cochlear implant 1

Cochlear implantDR DISHA

SHARMA

JR ENT-HNS

IGMC,SHIMLA

Definition

O Cochlear implants are surgically placed electrical device that receive sound and transmit the resulting electrical signals to electrodes implanted in the cochlea of the ear.

O The signals stimulate cochlea, allowing patient to hear.

O It is also known as Bionic ear.

HISTORY

1790-Alessandro Volta electric signal inauditory system can create perception ofsound.

1957-(French-Algerian surgeons AndreDjourno and Charles Eyries) ; They were thefirst who attempted to produce the firstcochlear implant

It was single channel device .

1961- Dr. William F. House, an Otologistconsidered the inventor of the cochlear implantalong with John Doyle (a neurosurgeon) andJames Doyle (an electrical engineer) commencedwork on a single-channel device.

• It was a single channel device but speech wasmodulated by 16 hz carrier.

December 1984, the Australian cochlear implantwas approved by the United States Food and DrugAdministration to be implanted in adults in the UnitedStates.

1964- Blair Simmons at Stanford Universityimplanted some recipients with a six-channel device.

However, it was Dr. Michelson's patent and ultimatedevice, which are thought of as the first cochlearimplants

1990 the FDA lowered the approved age forimplantation to two years, then 18 months in 1998,and finally 12 months in 2000, although off-label usehas occurred in babies as young as 6 months.

Cochlear Implant in India-1996 Prof MohanKaneswaran in Madras ENT Research foundationChennai

Cochlear Implant Group of India-Nov 2003

Selection criteria - children

O child above 12months below 7 years in pre –lingually deaf children.

At birth the cochlea is fully formed but the auditory pathway is not. Auditory pathway isdependent on stimulation for its maturation and this stimulation is vital to acquisition of speechand language skill as well as amount of cognitive development. Post lingual deaf no age limit

O degree of deafness- profound >90dB SNHL with poor discrimination in both ears with cochlear nerve.

O Respond to hearing aid- in those who do not benefit from a hearing aid ,at least 3 to 6 months of use.

O Absence of contraindications- cochlear aplasia or absent cochlear nerves are absolute contraindications to cochlear implantation.

Selection criteria- adult

O Severe or profound hearing loss with PTA of 70dB or greater heaing level.

O Little or no benefit from hearing aids

O Aided scores on open-set sentence test of less than 50%.

O No evidence of central auditory lesions or lack of an auditory nerve.

O No medical or radiological contraindications for surgery.

PREOPERATIVE EVALUATION

O Medical evaluation

History

• genetic hearing loss

• auditory neuropathy\dyssynchrony

• Acquired deafness

Physical examination-

O Audiological evaluationO to determine the type and severity of

hearing lossO testing the unaided air and bone

conduction thresholds, unaided speech discrimination, speech recognition threshold, speech detection threshold, tympanometry and acoustic reflexes. The degree of hearing loss

O The duration of hearing lossO Benefit from hearing aids

Electrophysiological test

O Auditory brainstem response (ABR)-

O a)verify audiometric test result

O b)identify patient with auditory dyssynchrony

O c)rule out possibility of functional deafness

Speech perception test in adult

O Monosyllabic test-a)north western university(NU-6)monosyllabic word test.

b)consonant nucleus test(CNC)

O Sentence material-

O a)hearing in noise test(HINT)

b)City university of New York(CUNY)

Speech perception test in children

O The Early Speech Perception (ESP): (Moog & Geers, 1990)

O The Low Verbal version of the test is administered to young children (2yrs and up)

O The Standard version is used with older children.

O MeaWord intelligibility by picture identification (Wipi) test; (Ross &Lerman, 1979)

O Craig lip inventory

O meaningful auditory integration scale(MAIS

O Monosyllabic Trochee Spondee Test (MTS); Erber And Alencewics; 1976Assesses the closed set word identification in children with hearing impairment

O Lexical Neighborhood Test (LNT) (Kirk, Pisoni, and Osberger, 1993 )

O Test (MLNT) Multisyllabic Lexical NeighborhoodThis is an open-set test of multisyllabic word recognition.

