HYPOACUSIS IN CHILDREN:

HYPOACUSIS
IN CHILDREN:
hearing to grow up
INTRODUCTION
Methodology
International bibliographic resources were used to analyze a number of international clinical
and laboratory studies involving the use of screening programs and hearing aids on children
suffering from hearing loss.
Project Working Group
This review is the result of a study of the scientific literature available on the topic conducted
by Prof. Edoardo Arslan, Audiology and Phoniatrics Department – University of Padua – Treviso
Hospital, Prof. Dr. med. Annette Limberger, Aalen University of Applied Sciences, Aalen, Germany,
Dr. Natalie Loundon, ENT Department – Prof. E. Garabedian équipe – Armand Trousseau Children’s
Hospital – Paris.
CONTENTS
01 Hearing loss in children: from early detection to treatment
3
02 Children and hearing aids, hearing loss rehabilitation
13
03 The use of cochlear implants in infant deafness
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This publication was made possible thanks to Amplifon’s contribution
Coordination
MSL Italia
Graphic design and printing
www.mercuriogp.eu
1
ABSTRACT
Most children with congenital hearing loss suffer from hearing impairment
at birth which can usually be detected through newborn infant hearing
screening. At least half of all cases of deafness and hearing impairment can
be prevented through early detection. Otherwise, acoustic amplification
or cochlear implants, supported by hearing and speech therapy, may be
necessary.
Fitting, verifying and validating the adequacy of hearing aids is challenging
and places great demands on the audiologist. The whole process has to
be double checked to make sure that the child is provided with adequate
amplification so that effective hearing can be restored through the
appropriate therapy.
Early detection and quality therapy are the most powerful ways to
optimize the impact of hearing rehabilitation on language development
in children with profound congenital hearing loss: the use of increasingly
sophisticated hearing aids or cochlear implants makes it possible to offset
the hearing loss and recover the hearing ability needed for satisfactory
language and speech perception development in almost all the instances
involving children suffering from impaired hearing.
The purpose of this review is to provide useful information about hearing
loss in children, diagnosis and possible solutions, in order to improve their
future and health.
The Authors
2
01Hearing loss
children:
in
from early detection
to
treatment
3
Hearing loss in children:
from early detection to treatment
Prof. Edoardo Arslan and Enrico Muzzi, Audiology and Phoniatrics Department – University of Padua – Treviso Hospital
Source: Siemens
problems. Typically conductive hearing loss is temporary,
with slight to moderate hearing loss and can be treated
either surgically or through drug therapy. Sensorineural
hearing loss is a pathology of the inner ear, cochlea or
hearing nerve; it is typically permanent and may require
the use of a hearing aid or cochlear implantation (CI),
along with hearing and speech therapy.
Congenital hearing loss can be hereditary or related to
problems encountered during pregnancy and childbirth.
The last position statement of the Joint Committee on
Infant Hearing (2007) discusses the key risk indicators
associated with permanent hearing loss in childhood.
These include admission of the newborn to neonatal
intensive care for more than 5 days or any of the
following, regardless of the duration: extracorporeal
membrane oxygenation (ECMO), assisted ventilation,
exposure to ototoxic medications (gentamycin and
tobramycin) or loop diuretics (furosemide/Lasix);
Key factors and global perspective
Hearing impairment in children worldwide constitutes
a particularly serious obstacle to their optimal
psychological development. Deafness can, in fact,
affect language acquisition, learning ability and social
integration. The cost of special education and lost
employment due to hearing impairment can be a burden
to a country’s economy. An estimated 1 to 2 out of every
1,000 newborns suffers from hearing impairment at birth
which is detectable through newborn infant hearing
screening. Some congenital hearing loss, however, may
not become evident until later in childhood [Erenberg et
al. 1999]. Severe, early deafness is present in 0.4 to 1.5
out every 1,000 children and at least 50% of these cases
is attributable to genetic causes [Marazita et al. 1993].
There are two types of hearing loss. Conductive hearing
loss is a problem in the outer or middle ear which affects
a child’s quality of life, as in the case of middle ear
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hyperbilirubinemia which requires a blood transfusion.
Other risk indicators include any viruses a mother may
have had during pregnancy, particularly during the first
three months such as German measles, toxoplasmosis,
and CMV [JCIH 2007 Pediatrics]. Acquired causes that
can lead to hearing loss at any age, mostly in childhood,
include infectious diseases like meningitis, measles,
mumps and syphilis. Use of ototoxic drugs at any age,
along with some antibiotic and anti-malarial drugs, can
damage the inner ear. Head injury or injury to the ear
can cause hearing impairment. Hearing impairment can
be the cause of a heavy social and economic burden for
individuals, families, communities and countries. Several
socio-economic studies report [Abrams et al. 2002] that
the social costs, in terms of rehabilitation and exclusion
from a county’s socio-economic system, are in fact
much higher when hearing impairment in children is not
detected early and adequately treated.
Hearing impairment in children may delay development
of language and cognitive skills, thus hindering progress
in school. The extent of the delay depends on the
degree of hearing loss. Later in life, hearing impairment
often makes it difficult to obtain, perform, and keep
jobs. Hearing-impaired children and adults are often
stigmatized and socially isolated. Globally, the poor
suffer more from hearing impairment because they
cannot afford the preventive and routine care needed
to avoid hearing loss. With limited or no access to ear
and hearing care services, they are unable to obtain the
hearing aids needed to make the disability manageable.
Hearing impairment may also make it more difficult for
these individuals to escape poverty or social isolation.
At least half of all cases of deafness and hearing
impairment are avoidable through early prevention.
A large percentage can be treated through secondary
preventive measures designed to reduce the hearing
disability through early detection and suitable
management as the correct rehabilitation can effectively
restore hearing. With regard primarily to underdeveloped
and some developing countries simple strategies for
global prevention must include:
- immunizing children against childhood diseases, including
measles, meningitis, German measles and mumps;
- immunizing adolescent girls and women of childbearing age against German measles before pregnancy;
- screening and treating for syphilis and other infections
in pregnant women;
- improving prenatal and perinatal care, including
promotion of safe deliveries;
- avoiding the use of ototoxic drugs, unless prescribed
by a qualified physician and properly monitored for
correct dosage;
- referring high risk babies, such as those with family
history of deafness, those born with life-threatening
conditions, for early hearing screening;
- assessment, diagnosis and treatment of hearing when
required.
