Auditory brainstem implants: an analysis of adverse events in the MAUDE database.

OBJECTIVE: Auditory Brainstem Implants (ABI) are used to restore hearing in patients lacking appropriate cochlear anatomy and/or cochlear nerve. The objective of this study was to examine the Manufacture and User Facility Device Experience (MAUDE) database to analyze adverse events. STUDY DESIGN: This is a study of a multi-institutional database maintained by the US FDA. SETTING: A database analysis was performed via collaboration of multiple clinicians at tertiary referral centers. METHODS: The MAUDE database was queried for Medical Device Reports (MDRs) relating to ABIs. MDRs were identified using the advanced search term "Implant, Auditory Brainstem" and reviewing all reports with the basic search term "Brainstem Implant". All collected reports were individually reviewed. RESULTS: A total of 265 individual patient reports were reviewed, of which 55 reports met inclusion criteria. Reports regarding audiologic outcome included failure to provide hearing benefit (n = 27), implant failure/device malfunction (n = 10), and device non-use (n = 6). Postoperative complications included local skin infection (n = 3), CSF leak (n = 3), elevated ICP (n = 1), surgical site dehiscence (n = 1), swelling (n = 1), seroma formation requiring drainage (n = 1), and meningitis (n = 2). Two patients had dislodged magnets during 1.5 Tesla MRI acquisition. There were 35 instances of full explantation of the device and 1 partial removal; 13 patients had a new device implanted following explantation. CONCLUSIONS: Poor hearing results, device failure, and non-use were commonly reported causes for explanation in this analysis. This information can aid physicians in counseling patients and family members and managing device expectations.

Auditory brainstem implants for hearing rehabilitation in NF2-schwannomatosis: A systematic review and single-arm meta-analysis.

BACKGROUND: NF2-schwannomatosis (NF2) is an autosomal dominant disorder prone to hearing loss. Auditory brainstem implants (ABIs) offer a promising solution for hearing rehabilitation in NF2. OBJECTIVE: To synthesize existing literature on ABI implantation in NF2, focusing on audiological outcomes and ABI-related complications. METHODS: The systematic review followed PRISMA guidelines and was registered in the PROSPERO database (CRD42022362155). Relevant studies were identified by searching PubMed, EMBASE, CENTRAL, CMB, and CNKI from inception to August 2023. Data on environmental sound discrimination, open-set discrimination, closed-set discrimination, and ABI-related complications were extracted and subjected to meta-analysis. Publication bias was evaluated using funnel plots and Egger's test. RESULTS: Thirty-three studies were included. The pooled estimate was 58% (95% CI 49-66%) for environmental sound discrimination and 55% (95% CI 40-69%) for closed-set discrimination. Regarding open-set discrimination, the pooled estimates were 30% (95% CI 19-42%) for sound only, 46% (95% CI 37-54%) for lip-reading only, and 63% (95% CI 55-70%) for sound plus lip-reading. The pooled occurrence of ABI-related complications was 33% (95% CI 15-52%). CONCLUSION: This meta-analysis underscores the effectiveness and safety of ABIs in NF2, providing valuable insights for evidence-based decision-making and hearing rehabilitation strategies.

Auditory brainstem implantation: surgical experience and audiometric outcomes in the pediatric population.

