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Cochlear Implantation
Joseph L. Russell, MD
Faculty Advisors: Dayton Young, MD and Tomoko Makishima, MD,PhD
Department of Otolaryngology, University of Texas Medical Branch
Grand Rounds Presentation
October 29, 2012
Overview
 History of cochlear implantation
 Current implant systems
 Pre-operative workup and planning
 Otologic
 Audiologic
 Radiologic
Overview
 Surgical Approach
 Complications
 Outcomes
 Recent advances
 Bilateral cochlear implants
 Electrical and acoustic stimulation (EAS)
 Future directions
History of Cochlear Implantation
 1800 Volta (Italy)
 1957 Djourno and Eyries (France)
 Implanted a coil electrode in a patient who had bilateral deafness and facial
paralysis from cholesteatoma surgeries
 High/low frequency discrimination; few words understood
 1961 House (USA)
 Implanted three patients with single electrodes into the scala tympani
through the round window; infection prompted early removal within weeks
in all patients
 Auditory results similar to Djourno and Eyries
 1960’s basic science objections
 Dynamic range of electric stimulation (10 dB) vs normal ear (120 dB)
 Insertional trauma
 Neural degeneration from electrical stimulation
History of Cochlear Implantation

1967 Simmons (USA)



Demonstrated in cat models that:

Electrodes could be inserted atraumatically

Long-term electrical stimulation did not lead to any significant neural degeneration in the cochlea
1972 House (USA)

Developed (with 3M Corporation) the first FDA-approved single-channel cochlear implant

Some improvement in speech discrimination, improved voice modulation, ability to hear environmental sounds

No open set speech discrimination

Over 1000 devices implanted from 1972 to mid-1980’s
1978 Clark (Australia)
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Implanted the first multi-channel electrode array

Some open set speech discrimination obtained
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1985 FDA approval for multi-channel implants in adults