O Imaging

High resolution temporal bone computed tomography

• Inner ear morphology

• Patency of cochlea

• Position of facial nerve

• Location of large mastoid emissary veins

• Size of facial recess

• Height of jugular bulb

Magnetic resonance imaging

O Labyrinthine ossifican

O Cochlear nerve

O CNS abnormalities

Psychological evaluation

O No unrealistic expectations, by both familyand the patient.

O The necessary cognitive and behavioralskills should been developed for successfulprogramming .

O The revised form of Wechsler intelligencescale is available for this purpose.

O If skills not developed –postpone theprocedure - help him to develop the skills

Factors that affect pediatriccochlear implant performance.

O Age of implantation

O Hearing experience

O Training with amplification in case of some residual hearing

O Presence of other disabilities

O Parent and family support.

Three modes of stimulation of auditory

system involving cochlear implant

O Electrical stimulation-complete electric stimulation when there is no residual hearing in both ear

O Electroacoustic stimulation- (hybrid implants) lower frequencies stimulated acoustically via hearing aid while higher frequencies electrically via cochlear implant.

O Bimodal stimulation-one ear uses implant while use a high gain hearing aid on other ear

Bilateral cochlear implant

O Localisation

O Head shadow

O Squelch

O Summation

Head shadow effect – when the sound has to

cross the head to reach the other side of the ear.

6dB loss in sound intensity occurs.

Device selection

Parts of cochlear implant

O External

O Microphone

O Speech processor

O Transmitter

O Internal

O Receiver and stimulator

O An array of up to 22 electrodes

Parts of cochlear implant

O External

O Microphone

O Speech processor

O Transmitter

O Internal

O Receiver and stimulator

O An array of up to 22 electrodes

Speech processor

O converts acoustical signal coded fortransmission to the internal device.

O The signal is sent via a wire to the transmitterlocated on the implant users’ head.

O The method by which a signal sent to theimplant recipient is derived is called the Codingstrategy

O Most cochlear implant systems utilize either afilter bank or a feature extraction procedure forcoding.

O In filter bank procedure, the signal is separated into anumber of frequency bands and transmitted as ananalogue input.

O The feature extraction procedure focuses on theaspect of the signal that theoretically provide thegreatest degree of speech recognition

Coding strategy

Method by which pitch, loudness and timing of sound are translated into series of electrical impulses.

Two types:

Simultaneous

Nonsimultaneous

Simultaneous strategies

Activation of more than one electrodes atthe same time.

Only produced by advanced bionics

Problem of signals interference

Benefit from modiolus hugging electrodearrays

Nonsimultaneous strategies

Continuous interleaved sampling strategiesstimulate each electrode serially (one afteranother).

No electrode is bypassed.

Cochlea receive the complete information aboutthe frequency composition of incoming signal.

Faster sequential stimulation –better speechrecognition.

Available with all three devices .

Electrode Array

O Consists of electrodes and electrode carrier

O Electrode carrier is the wire which extends from the receiver to the electrodes

O Electrodes are of 2 types:

O Extracochlear electrodes and intracochlearelectrodes

Type of electrodes

O Extra cochlear electrodes :

O Located outside the cochlea such as on the plate of the receiving coil or placed under the temporalis muscle.

O Used as a ground source for monopolar stimulation

Modiolus hugging electrode

O Modiolus – core of cochlear spiral-ganglioncells resides their.

O Electrodes in close approximation tomodiolus are referred- modiolus huggingelectrodes.

O Placed with stylette - keeps the electrodesstraight, stiff - easily inserted- stylettewithdrawn-springs back into its originalconfiguration-tightly around the modiolus.

Electrodes are inserted next to

modiolus

Special electrode arrayso Compressed array-same no. of electrodes

compressed into 60% of length.

o Useful for patients with labyrinthitisossificans.

o Less overlap of electrodes usingcompressed electrodes array.

o Double arrays-designed for subjects withlabyrinthitis ossificans.

o Separate cochleostomies are performedinto the inferior and middle turn ofcochlea.

