Auditory Brainstem Implant in Posttraumatic Cochlear Nerve Avulsion

Auditory and language skills in children with auditory brainstem implants

OBJECTIVE

The aim of this study is to characterize the development of auditory and language skills in children during the first 3 years of auditory brainstem implant (ABI) use.

METHOD

It is a retrospective longitudinal analysis of auditory and language skills in 12 children and pre-adolescents with pre-lingual deafness following ABI surgery (mean age at surgery: 4 years; age range: 2-11 years). Responses were analyzed aboutInfant Toddler Meaningful Auditory Integration Scale (IT-MAIS), MAIS, and Meaningful Use of Speech Scale (MUSS) at 1, 3, 6, 12, 18, 24, and 36 months after ABI activation.

RESULTS

Maximum IT-MAIS/MAIS and MUSS scores after 3 years of ABI use were 45.35% and 35.28%, respectively.

CONCLUSION

Pediatric patients exhibit slow progressive development of auditory and language skills following ABI activation.

Pediatric Auditory Brainstem Implantation: Surgical, Electrophysiologic, and Behavioral Outcomes

OBJECTIVES

The objectives of this study were to demonstrate the safety of auditory brainstem implant (ABI) surgery and document the subsequent development of auditory and spoken language skills in children without neurofibromatosis type II (NFII).

DESIGN

A prospective, single-subject observational study of ABI in children without NFII was undertaken at the University of North Carolina at Chapel Hill. Five children were enrolled under an investigational device exemption sponsored by the investigators. Over 3 years, patient demographics, medical/surgical findings, complications, device mapping, electrophysiologic measures, audiologic outcomes, and speech and language measures were collected.

RESULTS

Five children without NFII have received ABIs to date without permanent medical sequelae, although 2 children required treatment after surgery for temporary complications. All children wear their device daily, and the benefits of sound awareness have developed slowly. Intra-and postoperative electrophysiologic measures augmented surgical placement and device programming. The slow development of audition skills precipitated limited changes in speech production but had little impact on growth in spoken language.

CONCLUSIONS

ABI surgery is safe in young children without NFII. Benefits from device use develop slowly and include sound awareness and the use of pattern and timing aspects of sound. These skills may augment progress in speech production but progress in language development is dependent upon visual communication. Further monitoring of this cohort is needed to better delineate the benefits of this intervention in this patient population.

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.

Electrically Evoked Auditory Event-Related Responses in Patients with Auditory Brainstem Implants: Morphological Characteristics, Test-Retest Reliability, Effects of Stimulation Level, and Association with Auditory Detection

OBJECTIVE

This study aimed to (1) characterize morphological characteristics of the electrically evoked cortical auditory event-related potentials (eERPs) and explore the potential association between onset eERP morphology and auditory versus nonauditory stimulation; (2) assess test-retest reliability of onset eERPs; (3) investigate effects of stimulation level on onset eERPs; and (4) explore the feasibility of using the onset eERP to estimate the lowest stimulation level that can be detected for individual stimulating electrodes in patients with auditory brainstem implants (ABIs).

DESIGN

Study participants included 5 children (S1 to S5) and 2 adults (S6 to S7) with unilateral Cochlear Nucleus 24M ABIs. Pediatric ABI recipients ranged in age from 2.6 to 10.2 years (mean: 5.2 years) at the time of testing. S6 and S7 were 21.2 and 24.6 years of age at the time of testing, respectively. S6 and S7 were diagnosed with neurofibromatosis II (NF2) and implanted with an ABI after a surgical removal of the tumors. All pediatric subjects received ABIs after being diagnosed with cochlear nerve deficiency. The lowest stimulation level that could be detected (behavioral T level) and the estimated maximum comfortable level (C level) was measured for individual electrodes using clinical procedures. For electrophysiological measures, the stimulus was a 100-msec biphasic pulse train that was delivered to individual electrodes in a monopolar-coupled stimulation mode at stimulation levels ranging from subthreshold to C levels. Electrophysiological recordings of the onset eERP were obtained in all subjects. For studies evaluating the test-retest reliability of the onset eERP, responses were measured using the same set of parameters in two test sessions. The time interval between test sessions ranged from 2 to 6 months. The lowest stimulation level that could evoke the onset eERP was defined as the objective T level.

RESULTS

Onset eERPs were recorded in all subjects tested in this study. Inter- and intrasubject variations in morphological characteristics of onset eERPs were observed. Onset eERPs with complex waveforms were recorded for electrodes that evoked nonauditory sensations, based on feedback from subjects, as well as for electrodes without any indications of nonauditory stimulations. Onset eERPs in patients with ABIs demonstrated good test-retest reliability. Increasing stimulation levels resulted in increased eERP amplitudes but showed inconsistent effects on response latencies in patients with ABIs. Objective and behavioral T levels were correlated.

