The High Rate CIS Auditory Brainstem Implant for Restoration of Hearing in NF-2 Patients

Auditory Brainstem Implant Outcomes in Tumor and Nontumor Patients: A Systematic Review

OBJECTIVE

To elucidate the differences in auditory performance between auditory brainstem implant (ABI) patients with tumor or nontumor etiologies.

DATA SOURCES

PubMed, Embase, and Web of Science Core Collection from 1990 to 2021.

REVIEW METHODS

We included published studies with 5 or more pediatric or adult ABI users. Auditory outcomes and side effects were analyzed with weighted means for closed-set, open-set speech, and categories of auditory performance (CAP) scores. Overall performance was compared using an Adult Pediatric Ranked Order Speech Perception (APROSPER) scale created for this study.

RESULTS

Thirty-six studies were included and underwent full-text review. Data were extracted for 662 tumor and 267 nontumor patients. 83% were postlingually deafened and 17% were prelingually deafened. Studies that included tumor ABI patients had a weighted mean speech recognition of 39.2% (range: 19.6%-83.3%) for closed-set words, 23.4% (range: 17.2%-37.5%) for open-set words, 21.5% (range: 2.7%-48.4%) for open-set sentences, and 3.1 (range: 1.0-3.2) for CAP scores. Studies including nontumor ABI patients had a weighted mean speech recognition of 79.8% (range: 31.7%-84.4%) for closed-set words, 53.0% (range: 14.6%-72.5%) for open-set sentences, and 2.30 (range: 2.0-4.7) for CAP scores. Mean APROSPER results indicate better auditory performance among nontumor versus tumor patients (3.5 vs 3.0, P = .04). Differences in most common side effects were also observed between tumor and nontumor ABI patients.

CONCLUSION

Auditory performance is similar for tumor and nontumor patients for standardized auditory test scores. However, the APROSPER scale demonstrates better ABI performance for nontumor compared to tumor patients.

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 Implants-Hearing Restoration in Congenitally Deaf Children

BACKGROUND

Children who are born deaf can learn to hear and to speak with the aid of a cochlear implant (CI). If the implantation of a CI is not possible for anatomical reasons, an auditory brainstem implant (ABI) is the only surgical option for auditory rehabilitation. It is estimated that about 5 to 45 children could potentially benefit from this treatment in Germany each year. In this article, we present and discuss the current state of the scientific evidence.

METHODS

The PubMed and Embase databases were searched for relevant publications from 2010 onward. 15 articles reporting at least 10 cases with at least one year of auditory follow-up were included in the analysis. The results, including CAP ("categories of auditory performance") scores on a scale of 0 to 7, are presented and compared with the authors' own findings in a series of 38 patients.

RESULTS

All of the publications show that children who do not suffer from impairments of other kinds hear significantly better with an ABI than those with additional handicaps. Early implantation is advantageous, under the age of three years if possible. The results vary widely across publications and from patient to patient. The mean CAP score in all publications is 3.57 (standard deviation [SD], 1.04). 38.24% of the patients (SD 18.68) achieved the ability to understand spoken language (CAP ≥= 5), more specifically, the ability to communicate in everyday life without lip reading, in person and some even succeed in conversing over the telephone.

CONCLUSION

ABI is a safe and effective treatment for sensorineural deafness in congenitally deaf children who cannot be treated with a cochlear implant. In particular, children without any other impairments have a good chance of developing the ability to understand spoken language, especially if the implantation is performed early.

ABI-auditory brainstem implant

The Auditory Brainstem Implant (ABI) is based on the classic cochlear implant (CI) but uses a different stimulation electrode. At MED-EL, the early development activities on ABI started in the year 1994, with the suggestion coming from J. Helms and J. Müller from Würzburg, Germany in collaboration with the Univ. of Innsbruck Austria. The first ABI surgery in a neuro-fibromatosis (NF2) patient with the MED-EL device took place in the year 1997. Later, the indication of ABI was expanded to non-NF2 patients with severe inner-ear malformation, for whom a regular CI will not be beneficial. Key translational research activities at MED-EL in collaboration with numerous clinics investigating the factors that affect the hearing performance amongst ABI patients, importance of early ABI implantation in children, tools in pre-operative assessment of ABI candidates and new concepts that were pursued with the MED-EL ABI device. The CE-mark for the MED-EL ABI to be used in adults and children down to the age of 12 months without NF-2 was granted in 2017 mainly based on two long-term clinical studies in the pediatric population. This article covers the milestones of translational research from the first concept to the widespread clinical use of ABI in association with MED-EL.

Pediatric Auditory Brainstem Implant Users Compared With Cochlear Implant Users With Additional Disabilities

OBJECTIVES

To evaluate long-term language development in children with prelingual deafness who received auditory brainstem implants (ABIs) compared with children who received cochlear implants (CIs) at the same hospital. Additional non-auditory disabilities were taken into account.

STUDY DESIGN

Retrospective cohort study.

SETTING

Tertiary referral center.

PATIENTS

Ten children with bilateral malformations of the cochlea and/or cochlear nerve who received ABIs, including seven with additional disabilities, and 147 children with CIs as a reference group, including 22 children with additional disabilities.

INTERVENTION

ABIs were implanted at 1.3 to 6.2 years of age. Follow-up ranged from 1.1 to 7.7 years.

MAIN OUTCOME MEASURES

Receptive and expressive language abilities were assessed using the Infant Toddler Meaningful Auditory Integration Scale (IT-MAIS), the Categories of Auditory Performance (CAP), the Meaningful Use of Speech Scale (MUSS), and the Speech Intelligibility Rate (SIR).

RESULTS

Of the 10 children with ABIs, seven had long-term follow-up data. Within 1 year, six of the seven children with ABIs could identify sounds, respond to speech, and use their voice to attract attention. Language skills developed at a slower rate than in children with CIs and reached the same competence level when additional disabilities were absent. These language skills matched, on average, those of children with CIs with additional disabilities.

CONCLUSION

For deaf children with bilateral inner ear malformations, ABIs provide satisfactory auditory input. Children with ABIs are able to develop receptive and expressive language skills comparable to those of children with CIs with additional disabilities. Using this knowledge, preoperative parent counselling can be refined.

Auditory Brainstem Implantation for Adults With Neurofibromatosis 2 or Severe Inner Ear Abnormalities: A Health Technology Assessment

BACKGROUND

Neurofibromatosis 2 (NF2) is a rare genetic disorder that causes vestibular schwannomas to develop in both eighth cranial nerves. Almost all people with NF2 eventually become completely deaf as a result of progressive tumour enlargement or following surgical or radiotherapy treatment. Other rare abnormal conditions in the inner ears can also cause complete deafness. For people with either indication who are not candidates for cochlear implantation, auditory brainstem implantation is the only treatment option to restore some functional hearing. We conducted a health technology assessment of auditory brainstem implantation for adults with NF2 and severe inner ear abnormalities, which included an evaluation of effectiveness, safety, cost-effectiveness, the budget impact of publicly funding auditory brainstem implantation, and patient preferences and values.