OBJECTIVE: Pediatric data regarding treatment via an auditory brainstem implant (ABI) remains sparse. The authors aimed to describe their experience at their institution and to delineate associated demographic data, audiometric outcomes, and surgical parameters. METHODS: An IRB-approved, retrospective chart review was conducted among the authors' pediatric patients who had undergone auditory brainstem implantation between 2012 and 2021. Demographic information including sex, age, race, coexisting syndrome(s), history of cochlear implant placement, average duration of implant use, and follow-up outcomes were collected. Surgical parameters collected included approach, intraoperative findings, number of electrodes activated, and complications. RESULTS: A total of 19 pediatric patients had an ABI placed at the authors' institution, with a mean age at surgery of 4.7 years (range 1.5-17.8 years). A total of 17 patients (89.5%) had bilateral cochlear nerve aplasia/dysplasia, 1 (5.3%) had unilateral cochlear nerve aplasia/dysplasia, and 1 (5.3%) had a hypoplastic cochlea with ossification. A total of 11 patients (57.9%) had a history of cochlear implants that were ineffective and required removal. The mean length of implant use was 5.31 years (0.25-10 years). Two patients (10.5%) experienced CSF-related complications requiring further surgical intervention. The most recent audiometric outcomes demonstrated that 15 patients (78.9%) showed improvement in their hearing ability: 5 with sound/speech awareness, 5 able to discriminate among speech and environmental sounds, and 5 able to understand common phrases/conversation without lip reading. Nine patients (47.4%) are in a school for the deaf and 7 (36.8%) are in a mainstream school with support. CONCLUSIONS: The authors' surgical experience with a multidisciplinary team demonstrates that the retrosigmoid approach for ABI placement in children with inner ear pathologies and severe sensorineural hearing loss is a safe and effective treatment modality. Audiometric outcome data showed that nearly 79% of these patients had an improvement in their environmental and speech awareness. Further multicenter collaborations are necessary to improve these outcomes and potentially standardize/enhance electrode placement.

Evaluation of language, attention, and memory skills in children with auditory brainstem implants.

PURPOSE: This study aimed to evaluate attention, memory, and language skills in children with auditory brainstem implants and cochlear implants. METHODS: This study included 20 children with auditory brainstem implants (ABI) and 20 cochlear implanted (CI) children between the ages of 6 years and 8 years 11 months and their families. "Test of Language Development: Primary (TOLD-P:4)" was used to assess language skills, "STROOP Test, Visual-Aural Digit Span (VADS) test, and Cancellation Test" were used to evaluate attention and memory skills. In addition, the functional outcomes of hearing skills in daily life were scored by "Auditory Behavior in Everyday Life (ABEL) scale". The significance level was determined as 0.05. RESULTS: Children with ABI showed lower language skills than children with CI in terms of TOLD-P:4 language test scores, STROOP sub-test completion times, and the VADS and Cancellation test scores (p < 0.05). In addition, statistically significant correlations were found between language, attention, memory skills, and auditory behavior scale. CONCLUSIONS: This study is one of the limited numbers of studies investigating cognitive processes in children with ABI. Since attention and memory are correlated with language skills, it is recommended that the development of cognition should be considered in follow-up and intervention approaches of children with ABI and/or CI.

Electrically evoked auditory responses: A classification for brainstem implant placement in Neurofibromatosis Type 2.

OBJECTIVE: In auditory brainstem implant (ABI) surgery, array placement may be optimized by electrophysiological information of adequate brainstem activation gained from electrically evoked auditory brainstem responses (EABR). This study aims 1) to characterize in detail the EABR from ABI implantation, 2) to introduce an EABR Classification Scheme, and 3) to analyze data for their correlation with individual patients' findings. METHODS: Out of a continuous series of 54 patients who received an ABI between 2005 and 2019, 23 Neurofibromatosis Type 2 patients with complete documentation of 154 recordings were selected for offline analysis and for development and evaluation of a new EABR Classification Scheme comprising Class A: three vertex positive peaks, Class B:two peaks, Class C: a combination of one peak and a second melted double peak, Class D: one sole vertex positive peak and Class E: no peaks. RESULTS: All 23 subjects showed EABR at final ABI position and experienced auditory sensations at first activation. The most frequent morphology consisted of two peaks, Classes B and C. Identified mean latencies were for P1 0.42 ms (±0.095), P2 1.42 ms (±0.244) and P3 2.41 ms (±0.329). Peak latencies correlated positively with tumor extensions (p < 0.005). CONCLUSIONS: This study provides clear instructions on optimal EABR performance and evaluation. SIGNIFICANCE: The new EABR Classification Scheme relies on a fast "online" identification of vertex positive peaks at the estimated post-artifact phase. The variability in EABR morphology provides an individual snapshot of the actual structural and functional status of the brainstem.

Evaluation of auditory brainstem implant (ABI) users' auditory behavior in everyday life.