Conductive hearing impairment can be prevented by
increasing the prevention of otitis in children with
adequate specialized medical care and surgery. It should
be noted, however, that the global production of hearing
aids meets less than 10% of global demand. In developing
countries, fewer than 1 out of 40 people who need a
hearing aid have one [WHO 2012].
New insights into auditory plasticity
Early rehabilitation of a deaf child’s auditory function can
help to correct the hearing deficit, as well as facilitate
the maturation of the central auditory system and the
auditory cortex as has been demonstrated in experiments
involving deaf animals and humans. Patients with
cochlear implants are useful in the study of hearing loss
and help to understand how and when the brain can
overcome the lack of auditory input. Electrophysiological
studies in humans show maturation of evoked responses
with cochlear implantation (CI) stimulation [Sharma et
al., 2007]. However, a period of maximum receptiveness
to auditory stimulation (sensitive period) occurs both in
animals and in humans which is controlled by genetically
determined processes and during which the principal
changes and the organization of the neural pathways which
are the foundation of hearing and language perception
take place. If, during this period, the peripheral auditory
input is not adequate the organization of the central
hearing pathways will take place but in an incomplete
manner. The absence of hearing experience during this
sensitive period results in a substantial reduction of
synaptic activity (computational power) of the cortex in
deaf animals as compared with hearing animals.
The auditory cortex, located in the temporal lobe (Figure 1)
contains the majority of neurons present in our brains at
the time of birth, but they have few and randomly
distributed synaptic connections.
5
Synapses, at the basis of the neural circuits, develop very
rapidly during the first two years of life and are tightly
linked to the hearing experience. They then decrease
from the third year of age on and constitute the base
of the neural circuits devoted to hearing perception,
specifically of language, which is the most
important distinguishing characteristic of man’s ability
to hear.
Figure 1
(taken from Kral A, O’Donoghue GM. 2010) Development of the synapses in the Central Auditory System and Auditory cortex. The postnatal
development on the auditory cortex shows that the number of dendritic trees is highest at the age of 4 years in children with normal hearing
(Huttenlocher and Dabholkar AS. 1997). Peak synaptic density has been observed at 2 to 4 years in children with normal hearing. Subsequently,
synaptic counts decrease because unused synapses are eliminated.
The same behaviour can be observed in congenitally deaf cats: the lack of auditory input in newborns, as shown in the lower part of the figure,
has two main effects: retarded growth of synaptic circuits and a slight increase in the overall amount, probably explained by the permanence of
non-functioning synaptic circuits.
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conditions (such as birth asphyxia, low birth weight and
hyperbilirubinaemia) and head trauma can also cause
hearing loss. Regardless of its cause, unidentified hearing loss
at birth or during the first few years of life adversely affects
speech and language development, as well as success in
school and social-emotional development. In the absence
of universal hearing screening programs for newborns and
infants, a significant number of cases of children with
hearing loss are not detected until well beyond the critical
period resulting in a state of irreversible hearing loss. In fact,
it is not unusual for the diagnosis of milder hearing loss
and unilateral hearing loss to be delayed until children are
six years of age or older. When detection and intervention
occur during the first few months of life, infants and young
children with hearing loss perform dramatically better in
scholastic activities including vocabulary development,
articulation, social adjustment and behaviour.
Most existing newborn and infant hearing screening
programs target permanent sensory or conductive
hearing loss, averaging 30-40 dB or more in the frequency
region important for speech recognition (approximately
500-4000 Hz).There is growing agreement that milder hearing
loss (20-30 dB) is also important and needs to be detected
and treated early because of the negative consequences
of such loss on the later development of children. Some
programs are designed to identify only bilateral hearing loss,
but there is again growing agreement that the identification
of unilateral hearing loss is also important and valuable.
Similarly, fluctuating conductive hearing loss caused by
otitis media are generally not targeted by newborn hearing
screening programs, even though chronic otitis media has
serious negative consequences.
A number of different approaches can be used to
identify hearing loss in newborns and infants. There is
widespread agreement that the best approach is the
universal newborn screening procedure using otoacoustic
emissions (OAE) testing or auditory brainstem response
(ABR). However, where such programmes are not possible
because of financial limitations, or because appropriate
equipment and personnel are not available, or because
of other constraints – other approaches can be valuable
ad interim. These include family questionnaires or
behavioural analyses. Such methods produce high levels
of both false negatives and false positives with babies less
than 12 months old. OAE or ABR measurements have been
shown to be effective methods of screening for hearing
loss in newborns and infants. OAEs measure the status of
the peripheral auditory system extending to the cochlear
outer hair cells. OAE measurements are obtained from
the ear canal by using a sensitive microphone within a
Universal newborn hearing screening
The basic treatment for hearing impairment in children
consists in early detection, along with the selection of
adequate hearing aids and rehabilitation. Countries with
different healthcare systems, as well as economic and
social circumstances, have successfully implemented
newborn and infant hearing screening programs. Although
the aetiology of congenital or early-onset hearing loss most
likely varies from country to country, there is widespread
agreement that at least half of such hearing loss is due
to genetic mutations. Viruses (such as cytomegalovirus,
German measles, and meningitis); diseases (such as
measles, mumps and chronic otitis media); adverse perinatal
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Delaying effective auditory abilitation beyond this
window markedly decreases brain adaptability and
speech comprehension. This situation, called auditory
deprivation, results in a lack of organization by the
central auditory processor which affects the size and
structure of the neural networks (they become smaller)
and the synapses which becomes less reversible after
the physiological period of language development.
