Download Cochlear Implantation

Cochlear Implantation
October 2012
TITLE: Cochlear Implantation
SOURCE: Grand Rounds Presentation, Department of Otolaryngology
The University of Texas Medical Branch (UTMB Health)
DATE: October 29, 2012
RESIDENT PHYSICIAN: Joseph L. Russell , MD
FACULTY PHYSICIAN ADVISOR: Dayton Young, MD
FACULTY PHYSICIAN ADVISOR: Tomoko Makishima, MD, PhD
DISCUSSANT: Dayton Young , MD
SERIES EDITOR: Francis B. Quinn, Jr., MD
ARCHIVIST: Melinda Stoner Quinn, MSICS
"This material was prepared by resident physicians in partial fulfillment of educational requirements established
for the Postgraduate Training Program of the UTMB Department of Otolaryngology/Head and Neck Surgery and
was not intended for clinical use in its present form. It was prepared for the purpose of stimulating group
discussion in a conference setting. No warranties, either express or implied, are made with respect to its
accuracy, completeness, or timeliness. The material does not necessarily reflect the current or past opinions of
members of the UTMB faculty and should not be used for purposes of diagnosis or treatment without consulting
appropriate literature sources and informed professional opinion."
Introduction
The cochlear implant stands unparalleled in its ability to restore one of the human senses.
Since the first patients were implanted just over 50 years ago, the cochlear implant has rapidly
evolved from single-channel electrodes that provided little more than the awareness of sound in
the environment to complex multi-channel electrode arrays coupled with innovative speech
processing technology to provide many implanted patients with near normal understanding of
speech and, in some cases, enjoyment of music.
History of Cochlear Implantation
Although the development of cochlear implants has occurred only over the last 50 years,
Alessandro Volta of Italy in 1800 described an experiment on himself that gave evidence that
electrical stimulation of the ear could produce a sense of noise:
“I (Volta) introduced right into both ears two probes or rods of metal with rounded
ends; I linked them up immediately to the two extremities of the apparatus. At the
moment when the circuit was completed in this way, I received a jolt in the head;
and a few moments later (the circuit operating continuously without any
interruption), I began to feel a sound, or rather a noise, in my ears which I cannot
define clearly; it was a kind of jerky crackling or bubbling, as though some paste or
tenacious matter was boiling. This noise continued without stopping and without
increasing all the time the circuit was complete… The disagreeable sensation of the
jolt in the brain, which I feared might be dangerous, was such that I did not repeat
the experiment several times.1”
Over one hundred and fifty years later in 1957, André Djourno, an otolaryngologist, and
Charles Eyriès, an electrophysiologist, both of France, collaborated to implant a coil electrode
into the shredded stump of the cochlear nerve of a patient with bilateral deafness and facial
paralysis following multiple cholesteatoma surgeries. The patient was able to discriminate high
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versus low frequency sounds, could detect environmental sounds and even a few words, but
could not understand speech.
In 1961, inspired by the work of Djourno and Eyriès, William House in Los Angeles
implanted single electrodes into the scala tympani of three profoundly deaf patients. The
patients’ hearing results were similar to those of Djourno and Eyriès’ patient; unfortunately all
electrodes had to be removed within weeks of implantation due to wound infections. Over the
next few years both F. Blair Simmons of Stanford University and Robin Michelson of the
University of California-San Francisco also began implanting patients with single electrode
devices.1,2
During the 1960s there were several objections to human cochlear implantation by many
in the basic science community. Essentially, it was believed to be physically impossible for any
meaningful hearing to be achieved based on what was known at the time of the physiology and
physics of the ear. Objections cited previous studies that had shown that there was only a 10
decibel dynamic range for electrical stimulation of the ear, which, when compared to the 120
decibel dynamic range of the normal ear was felt to be too small to be usable. Additionally, it
was thought that trauma from the electrode insertion would ultimately lead to spiral ganglion cell
deterioration; furthermore, if those cells did survive the electrode placement, long term electrical
stimulation was posited to ultimately lead to their demise. In 1967, Simmons published results
of his studies in cats that showed the electrodes could be inserted into the cochlea without
subsequent widespread cochlear degeneration and that long term electrical stimulation of spiral
ganglion cells did not lead to any significant deterioration.1
In 1972 House developed, in cooperation with the 3M Corporation, what would become
the first FDA-approved single-channel cochlear implant. Between 1972 and the mid-1980s, over
1000 patients received this implant. Patients were found post-implantation to have some
improvement in speech discrimination, improved voice modulation, and the ability to hear
environmental sounds; however, open set speech discrimination was not obtained.2 In 1978,
Graeme Clark of Australia implanted the first multi-channel electrode array in a human subject;
this patient was able obtain some meaningful open set speech discrimination. Results from
subsequent implantees would eventually lead to the consensus that multi-channel electrode
arrays were superior to single-channel electrodes.1
Over the next two decades cochlear implant development proceeded steadily with everimproving results. In 1985, the FDA approved the first multi-channel implant for adults. In
1990, after several successful trials in children, FDA approval was given for multi-channel
implantation in children as young as 2 years old.2 Ten years later (2000), FDA approval was
given for cochlear implantation in children as young as 12 months of age, where the lower age
limit currently stands. Nevertheless, several institutions have been implanting children as young
as 6 months of age in clinical trials, with good results.