PURPOSE: This study aims to evaluate the everyday listening status of pediatric ABI users using the Turkish ABEL questionnaire. METHODS: The study included 33 parents of children with auditory brainstem implant, and 28 parents of children with cochlear implant were included as a control group. All implant users were between the ages of 4-14. Parents answered the ABEL questionnaire to assess their child's auditory behavior in their daily living environment. In addition, Categories of Auditory Performance (CAP) and Speech Intelligibility Rating (SIR) scales were used to evaluate speech perception and production. RESULTS: Auditory-aural, auditory awareness and ABEL total score of ABI users were statistically significantly lower than the CI group (p < 0.05). There was no statistically significant difference between the groups in the Conversational/Social skills subgroups. It was found that as the duration of ABI use increased, auditory-verbal, social skills and total scores increased significantly. In addition, correlations were obtained between ABEL total and subscale scores and CAP and SIR scores. CONCLUSIONS: Parents believe that their children adapt nicely to ABI and are aware of environmental sounds. This study reveals the auditory, aural, and social skills of children using ABI through the regards of their parents. This study showed that the ABEL questionnaire, which was used in previous studies to express parental views of children with hearing aids and cochlear implants, can also be used for parents of children using ABI.

Efficacy of Cochlear Implantation in Neurofibromatosis Type 2 Related Hearing Loss.

OBJECTIVE: To investigate the results of cochlear implantation in subjects with neurofibromatosis type 2 (NF2) and bilateral vestibular schwannomas (VS). STUDY DESIGN: Retrospective case series. SETTING: University-based tertiary referral center. SUBJECTS: Five subjects with NF2 and severe-to-profound sensorineural hearing loss. INTERVENTION: Cochlear implantation. MAIN OUTCOME MEASURE: Surgical outcomes and audiometric performance after cochlear implantation. RESULTS: Five subjects (3 female, 2 male) were included in the study. The mean age at the time of implantation was 54 years old (range 35-78 years). Follow-up after cochlear implantation averaged 38 months (range 21-106 months). In the 5 implanted ears, 2 had no prior treatment, 1 had undergone prior radiation therapy, 1 underwent prior microsurgical removal, and 1 underwent prior microsurgical removal with adjuvant radiation therapy. The mean ipsilateral VS dimensions at time of implantation were 14 mm × 7.2 mm × 6.1 mm (mediolateral × anteroposterior × craniocaudal). Following cochlear implant activation, all 5 subjects achieved sound awareness, open set speech recognition, and 4 continue to be daily users of the devices. CONCLUSION: Cochlear implantation is a viable hearing rehabilitation option for subjects with NF2 and severe-to-profound sensorineural hearing loss. All subjects reported benefit with their cochlear implant, including open set speech recognition, enhanced lip-reading skills and environmental awareness of sound. Four subjects continued to demonstrate improved open-set speech recognition at the time of their last evaluations.

Hearing and language development in children with brainstem implants: a systematic review

Abstract Objective: To present scientific evidence, based on a systematic review of the literature, on the benefit of brainstem implants in auditory rehabilitation and language development in children. Methods: A systematic search was used to identify studies that contain information about the benefit of brainstem implants in the auditory rehabilitation and language development of children. The review was conducted based on a structured literature search, following the Preferred Reporting Items for Systematic Reviews and Meta-analysis (PRISMA) checklist. The search was carried out in the PubMed, Web of Science and Scopus databases, using the combination "Auditory brainstem implants" AND "Pediatric", without restriction of language, period, and location. The quality assessment of the articles was performed using the Study Quality Assessment Tools. Results: Regarding hearing, children with brainstem implants showed sound detection, access to most speech sounds, basic auditory perception skills, recognition of ambient sounds, recognition of some frequently used words and phrases, in addition to some closed-set word discrimination capability. Expressive and comprehensive language were identified in children using auditory brainstem implants, increasing significantly in the short and long terms in most cases; however, in some of the children, such skills remained stable. Conclusion: The auditory brainstem implant can be considered an effective alternative for children with cochlear malformation and/or auditory nerve deficiency and for those who cannot benefit from cochlear implant surgery.