In other words, the auditory input serves as a modulator
and regulator of development of the central auditory
processor which organizes itself around the acoustic
information and neural impulses coming from the
periphery. With regard, specifically to the auditory system,
the lack of auditory stimulus will result in incomplete or
inadequate development of the linguistic processor.
The development of the human auditory system involves
several sensitive periods relating to the auditory, phonetic
and phonologic, syntactic, and semantic aspects of
language. These periods probably reflect the maturation
of the various cortical areas. Normal brain maturation
also calls for the ability to respond through appropriate
multimodal interaction, which is affected by deprivation.
In persons who have become deaf after the acquisition
of spoken language, brain activity triggered by a CI can
be observed in non-auditory regions, with visual centres
contributing to comprehension of speech through
lip-reading. However, cross-modal reorganization can
also cause deterioration of the auditory performance
in persons and animals with congenital deafness if the
critical period is exceeded. Based on these findings
and language testing, effective hearing abilitation is
recommended in the first 1 to 2 years of life, including
CI surgery if needed. With the use of universal newborn
hearing screening, this is feasible in the first year of life
[Kral and O’Donoghue 2010].
treatment. Auditory brainstem response (ABR) and
otoacoustic emissions (OAE) screening techniques
paved the way for quick, effective ways to screen the
hearing of babies. Healthy People 2000, a national health
promotion and disease prevention initiative in the US,
indicated that testing for congenital hearing loss should
be begin at 12 months of age. A decade later, Healthy
People 2010 includes additional benchmarks: hearing
screenings by one month, audiologic evaluation by
three months, and early intervention by six months of
age. If amplification is indicated for a baby with hearing
loss, early, appropriate amplification requires accurate
estimates of hearing sensitivity. For infants, a typical
audiological test battery consists of ABR, tympanometry
and acoustic reflex testing, and OAEs, with behavioural
audiometric testing when developmentally feasible.
Data about threshold agreement between ABR and
behavioural audiometric tests for children have been
published, supporting the use of both tools. Delays
in finding the correct amplification may be due to
problems with scheduling, the need for repeat tests,
suspicion of auditory neuropathy/dys-synchrony, and
the cost of hearing aids. Delays in fitting the hearing
aid are also likely for babies who are medically fragile
or very premature.
After the diagnostic procedure, the first step is to fit the
child with a hearing aid. The process can be thought of
as a five-step approach:
1. Selection
3. Counselling
2. Fitting
4. Fine-tuning
5. Follow-up
The selection stage coincides with the beginning of the
process that will lead to the development of the infant’s
communication skills. The family helps choose earmolds
and hearing instruments; options are restricted by
the relatively small size of infants’ ears. The earmold
material should be a soft material, typically silicone or
vinyl, which does not hurt the infant’s ears. Typically
recommended pediatric hearing aids are binaural
behind-the-ear and FM-compatible with flexible
electroacoustic characteristics. Acoustic feedback
occurs often with babies, as they quickly outgrow
earmolds, but nowadays the digital hearing aids have
feedback reduction circuits, which make maintenance
of the earmold less critical.
In general there is some agreement, albeit from varying
sources, as to the specific circuitry to be used with
infants. Wide Dynamic Range Compression (WDRC)
probe that records cochlear responses to acoustic stimuli.
The ABR measurements are obtained from surface
electrodes that record neural activity generated in the
auditory nerve and brainstem in response to acoustic
stimuli delivered via an earphone. Screening ABR
measurements are usually automated (AABR) and reflect
the status of the peripheral auditory system, the eighth
nerve, and the brainstem auditory pathway.
The benefits of early hearing detection and intervention
(EHDI) programs which facilitate early detection of and
therapy for infant deafness are well known. It is only
through these preventive steps and the subsequent
therapy that today we are able to detect deafness in
the first few months of life and subsequently program
audiological and diagnostic procedures, as well as
determine the medical treatment, surgery and devices
needed while also helping to educate the children
suffering from hearing impairment and their families.
Successful newborn and infant hearing screening
programs have been implemented in many different
countries using a variety of screening methods and
protocols, while working closely with the public
healthcare agencies, social services and schools.
Such programs are widely accepted as both highly
worthwhile, with acceptable cost/benefit ratios and
should, therefore, be offered in all countries. Although
every nation should work to implement universal
newborn hearing screening using OAE or AABR, interim
approaches using targeted screening of children based
on risk indicators or based on questionnaires can also
be beneficial. Whatever approach is used, it is important
that the EHDI program is linked to existing healthcare
programs, as well as social and educational services, and
that the procedures and outcomes of the program be
documented so that ongoing quality control activities
can be implemented and experiences shared [WHO
2009].
Early rehabilitation of hearing and
language
Improved and more widespread screening programs
make it possible to identify more infants with hearing
loss at an increasingly younger age. Helping families
find and access appropriate therapies for their infants
is the key to the success of screening programs. Until
the 1990s, children born with significant hearing loss
typically were not identified until they reached 2436 months of age. Better coordinated and responsive
follow-up systems ensure earlier detection and
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Subsequent assessment should be based on the hearing
sensitivity of the child wearing the hearing aid and
the hearing aid’s electroacoustic inputs and determine
whether speech is audible using a wide range of inputs.
Electroacoustic assessment is frequently the only
feasible option with very young babies. It provides
frequency-specific information about the audibility of a
wide variety of speech inputs, as well as estimating the
individual ear amplification response (RESR).
Because infants are unlikely to tolerate the repeated
use of probe-microphone devices, electroacoustic
assessment for them includes real-ear-to-couplerdifference (RECD) measures combined with coupler
values to predict the real-ear-aided-response (REAR)
and RESR, taking in account the rapid physiological
growth of the ear in babies.
To promote the consistent use of a hearing aid, parents
and/or caregivers need information about proper care,
the appearance and benefits of the devices. It is very
important that parents are involved in the fitting
of the hearing aid. Parents should be shown how to
take care of the earmolds and hearing aids; insert the
earmolds and put the hearing aids in place; as well
as remove the devices. Daily sound checks are vital
because infants cannot tell anyone when a hearing aid
is malfunctioning. The family must be supplied with
hearing aid maintenance tools. Child-friendly retention
devices, including pediatric tone hooks, help babies
accept and keep the devices. Many manufacturers
provide hearing device care kits.