METHODS

We performed a systematic literature search of the clinical evidence. We assessed the risk of bias of each included study using the Risk of Bias in Non-randomized Studies-of Interventions (ROBINS-I) tool and the quality of the body of evidence according to the Grading of Recommendations Assessment, Development, and Evaluation (GRADE) Working Group criteria. We performed a systematic economic literature search. We did not conduct a primary economic evaluation because the outcomes identified in our clinical evidence review were difficult to translate into measures appropriate for health economic modelling. We also analyzed the net budget impact of publicly funding auditory brainstem implantation over the next 5 years in Ontario, including the device, presurgical assessment, surgical procedure, and postsurgical rehabilitation. To contextualize the potential value of auditory brainstem implants, we spoke with six people with lived experience of NF2 and severe inner ear abnormalities.

RESULTS

We included 22 publications (16 in NF2, five in severe inner ear abnormalities, and one in complications of auditory brainstem implantation) in the clinical evidence review. In adults with NF2, auditory brainstem implantation when compared with no intervention allows any degree of improvement in sound recognition (GRADE: High), allows any degree of improvement in speech perception when used in conjunction with lip-reading (GRADE: High), and provides subjective benefits of hearing (GRADE: High). It likely allows any degree of improvement in speech perception when using the implant alone (GRADE: Moderate) and may improve quality of life (GRADE: Low). In adults with severe inner ear abnormalities, auditory brainstem implantation when compared with no intervention likely allows any degree of improvement in sound recognition (GRADE: Moderate) and in any speech perception when using the implant alone (GRADE: Moderate). It may allow any degree of improvement in speech perception when used in conjunction with lip-reading (GRADE: Low), provide subjective benefits of hearing (GRADE: Low), and improve quality of life (GRADE: Low).We did not identify any economic studies on auditory brainstem implantation for adults with NF2 or adults with deafness due to severe inner ear abnormalities. We estimated that the annual net budget impact of publicly funding auditory brainstem implantation in Ontario over the next 5 years would range from about $130,000 in year 1 for two procedures to about $260,000 in year 5 for four procedures.People with whom we spoke who had received an auditory brainstem implant reported that it restored some hearing ability and improved their quality of life, though they also reported ongoing challenges in using the device or side effects from the procedure.

CONCLUSIONS

When compared with no intervention, auditory brainstem implantation provides some benefit for completely deaf adults with NF2 or severe inner ear abnormalities who are not candidates for cochlear implantation. Based on evidence of moderate to high quality, auditory brainstem implants allow any degree of improvement in sound recognition and in speech perception when used in conjunction with lip-reading for people with NF2. The quality of evidence on these outcomes was low to moderate for people with severe inner ear abnormalities. These functional outcomes lead to subjective benefits of hearing which are consistently reported in the literature and in interviews with patients. We were unable to determine the cost-effectiveness of this treatment. We estimate that publicly funding auditory brainstem implantation in Ontario would result in additional costs of about $130,000 to $260,000 annually over the next 5 years.

An auditory brainstem implant for treatment of unilateral tinnitus: protocol for an interventional pilot study

INTRODUCTION

Tinnitus may have a very severe impact on the quality of life. Unfortunately, for many patients, a satisfactory treatment modality is lacking. The auditory brainstem implant (ABI) was originally indicated for hearing restoration in patients with non-functional cochlear nerves, for example, in neurofibromatosis type II. In analogy to a cochlear implant (CI), it has been demonstrated that an ABI may reduce tinnitus as a beneficial side effect. For tinnitus treatment, an ABI may have an advantage over a CI, as cochlear implantation can harm inner ear structures due to its invasiveness, while an ABI is presumed to not damage anatomical structures. This is the first study to implant an ABI to investigate its effect on intractable tinnitus.

METHODS AND ANALYSIS

In this pilot study, 10 adults having incapacitating unilateral intractable tinnitus and ipsilateral severe hearing loss will have an ABI implanted. The ABI is switched on 6 weeks after implantation, followed by several fitting sessions aimed at finding an optimal stimulation strategy. The primary outcome will be the change in Tinnitus Functioning Index. Secondary outcomes will be tinnitus burden and quality of life (using Tinnitus Handicap Inventory and Hospital Anxiety and Depression Scale questionnaires), tinnitus characteristics (using Visual Analogue Scale, a tinnitus analysis), safety, audiometric and vestibular function. The end point is set at 1 year after implantation. Follow-up will continue until 5 years after implantation.

ETHICS AND DISSEMINATION

The protocol was reviewed and approved by the Institutional Review Board of the University Medical Centre Groningen, The Netherlands (METc 2015/479). The trial is registered at www.clinicialtrials.gov and will be updated if amendments are made. Results of this study will be disseminated in peer-reviewed journals and at scientific conferences.

TRIAL REGISTRATION NUMBER

NCT02630589.

TRIAL STATUS

Inclusion of first patient in November 2017. Data collection is in progress. Trial is open for further inclusion. The trial ends at 5 years after inclusion of the last patient.

Novel Statistical Analyses to Assess Hearing Outcomes After ABI Implantation in NF2 Patients: Systematic Review and Individualized Patient Data Analysis

BACKGROUND

Patients with neurofibromatosis type 2 develop bilateral vestibular schwannomas with progressive hearing loss. Auditory brainstem implants (ABIs) stimulate hearing in the cochlear nuclei and show promise in improving hearing. Here, we assess the impact of ABI on hearing over time by systematically reviewing the literature and re-analyzing available individual patient data.

METHODS

A multidatabase search identified 3 studies with individual patient data of longitudinal hearing outcomes after ABI insertion in adults. Data were collected on hearing outcomes of different sound complexities from sound to speech using an ABI ± lip reading ability plus demographic data. Because of heterogeneity each study was analyzed separately using random effects multilevel mixed linear modeling.

RESULTS

Across all 3 studies (n = 111 total) there were significant improvements in hearing over time from ABI placement (P < 0.000 in all). Improvements in comprehension of sounds, words, sentences, and speech occurred over time with ABI use + lip reading but lip reading ability did not improve over time. All categories of hearing complexity had over 50% comprehension after over 1 year of ABI use and some subsets had over 75% or near 100% comprehension. Vowel comprehension was greater than consonant, and word comprehension was greater than sentence comprehension (P < 0.0001 in both). Age and sex did not predict outcomes.

CONCLUSIONS

ABIs improve hearing beyond lip reading alone, which represents baseline patient function prior to treatment, and the benefits continue to improve with time. These findings may be used to guide patient counseling regarding ABI insertion, rehabilitation course after insertion, and future studies.