Current Implant Technology
There are currently three companies that manufacture FDA-approved cochlear implants:
Advanced Bionics Corporation, Cochlear Corporation, and Med-El Incorporated. The current
implant systems produced by these companies at the time of this writing are the HR90 K,
Nucleus 5, and Sonata ti100, respectively. The general design of these systems share common
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functional components (see slides for figures). Sound is received by a microphone located on the
behind-the-ear (BTE) sound processor; it is processed and coded, then sent via the
transcutaneous radiofrequency link to the implanted receiver-stimulator; data are decoded and
sent to the multi-electrode array, stimulating spiral ganglion neurons, which then transmit the
signal via the auditory nerve toward higher processing centers.3
In addition to standard electrode arrays with 12 to 22 single or paired electrodes, there are
several special electrode arrays designed for implantation of partially ossified cochleas, for
implantation of common cavity cochleas, and for electric and acoustic simulation (EAS).
Candidate Selection and Preoperative Evaluation
ADULT SELECTION CRITERIA4,5




Best-aided scores on open-set sentence tests of <50% in the ear to be implanted and
<60% in contralateral ear
 For Medicare patients, <30% in the ear to be implanted and <40% in the
contralateral ear
Failure with conventional hearing aids
No evidence of central auditory lesions or lack of auditory nerve
No evidence of contraindications to surgery in general
PEDIATRIC SELECTION CRITERIA4,5





Patient age 12 months to 17 years 11 months
Lack of auditory progression with minimal benefit from hearing aids (after 3-6
month trial)
 In children <2 year old, determined by lack of auditory milestones
 In children ≥2 years old, scores of <30% on single-syllable word tests
Profound SNHL with unaided pure tone average of ≥90 dB HL for children 12 to 24
months old and ≥70 dB HL for children ≥2 years old (reference points, not strict
criteria)
No evidence of central auditory lesions or lack of an auditory nerve
No evidence of contraindications to surgery in general
Absolute contraindications for cochlear implantation are cochlear aplasia and absence of
the auditory nerve.
OTOLOGIC ASSESSMENT
The otologic assessment begins with a complete history and physical examination. The
history should include the onset, etiology (if known), and progression of hearing loss, the
patient’s experience with amplification, history of meningitis (if applicable), the number of past
and recent ear infections, and previous otologic surgeries. The examination should include a
diligent search for signs of active otitis media or externa, perforations, and the presence of
tympanostomy tubes, as these conditions must be remedied prior to implantation.4,5
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AUDIOLOGIC ASSESSMENT4-7
For adults, the audiologic assessment includes unaided and aided thresholds for pure
tones and the Minimum Speech Test Battery (MSTB). The MSTB is used at many cochlear
implant centers to assess preoperative and postoperative hearing performance. It consists of sets
of compact disc recordings and includes the Consonant-Nucleus-Consonant (CNC)
Monosyllable Word Test, the Arizona Biomedical (AzBio) Sentences (in quiet and in noise), and
the Bamford-Kowal-Bench Sentences in Noise (BKB-SIN) Test. Hearing-in-noise (HINT)
sentences were previously part of the MSTB but have fallen out of favor due to a ceiling effect
for post-implant performance.