CONCLUSIONS

eERPs could be recorded in both non-NF2 and NF2 patients with ABIs. eERPs in both ABI patient groups show inter- and intrasubject variations in morphological characteristics. However, onset eERPs measured within the same subject in this study tended to be stable across study sessions. The onset eERP can potentially be used to estimate behavioral T levels in patients with ABIs. Further studies with more adult ABI recipients are warranted to investigate whether the onset eERP can be used to identify electrodes with nonauditory stimulations.

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.

The value of intraoperative EABRs in auditory brainstem implantation

OBJECTIVE

To compare the intraoperative electrically evoked auditory brainstem response (EABR) morphologies between neurofibromatosis II (NF2) adult auditory brainstem implant (ABI) recipients who had auditory percepts post-operatively and those who did not and between NF2 adult ABI recipients and non-NF2 pediatric ABI recipients.

METHODS

This was a retrospective case series at a single tertiary academic referral center examining all ABI recipients from 1994 to 2016, which included 34 NF2 adults and 11 non-NF2 children. The morphologies of intraoperative EABRs were evaluated for the number of waveforms showing a response, the number of positive peaks in those responses, and the latencies of each of these peaks.

RESULTS

27/34 adult NF2 patients and 9/10 children had EABR waveforms. 20/27 (74.0%) of the adult patients and all of the children had ABI devices that stimulated post-operatively. When comparing the waveforms between adults who stimulated and those who did not stimulate, the proportion of total number of intraoperative EABR peaks to total possible peaks was significantly higher for the adults who stimulated than for those who did not (p < 0.05). Children had a significantly higher proportion of total number of peaks to total possible peaks when compared to adults who stimulated (p < 0.02). Additionally, there were more likely to be EABR responses at the initial stimulation than intraoperatively in the pediatric ABI population (p = 0.065).

CONCLUSIONS

The value of intraoperative EABR tracing may lie in its ability to predict post-operative auditory percepts based on the placement of the array providing the highest number of total peaks.

Does cerebellar flocculus size affect subjective outcomes in pediatric auditory brainstem implantation

OBJECTIVES

The objectives of study was to 1) Describe relevant surgical anatomy in defining and accessing the lateral recess for placement of electrode, 2) Propose a working classification for grades of Flocculus; 3) To determine if different grades of cerebellar flocculus effects placement of ABI electrode and subjective outcomes in implantees.

METHODS

Our study was a prospective study, and comprised of cohort of 12 patients who underwent ABI surgery via retrosigmoid approach between 1 Jan 2012 to 31 Dec 2014. All children with congenital profound sensorineural hearing loss with either absent cochlea or cochlear nerve were included in the study. Relevant anatomy was noted. We also noted down the difficulty encountered during the placement of ABI electrode. Auditory perception and speech intelligibility was scored post operatively for 1 year.

RESULTS

Cerebellar flocculus was divided into 4 grades depending on the morphology of cerebellar flocculus. It was noted that Grade 3 & 4 flocculus (Group B) had difficult ABI electrode placement in comparison to Grade 1 & 2 flocculus (Group A). The subjective outcomes of Group A was better than Group B. However the p value was not statistically significant.

CONCLUSION

Cerebellar flocculus can be graded depending on morphology and size. Flocculus of higher grades can make the placement of ABI electrodes difficult and adversely effects the postoperative subjective outcomes.

Satisfaction and quality of life in users of auditory brainstem implant

Purpose To evaluate satisfaction and quality of life of users of Auditory Implant Brainstem. Methods This is a cross-sectional and descriptive study conducted at Divisão de Clínica Otorrinolaringológica of Hospital das Clínicas of Faculdade de Medicina da Universidade de São Paulo, Brazil. For the research, 19 users of an Auditory Brainstem Implant answered the following questionnaires: KINDLR (Questionnaire for Measuring Health-Related Quality of Life in Children and Adolescents), for children and adolescents, their parents and/or caregivers; WHOQOL-BREF questionnaire, for adult participants; and the Satisfaction with Amplification in Daily Life (SADL) questionnaire culturally adapted to Brazilian Portuguese. Results The quality of life of children using Auditory Brainstem Implant from the perspective of their parents showed global results above average, as for most domains, except for the emotional well-being domain. Adults showed results above average for all domains. Regarding satisfaction with the device, the adult users of auditory brainstem implant were satisfied in general, except with regard to personal image. The parents of the children showed dissatisfaction in all subscales, except for the subscale of services and cost. Conclusion The results indicated that although patients are dissatisfied with the device in some aspects, overall the quality of life was rated as good for most of the aspects assessed.