Responses of neurons in the feline inferior colliculus to modulated electrical stimuli applied on and within the ventral cochlear nucleus; Implications for an advanced auditory brainstem implant

Auditory brainstem implants (ABIs) can restore useful hearing to persons with deafness who cannot benefit from cochlear implants. However, the quality of hearing restored by ABIs rarely is comparable to that provided by cochlear implants in persons for whom those are appropriate. In an animal model, we evaluated elements of a prototype of an ABI in which the functions of macroelectrodes on the surface of the dorsal cochlear nucleus would be integrated with the function of multiple penetrating microelectrodes implanted into the ventral cochlear nucleus. The surface electrodes would convey most of the range of loudness percepts while the intranuclear microelectrodes would sharpen and focus pitch percepts. In the present study, stimulating electrodes were implanted chronically on the surface of the animal's dorsal cochlear nucleus (DCN) and also within their ventral cochlear nucleus (VCN). Recording microelectrodes were implanted into the central nucleus of the inferior colliculus (ICC). The electrical stimuli were sinusoidally modulated stimulus pulse trains applied on the DCN and within the VCN. Temporal encoding of neuronal responses was quantified as vector strength (VS) and as full-cycle rate of neuronal activity in the ICC. VS and full-cycle AP rate were measured for 4 stimulation modes; continuous and transient amplitude modulation of the stimulus pulse trains, each delivered via the macroelectrode on the surface of the DCN and then by the intranuclear penetrating microelectrodes. In the proposed clinical device the functions of the surface and intranuclear microelectrodes could best be integrated if there is minimal variation in the neuronal responses across the range of modulation depth, modulation frequencies, and across the four stimulation modes. In this study VS did vary as much as 34% across modulation frequency and modulation depth within a stimulation mode, and up to 40% between modulation modes. However, these intra- and inter-mode variances differed for different stimulation rates, and at 500 Hz the inter-mode differences in VS and across the range of modulation frequencies and modulation depths was<Roman> = </Roman>24% and the intra-modal differences were<Roman> = </Roman>15%. The findings were generally similar for rate encoding of modulation depth, although the depth of transient amplitude modulation delivered by the surface electrode was weakly encoded as full-cycle rate. Overall, our findings support the concept of a clinical ABI that employs surface stimulation and intranuclear microstimulation in an integrated manner.

Favorable Long-Term Functional Outcomes and Safety of Auditory Brainstem Implants in Nontumor Patients

BACKGROUND

Auditory brainstem implants (ABIs) were designed to restore hearing in deaf patients with auditory tumors or those unable to receive cochlear implants. Although ABIs may help some patients, their long-term outcomes have been rarely studied.

OBJECTIVE

To assess the long-term benefits and safety of ABIs in nontumor patients with sensorineural hearing loss (SNHL).

METHODS

We retrospectively reviewed the histories of 15 deaf patients (8 females, 7 males; mean age, 15.5 yr; range, 1-56 yr) who received ABIs for treatment of SNHL at our hospital from July 2008 to November 2015. These included 11 children with narrow internal auditory canals and 4 deaf adults with severe cochlear ossification. In each patient, a 12-channel ABI electrode was placed in the cochlear nucleus complex via a retrosigmoid approach. Auditory performance was evaluated using the Categories of Auditory Performance (CAP) index and sound detection and word identification tests.

RESULTS

One year after ABI placement, 13 of 15 patients showed adequate or significantly improved auditory function based on the CAP scores at the last follow-up. Generally, adult patients tended to show better CAP scores (3.50) than pediatric patients (2.15), but the difference was not significant (P = .058). Postoperative complications included electrode migration, cerebrospinal fluid leakage, nonauditory stimulation, and minor seizures without severe sequelae or mortality.

CONCLUSION

ABIs show favorable functional outcomes and long-term safety in nontumor deaf patients with limited treatment options. Collectively, our data indicate that ABIs represent an important treatment option for SNHL.

Auditory Brainstem Implantation in Neurofibromatosis Type 2: Experience From the Manchester Programme

OBJECTIVE

To describe the experience of auditory brainstem implantation (ABI) in patients with Neurofibromatosis type 2 (NF2).

STUDY DESIGN

Retrospective case review.

SETTING

Tertiary referral centre.

PATIENTS

Implanted with a Cochlear ABI22 or ABI24M between 1994 and 2009 because of NF2 disease.

INTERVENTION(S)

Rehabilitative.

MAIN OUTCOME MEASURE(S)

Surgical complication rate; audiological outcomes.

RESULTS

There were 50 primary ABI insertions in 49 patients, including 16 inserted at the time of first side tumor removal as a sleeper, and two revision repositionings which failed to improve outcome. Postoperatively three patients had cerebrospinal fluid leaks which did not require reoperation, one patient had meningitis, and eleven patients suffered either temporary or permanent lower cranial nerve dysfunction. Twenty-nine patients became full time users; a further 12 patients became non-users. Three patients died while their device was inactive. Five patients retain serviceable contralateral hearing. Audiological open set testing of users showed means of: environmental sounds discrimination 51%; phoneme discrimination: with ABI alone 22%/lip reading (LR) 45%/ABI with LR 65%; sentence testing: with ABI alone 13%/LR 19%/ABI with LR 54%.

CONCLUSIONS

The majority of patients with NF2 implanted with an ABI find the device a useful aid to communication in conjunction with LR and in recognizing common environmental sounds. A small proportion gain open set discrimination. Almost a third of patients may end up as non-users. There is probably an increased risk of postoperative lower cranial nerve dysfunction so careful preoperative assessment is advised.

Tinnitus Suppression After Auditory Brainstem Implantation in Patients With Neurofibromatosis Type-2

OBJECTIVE

To evaluate whether an auditory brainstem implant (ABI) can impact levels of tinnitus in neurofibromatosis type-2 (NF2) patients who have undergone translabyrinthine craniotomy for vestibular schwannoma (VS) removal and to evaluate the burden of tinnitus in these patients.

STUDY DESIGN

A retrospective case series and patient survey.

SETTING

Tertiary neurotologic referral center.

PATIENTS

NF2 patients who underwent translabyrinthine removal of VS and ABI placement between 1994 and 2015.

INTERVENTIONS

A survey, retrospective review and two validated tinnitus handicap questionnaires (tinnitus handicap inventory [THI] and tinnitus visual analogue scale [VAS]) were used to characterize the degree of tinnitus in NF2 patients and whether an ABI can alter tinnitus levels.

MAIN OUTCOME MEASURES(S)

Survey results, THI and VAS scores.

RESULTS

One hundred twelve ABI users were contacted and 43 patients (38.3)% responded to our survey. Tinnitus was reported in 83.7% of patients. The THI score for responders was 17.8 ± 20.5 standard deviation (SD). For survey participants, the ABI reduced tinnitus levels (mean VAS: Off = 3.5; On 1-h = 2.1; p = 0.048). For patients who subjectively reported that the ABI reduced tinnitus loudness, tinnitus levels were immediately reduced on ABI activation and after 1 hour of use (mean VAS: Off = 4.8; On = 2.4; On 1-h = 1.8; p < 0.01). Suppression did not continue after the device was turned off. Audiological performance with the ABI did not correlate with tinnitus suppression.

CONCLUSION

NF2 patients who have undergone removal of VS have a significant tinnitus handicap and benefit from tinnitus suppression through utilization of an ABI possibly through masking or electrical stimulation of the auditory brainstem.

