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Cochlear Implants – An insight
Dr. Atul JainSr. Consultant and Head,
Department of ENT Head & Neck Surgery
Pushpanjali Crosslay Hospital, NCR
Understanding the human ear
Cochlea cross-section & organ of Corti
No Hair Cells
• Conductive and Sensorineural components• Conductive hearing loss
– Causes in external ear– Causes in middle ear
• Sensorineural hearing loss– Cochlear deafness– Auditory nerve deafness
• Hearing impairment can be due to deficiency in either or both components
Hearing Loss
Treatment of SNHL
• Sensorineural hearing loss can be treated by– Hearing Aids– Speech therapy / Sign language– Cochlear Implants
• Cochlear Implants : Boon in profound bilateral deafness when hearing aids are unable to rehabilitate
Basics of a cochlear implant• Cochlear Implants : First true bionic
sense organs• The human cochlea: An
electromechanical transducer• Cochlear implants, like the human hair
cell, also receive mechanical sound energy and convert it into a series of electrical impulses
• Very different from hearing aids, which only amplify the mechanical sound waves
• Internal Device - surgically implantedunder the skin– Electronics package
(receiver-stimulator) with magnet– Electrode array placed inside the
cochlea
• External Device– Worn on the body or at ear level– Sound/speech processor– Microphone– Coil with magnet
Cochlear Implant Components
An Implantee with the external parts of the implant in position
Mechanism of the implant• Hair cells of the cochlea if damaged, do
not function and hearing becomes impaired.
• Intact auditory nerve fibres capable of transmitting electrical impulses to the brain become unresponsive because of hair cell damage.
• A cochlear implant makes use of this intact auditory pathway by bypassing the damaged hair cells of the cochlea.
Electrode Array in the Cochlea
Electrode in Scala Tympani
– Sounds are picked up by a microphone.
– A speech processor filters, analyzes and digitizes sound into coded signals.
How a Cochlear Implant Works?
Pulses are sent to the coil and transmitted trough the skin to the implant.
How a Cochlear Implant Works?
The implant sends the pulses to the electrodes in the cochlea.
How a Cochlear Implant Works?
– The auditory nerve picks up the signal and sends it to the auditory centre in the brain.
– The brain recognizes these signal as sound
How a Cochlear Implant Works?
• Cochlear implants as we know them now are the result of intensive research over the last four decades.
• However, there is a long history of attempts to provide hearing by the electrical stimulation of the auditory system.
• The centuries old interest in the biologic application of electricity was the basis for the development of cochlear implants.
History
Volta (1800)• First electrical stimulation of
the auditory system.• As part of his experiments he
connected two metal rods to a 50V battery and closed the circuit by placing one rod in each ear
• Heard a noise like "the boiling of thick soup“
History
• Djourno and Eyries(1953)- directly stimulated Auditory nerve- the patient heard sounds that resembled a “roulette wheel” ora “cricket”
• House and Doyle(1961) - Scala tympani approach• Simmons(1966)
- electrodes were placed directly into the modiolar segment of the auditory nerves- able to discern the length of signal duration, some degree of tonality could be achieved
• House(1972) - first commercially available device - The House 3M Single-Electrode Implant
History
Candidates for a cochlear implant • Pre-lingual candidates
– Onset of deafness before the development of speech usually congenital
– Ideal candidates should be less than 6 years of age– Older pre-lingual candidates are not ideal due to
neural plasticity and inability to understand sound• Post-lingual candidates – More suitable
– Onset of deafness after the development of speech– E.g. Bilateral deafness due to meningitis/viral
infections
Audiologic Criteria
Post–lingual Deafness• Pure tone average greater than 70 dB (FDA)• Standard Speech Discrimination score less than
20 to 30%
Pre–lingual Deafness• Brainstem Evoked Response Audiometry
Evaluation and Planning• Otologic Evaluation: Rule out congenital or
acquired abnormalities and/or infections• Audiologic Evaluation: PTA and/or BERA• Radiological Evaluation: HRCT Temporal
bones or MRI • General, Cardiovascular and Neurological
Examination• Psychological evaluation and counselling
Syndromic candidates• Usher’s syndrome- Retinitis pigmentosa with
SNHL• Pendred’s syndrome- Profound SNHL with
colloid goitre• Jervell-Lange-Nielsen Syndrome –
Congenital deafness with ECG abnormalities, sudden fainting attacks and sudden death
• Alport’s Syndrome – Nephropathy with SNHL
Look at the candidate as a whole, not just the deafness and plan accordingly.
