Dr. Supreet Singh Nayyar, AFMC
2010
Cochlear Implantation for more interesting interesting ENT topics topics & presentations, presentations, please visit visit www.nayyarENT.com ) ( for
Introduction
A cochlear implant is a surgically implantable implantable electronic device that convert sound signals into electrical impulses which then directly stimulate the cochlear nerve bypassing the damaged cells of the cochlea
In the past deaf person had to learn to cope to live as normally as possible in the absence of hearing
It was accepted that means of educating deaf children was sign language utilizing visual system
For the adult deafened later in life, deafness entailed learning lip reading
Cochlear implants radically changed the outlook for profoundly deaf adults and children
It can provide sufficient hearing sensations sensations to enable most deafened persons persons to continue communicating using speech and can provide opportunity for the children born deaf or deafened early in life to use speech as their primary means of communication
Deafness typically results from lost or dysfunctional cochlear hair cells
And a resultant lack of synaptic activity that occurs between hair cells and auditory nerve afferents
However large reserves of viable nerve fibres remain in the auditory nerve which remain excitable
Cochlear implants generate auditory perceptions by receiving, processing & transmitting acoustic info via electric stimulation
Electrode contacts implanted within the cochlea serve to bypass non functional cochlear transducers and directly depolarize auditory nerve fibres.
Historical Aspects
1790 - Alessandro Alessandro Volta inserted a metal rod in each ear and then subjected himself to approximately 50 volts of electricity sensation of sound of thick soup boiling
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Dr. Supreet Singh Nayyar, AFMC
2010
Benjamin Franklin has also been attributed to have suggested that electricity would be used to produce sound
1953 - Djourno and Eyries – Placed an electrode directly on the eighth nerve in a patient undergoing surgery for cholesteatoma
patient reported hearing sounds like crickets
or a roulette wheel. He was able to distinguish simple words and noted improvement of his speech reading ability.
1961 - House and Doyle – implanted single electrode in cochlea via scala tympani
1964 - Simmons - placed electrode through through promontory & vestibule vestibule directly into modiolar segment of auditory nerve
House and Michelson – refined the clinical applications of implantation of electrodes & stimulation of eighth nerve
1972 – House -first commercially available device with single electrode and wearable speech processor
1984 - multiple channel devices by Clark & co workers – 22 channel by Nucleus
1994 – Nucleus 24 device – recognition of speech without contextual clues
1997 - 20,000 people with cochlear implants
2010 - > 110,000 Implantees worldwide
Basics of cochlear implant 1) Microphone
Picks up sound converts to electric wave form
2) Speech processor
Alters the electrical signals to emphasize the speech signals Divides the signals into components for various electrodes Uses speech processing strategies o Earlier CA (Compressed Analogue Processing) MSP (Mini Speech Processor) 2
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Dr. Supreet Singh Nayyar, AFMC
o
Now
2010
CIS (Continuous Interleaved Sampling) SPEAK (Spectral Peak Extraction) Advanced combination encoder
Two types o Body worn o Behind the ear
3) Transmitter coil
Transmits the signal to implanted coil without the need for any wires passing through the skin
4) Receiver coil
Implanted into bone of skull behind the ear
Receives signal and the signals are decoded and converted to different electrical voltage depending on different frequencies and this is relayed to the electrodes
5) Electrodes
Usually placed within the cochlea inside scala tympani
Earlier single electrode. Now multiple (24) electrodes
Types of Cochlear Implants
Based upon Speech processing strategies CIS, SPEAK Analog vs digital encoding Single vs. Multiple channels Number of electrodes Monopolar or bipolar stimulation
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Dr. Supreet Singh Nayyar, AFMC
2010
Candidacy Categories Candidacy categories
Pre Lingual
Post Lingual
Primary Candidates
Secondary
Change over
- Not acquired
Candidate – Have
candidate – Have
language by any
used another
developed
other means of
mode of
auditory skills
communication
communication
using a hearing aid
Peri lingual
(usually sign) to develop language
Patient Selection
Adults
Severe or profound hearing loss with a PTA ≥ 70 dB hearing level
Use of appropriately fit hearing aid or a trial with amplification
Aided scores on open set sentence tests of < 50%
No evidence of central auditory lesion or lack of an auditory nerve
No evidence of contraindication for surgery in general and cochlear implant in particular
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Dr. Supreet Singh Nayyar, AFMC
2010
Paediatric
Age – 6 months to 17 yrs old
Profound Sensorineural hearing loss (unaided pure tone average thresholds of 90 dB HL or greater)
Minimal benefit from hearing aids which is defined as < 20-30% on single syllable word tests, or for younger children lack of developmentally appropriate auditory milestones measured using parent report scales
No evidence of central auditory lesion or lack of an auditory nerve
No evidence of contraindication for surgery in general and cochlear implant in particular
Assessment & Investigations
History
Onset, duration & cause of hearing loss (eg. congenital, meningitis, trauma) Whether hearing aid has been useful Mode of communication or any usable speech Language level Any other major health problem Peri natal history Any developmental delay Past otological history Ear infection Ear surgery OME Examination Any congenital stigmata Abnormal behavior Status of EAC, TM, ME Nose throat Gen Exm Psychological evaluation To assess Child’s verbal & non verbal intelligence e.g. Autism
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Dr. Supreet Singh Nayyar, AFMC
2010
Attention & memory skills e.g attention deficit disorders Visual – motor integration Paediatric evaluation Speech Therapist Lab – CBP, RFT, LFT Radiological Xray - PNS, Mastoids HRCT Temporal Bone Narrow IAC – contra indication Congenital abnormalities of otic capsule Wide vestibular Acqueduct Acqueduct Labyrinthitis Ossificans Demineralization in severe otosclerosis MRI Temporal Bone th Visualize 8 nerve Wide vestibular aqueduct Determining whether scala tympani with partial ossification or fibrosis contains perilymph PTA Impedance Audiogram Speech Discrimination Electrocochleography Otoacoustic emissions BERA