Hearing optimisation in neurofibromatosis type 2: A systematic review

BACKGROUND

It is common for patients with neurofibromatosis type 2 to develop bilateral profound hearing loss hearing loss, and this is one of the main determinants of quality of life in this patient group.

OBJECTIVES

The aim of this systematic review was to review the current literature regarding hearing outcomes of treatments for vestibular schwannomas in neurofibromatosis type 2 including conservative and medical management, radiotherapy, hearing preservation surgery and auditory implantation in order to determine the most effective way of preserving or rehabilitating hearing.

SEARCH STRATEGY

A MESH search in PubMed using search terms (('Neurofibromatosis 2' [Mesh]) AND 'Neuroma, Acoustic'[Mesh]) AND 'Hearing Loss' [Mesh] was performed. A search using keywords was also performed. Studies with adequate hearing outcome data were included. With the exception of the cochlear implant studies (cohort size was very small), case studies were excluded.

EVALUATION METHOD

The GRADE system was used to assess quality of publication. Formal statistical analysis of data was not performed because of very heterogenous data reporting.

RESULTS

Conservative management offers the best chance of hearing preservation in stable tumours. The use of bevacizumab probably improves the likelihood of hearing preservation in growing tumours in the short term and is probably more effective than hearing preservation surgery and radiotherapy in preserving hearing. Of the hearing preservation interventions, hearing preservation surgery probably offers better hearing preservation rates than radiotherapy for small tumours but recurrence rates for hearing preservation surgery were high. For patients with profound hearing loss, cochlear implantation provides significantly better auditory outcomes than auditory brainstem implantation. Patients with untreated stable tumours are likely to achieve the best outcomes from cochlear implantation. Those who have had their tumours treated with surgery or radiotherapy do not gain as much benefit from cochlear implantation than those with untreated tumours.

CONCLUSIONS

This review summarises the current literature related to hearing preservation/rehabilitation in patients with NF2. Whilst it provides indicative data, the quality of the data was low and should be interpreted with care. It is also important to consider that the management of vestibular schwannomas in NF2 is complex and decision-making is determined by many factors, not just the need to preserve hearing.

Auditory brainstem implant program development

OBJECTIVE

Auditory brainstem implants (ABIs), which have previously been used to restore auditory perception to deaf patients with neurofibromatosis type 2 (NF2), are now being utilized in other situations, including treatment of congenitally deaf children with cochlear malformations or cochlear nerve deficiencies. Concurrent with this expansion of indications, the number of centers placing and expressing interest in placing ABIs has proliferated. Because ABI placement involves posterior fossa craniotomy in order to access the site of implantation on the cochlear nucleus complex of the brainstem and is not without significant risk, we aim to highlight issues important in developing and maintaining successful ABI programs that would be in the best interests of patients.

DATA SOURCES

Especially with pediatric patients, the ultimate benefits of implantation will be known only after years of growth and development. These benefits have yet to be fully elucidated and continue to be an area of controversy. The limited number of publications in this area were reviewed.

REVIEW METHODS

Review of the current literature was performed.

RESULTS

Disease processes, risk/benefit analyses, degrees of evidence, and U.S. Food and Drug Administration approvals differ among various categories of patients in whom auditory brainstem implantation could be considered for use.

CONCLUSION

We suggest sets of criteria necessary for the development of successful and sustaining ABI programs, including programs for NF2 patients, postlingually deafened adult nonneurofibromatosis type 2 patients, and congenitally deaf pediatric patients. Laryngoscope, 127:1909-1915, 2017.

Auditory brainstem implantation: anatomy and approaches

BACKGROUND

Auditory brainstem implantation at the cochlear nuclei used mainly for neurofibromatosis type 2 patients with bilateral loss of the cochlear nerves has more recently been extended to the inferior colliculus.

OBJECTIVE

To examine the microsurgical and endoscopic anatomy of the cochlear nuclei and inferior colliculus as seen through the translabyrinthine and retrosigmoid approaches used for cochlear nuclei and inferior collicular implantation.

METHODS

Ten cerebellopontine angles of formalin-fixed adult cadaveric heads were examined with the aid of the surgical microscope and endoscope. The ascending auditory pathways between the cochlear nuclei and inferior colliculi and above were examined by the fiber dissection technique.

RESULTS

Both the translabyrinthine and retrosigmoid routes provide sufficient exposure for concurrent tumor removal and implantation at either the cochlear nuclei or inferior colliculus. The position of the inferior colliculus in the auditory pathways and its accessibility in the infratentorial supracerebellar exposure directed through either the translabyrinthine or retrosigmoid approach makes it an alternative site for electrode placement if the cochlear nuclei are not functionally or structurally suitable for implantation. Endoscopic assistance may aid the exposure and electrode placement at either site.

CONCLUSION

The translabyrinthine or retrosigmoid approaches provide access to the cochlear nuclei for implantation and also to the inferior colliculus through the translabyrinthine or retrosigmoid infratentorial supracerebellar route. The endoscope may aid in exposing either site.

Auditory implant research at the House Ear Institute 1989-2013

The House Ear Institute (HEI) had a long and distinguished history of auditory implant innovation and development. Early clinical innovations include being one of the first cochlear implant (CI) centers, being the first center to implant a child with a cochlear implant in the US, developing the auditory brainstem implant, and developing multiple surgical approaches and tools for Otology. This paper reviews the second stage of auditory implant research at House - in-depth basic research on perceptual capabilities and signal processing for both cochlear implants and auditory brainstem implants. Psychophysical studies characterized the loudness and temporal perceptual properties of electrical stimulation as a function of electrical parameters. Speech studies with the noise-band vocoder showed that only four bands of tonotopically arrayed information were sufficient for speech recognition, and that most implant users were receiving the equivalent of 8-10 bands of information. The noise-band vocoder allowed us to evaluate the effects of the manipulation of the number of bands, the alignment of the bands with the original tonotopic map, and distortions in the tonotopic mapping, including holes in the neural representation. Stimulation pulse rate was shown to have only a small effect on speech recognition. Electric fields were manipulated in position and sharpness, showing the potential benefit of improved tonotopic selectivity. Auditory training shows great promise for improving speech recognition for all patients. And the Auditory Brainstem Implant was developed and improved and its application expanded to new populations. Overall, the last 25 years of research at HEI helped increase the basic scientific understanding of electrical stimulation of hearing and contributed to the improved outcomes for patients with the CI and ABI devices. This article is part of a Special Issue entitled .