For children, the audiologic assessment is frequently more difficult due the fact that the
patients are frequently too young to participate in speech discrimination tests and benefit most
from being implanted before the age of normal speech development. Therefore, assessments rely
heavily on electrophysiologic testing and behavioral observations. Both auditory brainstem
response (ABR) and otoacoustic emission (OAE) testing should be performed. Implant
candidates typically have no response at the limits of the testing equipment. If a patient is found
to have auditory neuropathy as indicated by absent ABR response but present OAEs, it is
imperative that these patients undergo MRI prior to implantation, as 16% of these patients will
have an absent or hypoplastic auditory nerve. Speech perception tests include the Meaningful
Auditory Integration Scale (MAIS), Early Speech Perception (ESP) Test, and the Lexical
Neighborhood Test (LNT). The MAIS is a questionnaire that is completed by family members
of children too young to participate in other speech perception tests. In the ESP Test a word is
spoken without visual cues and the patient selects the correct object or picture that relates to the
stimulus. The LNT consists of 50 monosyllabic words ranging from “easy” (high frequency, few
lexical neighbors) to “hard” (low frequency, many lexical neighbors).
IMAGING: CT VERSUS MRI8-10
High-resolution computed tomography (HRCT) has traditionally been the gold-standard
imaging modality for preoperative planning for cochlear implantation. It provides superior
visualization of the bony structure of the otic capsule and the course of the facial nerve; however,
its weaknesses are that it can miss cochlear fibrosis, retrocochlear pathology, central nervous
system abnormalities, and cochlear nerve hypoplasia/aplasia. Magnetic resonance imaging
(MRI) is more effective at identifying cochlear fibrosis and is able to identify the presence or
absence of cochlear fibrosis. The weaknesses of MRI include inferior visualization of bony
anatomy, particularly of the fallopian canal; inability to detect the presence of the round window,
oval window, or an enlarged vestibular aqueduct; and it often requires anesthesia for young
patients. In recent retrospective studies, MRI has been shown to be both more sensitive and
specific than CT in identifying inner ear abnormalities that affect surgical planning; in fact, MRI
is now the preferred imaging modality in some centers. However, it should be noted that HRCT
is still advocated at these centers in cases of malformed external canals, semicircular canals, or
vestibule due to the high incidence of an anomalous facial nerve in these patients.
VACCINATION14
Children with cochlear implants are at higher risk for meningitis, although the overall rate
is low (<0.6%). Streptococcus pneumoniae has been the most common organism isolated in
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children with cochlear implants who developed meningitis. Therefore, the current vaccine
recommendations are as follows:





Patients <2 years old
Prevnar (7-valent) only
Patients 2-5 years old
Prevnar and Pneumovax (23-valent)
Patients >5 years old
Pneumovax only
Additionally, all patients <5 year old should receive the Hib vaccine
Vaccination should be completed at least 2 weeks prior to surgery
Surgical Approach11-13 (see slides for images)
The standard procedure for cochlear implantation is a transmastoid facial recess approach
to the round window and basal turn of the cochlea. Continuous facial nerve monitoring is used.
The skin is marked with a dummy sound processor and transmitter. Methylene blue can be
injected through the skin to periosteum with an 18 gauge needle to mark position of the receiverstimulator package. The incision is a modification of the standard post-auricular incision with a
posterosuperior extension to provide exposure to seat the receiver-stimulator. When planning
the incision and placement of the receiver-stimulator package, there should be 1 cm between the
skin incision and the periosteal incision and 1 cm between the periosteal incision and the edge of
the receiver-stimulator. The patient is prepped and draped in standard fashion for a
mastoidectomy. When making the incision, it is carried to the level of the temporalis fascia
superiorly and to the level of the mastoid periosteum inferiorly. Skin flaps are developed
anteriorly to the external auditory canal and posteriorly to allow for placement of receiverstimulator. Next, a musculoperiosteal flap is created by incising the temporalis fascia, muscle,
and periosteum vertically, then raising this flap anteriorly to the bony EAC, revealing the spine
of Henle. A similar flap is raised posteriorly to create a pocket for the receiver-stimulator. A
cortical mastoidectomy is then performed; however, the superior and posterior margins are not
saucerized to aid in containment of the excess electrode within the mastoid cavity.
