Cochlear implant

DR.ROOHIA

Definition

• 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.

• The signals stimulate cochlea, allowing patient to hear.

• It is also known as Bionic ear.

Parts of cochlear implant

• External– Microphone– Speech processor– Transmitter

• Internal– Receiver and stimulator– An array of up to 22

electrodes

TYPES OF COCHLEAR IMPLANTS– Advanced Bionics– nucleus– MED-EL

Advanced Bionics • Clarion and Bionic Ear

– HiRes 90K internal

– Platinum Series Processor

– Auria BTE Processor

NUCLEUS• Nucleus

– Contour and Contour Advance internals

– SPrint processor

– ESPrit 3G BTE Processor

MED-EL

• Combi 40+ internal

• Tempo+ BTE processor with 5 modular options

• CIS-PRO+ body processor

Common Features of CI Sound Processors

• Power Switch– On-Off

• Battery– Charge Meter

• Display• Lights

• Program Control– Selects Program or MAP loaded into the processor

• Individual programs may have differing parameters such as speech encoder strategy, rate of stimulation, pulse width

• Individual programs have different electrical dynamic ranges for each electrode which affect the perception of soft, average, and loud sounds

How does the cochlear implant works

Complications:

Cochlear Implant Surgery

• Operation lasts about three hours.(GA)• Usually performed as outpatient• Performed by Otolaryngologist

CANDIDACY PROFILE FOR COCHLEAR IMPLANTS

• B/L severe to profound SNHL• Little or no benefit from hearing aids• No medical contrindication for surgey• Realistic expectation• Good family &social support towards

habilitation• Adequate cognitive function to be able to use

the device.

Pre-implantation Process• Medical Evaluation. ENT examines the outer,

middle and inner ear (otological examination)• Physical examination• Imagery Evaluation: x-ray, CT scans, MRI• Audiological evaluation: Audiologist tests

hearing. PTA Speech discrimination Tympanometry OAE ABR Auditory steady state response(ASSR)

• Speech and Language Testing

• Psychological examination • Vaccination

SURGICAL TECHNIQUE

• Facial recess approach • Pericanal techniques eg;suprameatal approach

Step 1 - Flap marking and incision design

• After the skin/subcutaneous tissue flap has been elevated, a separate anteriorly based pericranial flap is then elevated

• The subcutaneous pericranial flap should be 2 to 3 cm in the cephalocaudal dimension and at least 2 cm in length

Step 2 - Mastoidectomy and posterior tympanotomy

• The mastoidectomy cavity should not be• saucerized. The edges should be left as acute

as possible.• These edges will help retain the electrode

leads• within the confines of the mastoid cavity

Step 3 - Cochlear implant receiver well drill out with tie-down holes

• Using a mock-up of the transducer for sizing, a well is drilled into the outer cortex of the parietal bone to accept the transducer magnet housing

• Small holes are drilled at the periphery of the well to allow stay sutures to pass through.

• These suture will be used to secure down the implant

• Stay sutures are then passed through the holes

Step 4 - Cochleostomy

• Using the incus as a depth level, the facial recess is then drilled out

• Through the facial recess, the round window niche should be visualized

• Using a 1 mm diamond burr, a cochleostomy is made just anterior to the round window niche

• varies from 1.0 to 1.4 mm. The endosteum may be opened with a 25-gauge spinal needle, straight pick, or Beaver 59-10 cataract knife

Step 5 - Implant tie down and electrode insertion

• The pocket for the receiver stimulator is copiously irrigated with dilute bacitracin solution,

• any final hemostasis necessary is undertaken. Monopolar electrocoagulation systems are turned off and unplugged.

• The transducer is then laid into the well and secured with the stay sutures

• Hyaluronic acid or 50% glycerine may be used to keep blood out of the scala during electrode insertion and to lubricate the electrode

• The electrode array is then inserted into the cochleostomy and the accompanying guidewire is removed

• Small pieces of harvested periosteum are packed in the cochleostomy around the electrode array, sealing the hole

• Fibrin glue is then used to help secure the electrode array in place

• The wound is then closed in layered fashion and a standard mastoid dressing is applied

• Goals of Surgery:• The surgical technique used for cochlear

implants aims to:• Insert the electrode array without causing

damage to the scala tympani• Place the implant package against the side of

the head so it is less prone to external trauma

• To secure both the electrode array and the implant package to prevent migration after surgery

• To implant all the internal components without damaging the tympanic membrane, ear canal, facial nerve, scalp or any other surrounding tissue

COMPLICATIONS• (1) Scalp Flap Problems – can include infection, necrosis

and thickness. Infections require immediate treatment with antibiotics.. In this case, thick flaps have to be carefully thinned by a surgeon.