Hearing and language development in children with brainstem implants: a systematic review.

OBJECTIVE: To present scientific evidence, based on a systematic review of the literature, on the benefit of brainstem implants in auditory rehabilitation and language development in children. METHODS: A systematic search was used to identify studies that contain information about the benefit of brainstem implants in the auditory rehabilitation and language development of children. The review was conducted based on a structured literature search, following the Preferred Reporting Items for Systematic Reviews and Meta-analysis (PRISMA) checklist. The search was carried out in the PubMed, Web of Science and Scopus databases, using the combination "Auditory brainstem implants" AND "Pediatric", without restriction of language, period, and location. The quality assessment of the articles was performed using the Study Quality Assessment Tools. RESULTS: Regarding hearing, children with brainstem implants showed sound detection, access to most speech sounds, basic auditory perception skills, recognition of ambient sounds, recognition of some frequently used words and phrases, in addition to some closed-set word discrimination capability. Expressive and comprehensive language were identified in children using auditory brainstem implants, increasing significantly in the short and long terms in most cases; however, in some of the children, such skills remained stable. CONCLUSION: The auditory brainstem implant can be considered an effective alternative for children with cochlear malformation and/or auditory nerve deficiency and for those who cannot benefit from cochlear implant surgery.

A Retrospective Evaluation to Assess Reliability of Electrophysiological Methods for Diagnosis of Hearing Loss in Infants.

Background: An electrophysiological investigation with auditory brainstem response (ABR), round window electrocochleography (RW-ECoG), and electrical-ABR (E-ABR) was performed in children with suspected hearing loss with the purpose of early diagnosis and treatment. The effectiveness of the electrophysiological measures as diagnostic tools was assessed in this study. Methods: In this retrospective case series with chart review, 790 children below 3 years of age with suspected profound hearing loss were tested with impedance audiometry and underwent electrophysiological investigation (ABR, RW-ECoG, and E-ABR). All implanted cases underwent pure-tone audiometry (PTA) of the non-implanted ear at least 5 years after surgery for a long-term assessment of the reliability of the protocol. Results: Two hundred and fourteen children showed bilateral severe-to-profound hearing loss. In 56 children with either ABR thresholds between 70 and 90 dB nHL or no response, RW-ECoG showed thresholds below 70 dB nHL. In the 21 infants with bilateral profound sensorineural hearing loss receiving a unilateral cochlear implant, no statistically significant differences were found in auditory thresholds in the non-implanted ear between electrophysiological measures and PTA at the last follow-up (p > 0.05). Eight implanted children showed residual hearing below 2000 Hz worse than 100 dB nHL and 2 children showed pantonal residual hearing worse than 100 dB nHL (p > 0.05). Conclusion: The audiological evaluation of infants with a comprehensive protocol is highly reliable. RW-ECoG provided a better definition of hearing thresholds, while E-ABR added useful information in cases of auditory nerve deficiency.

Speech intelligibility of children with an auditory brainstem implant: a triple-case study.

Auditory brainstem implantation (ABI) is a relative recent development in paediatric hearing restoration. Consequently, young-implanted children's productive language has not received much attention. This study investigated speech intelligibility of children with ABI (N = 3) in comparison to children with cochlear implants (CI) and children with typical hearing (TH). Spontaneous speech samples were recorded from children representing the three groups matched on cumulative vocabulary level. Untrained listeners (N = 101) rated the intelligibility of one-word utterances on a continuous scale and transcribed each utterance. The rating task yielded a numerical score between 0 and 100, and similarities and differences between the listeners' transcriptions were captured by a relative entropy score. The speech intelligibility of children with CI and children with TH was similar. Speech intelligibility of children with ABI was well below that of the children with CI and TH. But whereas one child with ABI's intelligibility approached that of the control groups with increasing lexicon size, the intelligibility of the two other children with ABI did not develop in a similar direction. Overall, speech intelligibility was only moderate in the three groups of children, with quite low ratings and considerable differences in the listeners' transcriptions, resulting in high relative entropy scores.