1990 FDA approval for multi-channel implants in children 2-18 years old

2000 FDA approval for use of cochlear implants in children as young as 12 months old
Current Implant Technology
Three companies currently have FDA approved implants
Advanced Bionics (California) —HR90 K
Cochlear (Australia) —Nucleus 5
Med-El (Austria) —Sonata ti100
Current Implant Technology
General design of cochlear implant systems
Sound is received by a microphone located on the BTE sound processor (1); it is processed and coded, then sent
via the transcutaneous radiofrequency link to the implanted receiver-stimulator (2); data are decoded and sent
to the multi-electrode array (3), stimulating spiral ganglion neurons, which then transmit the signal via the
auditory nerve (4) toward higher processing centers
Current Implant
Technology
Special electrode arrays
A—cannot see here, standard size
with electrodes distributed over 26.4
mm
B—compressed array with
electrodes distributed over 13 mm
C—medium array with electrodes
distributed over 21 mm
D—split array, one with 5 pairs of
electrodes, other with 7 pairs—for
severely ossified cochleas
E—thin and shortened electrode
array for EAS
F—common cavity electrode
Candidate Selection and
Preoperative Evaluation
Adult selection criteria
 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
NOTES: Hearing level used to be used as criteria, but recent shifts have moved to focus
on speech discrimination, as these scores most accurately reflect the patient’s disability
Pediatric selection criteria
 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
(MLNT/LNT)
 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
NOTES: MLNT = Multisyllabic Lexical Neighborhood Test
LNT = Lexical Neighborhood Test
Absolute contraindications for CI
 Cochlear aplasia
 Absence of the auditory nerve
Otologic assessment
 History
 Onset and progression of hearing loss
 Etiology of hearing loss
 History of amplification use
 History of meningitis
 Ear infections—past/current
 Previous otolgic surgeries
 Exam
 Active infection
 Perforations
 Tympanostomy tubes
NOTES: Preferable to remove ear tubes and close perforations prior to implantations,
though implants have been performed in these conditions without adverse events
Audiologic assessment
 Adults
 Unaided and aided thresholds for pure tones
 Minimum Speech Test Battery (MSTB)
 Used at many cochlear implant centers to assess pre and post-
implant performance
 Set of compact disc recordings for standardization
 Includes the following:
 Consonant-Nucleus-Consonant (CNC) Monosyllable Word Test
 Arizona Biomedical (AzBio) Sentences (in quiet and in noise)
 Bamford-Kowal-Bench Sentences in Noise (BKB-SIN)
 HINT sentences were previously part of the MSTB but have fallen
out of favor due to ceiling effect
Audiologic assessment
 Children
 ABR and OAEs
 Implant candidates typically have no response at limits of the
testing equipment
 Findings/implications in auditory neuropathy
 Unaided and aided thresholds for pure tones
 Speech perception tests
 Meaningful Auditory Integration Scale (MAIS)
 Early Speech Perception (ESP) Test
 Lexical Neighborhood Test (LNT), multisyllabic LNT (MLNT)
NOTES: Auditory neuropathy—all must have MRI due absence of auditory nerve in 16%
MAIS—questionnaire for family of children too young to participate in speech perception tests
ESP—word is spoken without visual cues, patient selects correct object or picture of the stimulus
LNT—50 monosyllabic words, ranging from “easy” (high frequency, few lexical neighbors) to “hard” (low frequency, many lexical
neighbors); MLNT 2-3 syllable words; open-set test
Imaging: CT vs. MRI
 High-resolution computed tomography (HRCT)
 Traditionally the gold-standard imaging modality
 Superior visualization of the bony structure of the otic capsule and
the course of the facial nerve
 Weakness: can miss cochlear fibrosis, retrocochlear pathology, CNS
abnormalities, and cochlear nerve hypoplasia/absence
 Magnetic resonance imaging (MRI)
 More effective at identifying cochlear fibrosis
 Able to identify presence/absence of cochlear nerve and caliber
 Weakness: 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; often
requires anesthesia for young patients
Imaging: CT vs. MRI
 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
 MRI is now the preferred imaging modality in some centers
 HRCT is still advocated in cases of malformed external
canals, semicircular canals, or vestibule due to the high
incidence of an anomalous facial nerve in these patients
Vaccination
 Children with cochlear implants are at higher risk for meningitis, though
overall rate is low (<0.6%)
 Streptococcus pneumoniae has been the most common organism isolated
in the children with cochlear implants who developed meningitis
 Current vaccine recommendations:
 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 Approach
Surgical Approach
 Transmastoid facial recess approach
 Continuous facial nerve monitoring
Skin marking with dummy sound processor and transmitter
•
•
Incision is modification of standard post-auricular incision with a posterosuperior extension to
provide exposure to seat the receiver-stimulator
Methylene blue can be injected with 18g needle to mark position of the receiver-stimulator
package
Placement of incisions
1. 1. Postauricular crease,
2. skin incision,
3. periosteal incision
2. Must have at least 1 cm between
edge of incision and receiverstimulator
3. Carry incision to temporalis
fascia superiorly and to mastoid
periosteum inferiorly
Flap elevation
Skin flaps are developed anteriorly to EAC and posteriorly to allow for placement
of receiver-stimulator
Exposure of the temporal bone
Create a musculoperiosteal flap—incise temporalis fascia, muscle and periosteum
vertically, then raise anteriorly to the bony EAC, revealing the spine of Henle; raise
posteriorly to create pocket for receiver-stimulator
Cortical mastoidectomy
Superior and posterior margins are not saucerized to aid in containment of the
electrode within the mastoid cavity
Facial recess
Use short process of incus as a pointer to define the level at which to open the facial recess; too medial=
into facial nerve, too lateral= into canal wall; keep incus buttress thin to optimize exposure
Round window niche usually visible just inferior to stapedius tendon—a small diamond burr is used to
remove the lip of the niche to expose the RW membrane
Cochleostomy vs round
window insertion (RWI)
•
History—why RWI was abandoned—
buckling of electrodes, cochlear trauma
•
Proponents for cochleostomy—”straight
shot,” less chance of trauma
•
Proponents for RWI—less chance of scala
vestibuli insertion, improved hearing
preservation
•
Recent study showed no difference in
hearing outcomes and complications
between RWI and cochleostomy
•
Cochleostomy is made at the
anteroinferior aspect of the round
window; should be as small as possible
Placement of the electrode array
•
•
•
•
•
Into scala tympani
Insertional trauma must be minimized
Do not force electrode array
Cochelostomy is sealed with muscle or fascia after electrode placement
At this point, only bipolar cautery should be used
Implanting the receiver-stimulator
•
•
A well is drilled in the calvarium to accommodate the receiver-stimulator—avoid dural
compromise, especially in children
Many advocate securing the implant with sutures to the calvarium, while others do not
Final result prior to closure
•
•
•
Coiled electrode in mastoid allows for the 1.7 cm increase in the distance between the electrode
array and receiver stimulator between infancy and adulthood
Close musculoperiosteal flap, followed by deep dermal sutures to close the skin flaps, then close skin
Standard mastoid dressing is placed and removed on the first post-operative day
Complications
 Wound complications—most common, about 4%
 Infection, flap necrosis, extrusion of receiver-stimulator
 Placement of incisions relative to receiver
 Flap thickness—6 to 7 mm ideal
 Otitis media (2%)
 Damaged or misplaced electrodes (1%)
 Persistent CSF leak (1%)
 Facial paresis (0.5%)
Complications
 Meningitis
 NEJM in 2003 showed incidence of Streptococcal meningitis in
children with cochlear implants was >30 times the incidence in
age-matched controls
 Study limitations
 11.5% of children with implants had prior history of meningitis
 8.5% of children had labyrinthine dysplasia