When well fitted hearing aids are still not enough to
assist speech perception, CI should be considered.
Several factors appear to influence the process involved
in deciding whether or not a child should have a CI,
including the family’s preferences, the child’s cognitive
and neurological state, and the amount of the child’s
residual hearing. Clinicians have, however, expressed
concern about whether children with hearing loss
more than 90 dB HL, average 500-1000-2000 Hz,
were appropriate candidates for cochlear implantation.
For thresholds ranging from 70 to 90 dB HL, borderline
cases, therefore, clinicians were more likely to rely on
additional information including the child’s spoken
language, progress in treatment, social interaction,
academic ability and classroom comprehension
[Fitzpatrick et al. 2009].
In light of the ever changing landscape relative to
CI eligibility, it is important to stay current on the
technology and the criteria used to determine eligibility
in order to be able to help families find the most
appropriate solution for their children.
An increasing amount of scientific evidence points to
the importance of implanting the devices at the right
time in a child’s life, particularly those with greater
amounts of residual hearing, as well as the importance
of reducing hearing aid trial periods. Future studies will
need to focus on providing the data needed to assist
clinicians in helping families make the right decisions
for their children [Tobey 2010].
In order to assess the benefits of hearing aids in older
children and adults speech perception is measured
while the device is being worn. Babies require further
assessment measures to be implemented, which often
are subjective and depend on feedback from parents
or the clinician’s observations. However, the ultimate
assessment tool is the measurement of speech and
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language development. In the early months of life,
babbling and phoneme development should be
monitored carefully. Tests have been developed in
many languages for testing speech perception abilities
in children based on age, beginning at 6 months.
The medical staff, parents, therapists and audiologists
all must collaborate in order to determine if changes in
amplification are needed.
Following the detection and confirmation that hearing
loss exists, and subsequent to the fitting of the hearing
aid, a reasonable follow-up schedule for children less
than 2 years old includes check-ups every three months.
At each check-up hearing is monitored, hearing aids are
tested and adjusted, and new earmolds are made when
needed. Check-ups every six months are appropriate
for most children from the ages of 2 to 6, with yearly
check-ups thereafter, unless risk factors indicating the
hearing loss could worsen are present [Hoffman and
Beauchaine 2007].
hearing aids are appropriate for children who have
mild to moderately severe hearing loss, according to
a review of the studies made by Palmer and Grimes
(2005). They state that evidence supports the use of
low compression thresholds, moderate compression
ratios, and fast attack times.
There is also an approach developed by pediatricians
designed to ensure that specified sensation levels for
inputs and outputs in amplified speech are reached.
The Desired Sensation Level (DSL) approach, developed
by Seewald and colleagues, works with these targets.
To conclude, today it is possible to say that the
condition of being deaf-mute, namely the most severe
communication disorder, which occurred 20 years ago
has finally disappeared.
The use of increasingly sophisticated hearing aids or cochlear
implants, in the case of severe hearing loss (Figure 3),
makes it possible to offset the hearing loss and recover
the hearing ability needed for satisfactory language and
speech perception development in almost all the instances
involving children suffering from impaired hearing.
Early Hearing Detection and Intervention programs
based on universal hearing screenings, early detection
and treatment are the key to diagnosing and treating
hearing impairment in children (Figure 2).
Birth Admission
Screening
Follow-up
Screen &
Diagnostic
Early
Intervention
Figure 2
The three Components of Early Hearing Detection and Intervention
Programs (from: http://www.jcih.org/).
FLOW CHART FROM SCREENING TO
HEARING RESTORATION IN CHILDREN
4
1
3
EARLY AUDIOLOGICAL
MEASUREMENTS
FIRST ACOUSTIC
AMPLIFICATION
SCREENING
2
0m
BEST ACOUSTIC FITTING
3m
6m
5
HEARING AND
LANGUAGE EVALUATION
HEARING AID
6
COCHLEAR IMPLANT
12 m
18 m
24 m
To act against auditory deprivation
To maximize Central Auditory System input
Figure 3
Diagnostic and therapeutic flow from birth to hearing restoration.
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1. Abrams H, Chisolm T, McArdle R: A cost-utility analysis of adult group audiologic rehabilitation: are the benefits
worth the cost? Journal of Rehabilitation Research and Development. 2002; 39(5):549-558.
2. American Academy of Pediatrics, Joint Committee on Infant Hearing. Year 2007 position statement: Principles and
guidelines for early hearing detection and intervention programs. Pediatrics. 2007;120:898-921.
3. Clark, J. G. Uses and abuses of hearing loss classification. Asha. 1981; 23, 493–500.
4. Erenberg A, Lemons J, Sia C, Trunkel D, Ziring P. Newborn and infant hearing loss: detection and intervention.
American Academy of Pediatrics. Task Force on Newborn and Infant Hearing, 1998- 1999. Pediatrics. 1999;103:527530.
5. Fitzpatrick E, Olds J, Durieux-Smith A, McCrae R, Schramm D, Gaboury, I. Pediatric cochlear implantation: how much
hearing is too much? Int J Audiol. 2009;48:91-97.
6. Hoffman J, Beauchaine K. Babies with hearing loss: steps for effective intervention. ASHA. 2007.
7. Huttenlocher and Dabholkar AS. Regional Differences in Synaptogenesis in Human Cerebral Cortex. J Comp Neurol
1997; 387:167-178.
8. Kral A, O’Donoghue GM. Profound deafness in childhood. N Engl J Med. 2010;363:1438-1450.
9. Marazita ML, Ploughman LM, Rawlings B, Remington E, Arnos KS, Nance WE. Genetic epidemiological studies of
early-onset deafness in the U.S. school-age population. Am J Med Genet. 1993;46:486-491.
