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Central Neural Auditory
Prosthesis
Chp. 161
Irene Kim
Auditory Brainstem Implant (ABI)
• Effective partial hearing
restoration in patients with NF2
• Most common indication for
ABI is NF2
– In US, criteria is for postlingual
NF2 patients 12 yrs or older
– First or second side vestibular
schwannoma removal
ABI in Non-NF2 Patients
• Patients who have failed CI
• Loss of 8th CN integrity 2/2 skull base fx,
traumatic avulsion
• Severe post-meningitic cochlear ossification
• Possible in cochlear dysplasia or cochlear
nerve aplasia
• Hearing outcomes SIGNIFICANTLY BETTER
than in NF2 patients
http://www.youtube.com/watch?v=kcCRmFNp
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ABI Benefits
• Limited to environmental sound perception
and aid to lip reading
• Rarely, open set speech understanding
• Definitely POORER hearing than with cochlear
implant
Current ABI
• 21-electrode array
• Stimulated similar to a cochlear implant
– Transcutaneous radiofrequency transmitter and
receiver
Timing of ABI Placement
• Usually placed at time of 2nd vestibular
schwannoma removal
• Can place at time of first side tumor removal
(“sleeper”)
• Second stage procedure after previous
vestibular schwannoma surgery
– Advantages/Disadvantages
Surgical Approach
• Translabyrinthine
– Favored by most surgeons for ABI placement in
NF2 patients
– More lateral view of brainstem
– Cerebellar retraction reduced or avoided
• Retrosigmoid
Surgical Approach
Auditory Performance
• Useful auditory perception
• Hearing level much less compared to CI
– Loss of peripheral tonotopic stimulation
• Improvement in auditory sensation
• Rare significant open set speech
understanding (telephone use)
Penetrating
Auditory Brainstem Implant
• Two generations
(combo of
penetrating and
surface arrays)
• Electode inserted
into cochlear
nucleus
• Outcomes are not
better than
surface electrode
ABI
Penetrating Auditory
Midbrain Implant
• Stimulate auditory midbrain proximal to
damaged cochlear nucleus
– Dorsal surface of inferior colliculus
• Penetrating electrode array
• Access tonotopic orientation of inferior
colliculus
Complications
• Cerebrospinal fluid fistula through the wound
and risk of infx in presence of ABI
• Possible hydrocephalus
• Displacement of electrode array
• Nonauditory/somatic sensations
– Ipsilateral facial tingling/throat discomfort
TAKE HOME POINTS
• 1. Effective method of partial hearing
restoration in patients with NF2
• 2. Provides environmental sound awareness
• 3. Open set speech perception achieved only
rarely.
• 4. Trials of penetrating ABI and AMI have not
shown improved hearing
• 5. Better speech perception in patients w/o NF2
Hearing Aids: Strategies of
Amplification
Chp. 162
Irene Kim
General
• HA predominantly for:
– SNHL with flat or sloping hearing loss
• Patient is candidate for HA depending on:
– 1. Degree of hearing loss
– 2. Extent of communication disorder resulting
from loss
– 3. Motivation of patient/attitude towards hearing
aid use
Hearing Aid Technology
• Component miniaturization
• Programmability
• Wireless connectivity
– Permits communication from one hearing aid to
another
– From hearing aids to other electronic devices and
signal sources
• FM radio, phones, computers
Hearing Aid
• Microphone, amplifier, receiver
– Microphone: converts acoustic energy into electric
energy
– Amplifier: adds gain to level of electric signal
– Receiver: receives amplified electric signal and
converts it back to acoustic energy
• Telecoil or t-coil
– Allows HA to receive electromagnetic signals directly,
bypassing microphone
– Classroom setting
Electroacoustic Characteristics
• Frequency gain
• Input-output
– Linear
– Non-linear
• Output limiting
Nonlinear Amplification
• Designed to address major problem with SNHL
– Reduced dynamic range
• Normal hearing: Range is 0 to 100 dB
• Patient w/ SNHL: Range is reduced
– Compression circuitry
– Peak clipping
Hearing Aid Features
• Directionality
– Directional microphone
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Noise reduction
Feedback reduction
Program management
Automatic adaptivity
Data logging
Hearing Aid Styles
• Behind-the-ear (BTE)
– Microphone and amplifier behind the ear
– Receiver may be in the canal or behind ear
– Potential for feedback lowest
• In-the-ear (ITE)
• In-the-canal (ITC)
• Completely-in-canal (CIC)
– Reduction of wind nose, ease
of phone/stethoscope use
Hearing Assistive Technology
• Assistive listening devices (ALDs)
– Personal amplifiers, FM systems
– Enhances acoustic signal over background noise
• Uses remote microphone
– Closed captioning of TV shows
HA Fitting
• Fitting
• Verification (objective measurements)
– Real-ear unaided response or gain (REUR/G)
– Real aided response or gain (REAR/G)
– REAG-REUG = real insertion gain (REIG)
Outcome Measurement
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Self-assessment scales
Assessment by spouses
Hearing Handicap Inventory for Elderly (HHIE)
Other Quality of Life measures
Hearing Aids in Children
• Always fitted w/ binaural hearing aids
• Children grow quickly; hearing aids often
adjusted
• Usually BTE
– Maximize audibility
– Can remake ear mold of BTE as ear canal grows