Transcript Cochlear Implant

Cochlear Implant
Prof. Hamad Al Muhaimeed
The Fundamental Concept of
Cochlear Implant
To bypass the damaged hair
cells.
History:
• Old generation: Sound awareness only
• New generation: Improved communication
abilities (auditory cues with lip reading, open
set speech)
• Since 1972 more than 16 different cochlear implants
• 1984 FDA approval for adults
• 1990 children approval
Anatomy
Anatomy
Anatomy
Scala tympani
Scala vestibuli
Cochlear duct
Basilar membrane
Vestibular membrane
Tectoral membrane
Hair cells (outer/inner)
Cochlear nerve fibers
Anatomy-micro
Physiology of Hearing
Anatomy
Sensorineural Hearing Loss
Death of hair cells vs. ganglion
cells
Otte, et al estimated we need
10,000 ganglion cells with 3,000
apically to have good speech
discrimination
Apical ganglion cells tend to
survive better (?acoustic
trauma)
Central neural system plasticity
Pathologic Anatomy
Anatomy of Speech
Mix of frequencies
Speech recognition is “top-down” process
Formant frequencies: frequency maximum
based on vocal tract
F0 is fundamental frequency
F1 & F2—contribute to vowel identification
F3—l,r (lateral and retroflex glides)
F4 & F5—higher frequency speech sounds
Some speech based on amplitude—k, f, l, s
Structure of Cochlear Implant
1. External components
2. Internal components
Components of Cochlear Implant
Types of Cochlear Implants
Single vs. Multiple channels
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Audio example of how a cochlear implant sounds with
varying number of channels
Monopolar vs. Bipolar
Speech processing strategies
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Spectral peak (Nucleus)
Continuous interleaved sampling (Med-El, Nucleus,
Clarion)
Advanced combined encoder (Nucleus)
Simultaneous analog strategy (Clarion)
Anatomy of a Cochlear Implant
How does it work?
Neural Responses to Sound
1. Temporal coding: Provide information
about timing cues (rhythm and intonation.
2. Place coding: Rely on the tonotopic
organization of a neural fibers.
3. Provide information about quality (timber
of a speech signal – sharp to dull)
Site of Stimulation
1. Extracochlear
2. Intracochlear
3. Retrocochlear (lateral recess of the
fourth ventricle over the cochlear
nuclei.
Stimulus
a. Stimulus type:
- Analog (continuous)
- Digital (pulsatile)
b. Stimulus configuration
1. Bipolar – localized site of stimulation
2. Monopolar – stimulates large
population of neurons
Speech Coding
As speech is produced, the mouth, nose & pharynx
modify the frequency spectrum so that peaks and
formants are produced at certain frequencies.
Speech processing used – 3 formants:
F0 = 100 to 200 Hz
F1 = 200 to 1200 Hz
F2 = 550 to 3500 Hz
Number of Channels
1. Single channel – no place
coding
2. Multi channel
Stimulation Mode
1. Simultaneous: More than one
electrode is activated at a given
succession - CIS
2. Sequential: A continuous series of
electrode activates in succession speak
Electrode Design
1. Single electrode
2. Multielectrode
Indication for Cochlear Implant
Adults
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18 years old and older (no limitation by age)
Bilateral severe-to-profound sensorineural
hearing loss (70 dB hearing loss or greater
with little or no benefit from hearing aids for 6
months)
Psychologically suitable
No anatomic contraindications
Medically not contraindicated
Indications for Cochlear
Implantation -- Children
12 months or older
Bilateral severe-to-profound sensorineural hearing loss
with PTA of 90 dB or greater in better ear
No appreciable benefit with hearing aids (parent survey
when <5 yo or 30% or less on sentence recognition
when >5 yo)
Must be able to tolerate wearing hearing aids and show
some aided ability
Enrolled in aural/oral education program
No medical or anatomic contraindications
Motivated parents
Factors Affecting Patient
Selection
a.
b.
c.
d.
e.
f.
g.