The facial recess is then developed. The short process of the incus is used as a pointer to
define the level at which to open the facial recess; drilling too medial will damage the facial
nerve, while drilling too lateral will lead to perforation of the canal wall. The incus buttress is
kept thin to optimize exposure. The round window niche usually is visible just inferior to the
stapedius tendon; a small diamond burr is used to remove the lip of the niche to expose the round
window membrane.
The next step is either a cochleostomy followed by electrode insertion or direct round
window insertion (RWI) of the electrode. RWI was the original means of electrode insertion;
however, as large arrays with more electrodes were developed, the RWI technique was
abandoned due to buckling of the electrodes upon insertion which led to severe cochlear trauma.
However, modern electrodes are much thinner and less prone to buckling, leading to a recent
reemergence of RWI. A recent study showed no difference in hearing outcomes or
complications when comparing RWI to cochleostomy.
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Regardless of which technique is used to place the electrode, the electrode is placed in the
scala tympani with every effort made to minimize the trauma of insertion. Once the electrode
array is in place, monopolar cautery should no longer be used due to the theoretical risk of injury
to the cochlea, the electrode array, or the receiver-stimulator. The cochleostomy or round
window is sealed with muscle or fascia.
Next, the receiver-stimulator is implanted. A well is drilled in the calvarium to
accommodate the receiver-stimulator. It is important during this step to avoid dural compromise,
especially in children, who have much thinner bone. Many surgeons advocate securing the
implant with sutures to the calvarium, while others do not. The excess electrode is left coiled in
the mastoid to allow for the 1.7 cm increase in the distance between the electrode array and
receiver stimulator that occurs with growth between infancy and adulthood. The
musculoperiosteal flap is closed, followed by deep dermal sutures to close the skin flaps; finally
the skin is closed. A standard mastoid dressing is placed and removed on the first post-operative
day.
Complications14
The most common complications of cochlear implantation are related to the surgical
wound—occurring in about 4% of cases. This includes infection, flap necrosis, and extrusion of
the receiver-stimulator. These complications can be avoided primarily by careful placement of
the incisions, as described above, and by keeping the skin flap over the receiver-stimulator 6-7
mm thick.
Other complications include acute otitis media (2%), damaged or misplaced electrodes
(1%), persistent cerebrospinal fluid leak (1%), and facial nerve paresis (0.5%).
Perhaps the most feared complication, meningitis, occurs rarely (<0.6%). In 2003, a
study in the New England Journal of Medicine showed that the incidence of streptococcal
meningitis in children with cochlear implants was >30 times the incidence in age-matched
controls. However, the study had several limitations—11.5% of children with implants in the
study had a prior history of meningitis, which predisposes a patient to future bouts of meningitis,
and 8.5% of children with implants in the study had labyrinthine dysplasia, which also
predisposes a patient to meningitis. Nevertheless, later studies showed that cochlear implants do
increase the risk of meningitis in rats and this risk was mitigated by the Pneumovax vaccine.
This has led to the implementation of Streptococcal and Haemophilus vaccination as a
requirement prior to cochlear implantation. Of note, the majority of the cases of meningitis prior
to 2002 were linked to a positioner device manufactured by Advanced Bionics that has since
been discontinued.
Revision Cochlear Implantation
The rates of revision cochlear implantation are 5.4 to 7% in adults and 8 to 12% in
children. The primary reasons for revision are hard failure of the device (46%), medical-surgical
related complications (wound complication, malposition, cholesteatoma formation, 37%), and
soft failure (device begins to not function well for the user even though diagnostic tests on the
device are normal, 15%). In general, patients perform as well after reimplantation as their best
performance prior to revision.
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Outcomes15-17
Measuring outcomes of cochlear implantation is challenging for several reasons. First
and foremost, the benefits of cochlear implantation vary widely across individuals, making the
average result not highly representative of what an individual achieves. Study methodology and
outcome metrics vary considerably, and most studies are relatively small due to rapid changes in
implant technology.
SPEECH PERCEPTION
For adults, after 6 months of implantation open-set word test scores typically range from
30 to 60%, though scores as high as 75% are being achieved with the most recent speech
processing strategies. Words-in-sentence testing scores are typically >75%.