10. Niskar AS, Kieszak SM, Holmes A, Esteban E, Rubin C, Brody DJ. Prevalence of hearing loss among children 6 to 19
years of age: the Third National Health and Nutrition Examination Survey. JAMA. 1998;279:1071-1075.
11. Sharma, A., Gilley, P.M., Dorman, M.F. & Baldwin, R. Deprivation-induced cortical reorganization in children with
cochlear implants. Int. J. Audiol. 2007; 46: 494–499.
12. Tobey E. The changing landscape of pediatric cochlear implantation: outcomes influence eligibility criteria. ASHA. 2010.
13. WHO Media Center. Deafness and hearing impairment. Fact sheet N°300; february 2012.
14. WHO Meeting Reports. Newborn and infant hearing screening: current issues and guiding principles for action.
Documents and Publications; November 2009.
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References
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Children and
hearing aids,
hearing loss
rehabilitation
02
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Children and hearing aids, hearing loss rehabilitation
Prof. Dr. med. Annette Limberger, Aalen University of Applied Sciences, Aalen, Germany
Source: Siemens
Fitting children with hearing aids is quite challenging and
the approach varies depending on the age of the child.
In babies and toddlers the fitting process is based primarily
on objective findings like ABR (auditory brainstem
response), otoacoustic emissions (OAE) and impedance
measurements. In older children, from age two and a half
or school-age children, the fitting procedure may rely much
more on subjective measurements like the VRA (visual
reinforcement audiometry) and speech audiometry.
Fitting hearing aids in babies
In this age group the audiologist is dependent on ABR,
otoacoustic emissions and impedance measurements.
It is important, therefore, to use frequency dependent
ABR measurements with both tone bursts or notched
noise signals. The measurements should be conducted
with insert earphones to measure each side separately
from the other.
The DSL method described by Scollie et al. involves an
instrument for fitting hearing aids in babies and children
which is widely accepted and scientifically proven to
be adequate. The method calls for amplification of low
level sounds like whispering, wind rustling in trees etc.
to make them audible. On the other hand, this method
limits the output level of the hearing aid, so that loud
sounds, i.e. crying, clapping hands, can never be too loud
(Scollie et al., 2005).
Based on this fitting procedure, it is possible to use
electroacoustic hearing threshold estimates particularly
for infants and very young children. The formula for
the hearing aid prescription, however, uses behavioral
thresholds. The levels detected in the frequency-specific
ABR measurements in dB nHL (normalized hearing level)
must therefore be corrected to behavioral thresholds
(dB HL); in infants with sensorineural hearing loss
(SNHL) the behavioral thresholds are 10-20 dB higher
than the ABR threshold estimates (Stapells, Gravel,
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& Martin, 1995). The DSL research group has established
a correction from nHL to eHL (estimated hearing level)
(Table 1). It is also based on the equipment and the
parameter settings, so each clinic has to determine
their own correction factors for each frequency. After
correcting the nHL levels, the values can be used for the
calculation of the amplification (Scollie et al., 2005).
Frequency (Hz)
500
1000
Correction factor
(substract from ABR nHL-thresholds)
-15
-10
Selecting the hearing aid
For infants, BTE-style (behind the ear) hearing aids are
standard, they should also be equipped with:
• Direct audio input
• Locking mechanism on the battery door and volume
control for safety reasons
• Ability to deactivate advanced features
- directional microphone
- noise reduction
- multiple memories
• Choice of bright colours
• Possibility of obtaining a substitute device in the case of
an emergency
• Appropriate number of frequency channels to allow for
frequency/output shaping
• Wide dynamic range compression (WDRC) to prevent
discomfort due to loud noise and distortion
2000 4000
-5
0
Table 1: Corrections for frequency-specific ABR measures (nHL → eHL)
Another main part of the fitting process is the
measurement of the RECD (real ear to coupler difference).
This means that it is necessary to measure the real ear
settings with the individual earmold because of the
smaller ear canal volume in small children. The smaller
volume leads to a higher sound pressure level (SPL)
in the eardrum. This would lead to over amplification
and could also harm the haircells in the inner ear.
To avoid this type of over amplification it is essential
to measure the RECD. It is enough to measure one
ear if the impedance measurements are the same for
both ears and if they look physiologically the same.
This measurement is also used to convert the dB HL
values in dB SPL values because the hearing instrument
also works in dB SPL. With this measurement it is possible
to convert the hearing aid amplification and output levels
to estimated real-ear measurements and to simulate
real ear verification to match the assessment targets.
The variation in the RECD is very high so if it is possible
to obtain a real measurement it should be done. The
RECD should also be re-measured when the earmold or
when the middle ear status changes, for example if the
child has ventilation tubes or suffered from transitory
middle ear otitis (Bagatto et al., 2006).
Advanced features are mostly unnecessary in infants or very
young children, but as they grow older and in the presence of
more challenging, noisier environments, it might be helpful
to activate noise reduction or directional microphones in
special situations (for example, during speech therapy).
Verification
“The responsible audiologist wants to know as much
as possible about the levels of the amplified sound that
hearing instruments deliver into the ears of infants and
young children. To this end, the audiologist must apply
comprehensive and evidence-based verification strategies
that are compatible with the characteristics and capabilities
of this unique population. This is because the long-term
implication of the fitting decisions we make are simply too
important.” (Richard Seewald)
After the audiological assessment, the RECD measurement
and the selection of the hearing aid, it is essential to
measure the amplification and the output levels to exclude
over or under amplification. In adults it is recommended to
measure the real ear aided response (REAR) with a probe
microphone in the ear canal. In infants this procedure is
difficult to conduct because they have to keep calm
for several minutes and the measurement of the
maximum pressure output (MPO) requires a high
intensity of narrow band signals
15
(90-100 dB SPL). This signal may be startling or
uncomfortable to the child. The RECD converts 2-cc
coupler measurements in the test box to predicted real-ear
measurements. With the SPLogram there is an additional
instrument to determine whether most sounds are audible
for the child and fit the dynamic range. The SPLogram
displays the threshold, the recommended targets for
average speech and the maximum power output as a
function of frequency. For modern hearing aids it is also
essential to use a speech based test signal like the ISTS
(international speech test signal).