Written language skills in children with auditory brainstem implants.

PURPOSE: This study aimed to assess the written language skills of children with auditory brainstem implants (ABI). METHODS: In this study, 15 children (from second to eighth grades) with ABI were evaluated for their written language abilities using a written expression skill assessment form. Five different features of written expression points were scored and analyzed, yielding a composite score for written expression skills. RESULTS: This study showed that all children with ABI needed more verbal cues than spontaneously written samples. Moreover, these children used short and simple sentences with limited vocabulary and repeated words and sentences. Furthermore, these children were deficient in writing an introduction, the body, and the conclusion paragraphs and could not write events in a logical sequence. CONCLUSIONS: The written language skills of children with ABI depend on age at implantation, duration of implant use, and additional handicaps. Written expression skills in children with ABI are highly complex skills. The findings highlight the importance of ABI during the critical language development period and the enhancement of training programs for written language skills in children who underwent ABI.

Evaluation of phoneme recognition skills in pediatric auditory brainstem implant users.

OBJECTIVES: This study aims to evaluate the relationship between phoneme recognition skills and language development skills in pediatric auditory brainstem implant (ABI) users. It further intends to identify the delays and problems that may occur in the phoneme recognition skills of children with ABI and shed light on rehabilitation programs. METHODS: Our study included 20 children using ABI and another 20 using cochlear implants (CI). They were aged between 6 and 8 years 11 months. The participants exhibited homogenous demographic and audiological characteristics. The Turkish version of the Test of Language Development-Primary: Fourth Edition (TOLDP:4) was used to evaluate the language development skills, and the Turkish version of the Phoneme Recognition Test (PRT) was applied to assess the phoneme recognition skills. RESULTS: There was a statistically significant difference (p < 0.05) in the PRT values as well as in the language development skills between the children with ABI and those with CI. It was observed that the values of the children with CI were significantly higher than those of children with ABI. CONCLUSION: Although children with ABI were not able to match the skills of their peers with CI, their language development and communication skills improved. It is believed that this study will contribute to the literature by demonstrating that the use of ABI improves phoneme recognition skills in children who are not eligible for CI or who do not adequately benefit from CI.

Novel microscope-based visual display and nasopharyngeal registration for auditory brainstem implantation: a feasibility study in an ex vivo model.

PURPOSE: An auditory brainstem implant (ABI) represents an alternative for patients with profound hearing loss who are constrained from receiving a cochlear implant. The positioning of the ABI electrode influences the patient's auditory capacity and, therefore, quality of life and is challenging even with available intraoperative electrophysiological monitoring. This work aims to provide and assess the feasibility of visual-spatial assistance for ABI positioning. METHODS: The pose of the forceps instrument that grasps the electrode was electromagnetically navigated and interactively projected in the eyepieces of a surgical microscope with respect to a target point. Intraoperative navigation was established with an experimental technique for automated nasopharyngeal patient registration. Two ABI procedures were completed in a human specimen head. RESULTS: An intraoperative usability study demonstrated lower localization error when using the proposed visual display versus standard cross-sectional views. The postoperative evaluations of the preclinical study showed that the center of the electrode was misplaced to the planned position by 1.58 mm and 3.16 mm for the left and the right ear procedure, respectively. CONCLUSION: The results indicate the potential to enhance intraoperative feedback during ABI positioning with the presented system. Further improvements consider estimating the pose of the electrode itself to allow for better orientation during placement.

Awake craniotomy for auditory brainstem implant in patients with neurofibromatosis type 2: Four case reports.