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Dr. Supreet Singh Nayyar, AFMC
2010
Final Assessment Meeting
Results are explained
Likely benefits outlined
Ear selection in adult
No response to acoustic stimulation in one ear
Yes
No
Select other ear
One of the ear will benefit from hearing aid
Yes
Choose other ear
No, none ear will
Both will equally
benefit from hearing
benefit from hearing
aid
aid
Choose better ear
Handedness Patient preference
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Dr. Supreet Singh Nayyar, AFMC
2010
Surgery
Basically o Cortical mastoidectomy o Limited post tympanotomy o Insertion of array of electrodes Steps o Post aural Incision ‘C’ shaped – now avoided due to risk of poor flap healing Vertical incision placed behind attachment of pinna, crosses mastoid cavity anteriorly, upper end at least 3 cm above pinna adequate exposure o Cortical mastoidectomy with overhanging edges – useful for containing electrode array o Limited post tympanotomy thru facial recess o Incus & superior bridge of bone left intact o Round window niche exposed o Well created in skull posterior to incision conforming to shape of implant o Tunnel drilled to carry electrode from implant i mplant to antrum to round window o 0.7 to 0.8 mm fenestra created antero inferiorly to round window o Electrodes are inserted gently thru this cochleostomy to prevent buckling o All active electrodes plus a few stiffening ri ngs are inserted o Temporalis muscle piece used to seal the fenestration o Post tympanotomy and attic are also obliterated with muscle o Electrodes are kept away from any site where facial nerve is exposed o Wound closed in two layers
Complications Complication rate only 5% Most common problems o Wound infection and wound breakdown Rarely o Extrusion of the device o Facial nerve injury o Bleeding o CSF leaks o Meningitis Device-related complications o Intracochlear damage o Slippage of the array o Breakage of the implant o Improper or inadequate insertion
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Dr. Supreet Singh Nayyar, AFMC
2010
Stimulation of the facial or vestibular nerve by stray electrode Long term o Hearing deterioration after long use o Fluctuation in hearing – viral flu o Perilymph fistula o Device breakdown o Extrusion of electrode array from cochlea o Extrusion of implant thru scalp o Numbness/ neuralgia over scalp o Loss of taste o Non use of device o
Switching on of the Device
External processor fit 3-4 wks after implantation
Audiologist maps out the stimulation threshold for maximum comfort levels
If implant doesn’t work on initial switch on, following possibilities o
Electrode array is misplaced X-ray mastoid, preferably Modified Stenver’s view should be obtained
o
No spiral ganglion cell survival Implant evoked brain stem potential is helpful
o
In pre lingual children, difficulty in recognizing response
o
Device is not functioning Electrode integrity test can be performed
Assessment of Benefit
Adults o
Evaluation of benefits largely focused on measuring gains in speech perception
o
Assessment is performed using multivariate analysis
Subject variables – age of onset, etiology, pre operative hearing, survival & location of spiral ganglion cells, patency of scala t ympani, cognitive skills, personality, visual attention, motivation, auditory memory
Device variables – processor, implant, electrode geometry, electrode number, speech processing unit
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Dr. Supreet Singh Nayyar, AFMC
o
2010
Test modalities
Closed set testing & sentence tests
Open set (auditory alone) tests of words & sentences
HINT (Hearing in noise test) Capabilities for understanding speech in noise can be assessed by altering signal to noise ratio
MSTB ( Minimum Speech test battery) –facilitates comparisons
CNC (Consonant/Nucleus/Consonant) (Consonant/Nucleus/Consonant) tests – Monosyllabic words with equal phonemic distribution
Children o
o
o
Substantial auditory gain are apparent in children implanted with multichannel devices The range of improvement varies widely between children & will depend heavily on duration of use Range of levels of speech perception are tested
Simple awareness of sound
Pattern perception
Closed set speech recognition
Open set speech recognition
Results
Improved speech perception is the primary goal of cochlear implants Various studies carried out show that multiple channel implants provide significantly higher levels of performance In children case control studies were carried out to bring out implant benefit relative to unimplanted controls Classification of children according to hearing levels & abilities can provide a common ground for comparison According to this, hearing aid users are classified according to pure tone thresholds Unaided thresholds o Gold 90 to 100 dB at 2 of 3 frequencies o “ Silver 101 to 110 o “ Bronze >110 In general gold category Boothroyd’s considerable residual hearing These are compared to implantees It is seen that after 2 years of implant experience Mean speech intelligibility scores of 10
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Dr. Supreet Singh Nayyar, AFMC
2010
implanted children surpass those of silver hearing aid users & 10% those of gold users Hence increased benefit with increased duration Improved speech reception reception in children implanted between 2-3 yrs of age relative to children implanted at an older age
Rehabilitation
Rehabilitation team o Speech language pathologist o Paediatric audiologist o Implant audiologist o Psychologist o Social worker o Parents o School support Programs of rehabilitation provide hierarchic approach o Sound detection o Discrimination o Identification o Comprehension Choice of communication communication methodology o Programs that focus on development of spoken language are indicated o Include Oral aural approach Oral verbal approach o Elimination of visual cues o Programs that fail to emphasize auditory input may exert an inhibitory effect o Sign language programmes are not appropriate
Recent Advances
Signal processing with noise cancellation for better speech understanding in noise MRI facilitation with implant Multichannel devices with non simultaneous stimulation of multiple electrodes cuts out channel interaction Binaural cochlear implantation
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