Selection of the side of implant• Ear with lesser duration of deafness • Better hearing ear – More residual neural
elements – Better performance• Anatomic factors: Dysplastic, hypoplastic ear
not preferred• Ear with no previous middle ear surgeries
preferred
Selection of the side of implant• Ear with more CNS activation preferred by
using brain-imaging techniques like single-photon emission CT, functional MRI, refined cortical auditory electrophysiology
• Ear with better labyrinthine function not operated, other ear preferred
• If no differences between ears on any parameters, surgeon’s choice: Left ear for right-handed surgeon
Age of implantation
• Youngest age can be even 9 – 12 months
• Earlier fears of electrode migration or extrusion secondary to skull growth have been proven wrong
• Younger age of implantation associated with better outcomes
• General anesthesia preferred• Big C shaped, or inverted U or inverted L
or inverted J shaped incision in postaural area
• Flaps elevated over the mastoid cortex• Well created for placement of the
stimulator-receiver• Conduit made to pass the electrodes into
the mastoid cavity
Surgical Procedure
Surgical Procedure• Mastoidectomy cavity created
• Facial recess identifed and posterior tympanotomy done
• Facial recess widely opened
• Cochleostomy of 1 to 1.5 mm done anteroinferior to the round window niche
• Electrode Array introduced into the scala tympani
Surgical Procedure
• Position of all electrodes confirmed by intra-operative mapping
• Cochleostomy sealed with tissue
• Receiver/Stimulator anchored in the well
• Ground electrodes inserted under the temporalis muscle
• Wound closure in layers
Post-operative course• Antibiotics, Labyrinthine sedatives,
Analgesics
• Can be discharged as day care
• Implant activation done about 4 weeks after surgery when wounds are well healed
• Intensive and meticulous rehabilitation by a speech-language pathologist
Complications
• Facial nerve injury• Taste alteration• Wound infection,
hematoma• Flap necrosis• Wound dehiscence• CSF leak• Balance
disturbances
• Postoperative meningitis
• Long standing pain• Displacement of
electrodes• Extrusion of device• Poor rehabilitation• Device Failure
Newer dimensions
• Cochlear implantation in old age– Working solution for profound hearing loss in old age
• Bilateral implantation– Advantages of binaural hearing– Better localization of sound– Better speech development
• Controversies:– 2nd ear can be kept reserved for better technology– Increased mapping difficulties– ? Bilateral vestibular dysfunction– Cost effectiveness
• Absent or thin auditory nerve bilaterally
• Neurological damage impeding auditory processing
• Medical risks of surgery that exceed the expected benefits of the cochlear implant
Contraindications
• Length of profound deafness• Age at implant• Etiology• Use of hearing aids prior to implantation• Amount and quality of re/habilitation
before and after implant• Family support and commitment• Educational methods and communication
mode
Factors that influence outcomes
• Coordinator/ Cochlear Implant Audiologist
• Administrative Assistant
• Aural Rehabilitation Audiologist
• Speech/Language Pathologist
• Surgeon• Social Worker• Developmental
Pediatrician• Representative from
school• Candidate & family
The Cochlear Implant Team
“After a lifetime in silence and darkness, to be deaf is a greater affliction than to be blind. Hearing is the soul of knowledge and information of a high order. To be cut off from hearing is to be isolated indeed."
– Helen Adams KellerDeaf-Blind American author, activist and lecturer
(1880-1968)