Medicine
     St. Louis, Missouri
Quentin Summerfield, Ph.D.
     "Cost-Effectiveness Considerations in Cochlear Implantation"
     Professor
     Medical Research Council
     Institute of Hearing Research
     Nottingham, United Kingdom
Emily A. Tobey, Ph.D.
     "Speech Production in Children"
     Professor and Nelle C. Johnston Chair in Early Childhood Communication
     Disorders
     Department of Communication Disorders
     Callier Center for Communication Disorders
     University of Texas at Dallas
     Dallas, Texas
Susan B. Waltzman, Ph.D.
     "Comparison of Implant Systems"
     Professor
     Department of Otolaryngology
     New York University
     School of Medicine
     New York, New York
Blake S. Wilson, B.S.E.E.
     "Continuous Interleaved Sampling and Related Strategies"
     Director
     Center for Auditory Prosthesis Research
     Research Triangle Institute
     Research Triangle Park, North Carolina
Teresa A. Zwolan, Ph.D.
     "Factors Affecting Auditory Performance With a Cochlear Implant by
     Prelingually Deafened Adults"
     Assistant Research Scientist
     Director, Cochlear Implant Program
     Department of Otolaryngology-Head and Neck Surgery
     Audiology and Electrophysiology Division
     University of Michigan Medical Center
     Ann Arbor, Michigan
Planning Committee
Amy M. Donahue, Ph.D.
     Chairperson
     Acting Chief, Hearing and Balance/Vestibular Sciences Branch
     Division of Human Communication
     National Institute on Deafness and Other Communication Disorders
     National Institutes of Health
     Bethesda, Maryland
Marin P. Allen, Ph.D.
     Chief
     Program Planning and Health Reports Branch
     National Institute on Deafness and Other Communication Disorders
     National Institutes of Health
     Bethesda, Maryland
Lucille B. Beck, Ph.D.
     Associate Chief
     Audiology and Speech Pathology Service
     Department of Veterans Affairs
     Washington, District of Columbia
Elsa A. Bray
     Program Analyst
     Office of Medical Applications of Research
     National Institutes of Health
     Bethesda, Maryland
Judith A. Cooper, Ph.D.
     Deputy Director
     Division of Human Communication
     National Institute on Deafness and Other Communication Disorders
     National Institutes of Health
     Rockville, Maryland
John H. Ferguson, M.D.
     Director
     Office of Medical Applications of Research
     National Institutes of Health
     Bethesda, Maryland
Marilyn Neder Flack, M.A.
     Senior Scientific Reviewer/Audiologist
     Ear, Nose, and Throat Devices
     Center for Devices and Radiological Health
     Office of Device Evaluation
     Food and Drug Administration
     Rockville, Maryland
George A. Gates, M.D.
     Conference and Panel Chairperson
     Professor of Otolaryngology-Head and Neck Surgery
     Director of Virginia Merrill Bloedel
     Hearing Research Center
     University of Washington
     Seattle, Washington
William H. Hall
     Director of Communications
     Office of Medical Applications of Research
     National Institutes of Health
     Bethesda, Maryland
F. Terry Hambrecht, M.D.
     Head, Neural Prosthesis Program
     National Institute of Neurological Disorders and Stroke
     National Institutes of Health
     Bethesda, Maryland
Norman Krasnegor, Ph.D.
     Chief
     Human Learning and Behavior Branch
     Center for Research for Mothers and Children
     National Institute of Child Health and Human Development
     National Institutes of Health
     Bethesda, Maryland
Andrew A. Monjan, Ph.D., M.P.H.
     Chief
     Neurobiology of Aging Branch
     Neuroscience and Neuropsychology of Aging Program
     National Institute on Aging
     National Institutes of Health
     Bethesda, Maryland
Ralph F. Naunton, M.D.
     Director
     Division of Human Communication
     National Institute on Deafness and Other Communication Disorders
     National Institutes of Health
     Rockville, Maryland
Conference Sponsors
     Office of Medical Applications of Research, NIH
     John H. Ferguson, M.D.
     Director
     National Institute on Deafness and Other Communication Disorders
     James B. Snow, Jr., M.D.
     Director
Cosponsors
     National Institute on Aging
     Richard J. Hodes, M.D.
     Director
     National Institute of Child Health and Human Development
     Duane F. Alexander, M.D.
     Director
     National Institute of Neurological Disorders and Stroke
     Zach W. Hall, Ph.D.
     Director
     U.S. Department of Veterans Affairs
     Jesse Brown
     Secretary
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