For children, >75% achieve substantial open-set speech recognition after 3 years of
implant use. Implanted patients have, on average, language learning rates that match normalhearing peers. Greater than 50% who use early education intervention exhibit age appropriate
vocabulary scores by kindergarten. Five years post-implantation, implant users have a 75% rate
of assignment to mainstream classrooms, compared to 12% of similar-hearing peers with hearing
aids.
COST OUTCOMES
The cost utility of cochlear implantation is highly favorable in adults, even more so than
for a knee replacement or heart transplant. The cost benefit is highly favorable in children, with
estimated net savings of $30,000 to $200,000 per child if implanted at age 3 years.
FACTORS AFFECTING IMPLANT PERFORMANCE
The age at implantation is a crucial factor impacting implant performance—the earlier,
the better. Children should be implanted by age 3 years, preferably by age 2 years, to maximize
the benefits of implantation. In cases of acquired profound hearing loss, the shorter the duration
of the loss, the better the implant will perform. The duration of implant use affects
performance—in fact, maximum benefit is not seen until at least 3-5 years post-implantation.
For patients who derived some benefit from amplification and attempts were made to facilitate
communication with the aids, these patients will perform better with implants than their peers
who did not have the early amplification/linguistic experience. If other disabilities are present in
a patient, especially cognitive disabilities, implant performance will be adversely affected;
however, these patients can still derive benefit from implantation. Of course, strong family
support results in improved implant performance while lack of such support has the opposite
effect.
Recent Advances15
BILATERAL COCHLEAR IMPLANTATION
A majority of cochlear implant centers are currently implanting the majority of children
bilaterally. Large multi-center long-term investigations are pending, but small studies have
shown improved sound localization and understanding of speech in noise with bilateral
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implantation. Other potential advantages include more natural hearing, reduced listening effort,
and improved quality of life. Disadvantages include the cost of an additional implant per patient
and the potential exclusion of the patients from future innovations, such as hair cell regeneration.
ELECTRIC AND ACOUSTIC STIMULATION
This is an option for patients with residual low frequency hearing. A shortened electrode
is inserted as atraumatically as possible into the cochlea to preserve this residual low frequency
hearing; a cochlear implant and hearing aid are then used on the same side. A subgroup of 11
patients at the University of Iowa improved their average CNC word scores from 32% correct
with binaural hearing aids to 75% correct with one implant and binaural hearing aids at 9 months
post-implant. Other benefits include improved hearing in noise and better appreciation of music
compared to a standard cochlear implant.
Future Directions
TOTALLY IMPLANTABLE COCHLEAR IMPLANTS18
In 2008, Briggs reported the results of three adult subjects implanted with a modified
Cochlear Corporation receiver-stimulator that contained an internal microphone and
rechargeable battery. All three had improved hearing results at 12 months; however, implantees
performed twice as well on CNC word scores when using an external (regular) processor
compared to the fully implanted mode. Additionally, swallowing and breathing were also noted
to interfere with hearing when using the fully implanted mode.
ROBOT-ASSISTED/IMAGE-GUIDED COCHLEAR IMPLANTATION19, 20
This innovative research is being conducted by groups at Hanover Medical School in
Germany and at Vanderbilt University in the USA. Percutaneous postauricular transmastoid
access to the basal turn of the cochlea is made with either an image-guided frame through which
a powered drill is guided (USA), or with an image-guided robot-controlled drill (Germany).
Cadaver studies with 6 to 10 specimens have been promising, showing no facial nerve injuries
with a total of two planned stapes injuries and three planned chorda tympani sacrifices. While
this research is in its infancy, it stands to become the foundation for minimally-invasive cochlear
implants in the future.