Optogenetic stimulation of the cochlear nucleus using channelrhodopsin-2 evokes activity in the central auditory pathways

Optogenetics has become an important research tool and is being considered as the basis for several neural prostheses. However, few studies have applied optogenetics to the auditory brainstem. This study explored whether optical activation of the cochlear nucleus (CN) elicited responses in neurons in higher centers of the auditory pathway and whether it elicited an evoked response. Viral-mediated gene transfer was used to express channelrhodopsin-2 (ChR2) in the mouse CN. Blue light was delivered via an optical fiber placed near the surface of the infected CN and recordings were made in higher-level centers. Optical stimulation evoked excitatory multiunit spiking activity throughout the tonotopic axis of the central nucleus of the inferior colliculus (IC) and the auditory cortex (Actx). The pattern and magnitude of IC activity elicited by optical stimulation was comparable to that obtained with a 50dB SPL acoustic click. This broad pattern of activity was consistent with histological confirmation of green fluorescent protein (GFP) label of cell bodies and axons throughout the CN. Increasing pulse rates up to 320Hz did not significantly affect threshold or bandwidth of the IC responses, but rates higher than 50Hz resulted in desynchronized activity. Optical stimulation also evoked an auditory brainstem response, which had a simpler waveform than the response to acoustic stimulation. Control cases showed no responses to optical stimulation. These data suggest that optogenetic control of central auditory neurons is feasible, but opsins with faster channel kinetics may be necessary to convey information at rates typical of many auditory signals.

Methods and preliminary outcomes of pediatric auditory brainstem implantation

OBJECTIVE

The objective was to provide information about methods used and preliminary outcomes for pediatric ABI (auditory brainstem implant).

STUDY DESIGN

An analysis of outcome was performed in children who received an ABI.

METHODS

Twelve children received a MED-EL ABI system. Progress in audition and language was monitored through parental reports, questionnaires, profiles, and closed-set tests.

RESULTS

The median number of active electrodes was 9 of 12. Seven of 12 users consistently respond to sound, and 5 of 12 do not. Highest performers can recognize words in small sets and have begun to use some words.

CONCLUSION

Auditory brainstem implants appear to be beneficial for some pediatric patients who cannot benefit from traditional cochlear implant surgery. Benefits in the short-term can be recognition of environmental sounds, recognition of some words and very commonly used phrases, and the beginning use of words. Although some of our ABI users demonstrate no response to sound, they do want to wear their sound processors all waking hours. The cause of lack of response may be related to the second intervention, which might have led to displacement of the electrode array, or presence of additional handicaps or syndromes. However, the results are less than optimal. The relatively short postoperative follow-up duration is a considered weakness of this study.

Effect of cochlear nerve electrocautery on the adult cochlear nucleus

HYPOTHESIS

Electrocauterization and subsequent transection of the cochlear nerve induce greater injury to the cochlear nucleus than sharp transection alone.

BACKGROUND

Some studies show that neurofibromatosis Type 2 (NF2) patients fit with auditory brainstem implants (ABIs) fail to achieve speech perception abilities similar to ABI recipients without NF2. Reasons for these differences remain speculative. One hypothesis posits poorer performance to surgically induced trauma to the cochlear nucleus from electrocautery. Sustained electrosurgical depolarization of the cochlear nerve may cause excitotoxic-induced postsynaptic nuclear injury. Equally plausible is that cautery in the vicinity of the cochlear nucleus induces necrosis.

METHODS

The cochlear nerve was transected in anesthetized adult gerbils sharply with or without bipolar electrocautery at varying intensities. Gerbils were perfused at 1, 3, 5, and 7 days postoperatively; their brainstem and cochleas were embedded in paraffin and sectioned at 10 μm. Alternate sections were stained with flourescent markers for neuronal injury or Nissl substance. In additional experiments, anterograde tracers were applied directly to a sectioned eighth nerve to verify that fluorescent-labeled profiles seen were terminating auditory nerve fibers.

RESULTS

Cochlear nerve injury was observed from 72 hours postoperatively and was identical across cases regardless of surgical technique. Postsynaptic cochlear nucleus injury was not seen after distal transection of the nerve. By contrast, proximal transection was associated with trauma to the cochlear nucleus.

CONCLUSION

Distal application of bipolar electrocautery seems safe for the cochlear nucleus. Application near the root entry zone must be used cautiously because this may compromise nuclear viability needed to support ABI stimulation.

Auditory brainstem implants in neurofibromatosis Type 2: is open speech perception feasible?

OBJECT

Patients with bilateral auditory nerve destruction may perceive some auditory input with auditory brainstem implants (ABIs). Despite technological developments and trials in new stimulation sites, hearing is very variable and of limited quality. The goal of this study was to identify advantageous and critical factors that influence the quality of auditory function, especially speech perception.

METHODS

The authors conducted a prospective study on ABI operations performed with the aid of multimodality neuromonitoring between 2005 and 2009 in 18 patients with neurofibromatosis Type 2. Outcome was evaluated by testing word recognition (monotrochee-polysyllabic word test at auditory-only mode [MTPa]) and open speech perception (Hochmair-Schulz-Moser [HSM] sentence test), both in pure auditory mode. The primary outcome was the HSM score at 24 months. The predictive meaning of general clinical data, tumor volume, number of active electrodes, duration of deafness, and early hearing data was examined.

RESULTS

In 16 successful ABI activations the average score for MTPa was 89% (SD 13%), and for HSM it was 41% (SD 32%) at 24 months. There were 2 nonresponders, 1 after radiosurgery and the other in an anatomical variant. Direct facial nerve reconstruction during the same surgery was followed by successful nerve recovery in 2 patients, with a simultaneous very good HSM result. Patients' age, tumor extension, and tumor volume were not negative predictors. There was an inverse relationship between HSM scores and deafness duration; 50% or higher HSM scores were found only in patients with ipsilateral deafness duration up to 24 months. The higher the deafness sum of both sides, the less likely that any HSM score will be achieved (p = 0.034). In patients with total deafness duration of less than 240 months, higher numbers of active electrodes were significantly associated with better outcomes. The strongest cross-correlation was identified between early MTPa score at 3 months and 24-month HSM outcome.

CONCLUSIONS

This study documents that open-set speech recognition in pure auditory mode is feasible in patients with ABIs. Large tumor volumes do not prevent good outcome. Positive preconditions are short ipsilateral and short bilateral deafness periods and high number of auditory electrodes. Early ability in pure auditory word recognition tests indicates long-term capability of open speech perception.

Encoding of the amplitude modulation of pulsatile electrical stimulation in the feline cochlear nucleus by neurons in the inferior colliculus; effects of stimulus pulse rate

OBJECTIVES

Persons without a functional auditory nerve cannot benefit from cochlear implants, but some hearing can be restored by an auditory brainstem implant (ABI) with stimulating electrodes implanted on the surface of the cochlear nucleus (CN). Most users benefit from their ABI, but speech recognition tends to be poorer than for users of cochlear implants. Psychophysical studies suggest that poor modulation detection may contribute to the limited performance of ABI users. In a cat model, we determined how the pulse rate of the electrical stimulus applied within or on the CN affects temporal and rate encoding of amplitude modulation (AM) by neurons in the central nucleus of the inferior colliculus (ICC).