O Insertion depth:

O The mean length of human being cochlea is 33–36 mm.

O the implants don't reach to the apical tip . it may reach up to 25 mm which corresponds to a tonotopical frequency of 400hz

Nucleus 24 freedomN6 with contour advance electrode

Manufactured by cochlear ltd. Sydney, Australia

Uses flexible silicone housing surrounds titanium case for reciever/ stimulator

Age 12months

Electrode arrray is curved consist of 22 half banded platinum electrodes space over 15mm

MRI compatibility -1.5 T with replaceable magnet

Advanced bionics Hi Res Sylmar

Electrode (hifocus 1j) system –banana shaped curved towards Modiolus

Age :12 months

No. of electrodes: 16 spaced at 1.1mm over 17mm.

No. channels :16

MRI compatibility-1.5 T with magnet removed

Med-el Pulsar Innsbruck ,Austria

Age 12 yrs Reciever/stimulator housed in titanium case that is

25.4mm wide :45.7mm long.

No.of electrodes:26

No. of channels:12

MRI compatibility-1.5T

vaccination

O Two vaccines available

O PPV-23(pneumoccocal polysacharide vaccine)

O PCV-13(pnemococcal conjugated vaccine)

O Children <2 yrs-receiving implant should receive PCV13

O CHILDREN >2yrs who have completed PCV-13 should receive PPV23

O Child planned for implant should be up to date on age-appropriate pnemococcal vaccination >2 weeks before surgery if possible.

O all children should receive three doses of pneumococcal conjugated vaccine before age of one

O Children aged 24--59 months who have not received PCV13 should receive PCV13 2month apart and one dose of PPV23 2month later

O Children who have completed the PCV13 series should receive PPV23 >2 months after vaccination with PCV13.

O Persons aged 5--64 years should receive PPV23 a single dose is indicated

Surgical procedure

Incision and skin flap

o Incision may be C-shaped ,inverted U, J-shaped.

o The flap is elevated, it includesperiosteum of the mastoid, temporalisfascia, and temporalis muscle.

o Flap thickness should not be greater than6mm.

C- Shaped incision

Inverted

U

INVERTED

-J -

INCISION

The wello For the placement of stimulator.

o More superior placement in small children in thearea temporal squama, in adults occipital portionof temporal bone.

o In children stimulator placed over exposed Dura.

o Channel formed over the bone to pass theelectrode lead.

o During drilling the well and tie down holes theCSF leak may occur.

mastoidectomy It is performed after creating the site for well.

The mastoidectomy cavity should not be saucerizedas edges help to retain the electrode leads.

Facial recess is identified and widely opened .

Care should be taken of the anomalous facial nerve..Or absent facial nerve.

The most inferior part facial recess is important forvisualization of round window niche.

cochleostomy

Round window niche is clearly seen afteropening the facial recess.

Cochleostomy is created inferior to inferiorattachment of round window membrane.

The size of cochleostomy varies between 0.8mm to 1.2mm in diameter.

Insertion of electrode array• When device is brought into operative field the

monopolar cautery is to be removed.

• The electrode array is inserted into thecochleostomy.

• The tip of the electrode array should be directedinferiorly so that it will slide along the lateral wallof the scala tympani.

• Lubricant like healon and mixture of water andglycerine is used .

• Incomplete insertion may occur in cases oflabyrinthine ossificans.

fixation

The stimulator is fixed to skull with sutures. Drill holes are made above and below the

receptacle site and sutures are passed throughthem.

It can cause perforation and CSF leak inchildren.

Alternatevely a strip of material is placed overthe stimulator secured with miniplates.

Nonabsorbable material like gortex orabsorbable material like alloderm can be used.

The skin incision is closed in layers.

From Advanced Bionics

O Device should be handled gently.

O Monopolar cautery should be discarded when device is brought into operative field.

O Surgeon should have the clear view of round window and should be assure about scalatympani.

Precautions:

Middle Cranial Fossa approach

O Number of surgeons capable of performing this approach are limited.