• (2) Otitis Media – is an infection of the middle ear, administration of antibiotics and sometimes pain reliever.

• (3) Meningitis –. This is a rare postoperative complication but has the potential to be serious. Cerebrospinal fluid (CSF) may leak and cause problems with the implant. Packing the cochlea with tissue after the cochleostomy and draining the CSF may avoid leakage.

• 4) Facial nerve paralysis – Electromyographic monitoring of the facial during the surgery can help reduce the possibility of paralysis.

• (5) Tinnitus –. Tinnitus may be the result of further damage to existing hair cells.

• (6) Vertigo – or dizziness may be caused by labyrinthitis, inflammation of the part of the ear responsible for balance, and is a larger issue for the elderly who have more difficulty compensating.

• 7) Device migration – is a rare complication. If the implant package is not secured it may create shear forces that can break the electrode.

• (8) Device failure – can result from manufacturing defects or from trauma. Delayed device failure occurs in about 1.5% of implants and need to be replaced.Tests during the operation procedure can avoid implanting a defective device.

• (9) Facial nerve stimulation – occurs when stimulation to the electrode is conducted through bone and also stimulates the facial nerve. This type of complication is fixed by changing the programming of a device to not send pulses to the electrode causing the facial nerve stimulation

Activation and Initial Fitting

• An audiologist fits the patient with:– A microphone (resembles a BTE hearing aid)– A speech processor (may behoused with the microphone or worn at chest-level)

Activation and Initial Fitting• Audiologist runs standard check of the speech processor• Initial activation and programming (mapping) of the implant

– Mapping- a set of parameters of electrode stimulation that gives the patient maximum hearing

– Establishment of electrical dynamic range – May occur over several appointments because the

patient will adjust to sound as s/he gains experience with the implant

• How is mapping conducted?• Using speech (subjective)• Using tones/beeps/bursts (subjective)• Neural Response Telemetry (objective)

– Telemetry is the remote measurement of various electrical parameters (in our case, through implant feedback)

– Neural Response Telemetry measures the response of the auditory nerve to electrical stimulation via a cochlear implant (The Hearing House).

– NRT takes about 5 minutes to complete

Follow-Up to Initial Fitting• May include several visits over the span of weeks or months• Why is this such a lengthy process?

– Each electrode in the cochlea is activated– Each electrode must be programmed and adjusted into the

speech processor– Can create programs for special listening situations– The patient develops more skill from using the implant, thus

more adjustments must be made as skill improves– Over time, less adjustments are necessary and the patient will

return to the CI center every 6 months or annually– Appointment time can be spent on education and rehabilitation

Aural RehabilitationTeaches the patient how to use the CI and respond to auditory input

– Listen to an array of auditory stimuli– Improve speech (expressive and receptive)– Use speech-reading

Complications: • Early complications• (1) Scalp Flap Problems • (2) Meningitis • (3) Facial nerve paralysis• (4) Tinnitus• (5) Vertigo• (6) Device migration• (7) Device failure• (8) Facial nerve

stimulation

• Late complications• 1)exposure of device

&extrusion• 2)pain at the site of

implant • 3)migration/

displacement of device• 5)late device failure• 6)otitis media

COCHLEAR IMPLANT FAILURE

• Hard Failures occur when the device fails to deliver any stimulation to the cochlea– Stimulator fails– Speech processor fails to establish link with implanted system– no auditory input to patient

• Soft Failures occur when the speech processor maintains a lock with the internal system but fails to deliver proper stimulation– Auditory symptoms - subjective decrease in performance, lack of sound perception, severe tinnitus, sound

hypersensitivity, atypical tinnitus (thumping, engine like noise, airplane sounds, clicks, pops, sirens)– Non auditory symptoms – pain, shocking sensations, vertigo, facial twitching– Performance-related issues

• Medcal complications (asom/csom)• Skin infection• Device misplacement• Electrode extrusion • Implantation cholesteatoma

Implant Failure Diagnosis• Initial testing

– Patient’s history – Recent changes in MAP (patient’s individualized fitting program)– Reprogramming MAP if necessary– Check external components - cables

• Impedance testing of electrode using clinical software• EFI(Electrical field imaging) • Link Test

– Integrity of linkage between the inside and outside of device – Determine if there is sufficient energy to power device at all instances

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