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

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 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

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

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

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 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

Robot-assisted/image-guided cochlear implantation

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