APPROACH

Stimulating microelectrodes were implanted chronically in and on the cats' CN, and multi-site recording microelectrodes were implanted chronically into the ICC. Encoding of AM pulse trains by neurons in the ICC was characterized as vector strength (VS), the synchrony of neural activity with the AM, and as the mean rate of neuronal action potentials (neuronal spike rate (NSR)).

MAIN RESULTS

For intranuclear microstimulation, encoding of AM as VS was up to 3 dB greater when stimulus pulse rate was increased from 250 to 500 pps, but only for neuronal units with low best acoustic frequencies, and when the electrical stimulation was modulated at low frequencies (10-20 Hz). For stimulation on the surface of the CN, VS was similar at 250 and 500 pps, and the dynamic range of the VS was reduced for pulse rates greater than 250 pps. Modulation depth was encoded strongly as VS when the maximum stimulus amplitude was held constant across a range of modulation depth. This 'constant maximum' protocol allows enhancement of modulation depth while preserving overall dynamic range. However, modulation depth was not encoded as strongly as NSR.

SIGNIFICANCE

The findings have implications for improved sound processors for present and future ABIs. The performance of ABIs may benefit from using pulse rates greater than those presently used in most ABIs, and by sound processing strategies that enhance the modulation depth of the electrical stimulus while preserving dynamic range.

Neuromodulation for brain disorders: challenges and opportunities

The field of neuromodulation encompasses a wide spectrum of interventional technologies that modify pathological activity within the nervous system to achieve a therapeutic effect. Therapies including deep brain stimulation, intracranial cortical stimulation, transcranial direct current stimulation, and transcranial magnetic stimulation have all shown promising results across a range of neurological and neuropsychiatric disorders. While the mechanisms of therapeutic action are invariably different among these approaches, there are several fundamental neuroengineering challenges that are commonly applicable to improving neuromodulation efficacy. This paper reviews the state-of-the-art of neuromodulation for brain disorders and discusses the challenges and opportunities available for clinicians and researchers interested in advancing neuromodulation therapies.

Auditory brainstem implants: how do they work?

This review covers the design, structure, and function of auditory brainstem implants. Auditory brainstem implants (ABIs) are auditory prostheses initially designed to treat deafness in patients with neurofibromatosis type 2 (NF2). NF2 typically results in deafness due to disruption of the cochlear nerves. When the tumors are removed the auditory nerve is usually cut or nonfunctional anymore. In these cases, patients cannot benefit from peripheral devices such as cochlear implants (CI). Another cause of VIII nerve loss is bilateral temporal bone fracture. Worldwide, more than 500 persons have received an ABI after removal of the tumors that occur with NF2. More recently, some extensions of indications have been proposed to include subjects who would not benefit enough from a cochlear implant (i.e. cochlear ossification). The ABI is similar in design and function to a CI, except that the electrode is placed on the first auditory relay station in the brainstem, the cochlear nucleus (CN). The ABI electrode array is a small paddle that contains plate electrode contacts. The CN has not a single linear tonotopic organization from base to apex like the cochlea but different tonotopic subunits. The CN comprises multiple neuron types that are characterized by specific properties (morphology, regional distribution and cell-membrane characteristics), synaptic input and responses to acoustic stimuli. As the ABI electrode array is placed along the surface of the CN, each electrode likely activates a variety of neuron types, possibly with different characteristic frequencies. Patients undergoing ABI have variable benefit with regard to sound and speech comprehension. For the majority of patients, this improvement is essentially obtained by an augmentation of lip reading performances. Speech comprehension without lip-reading is not as good as with cochlear implants.

An in vivo investigation of inferior colliculus single neuron responses to cochlear nucleus pulse train stimulation

The auditory brain stem implant (ABI) is being used clinically to restore hearing to patients unable to benefit from a cochlear implant (CI). Speech perception outcomes for ABI users are typically poor compared with most CI users. The ABI is implanted either on the surface of or penetrating through the cochlear nucleus in the auditory brain stem and uses stimulation strategies developed for auditory nerve stimulation with a CI. Although the stimulus rate may affect speech perception outcomes with current stimulation strategies, no studies have systematically investigated the effect of stimulus rate electrophysiologically or clinically. We therefore investigated rate response properties and temporal response properties of single inferior colliculus (IC) neurons from penetrating ABI stimulation using stimulus rates ranging from 100 to 1,600 pulses/s in the rat. We found that the stimulus rate affected the proportion of response types, thresholds, and dynamic ranges of IC activation. The stimulus rate was also found to affect the temporal properties of IC responses, with higher rates providing more temporally similar responses to acoustic stimulation. Suppression of neural firing and inhibition in IC neurons was also found, with response properties varying with the stimulus rate. This study demonstrated that changes in the ABI stimulus rate results in significant differences in IC neuron response properties. Due to electrophysiological differences, the stimulus rate may also change perceptual properties. We suggest that clinical evaluation of the ABI stimulus rate should be performed.

Neurofibromatosis 2: hearing restoration options

Neurofibromatosis 2 (NF2) is an autosomal dominant disease in which hearing loss is predominant. Auditory restoration is possible using cochlear implants (CI) or auditory brainstem implant (ABI).

Objective

To assess the auditory results of CI and ABI in NF2 patients and review the literature.

Methods

Four NF2 patients were prospectively evaluated. They were submitted to tumor resection followed by ipsilateral CI or ABI depending on cochlear nerve preservation. Long term auditory results were described for CI (12 months) and ABI (48 months).

Results

All patients achieved auditory perception improvements in their hearing thresholds. The CI patient does not recognize vowels or sentences. The 3 ABI patients discriminate 70% of vowels and 86% in the 4-choice test. One of them does not recognize sentences. The other two recognize 100% of closed sentences and 10% and 20% of open sentences.

Conclusion

The choice of implant type to restore hearing to NF2 patients will relay on anatomical and functional cochlear nerve preservation during tumor resection surgery. Although our experience was different, the literature shows that if this condition is achieved, CI will offer better auditory results. If not, ABI is recommended.

Auditory cortex stimulation to suppress tinnitus: mechanisms and strategies

Brain stimulation is an important method used to modulate neural activity and suppress tinnitus. Several auditory and non-auditory brain regions have been targeted for stimulation. This paper reviews recent progress on auditory cortex (AC) stimulation to suppress tinnitus and its underlying neural mechanisms and stimulation strategies. At the same time, the author provides his opinions and hypotheses on both animal and human models. The author also proposes a medial geniculate body (MGB)-thalamic reticular nucleus (TRN)-Gating mechanism to reflect tinnitus-related neural information coming from upstream and downstream projection structures. The upstream structures include the lower auditory brainstem and midbrain structures. The downstream structures include the AC and certain limbic centers. Both upstream and downstream information is involved in a dynamic gating mechanism in the MGB together with the TRN. When abnormal gating occurs at the thalamic level, the spilled-out information interacts with the AC to generate tinnitus. The tinnitus signals at the MGB-TRN-Gating may be modulated by different forms of stimulations including brain stimulation. Each stimulation acts as a gain modulator to control the level of tinnitus signals at the MGB-TRN-Gate. This hypothesis may explain why different types of stimulation can induce tinnitus suppression. Depending on the tinnitus etiology, MGB-TRN-Gating may be different in levels and dynamics, which cause variability in tinnitus suppression induced by different gain controllers. This may explain why the induced suppression of tinnitus by one type of stimulation varies across individual patients.