Onset of deafness (congenital or adventitious)
Year of deafness
Length of sensory deprivation (i.e. no hearing aids)
Socioeconomic factors
Educational level
Individual ability to use minimal cues
General health
Factors Affecting Pt. (cont.)
h. Personality
i. Willingness to participate in rehabilitation program
j. Language skills
k. Appropriate expectations
l. Desire to communicate in a hearing society
m. Psychological stability
n. Cochlear patency
Audiologic Evaluation
1. Pure tone audiometry under headphones
2. Warble tone audiometry with a hearing aid
in a monitored free field
3. Immittance testing
4. Speech recognition testing
5. Speech awareness testing
Audiologic Evaluation (cont.)
6. Environmental sounds (closed and open set)
7. Speech reading (lip reading) ability
8. Electrical response audiometry
9. Auditory discrimination
10.Transtympanic electrical stimulation
(promontory or round window test)
Medical Evaluation
1.
2.
3.
4.
5.
6.
7.
8.
9.
Clinical history and initial interview
Preliminary examination
Complete medical and neurologic examination
Cochelar imaging using computed tomography
(CT or magnetic resonance imaging (MRI)
Vestibular examination (electronystagmography)
Pathology tests
Psychologic or psychiatric assessment or both
Vision testing
Assessment for anesthetic procedures
CT Findings
Contraindications
Incomplete hearing loss
Neurofibromatosis II, mental retardation, psychosis,
organic brain dysfunction, unrealistic expectations
Active middle ear disease
CT findings of cochlear agenesis (Michel deformity) or
small IAC (CN8 atresia)
Dysplasia not necessarily a contraindication, but
informed consent is a must
H/O CWD mastoidectomy
Labyrinthitis ossificans—follow scans
Advanced otosclerosis
Surgical Procedure
All electrode insertions are carried out through the facial
recess approach. Various incision designs are used to
allow wide exposure of the mastoid and squamous
portions of the temporal bone. The temporalis muscle
and periosteum are widely stripped to accommodate a
“table” for the pedestal of the Ineraid device or the
receiver-stimulator of the other devices. The
mastoidectomy is not widely saucerized, but instead
overhanging ledges are purposefully maintained. Care
must be exercised so as not to damage the fibrous
annulus during the facial recess approach..
Surgical Technique
Complications:
A. Intraoperative
1. Intraoperative cannot be placed
appropriately.
2. Insertion trauma
3. Gusher
Complications (cont.):
B. Postoperative
1. Postauricular flap edema, necrosis or separation
2. Facial paralysis
3. Transient vertigo is more likely to occur on a
totally nonfunctioning vestibular system.
4. Pain is usually associated with stimulation of
Jacobson’s nerve, the tympanic branch of the
glossopharyngeal nerve.
5. Facial nerve stimulation
6. Meningitis
7. Device extrusion
Rehabilitation
Tuning or mapping of the external processor to
meet individual auditory requirements after 3 - 4
weeks postop.
1. Multisensory approach
2. Bimodal stimulation
3. Suprasegmental discrimination training
4. Segmental discrimination and recognition
training
5. Speech tracking
6. Counseling
Rehabilitation
Rehabilitation
Rehabilitation
Rehabilitation
Rehabilitation
Rehabilitation
Rehabilitation
Pediatric Implantation
Five years after approval was given for adult
implanta-tion by FDA, approval of cochlear implants
for use in patients ages 2 to 17 years was granted. The
major concerns regarding implantation in children
included difficulty in evaluating the young child’s
hearing impairment, assessing the performance and
effect of implantation on the child’s development
compared with traditional types of training, the risks
of implantation (both intraoperative and long term),
the effects of implantation on the auditory system, and
the challenges of effectively programming such
sophisticated devices in children.
Auditory Brain Stem
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