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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 oxI 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 • • • • • 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 • • • • 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