Discussant’s Remarks
DR. DAYTON YOUNG’S REMARKS ON DR. RUSSELL’S PRESENTATION ON COCHLEAR
IMPLANTATION, OCTOBER 29, 2012
There’s a lot of confusion in what people think about cochlear implantation, in particular
regarding what the hearing level should be marking the patient as an implant candidate. The bottom
line is that’s not really the way it’s done. It’s really a clinical evaluation of the patient and what he can
hear and what he can’t hear, usually done by the audiologist. The driver for this measurement is the
speech discrimination score, which is tough in children. You can’t figure out what a child’s speech
discrimination is before they learn how to speak. The old FTA criteria for adults was 70 db, but when the
patient drops below a certain speech discrimination score, they essentially can’t communicate anymore
and that’s when they become an implant candidate. The standard we use is when it’s less than 50%
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word discrimination or sentence discrimination determined by a battery of tests. You basically stick a
hearing aid on a patient, you optimize that hearing aid to get the best possible hearing and then you run
word discrimination or speech discrimination testing on them. If they do less than 50% with the hearing
aid, that’s basically the criterion for implantation.
In children and in infants that’s harder, because how can you assess speech discrimination in the
very young? So, what we do is use surrogate markers. With a newborn with profound hearing loss, you
measure that with an ABR. When they get to be about two years old, we look for a severe hearing loss,
about 70 db. All the while that you’re testing them, you’re putting hearing aids on these kids. And you
watch how they progress. This is done by the parents, the audiologist, and the speech pathologist as
well. Sometimes it boils down to a parental questionnaire, and what the audiologist and the speech
pathologist think about this child and how it’s progressing.
A big thing on the horizon for cochlear implants is that for a long time it’s been an adage that
you don’t implant a patient with unilateral deafness. That’s actually changing and they’re doing it now
in Europe. Whereas we always thought that it would be like hearing normal English in one ear and
Chinese in the other, but that’s really not so, and the patients actually do better with an implant in the
deaf ear.
To buy the implant from the manufacturer is $30,000. The surgery itself may run another
$100,000. The post-implantation therapy is also expensive, but when you compare these costs to the
amount of money actually saved in the education of what would otherwise be a deaf child, as well as
their employability and life-long productivity as a hearing adult, ultimate cost of implantation tends to
level out and becomes less daunting. Commercial insurance companies will cover these costs, and
although Medicare is our worst payer, and believe it or not, Medicaid is our best.
References
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Springer-Verlag, 2003. 1-57. Print.
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2009. 89-93. Print.
3. Carlson ML, Driscoll CL, Gifford RH, and McMenomey SO. Cochlear implantation:
current and future device options. Otolaryngology Clinics of North America 2012;
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cochlear implant recipients. Audiol Today 21:36-43, 2009.
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11. Ying YL and Toh EH. Chapter 129--Cochlear implantation. In Operative
Otolaryngology. 2nd ed. Ed. Myers EN. Saunders Elsevier, 2008. Online.
www.expertconsult.com
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www.expertconsult.com
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“cochleostomy” of choice? Experience in 130 consecutive cochlear implants. Otol
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considerations. . In Cummings Otolaryngology: Head & Neck Surgery. 5th ed. Ed. Flint
PW, et al. China: Mosby Elsevier, 2010. 2234-42. Print.
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Implants: Principles & Practice. 2nd ed. Ed. Niparko JK. Philadelphia, PA: Lippincott
Williams & Wilkins, 2009. 191-222. Print.
16. Lin FR, Niparko JK, Francis HW. Outcomes in cochlear implantation: assessment of
quality-of-life impact and economic evaluation of the benefits of the cochlear
implant in relation to costs. In Cochlear Implants: Principles & Practice. 2nd ed. Ed.
Niparko JK. Philadelphia, PA: Lippincott Williams & Wilkins, 2009. 229-44. Print.
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results, outcomes, rehabilitation, and education. In Cummings Otolaryngology: Head
& Neck Surgery. 5th ed. Ed. Flint PW, et al. China: Mosby Elsevier, 2010. 2243-57.
Print.
18. Briggs RJ, Eder HC, Seligman PM, et al. Initial clinical experience with a totally
implantable cochlear implant research device. Otol Neurotol 2008;29:114-9.
19. Majdani O, Rau TS, Baron S, et al. A robot-guided minimally invasive approach for
cochlear implant surgery: preliminary results of a temporal bone study. Int J Comput
Assist Radiol Surg 2009; 4:475-86.
20. Balachandran R, Mitchell JE, Blachon G, et al. Percutaneous cochlear implant drilling
via customized frames: an in vitro study. Otolaryngol Head Neck Surg 2010;142:4216.
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