Auditory Rehabilitation in Rhesus Macaque Monkeys (Macaca mulatta) with Auditory Brainstem Implants

Background:

The auditory brainstem implants (ABIs) have been used to treat deafness for patients with neurofibromatosis Type 2 and nontumor patients. The lack of an appropriate animal model has limited the study of improving hearing rehabilitation by the device. This study aimed to establish an animal model of ABI in adult rhesus macaque monkey (Macaca mulatta).

Methods:

Six adult rhesus macaque monkeys (M. mulatta) were included. Under general anesthesia, a multichannel ABI was implanted into the lateral recess of the fourth ventricle through the modified suboccipital-retrosigmoid (RS) approach. The electrical auditory brainstem response (EABR) waves were tested to ensure the optimal implant site. After the operation, the EABR and computed tomography (CT) were used to test and verify the effectiveness via electrophysiology and anatomy, respectively. The subjects underwent behavioral observation for 6 months, and the postoperative EABR was tested every two weeks from the 1^st month after implant surgery.

Result:

The implant surgery lasted an average of 5.2 h, and no monkey died or sacrificed. The averaged latencies of peaks I, II and IV were 1.27, 2.34 and 3.98 ms, respectively in the ABR. One-peak EABR wave was elicited in the operation, and one- or two-peak waves were elicited during the postoperative period. The EABR wave latencies appeared to be constant under different stimulus intensities; however, the amplitudes increased as the stimulus increased within a certain scope.

Conclusions:

It is feasible and safe to implant ABIs in rhesus macaque monkeys (M. mulatta) through a modified suboccipital RS approach, and EABR and CT are valid tools for animal model establishment. In addition, this model should be an appropriate animal model for the electrophysiological and behavioral study of rhesus macaque monkey with ABI.

The electrically evoked cortical auditory event-related potential in children with auditory brainstem implants

OBJECTIVE

This study explored the feasibility of measuring electrically evoked cortical auditory event-related potentials (eERPs) in children with auditory brainstem implants (ABIs).

DESIGN

Five children with unilateral ABIs ranging in age from 2.8 to 10.2 years (mean: 5.2 years) participated in this study. The stimulus was a 100-msec biphasic pulse train that was delivered to individual electrodes in a monopolar stimulation mode. Electrophysiological recordings of the onset eERP were conducted in all subjects.

RESULTS

The onset eERP was recorded in four subjects who demonstrated auditory perception. These eERP responses showed variations in waveform morphology across subjects and stimulating electrode locations. No eERPs were observed in one subject who received no auditory sensation from ABI stimulation.

CONCLUSIONS

eERPs can be recorded in children with ABIs who develop auditory perception. The morphology of the eERP can vary across subjects and also across stimulating electrode locations within subjects.

Subtotal Petrosectomy for Cochlear Implantation

Objectives:

The purpose of this study was to review the indications for subtotal petrosectomy for cochlear implantation, report our management of complications, as well as review those technical factors that are critical for successful implantation.

Methods:

Patients (n = 104) that underwent subtotal petrosectomy with closure of the external auditory canal and obliteration of the cavity with abdominal fat in combination with cochlear implantation were analyzed.

Results:

The most frequent indication for subtotal petrosectomy was the existence of a previous canal wall down technique. Postoperative complications occurred in 13 patients (11.83%). Extrusion of the device took place in 5 cases (4.55%).

Conclusions:

Subtotal petrosectomy in cochlear implantation permits obtaining a cavity isolated from the external environment, and when needed, it improves the access and visibility during the surgical procedure. Subtotal petrosectomy is a safe technique, with a low rate of complications.

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.

Systematic Review of Nontumor Pediatric Auditory Brainstem Implant Outcomes

OBJECTIVE

The auditory brainstem implant (ABI) was initially developed for patients with deafness as a result of neurofibromatosis type 2. ABI indications have recently extended to children with congenital deafness who are not cochlear implant candidates. Few multi-institutional outcome data exist. Herein, we aim to provide a systematic review of outcomes following implantation of the ABI in pediatric patients with nontumor diagnosis, with a focus on audiometric outcomes.

DATA SOURCES

PubMed, Embase, and Cochrane.

REVIEW METHODS

A systematic review of literature was performed using the PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-analyses) recommendations. Variables assessed included age at implantation, diagnosis, medical history, cochlear implant history, radiographic findings, ABI device implanted, surgical approach, complications, side effects, and auditory outcomes.