Tinnitus suppression by electrical stimulation of the rat dorsal cochlear nucleus

Previous studies indicate that the dorsal cochlear nucleus (DCN) may serve as a generator and/or modulator of noise-induced tinnitus. This prompted an interest to investigate the modulatory role of the DCN in tinnitus suppression. In this study, we chronically implanted the DCN of rats with behavioral evidence of intense tone-induced tinnitus. Behavioral evidence of tinnitus was measured using a gap detection acoustic startle reflex paradigm. Our results demonstrated that electrical stimulation of the DCN suppressed behavioral evidence of tinnitus, especially at high frequencies. The data suggest that the DCN may be used as a target to suppress tinnitus through a bottom-up neuromodulation approach. The underlying mechanism of DCN-stimulation-induced tinnitus suppression was discussed by comparing it with other stimulation modalities.

Advances in auditory prostheses

PURPOSE OF REVIEW

Auditory prostheses use electric currents on multiple electrodes to stimulate auditory neurons and recreate auditory sensations in deaf people. Cochlear implants have restored hearing in more than 200  000 deaf adults and children to a level that allows most to understand speech. Here we review the reasons underlying these results and describe new directions in restoring hearing to additional patient populations and the design of new devices.

RECENT FINDINGS

From their early development about 50 years ago, cochlear implants have been well received and beneficial to people who had lost their hearing. Although those first implants did not allow high levels of speech understanding, they provided auditory information that worked synergistically with lip reading to improve communication. Present day cochlear implants provide excellent speech understanding in children and in postlingually deafened adults. Research is focused on improved signal processing and new electrode designs. Electric stimulation of the auditory brainstem can also produce excellent hearing in some children and adults.

SUMMARY

Auditory prostheses, both at the level of the sensory nerve and at the brainstem, can restore patterns of neural activation that are sufficient for high levels of speech understanding. These prostheses are not only clinically successful but also important tools for understanding sensory processing in the brain.

Early surgical results of auditory brainstem implantation in nontumor patients

OBJECTIVES/HYPOTHESIS

An auditory brainstem implant (ABI) that stimulates the cochlear nucleus in the brainstem was initially designed for patients with neurofibromatosis type-2. Recently, promising surgical outcomes after ABI have been reported in nontumor patients with sensorineural hearing loss including those with cochlear nerve aplasia or ossified cochlea. We herein describe the surgical results and auditory outcomes of ABI in nontumor patients.

STUDY DESIGN

Retrospective case series at a tertiary hospital.

METHODS

Eleven deaf patients who received ABI from 2008 to 2010 were included in this study. The first group included eight patients with narrow internal auditory canals (IACs) and the second group consisted of three postlingually deaf adults with cochlear ossification. Pulsar CI100 ABI (Med-El Co., Innsbruck, Austria) was implanted via the suboccipital approach.

RESULTS

All eight patients with narrow IACs clearly demonstrated behavioral responses following initial stimulation using an ABI. The category of auditory performance (CAP) scores were progressively improved to reach auditory performances of CAP 4 in three patients, CAP 3 in two patients, CAP 2 in two patients, and CAP 1 in one patient. The three patients with ossified cochlea also reported auditory sensations when the ABI was activated. Two of them showed an auditory performance of CAP 4 or 5, but the third patient could not use the device due to nonauditory stimulation.

CONCLUSIONS

Based on our experience, ideal nontumor candidates for ABI include congenitally deaf children who experienced failure after cochlear implantation owing to cochlear nerve deficiency and postlingually deaf adults with severe cochlear ossification.

The keyhole retrosigmoid approach to the cerebello-pontine angle: indications, technical modifications, and results

OBJECTIVES

Establish the versatility and usefulness of the keyhole retrosigmoid approach to the cerebello-pontine angle (CPA) in various pathologies.

DESIGN

Prospective clinical study.

SETTING

Tertiary referral university hospital.

METHODS

One hundred twenty-one patients with various pathologies of the CPA underwent the relevant investigations and were operated upon by the retrosigmoid microendoscopic approach. The technical modifications and progression of our technique are described.

RESULTS

This group consisted of 121 patients (103 men and 28 women). The pathologies included were 60 acoustic neuromas, 28 vestibular neurectomies, nine meningiomas, and four arachnoid cysts. For nonmass lesions, no additional facial nerve injury or deterioration of hearing occurred. Total excision of mass lesions was achieved in 94.5% of cases. Facial nerve integrity was preserved in 92.3% of cases with mass lesions and permanent facial paralysis occurred in 8.3%. There were no mortalities, and the most frequent complication was a delayed cerebrospinal fluid leak from the site of the wound (15%), which was managed conservatively in all cases.

CONCLUSIONS

The keyhole retrosigmoid approach is a versatile one. It can be used to deal with different pathologies through a unified access, and with the increasing exclusive use of endoscopes, a truly minimally invasive surgery can be achieved.

An in vivo investigation of first spike latencies in the inferior colliculus in response to multichannel penetrating auditory brainstem implant stimulation

The cochlear nucleus (CN) is the first auditory processing site within the brain and the target location of the auditory brainstem implant (ABI), which provides speech perception to patients who cannot benefit from a cochlear implant (CI). Although there is variance between ABI recipient speech performance outcomes, performance is typically low compared to CI recipients. Temporal aspects of neural firing such as first spike latency (FSL) are thought to code for many speech features; however, no studies have investigated FSL from CN stimulation. Consequently, ABIs currently do not incorporate CN-specific temporal information. We therefore systematically investigated inferior colliculus (IC) neuron's FSL response to frequency-specific electrical stimulation of the CN in rats. The range of FSLs from electrical stimulation of many neurons indicates that both monosynaptic and polysynaptic pathways were activated, suggesting initial activation of multiple CN neuron types. Electrical FSLs for a single neuron did not change irrespective of the CN frequency region stimulated, indicating highly segregated projections from the CN to the IC. These results present the first evidence of temporal responses to frequency-specific CN electrical stimulation. Understanding the auditory system's temporal response to electrical stimulation will help in future ABI designs and stimulation strategies.

Preliminary results of auditory brainstem implantation in prelingually deaf children with inner ear malformations including severe stenosis of the cochlear aperture and aplasia of the cochlear nerve

OBJECTIVE

The aim of our study is to present the results of 11 children where auditory brainstem implantation (ABI) was successfully performed to restore hearing.

STUDY DESIGN

Case presentation. This study was conducted at the departments of Otolaryngology and Neurosurgery at Hacettepe University Ankara, Turkey.

PATIENTS

Between July 2006 and April 2008, 11 prelingual (30-56 mo) deaf children with several cochlear malformations had ABI.