O Post lingually deafened adult

O Individuals who have open canal wall down mastoidectomy cavities.

Veria technique

O Non mastoidectomy technique

O Done through endaural route for cochleostomy

O Transcanal tunnel drilled in the posterior canal wall

O Faster healing,ealier fitting of the processor

O Minimise trauma to facial nerve

Post-op complication

Facial nerve injury- ,incidence is less than 1%.however minor paresis of facial nerve is uncommon.

May occur in patients with anomalous facial nerve associated with dysplastic semicircular canal.

Taste disturbance due to injury to chordatympani.

Hematoma- formation of more than 10cc requires evacuation.

Generally trivial and can be handled by gentlyopening the wound and treating with antibiotics.

Device removal is not required.

Infections:

O If small can be left to heal by secondary intention orsecondary closure can be done.

O Flap necrosis-most serious complication –deviceremoval may be required. It occurs in cases ofaggressive thining of flap.

O Scalp rotation flap ,temporoparietal facial flap canbe required.

Wound dehiscence:

Early Device Failure:O Out of box failure

O Due to factory defects or during surgical manipulation.

O Extracochlear implantation can occur when hypotympanic cells are mistaken for scalatympani.

O The electrode array may get migrated after correct placement.

O Most common cause of displaced electrode is movement of electrodes array after drill out procedure

Cerebrospinal fluid leak:

Can occur when placing the stimulator, morelikely in young children as skull is very thin.Also occurs during drilling for tie downsutures.

Can also occur during opening the scalatympani. Chances are increased when cochleardysplasia is there.

O This can be treated by packing the common cavity with muscle tissue.

O If this does not controls the leak the ear must be closed by plugging the eustachian tube filling the middle ear and mastoid with fat.

Balance disturbances :

O Incidence is less than 10%.

O It gets resolved with in few weeks by itself.

Meningitis:

O Individuals with CSF leak and inner earmalformations are at more risk.

O Lumbar puncture is required for diagnosis.

O Broad spectrum antibiotics are started.

Extrusion or exposure of the device:

• Suture line should be kept away from the edges ofthe implant.

• Repair must remove skin to avoid suture line thatparallel the implant edge closer than 1-1/2 cm

• A pericranial flap should be rotated to fully coverthe device with or without a temporoparietal flap.

Late complication

Displacement :

Due to physical injury.

During scar formation.

Assessed by fine cut CT of the temporal bone.

Late device failure:

O Usually due to internal device failure-due to traumaor spontaneously.

O External component is first replaced, sometimes thatsolves the problem - fine cut CT of temporal bone tolook for the position of stimulator and electrodes.

Device activation

O 2 to 4 weeks postoperatively,

O referred as hook up”

O Determine stimulation mode-

O a)bipolar mode –active electrode paired with another electrode in intracochlear electrode array,narrow band of stimulation.

O b)monopolar mode-electrode in cochlea is grounded to extracochlearelectrode,resulting in wide current spread.

O Programming of device requires-threshold level and most comfortable loudness level for each active electrode.

O Objective method to assess threshold-

a)neural response telemetry(NRT)-use radiofrequency telemetry to measure the action potential in auditory nerve.

b)Electrical ABR

c)Stapedius reflex-stapedius reflex correlate with most comfortable loudness level.

Auditory rehabilitation after cochlear implant

O Development of speech preception with training in implant listeners.

O Programs of auditory training in children are with implant are often organised with hierarchic approach by which the child learns to associate meaning with unfamiliar and unnatural sounds

Auditory training in children with cochlear implant

O Detection

O Discrimination

O Identification

O Comprehension

O Auditory feedback loop (imitation or

approximation of speech sound)

O Children with implants need the implant system to be working well, and it should be worn consistently in good listening conditions when good communication opportunities are available.

O Keep all external parts in good functioning order and working with an audiologist who specializes in CI on a regularly scheduled basis .

O to be successful in mainstream education classroom situation should be appropriate and has good acoustic and the technology is successfully managed .