Fitting the hearing aid
The younger the child the more we are dependent on the
observations of the parents and other caregivers, therefore
questionnaires are designed for parents and other
caregivers, such as teachers. As a result it is more important
to find out how the child uses what is heard in everyday
situations and not only what a child hears. Families are
the primary observers of the behavior of their infants
and young children, thus it is very important to teach the
families how to observe their child’s speech/language and
auditory behavior with and without amplification (Tharpe
& Ryan, 2011).
Follow-up
In the first stage of the fitting process it is mandatory
to see the child almost monthly, especially in the first
year of life. During this time the anatomy of the outer
ear changes very quickly and therefore it is necessary to
manufacture new earmolds every now and then. With
every new earmold the acoustic coupling changes and
a new RECD-measurement has to be performed. In the
second year a three month interval is recommended and
can be prolonged in the third year to a six month interval.
It is also of utmost importance to evaluate the speech and
language development regularly in order to understand if
cochlear implantation is opportune and to intervent at an
early stage.
Conclusion
Fitting, verifying and validating the adequacy of hearing
aids is challenging and places great demands on the
audiologist. The whole process has to be double checked
to make sure that the child is provided with the adequate
amplification.
Management of toddlers and older
children
The principles of hearing aid selection and amplification
are more or less the same. The audiological assessment
differs insofar as subjective measures become more
important, such as VRA and speech audiometry. The more
accurate the assessment of the child, especially with insert
earphones, the better the understanding of the behavioral
threshold and the calculation of the amplification and
maximum power output. With the utterance of the first
words and development of initial language skills it is
also possible to perform speech tests according to the
developmental age.
With the developing child additional features such as
directional microphones and FM-systems may be used
more often, but the audiologist has to make sure that the
parents and other caregivers are familiar with the use of
these and know to switch them off if they are not being
used, e.g. during training sessions.
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1. Bagatto, M., Seewald, R., Scollie, S., & Tharpe, A. (9 2006). Evaluation of a probe-tube insertion technique for
measuring the real-ear-to-coupler difference (RECD) in young infants. J Am Acad Audiol, 17, S. 573-81.
2. Scollie, S., Seewald, R., Cornelisse, L., Moodie, S. B., Laumagaray, D., Beaulac, S., et al. (4 2005). The Desired Sensation
Level multistage input/output algorithm. Trends Amplif, 9, S. 159-97.
3. Seewald, R., & Tharpe, A. M. (2011). Comprehensive Hanndbook of Pediatric Audiology. Abingdon, Oxfordshire,
United Kingdom: Plural Publishing.
4. Stapells, D., Gravel, J., & Martin, B. (4 1995). Thresholds for auditory brain stem responses to tones in notched noise
from infants and young children with normal hearing or sensorineural hearing loss. Ear Hear, 16, S. 361-71.
5. Tharpe, A. M., & Ryan, H. M. (2011). Hearing Instrument Orientation for Children and Their Families. In
R. Seewald, & T. A. Marie, Comprehensive Handbook of Pediatric Audology (S. 599-609). Abingdon, Oxfordshire:
Plural Publishing.
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03
References
18
03
The use of
cochlear
implants
in infant
deafness
03
19
The use of cochlear implants in infant deafness
Dr. Natalie Loundon - Prof. E.N Garabédian ENT Department - Armand Trousseau Children’s Hospital - Paris-France
Receiver
Electrode array
Transmitter
Auditory
Nerve
Processor
Pinna
Ear canal
Cochlea
Average to profound conditions of congenital hearing loss
affect 0.5-1 out of every 1,000 newborn babies 1,2. In cases
of severe to profound hearing loss, where the auditory
system leaves no hope of good-quality aural rehabilitation,
the question of a cochlear implant arises. This is an
aural rehabilitation device that most often proves to be
effective, but which requires a good understanding of
when it should be used and its limitations. In fact, building
a baseline aural-verbal system means the involvement
of peripheral hearing and the development of sensory
and motor areas, as well as cognitive factors. In children,
cochlear implants must be part of a long-term plan,
and take into account medical, psychological, social and
rehabilitation components.
How the cochlear implant works
A cochlear implant is an implantable prosthesis
comprising a removable part and an implanted part.
The external portion consists of a microphone, a voice
processor and an antenna; the internal portion comprises
a receiver and a strip of electrodes. The encoded sound
information is transmitted to the internal part via the
antenna. The intra-cochlear electrodes are activated
depending on the frequencies to be transmitted.
The spiral ganglion cells are thus directly stimulated
through the cochlea.
The auditory information is digitalized for frequency
bands ranging from 250 to 8,000Hz. The signal can
be processed in several ways, depending on whether
one gives priority to speed of stimulation or to
the number of channels activated simultaneously.
The encoding strategies will depend on the number
of functional electrodes and processors. Every implant
has its own specific ergonomic and electronic features,
but the results in terms of speech therapy are the
same 3,4.
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03
information needed. Each case is discussed with the team
before any decision is made.
During this time any medical conditions or progressive
pathologies for which special monitoring is required (visual,
neurological, vestibular or cardiac abnormalities) may also
be ascertained.
The choice of an implant will depend on what the team
is used to and the specific needs of each patient. Surgical
insertion of the internal part requires several hospitalization
days. During surgery, the effect of the stimulation can be
measured either by electric evoked response produced
through the implant, or by telemetry. These tests are
designed to check that the implant-nerve connection
is working and provide an indication of the effective
stimulation thresholds in the post-operative stage. The
implant is activated a few days after surgery. Approximately
ten adjustment visits will be required during the first year,
then just once or twice a year after that.
Pre-implant survey
The parents take part in a medical information session
during which they are told how the implant works.
The limitations and surgical risks are also discussed.
An audiogram, with and without the child wearing the
high-powered device, is used to verify the appropriateness
of the device. Both tonal and speech perception tests are
conducted in silence and in noisy conditions.