BACKGROUND: The auditory brainstem implant (ABI) is a significant treatment to restore hearing sensations for neurofibromatosis type 2 (NF2) patients. However, there is no ideal method in assisting the placement of ABIs. In this case series, intraoperative cochlear nucleus mapping was performed in awake craniotomy to help guide the placement of the electrode array. CASE SUMMARY: We applied the asleep-awake-asleep technique for awake craniotomy and hearing test via the retrosigmoid approach for acoustic neuroma resections and ABIs, using mechanical ventilation with a laryngeal mask during the asleep phases, utilizing a ropivacaine-based regional anesthesia, and sevoflurane combined with propofol/remifentanil as the sedative/analgesic agents in four NF2 patients. ABI electrode arrays were placed in the awake phase with successful intraoperative hearing tests in three patients. There was one uncooperative patient whose awake hearing test needed to be aborted. In all cases, tumor resection and ABI were performed safely. Satisfactory electrode effectiveness was achieved in awake ABI placement. CONCLUSION: This case series suggests that awake craniotomy with an intraoperative hearing test for ABI placement is safe and well tolerated. Awake craniotomy is beneficial for improving the accuracy of ABI electrode placement and meanwhile reduces non-auditory side effects.

Clinical and scientific innovations in auditory brainstem implants.

The auditory brainstem implant (ABI) was originally developed to provide rehabilitation of retrocochlear deafness caused by neurofibromatosis type 2 (NF2). Recent studies of the ABI have investigated outcomes in non-NF2 cohorts, such as patients with cochlear nerve aplasia or cochlear ossification and more recently, intractable tinnitus. New technologies that improve the ABI-neural tissue interface are being explored as means to improve performance and decrease side effects. Innovative discoveries in optogenetics and bioengineering present opportunities to continually evolve this technology into the future, enhancing spatial selectivity of neuronal activation in the cochlear nucleus and preventing side effects through reduction in activation of non-target neuronal circuitry. These advances will improve surgical planning and ultimately improve patients' audiological capabilities. ABI research has rapidly increased in the 21st century and applications of this technology are likely to continually evolve. Herein, we aim to characterize ongoing clinical, basic science, and bioengineering advances in ABIs and discuss future directions of this technology.

Two-phase survey on the frequency of use and safety of MRI for hearing implant recipients.

PURPOSE: Magnetic resonance imaging (MRI) is often used to visualize and diagnose soft tissues. Hearing implant (HI) recipients are likely to require at least one MRI scan during their lifetime. However, the MRI scanner can interact with the implant magnet, resulting in complications for the HI recipient. This survey, which was conducted in two phases, aimed to evaluate the safety and performance of MRI scans for individuals with a HI manufactured by MED-EL (MED-EL GmbH, Innsbruck, Austria). METHODS: A survey was developed and distributed in two phases to HEARRING clinics to obtain information about the use of MRI for recipients of MED-EL devices. Phase 1 focused on how often MRI is used in diagnostic imaging of the head region of the cochlear implant (CI) recipients. Phase 2 collected safety information about MRI scans performed on HI recipients. RESULTS: 106 of the 126 MRI scans reported in this survey were performed at a field strength of 1.5 T, on HI recipients who wore the SYNCHRONY CI or SYNCHRONY ABI. The head and spine were the most frequently imaged regions. 123 of the 126 scans were performed without any complications; two HI recipients experienced discomfort/pain. One recipient required reimplantation after an MRI was performed using a scanner that had not been approved for that implant. There was only one case that required surgical removal of the implant to reduce the imaging artefact. CONCLUSION: Individuals with either a SYNCHRONY CI or SYNCHRONY ABI from MED-EL can safely undergo a 1.5 T MRI when it is performed according to the manufacturer's safety policies and procedures.

Children with Auditory Brainstem Implant: How Do They Perform in Motor and Language Skills?