Advanced Bionics positioner device, discontinued in 2002
 Later studies in rats showed that cochlear implants do increase
risk of meningitis; this risk was mitigated with Pneumovax
vaccine
 Streptococcal and Haemophilus vaccination now required prior
to implantation
Revision cochlear implantation
 Rates
 Adults 5.4 to 7%
 Children 8 to 12%
 Reasons
 Hard failure (46% of cases)
 Medical-surgical (37% of cases)
 Wound healing, malposition, cholesteatoma
 Soft failure (15% of cases)
 In general, patients perform as well after reimplanation as
their best performance prior to revision
Outcomes
Like beauty, are often in the eye of the beholder
Challenges in tracking outcomes
 Benefits from cochlear implantation vary widely across
individuals
 Study methodology and outcome metrics vary
considerably
 Most studies are relatively small due to rapid changes in
technology
Outcomes
 Speech perception/spoken word recognition
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Adults, after 6 months of implantation
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Open-set word test scores 30 to 60%, up to 75% with most recent speech processing strategies
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Words-in-sentence testing scores >75%
Children
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>75% achieve substantial open-set speech recognition after 3 years of implant use
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Implanted patients have, on average, language-learning rates that match normal-hearing peers
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>50% who use early education intervention exhibit age-appropriate vocabulary scores by
kindergarten

After 5 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

Cost-utility highly favorable in adults, better than knee replacement and heart
transplant

Cost-benefit 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

Age at implantation -- the earlier the better, definitely by age 3, preferably by age 2
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Duration of profound loss -- the shorter, the better
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Duration of cochlear implant use -- maximum benefit not seen until at least 3-5 years
post-implant
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Training with amplification/early linguistic experience -- if some residual hearing present
and used, results are better with CI

Communication environment -- patients in oral only environment have better open-set
word recognition than those in total communication environment

Presence of other disabilities -- reduced performance in word recognition compared to
patients without other disabilities, though benefits are realized in speech and language
skills for those with other disabilities

Family support
Recent Advances
Bilateral cochlear implantation
 A majority of centers are currently implanting the majority
of children bilaterally
 Improved sound localization and understanding speech in
noise have been shown in small studies
 Other potential advantages include more natural hearing,
reduced listening effort, and improved quality of life
 Disadvantages: cost, potential exclusion from future
innovations, such as hair cell regeneration
 Large multi-center long-term investigations underway
Electric and acoustic stimulation
 For patients with residual low frequency hearing
 A shortened electrode array is inserted as atraumatically as
possible into the cochlea
 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
 Improved hearing in noise and appreciation of music over
standard cochlear implant
Future Directions
Totally implantable cochlear implants
 In 2008, Briggs reported results of three adult subjects
implanted with a modified Cochlear Corporation receiverstimulator that contained an internal microphone and
rechargeable battery
 All 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
 Swallowing and breathing also noted to interfere with
hearing
Robot-assisted/image-guided cochlear
implantation
 Research groups in Hanover Medical School, Germany and
Vanderbilt
 Percutaneous postauricular transmastoid access to the basal
turn of the cochlea 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; two planned stapes injuries and
three planned chorda tympani sacrifices
 Foundation for minimally-invasive cochlear implants
Robot-assisted/image-guided cochlear
implantation
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