A clinical ENT examination serves to eliminate any sources
of infection, and in particular to guide the search for
related pathologies in cases of syndromic and/or genetic
hearing loss, if that has not already been done. Depending
on each case, specialized pediatric examinations may
be called for, such as an ophthalmological exam or a
neuro-pediatric consultation. An ear scan is used to
detect any malformations of the inner ear and to
ascertain the surgical approach needed, and an MRI is
used to explore the labyrinth, the inner ear channel and
the cerebral parenchyma.
Speech therapy testing is essential as it makes it possible
to assess the child’s communication skills and linguistic
abilities. It also helps define a speech therapy plan
together with the family.
A meeting with the psychologist serves to assess the
child’s cognitive and psycho-affective development
and to better understand the family’s expectations and
motivations.
Before performing any implantation, it is essential that
optimal rehabilitation care will be available and that an
appropriate plan for schooling has been developed.
Indications
The criteria for pediatric implants were the subject of
an international consensus in 19955 and more recently
discussed in a French nationwide recommendation by
the National Health Authority (Haute Autorité de Santé HAS) in 2007, updated in 2011 (www.has-sante.fr):
- profound bilateral hearing loss
- thresholds with hearing aid greater than or equal to
60 dB
- open set word (OSW) intelligibility scores of less than
50%.
These guidelines are further developed based on results
reported and the experience acquired by the teams
involved with cochlear implantation and rehabilitation.
The implants were found to be called for primarily in the
presence of severe bilateral or asymmetric hearing loss,
as well as partial or fluctuating hearing loss.
The implantation team
The implantation team is multi-disciplinary and comprises,
in addition to a technical platform that suits the child, the
following specialists: an ENT (Ear, Nose, Throat) surgeon, a
speech therapist and a psychologist.
The role of this team is to determine whether the implant
gives hope for more improvement with respect to a
conventional device, and whether there are any obvious
contraindications (surgical problems, a progressive medical
pathology, psychological problems, etc.)
The pre-implant survey is an especially important time. The
rehabilitation team in charge of the child is encouraged
to discuss this project and provide the family with all the
Post-implantation
Several days after surgery, the first adjustments to the
implant begin, and it normally takes 2 months before
effective auditory thresholds are reached. The child’s
progress in speech therapy is assessed regularly, and
technical monitoring of the device is carried out in
tandem with this.
21
The implant team should have many years of experience
observing children with implants. This experience
allows them to make correct decisions and guarantee
the harmonious development of each child’s language
perception and use, as well as monitor the speech therapy
program. In general the results are good even if they depend
on variables which include the type of hearing loss, age
at the time of implantation, medical history, educational
program and socio-cultural environment, etc. 6-9.
Progress and results
Post-implant results will depend on a number of factors,
but the key factor for congenitally deaf children is how early
the surgery is performed. Neurological research has, in fact,
shown that there is a critical period for the development of
the senses in general, and of the central auditory system,
in particular. Development of the hearing-speaking loop
depends on the nature of this development. When a
child with profound hearing loss is given an implant, the
recordings of cortical response obtained during auditory
stimulation seem to confirm that normalization of the
tracings occurs if the surgery is performed before age 3 and
no normalization after age 7 10.
5 (G3). After 5 years, there was oral communication in
83% of the cases in G1, in 63.5% of G2 and in 45.1%
of G3. For children given implants before 24 months,
word intelligibility scores were in the normal range at
age 5. Children given implants before 16 months showed
they could develop a proto-language more rapidly than
children with no hearing loss and could catch up to them,
and their phonetic development subsequently followed
comparable patterns 15–17.
This language development also made it possible for
children to develop reading and educational skills at the
same rate as children with no hearing loss.
Geers et al. studied the reading abilities of 181 deaf
children, aged 8 to 10 years, who had had implants for 4
to 6 years. More than 51% of them achieved a reading
level comparable to normal children of the same age.
When there were no disorders associated with their
hearing loss, 2/3 of the children could follow a standard
school curriculum 18–20.
Cochlear implants are an effective means of
rehabilitation for perception and usually lead to
the development of oral language in children with
profound congenital hearing loss. If there are no
related problems, and if treatment is given early,
normal progress in school is feasible.
Analysis of brain functions confirms the notion
that there is an optimal period for rehabilitation of
profound congenital bilateral hearing loss.
Special indications
There are numerous clinical studies on the various
perceptive, linguistic and educational aspects of the
effect of implantation in only one ear. Improvement
in perception scores is constant when measured with
traditional indicators, even if to varying degrees.
The perception and oral language skills of a group of
children with congenital hearing loss who have had their
implant for at least 3 years were compared to those of
children with profound hearing loss without implants
of similar age. The results show a substantial difference
between the two groups 11. Comparison of children with
profound hearing loss and children with no loss show
that language tends to develop at the same rate in both
groups after implantation 12. Clinical findings confirm
the existence of a critical period during which children
with profound congenital hearing loss should receive
implants, namely around 24 months. There is a negative
correlation between OSW scores and age at implantation
in children with congenital hearing loss who receive
implants after 30 months 13. Watson et al. 14 studied
176 children after they received cochlear implants;
3 groups were set up based on age at implantation: prior
to age 3 (G1), between ages 3 and 5 (G2) and after age
Bilateral Implantation
Bilateral implantation may be offered to implant
candidates in cases of severe to profound bilateral
hearing loss. Unilateral implantation promotes the
development of oral language skills in deaf children
in most cases. The hypothetical value of bilateral
implantation is to rehabilitate the binaural hearing
function, which makes it easier to understand speech in
a noisy environment and helps with sound localization,
which is impossible in cases of unilateral rehabilitation.
The degree of aural comfort obtained with bilateral
implantation, which reduces the number of situations
where there is only partial reception, could have an
effect on the quality of speech and language skills in
the long term.
The benefits of bilateral implantation have been studied
in adults who have experienced hearing loss and, more
recently, in children with congenital hearing loss 4.