BACKGROUND: Young children are able to explore new objects and practice language through the acquisition of motor skills that lead to their overall development. Congenital hearing loss and total vestibular loss may contribute to the delay in speech and motor skill development. OBJECTIVES: To investigate the relationship between motor development performance, speech perception, and language performance in children with auditory brainstem implant (ABI). METHOD: Ten children, aged 4-17 years (mean age 9.76 ± 4.03), fitted with unilateral ABI for at least 2 years due to the presence of labyrinthine aplasia and rudimentary otocyst at least 1 side were included in the study. Several standardized tests, such as Bruininks-Oseretsky Motor Proficiency Test-2 (BOT-2), Children's Auditory Perception Test Battery, Meaningful Auditory Integration Scale (MAIS), and Test of Early Language Development-3, were performed to evaluate their skills of fine motor control, balance, manual dexterity, language, and auditory perception. RESULTS: A significant correlation was established between the BOT-2 manual dexterity and MAIS scores (r = 0.827, p < 0.05) and between the manual dexterity and language skills (for expressive language, r = 0.762, p < 0.05; for receptive language, r = 0.650, p < 0.05). Some of the BOT-2 balance tasks, such as standing on 1 leg on a line with eyes closed, standing on 1 leg on a balance beam with eyes open, standing heel-to-toe on a balance beam, and walking forward heel-to-toe on a line, showed a strong correlation with their receptive and expressive language performance (p < 0.05). CONCLUSION: The current study has indicated that significantly poor manual and balance performances are associated with poor speech perception and language skills in children with ABI. The authors recommend performing a vestibular assessment before and after ABI surgery and the use of a holistic rehabilitation approach, including auditory and vestibular rehabilitation, to support development of the children with ABI.

Assessing temporal responsiveness of primary stimulated neurons in auditory brainstem and cochlear implant users.

The reasons why clinical outcomes with auditory brainstem implants (ABIs) are generally poorer than with cochlear implants (CIs) are still somewhat elusive. Prior work has focused on differences in processing of spectral information due to possibly poorer tonotopic representation and higher channel interaction with ABIs than with CIs. In contrast, this study examines the hypothesis that a potential contributing reason for poor speech perception in ABI users may be the relative lack of temporal responsiveness of the primary neurons that are stimulated by the ABI. The cochlear nucleus, the site of ABI stimulation, consists of different neuron types, most of which have much more complex responses than the auditory nerve neurons stimulated by a CI. Temporal responsiveness of primary stimulated neurons was assessed in a group of ABI and CI users by measuring recovery of electrically evoked compound action potentials (ECAPs) from single-pulse forward masking. Slower ECAP recovery tended to be associated with poorer hearing outcomes in both groups. ABI subjects with the longest recovery time had no speech understanding or even no hearing sensation with their ABI device; speech perception for the one CI outlier with long ECAP recovery time was well below average. To the extent that ECAP recovery measures reveal temporal properties of the primary neurons that receive direct stimulation form neural prosthesis devices, they may provide a physiological underpinning for clinical outcomes of auditory implants. ECAP recovery measures may be used to determine which portions of the cochlear nucleus to stimulate, and possibly allow us to enhance the stimulation paradigms.

Bilateral Auditory Brainstem Implants in Patients With Neurofibromatosis 2.

OBJECTIVE: To discuss indications for bilateral auditory brainstem implants (ABIs), compare audiometric outcomes of unilateral vs bilateral ABIs, and determine if patients have improved outcomes with addition of a second-side implant. STUDY DESIGN: Retrospective review of 24 patients with neurofibromatosis 2 (NF2) who underwent sequential placement of ABIs from 1989 to 2019. SETTING: Tertiary referral center. METHODS: Charts were reviewed for indication for second-side surgery, use of implants, and audiometric outcomes. Implants placed in the past 30 years were included in the study. Northwestern University Children's Perception of Speech (NU-CHIPS) and/or City University of New York (CUNY) sentence scores were compared in unilateral and bilateral conditions. RESULTS: Indications for a second-side implant included first-side implants with severe nonauditory symptoms (11), marginal audiometric results (9), outdated technology (2), or deterioration of first side (2). Seven patients are bilateral users and 1 patient discontinued bilateral use after a year due to no significant improvement over unilateral use. One patient with initial bilateral use was lost to follow-up. Thirteen patients are unilateral users due to nonaudiometric side effects or poor audiometric outcomes with the first side. Two patients are complete nonusers. Seventy-five percent had improved audiometric outcomes after the second-side implant, and 20% had stable findings. CONCLUSIONS: Second-side ABIs should be consider in patients with poor performance from a first-side implant. Most patients demonstrate subjective improvement with the second ABI. More research is needed for better objective assessments of improvements.