INTERVENTION

All patients were programmed and were enrolled in auditory verbal therapy sessions and family counseling programs at Hacettepe Auditory Verbal Center. The evaluation was performed at preimplant and again 1, 3, 6, 9, and 12 months post-switch on.

MAIN OUTCOME MEASURES

The main test components composing this test battery were Ling 6 Sound Detection-Identification Test, Word Identification Test in Turkish, Meaningful Auditory Integration Scale, and Meaningful Use of Speech Scale.

RESULTS

Successful brainstem implantations were performed in all patients with retrosigmoid approach. Six children gained basic audiologic functions and were able to recognize and discriminate sounds, and many could identify environmental sounds such as a doorbell and telephone ring by the third month of ABI. Improvement in mean performance on Meaningful Auditory Integration Scale is apparent for all ABI children. Improvement in Meaningful Use of Speech Scale scores in 2 patients, demonstrating that the child using its own voice for speech performance, was observed between the baseline and 12th month. First, 5 children were able to identify Ling's 6 sound by the end of 2 to 6 months, and 2 of them also started to identify words due to their pattern differences and multisyllabic word identification by 6 to 9 months. Two children with Attention Deficit Hyperactivity Disorder have made slower progress than the other children with ABIs.

CONCLUSION

Our preliminary results show that there is adequate contribution of brainstem implants in the development of auditory-verbal skills. Additional handicaps slow the progress of the prelingually deaf children.

Outcomes in nontumor adults fitted with the auditory brainstem implant: 10 years' experience

OBJECTIVES

Recently, open-set speech recognition performance has been observed with electric stimulation of the brainstem in some nontumor (NT) patients. These outcomes require that we reevaluate the criteria for patient selection and the rationale for expanding the application for the auditory brainstem implant (ABI) to NT adult patients with profound hearing loss. This study presents results from up to 10 years in adults, with analysis based on cause.

MATERIALS AND METHODS

In our Department, from April 1997 to September 2007, ABIs have been implanted in 112 patients (83 adults and 29 children) with tumor (T) and NT disorders. Of the 112 patients, 15 have previously had a cochlear implant elsewhere with no sound detection. This article presents speech recognition results from the 80 patients (32 neurofibromatosis type 2 and 48 NT) who had achieved at least 1-year follow-up. The retrosigmoid approach was used in all NT patients, and the retrosigmoid-transmeatal approach was used in all T patients.

RESULTS

All patients had a functioning implantation, and no complications were observed during the operation, activation, or long-term use of the ABI. At the most recent follow-up, NT adults scored from 10 to 100% in open-set speech perception tests (average, 59%), and T patients scored from 5 to 31% (average, 10%). The differences between these results are statistically significant (p = 0.0007). The best performance was observed in patients who lost their nerve VIII from head trauma or severe ossification. Lowest performance (although still highly beneficial to the patient) was observed in patients with neurologic disorders, neuropathy, and cochlear malformations.

CONCLUSION

Our experience clearly indicates that the ABI is an effective tool for hearing rehabilitation in patients with profound hearing loss who cannot be fitted with cochlear implants.

Auditory midbrain implant: a review

The auditory midbrain implant (AMI) is a new hearing prosthesis designed for stimulation of the inferior colliculus in deaf patients who cannot sufficiently benefit from cochlear implants. The authors have begun clinical trials in which five patients have been implanted with a single shank AMI array (20 electrodes). The goal of this review is to summarize the development and research that has led to the translation of the AMI from a concept into the first patients. This study presents the rationale and design concept for the AMI as well a summary of the animal safety and feasibility studies that were required for clinical approval. The authors also present the initial surgical, psychophysical, and speech results from the first three implanted patients. Overall, the results have been encouraging in terms of the safety and functionality of the implant. All patients obtain improvements in hearing capabilities on a daily basis. However, performance varies dramatically across patients depending on the implant location within the midbrain with the best performer still not able to achieve open set speech perception without lip-reading cues. Stimulation of the auditory midbrain provides a wide range of level, spectral, and temporal cues, all of which are important for speech understanding, but they do not appear to sufficiently fuse together to enable open set speech perception with the currently used stimulation strategies. Finally, several issues and hypotheses for why current patients obtain limited speech perception along with several feasible solutions for improving AMI implementation are presented.

Audiologic outcomes with the penetrating electrode auditory brainstem implant

OBJECTIVE

The penetrating electrode auditory brainstem implant (PABI) is an extension of auditory brainstem implant (ABI) technology originally developed for individuals deafened by neurofibromatosis type 2. Whereas the conventional ABI uses surface electrodes on the cochlear nuclei, the PABI uses 8 or 10 penetrating microelectrodes in conjunction with a separate array of 10 or 12 surface electrodes. The goals of the PABI were to use microstimulation to reduce threshold current levels, increase the range of pitch percepts, and improve electrode selectivity and speech recognition. PATIENTS AND PROTOCOL: In a prospective clinical trial, 10 individuals, all with neurofibromatosis type 2, received a PABI after vestibular schwannoma removal via a translabyrinthine approach. All study participants met strict requirements for informed consent as part of a Food and Drug Administration clinical trial. Approximately 8 weeks after implantation, PABI devices were activated and tested at our tertiary clinical and research facility. Mean follow-up time was 33.8 months.

STUDY DESIGN

Using a single-subject design, we measured thresholds and dynamic ranges, electrode-specific pitch percepts, and speech perception performance at regular intervals.

RESULTS

Penetrating electrodes produced auditory thresholds at substantially lower charge levels than surface electrodes, a wide range of electrode-specific pitch sensations, and minimal cross-electrode interference and could be used in speech maps either alone or in combination with surface electrodes. However, less than 25% of penetrating electrodes resulted in auditory sensations, whereas more than 60% of surface electrodes were effective. Even after more than 3 years of experience, patients using penetrating electrodes did not achieve improved speech recognition compared with those using surface electrode ABIs. In patients with usable penetrating electrodes, City University of New York Sentence Test scores with sound and visual information were 61.6% in the PABI group and 64.7% in a surface ABI cohort (p = not significant).

CONCLUSION

The PABI met the goals of lower threshold, increased pitch range, and high selectivity, but these properties did not result in improved speech recognition.

Dorsal cochlear nucleus hyperactivity and tinnitus: are they related?

PURPOSE

Eight lines of evidence implicating the dorsal cochlear nucleus (DCN) as a tinnitus contributing site are reviewed. We now expand the presentation of this model, elaborate on its essential details, and provide answers to commonly asked questions regarding its validity.

CONCLUSIONS

Over the past decade, numerous studies have converged to support the hypothesis that the DCN may be an important brain center in the generation and modulation of tinnitus. Although other auditory centers have been similarly implicated, the DCN deserves special emphasis because, as a primary acoustic nucleus, it occupies a potentially pivotal position in the hierarchy of functional processes leading to the emergence of tinnitus percepts. Moreover, because a great deal is known about the underlying cellular categories and the details of synaptic circuitry within the DCN, this brain center offers a potentially powerful model for probing mechanisms underlying tinnitus.