In the case of acquired or secondary hearing loss,
following a case of meningitis, for example, restoration
of binaural abilities can be quite good. These results,
however, cannot be directly applied to children with
congenital hearing loss as they have had no prior hearing
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Children without an auditory nerve detectable by MRI
(Magnetic Resonance Imaging) are, in principle, not
candidates for implantation. In some situations, there is
a divergence between the clinical diagnosis and imaging
results, which suggests that an underdeveloped nerve may
be present but not visible. In that case, the possibility of
an implantation may be discussed, but on average such
children show perception results that are more limited
than in other patients; so due care must be taken with
indications 36–38.
The effect of dual implantation on the development of
speech is, however, less well known, due to the many
factors involved in the acquisition of speech and to tiny
differences that are hard to determine. Studies made
of children who received dual implants before age 3,
whether simultaneously or sequentially, show that
when compared to peers with single implants there is a
tendency for more natural usage and earlier attempts at
oral communication 15,29.
Related Disabilities
Approximately 1/3 of deaf children also suffered from
related disabilities or ones that will subsequently appear as
the child develops. Some may suffer from visual deficiency,
while others will have quite limited speech and may not be
suitable for surgery (mental retardation, psychopathological
disorders). Children with mental retardation may benefit
from an implant in terms of hearing perception, but their
linguistic development will be limited or non-existent 39,40.
In order to optimize the development of binaural
hearing in a child suffering from profound hearing
loss at birth, it seems important to offer dual
implantation at a very early age.
It is, therefore, especially important to explain the limits
and constraints of the implant to the family, and to
ensure that appropriate therapy can be set up by the
rehabilitation team through careful examination of each
individual case 7,41.
The improvement in word recognition scores under
noisy conditions may be as much as 50% in cases
of bilateral rehabilitation. The effect of bilateral
implantation on speech acquisition and on quality
of life remains to be determined.
Early Implantation
In order to intervene during the critical period, a decision
must be made by 12 months of age. The hypothetical
advantages of very early implantation must be weighed
against problems specific to the newborn. It is indeed
not always easy to confirm a diagnosis of profound
hearing loss before 6 months of age, even using
current objective methods and subjective examination.
Furthermore, observation of the child’s development is
limited and any associated pathology may be hard or
impossible to detect. This may result in incorrect decisions
or cause the parents’ expectations to be unrealistic. Lastly,
one must be very familiar with how the infant copes with
surgery and anesthesia, as well as the technical problems
related to adjusting the implant. Treatment must be
provided by an implantation unit with experience working
with very young children. In this case, the risks related
to anesthesia and surgery are comparable to those
of children who receive implants after
Cochlear Ossification
After a case of bacterial meningitis, hearing loss may
occur due to incipient cochlear ossification, and may
do so in the 2 years following the disease. Under such
conditions, implantation becomes urgent, before
complete ossification occurs. In cases of advanced
ossification, certain surgical techniques may be employed
(micro-drilling, bundles of electrodes), but the results
continue to be disappointing 8,30–33.
Ear Malformations and Hypoplasia of the Auditory
Nerves
In cases of cochlear malformations, a number of problems
arise. The cochlear or cochleo-vestibular cavity must be
large enough to admit a minimum number of electrodes
23
03
and the cavity must be anatomically accessible. It is also
necessary to ensure that the auditory nerve is present. In
cases of complex malformations, the neural interface is not
always functional. Surgical risks include geysers, traumatic
facial paralysis, migration of the electrode support and
meningitis. Speech results are contingent on the type of
malformation and on auditory experience 34,35.
experience and above all they have not developed
binaural perception which depends on the development
of the central hearing system. Gordon et al. 21–24 found
evidence of incomplete processing of bilateral cortical
responses in cases of late implantation of two separate
devices which were implanted more than 2 years apart.
These objective factors confirm the clinical findings
that show better results in children given both implants
before the age of 18 months. The most obvious effect of
dual implantation to be highlighted is the improvement
in hearing in noisy environments, which may range from
2 to 6 dB 25,26. It is possible that a certain degree of
localization may be recovered, but this depends on prior
hearing experience, age at implantation, and the time
lapsed between the two implantations 27,28.
12 months (3.2% versus 2.3% - 4.1%) 42. In clinical terms,
it is hard to detect any difference in development between
the group of children implanted before 12 months and
children implanted between 12 and 24 months. A recent
review of the literature nevertheless found that 40% of
infants showed improved scores in comparison to those
given an implant between ages 12 and 24 months 43.
Residual Auditory Function
The idea of implantation in cases of residual audition is
initially based on the possibility of preserving audition
despite the insertion of the electrode support into the
cochlea. Preserving audition requires a minute, flexible
electrode design and a minimally invasive surgical
technique. For a group of children and adults, Skarzynski
et al. found a post-operative loss of less than 5 dB in more
than half of the patients implanted 44–49. More recently,
Brown et al. found partial auditory preservation in 90% of a
pediatric group implanted with a long electrode 50. Dowell
et al. 51,52 found an improvement in OSW (open set words)
perception in 98% of cases in comparison to those using
a hearing aid.
Comparative studies show that children with residual
hearing function and implants produce better results than
their peers with the same level of hearing loss who used
hearing aids, and that they were no different from those
with an average hearing loss 53.
Conclusion
In children with profound congenital hearing loss, even
if positive results in terms of perception most often
appear quite rapidly after the use of the implant, the
development of language is variable. One quarter of
the children show progress in language, but slower than
that of other normal children of their age group, and
some have very serious language problems. These results
clearly illustrate the effectiveness of the implant in the
treatment of profound hearing loss, even if we must
consider that language development is affected by many
other factors, especially cognitive ones.
However, early implantation and quality speech therapy
are the most powerful ways to optimize the impact
of hearing rehabilitation on language development in
children with profound congenital hearing loss. In postverbal hearing loss, the results in terms of perception
are excellent. The quality of implant technology has also
caused this therapy to be used with children suffering
from severe or partial hearing loss.
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BRINGING SOUND
TO LIFE.