joseph l. russell, md faculty advisors: dayton … · cochlear (australia) —nucleus 5 med-el...
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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)
Implanted the first multi-channel electrode array
Some open set speech discrimination obtained
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
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
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
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 receiver-
stimulator
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
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
Adults, after 6 months of implantation
Open-set word test scores 30 to 60%, up to 75% with most recent speech processing strategies
Words-in-sentence testing scores >75%
Children
>75% achieve substantial open-set speech recognition after 3 years of implant use
Implanted patients have, on average, language-learning rates that match normal-hearing peers
>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
Duration of profound loss -- the shorter, the better
Duration of cochlear implant use -- maximum benefit not seen until at least 3-5 years post-implant
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
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
Totally implantable cochlear implants
In 2008, Briggs reported results of three adult subjects implanted with a modified Cochlear Corporation receiver-stimulator 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
References
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