RESULTS

The initial search identified 304 articles; 21 met inclusion criteria for a total of 162 children. The majority of these patients had cochlear nerve aplasia (63.6%, 103 of 162). Cerebrospinal fluid leak occurred in up to 8.5% of cases. Audiometric outcomes improved over time. After 5 years, almost 50% of patients reached Categories of Auditory Performance scores >4; however, patients with nonauditory disabilities did not demonstrate a similar increase in scores.

CONCLUSION

ABI surgery is a reasonable option for the habilitation of deaf children who are not cochlear implant candidates. Although improvement in Categories of Auditory Performance scores was seen across studies, pediatric ABI users with nonauditory disabilities have inferior audiometric outcomes.

The role of subtotal petrosectomy in cochlear implant surgery--a report of 32 cases and review on indications

OBJECTIVE

To report and review 32 cases of subtotal petrosectomy (SP) in cochlear implant (CI) surgery and to define the indications and contraindications for this procedure.

STUDY DESIGN

Retrospective case review + case reports.

SETTING

Tertiary skull base center.

PATIENTS

Cochlear implant database: 32 subtotal petrosectomies in 31 patients.

INTERVENTIONS

Subtotal petrosectomy with blind sac closure of the external auditory canal, closure of Eustachian tube, and abdominal fat obliteration in combination with cochlear implantation.

RESULTS

Indications for SP in CI surgery were as follows: chronic otitis media (n = 4), previous radical cavity (n = 13), previous subtotal petrosectomy (n = 4), ossification of the cochlea (n = 5), malformation of the inner ear (n = 2), and temporal bone fracture (n = 4). One patient was simultaneously bilaterally implanted; 2 cases were revisions. All procedures were performed in 1 stage. In 2 cases, complications were encountered (6%), one of which lead to reoperation (3%). None of the patients was explanted.

CONCLUSION

Subtotal petrosectomy combined with cochlear implantation is a procedure required in specific situations and lowers the risk of repetitive ear infections, CSF leakage, and meningitis by closing off all connection with the external environment. Additionally, it gives excellent visibility and access in difficult anatomy or in drill-out procedures. The complication rate of 6% is comparable with normal cochlear implantation. Preservation of residual hearing can be considered the only absolute contraindication as an open external meatus is necessary for use of electroacoustic stimulation. Risks of the SP+CI procedure are infection of the abdominal fat, breakdown of the blind sac closure, and entrapped cholesteatoma. Follow-up with CT imaging is therefore mandatory.

Cochlear implantation versus auditory brainstem implantation in bilateral total deafness after head trauma: personal experience and review of the literature

OBJECTIVE

To determine the effectiveness of cochlear implant (CI) in hearing restoration after temporal bone (TB) fractures and investigate the adequacy of auditory brainstem implant (ABI) indication for TB fractures.

STUDY DESIGN

Retrospective clinical study; a systematic review of the literature in PubMed was also performed to identify all published cases of bilateral TB fractures or bilateral deafness after head trauma treated by means of CI or ABI.

SETTINGS

Quaternary otology and skull base surgery referral center.

PATIENTS

Eleven consecutive patients presented with bilateral severe-to-profound sensorineural hearing loss after head trauma.

INTERVENTIONS

CI as primary intervention or following a previous treatment.

MAIN OUTCOME MEASURES

CI performances were evaluated in the auditory-only condition in both closed-set and open-set formats.

RESULTS

Fourteen CI were placed, 11 as primary treatment and 3 after ABI failure. At the last follow-up, all patients gained useful open-set speech perception. In secondary CI, all patients obtained better auditory results with the CI if compared with ABI. CI performance did not decrease with time in any case.

CONCLUSION

Cochlear implantation after TB fractures has proved to have excellent audiometric results. The aim of the initial evaluation of a patient with bilateral anacoustic ears from head trauma should always be to rehabilitate their hearing with a CI. The incidence of labyrinthitis ossificans, negative electrophysiologic testing, the risk of postoperative meningitis or facial nerve stimulation should not be the determinant factors that favor ABI placement.

Indications and contraindications of auditory brainstem implants: systematic review and illustrative cases

The number of non-neurofibromatosis type 2 (NF2) indications for auditory brainstem implant (ABI) in the literature is increasing. The objective of this study was to analyze and discuss the indications for ABI. Retrospective chart review and systematic review were conducted at Quaternary referral skull base center and referring centers. Analysis of ABI cases with non-NF2 indications and systematic review presenting non-NF2 ABI cases were performed. Fourteen referred cases with ABI were identified. All cases had unsatisfactory results of ABI and all could have been rehabilitated with a cochlear implant (CI). Of these 14 cases, 9 improved with a cochlear implant, and 2 with a hearing aid, two are still planned for CI, one received bilateral CI, no ABI. In literature, we found 31 articles presenting 144 non-NF2 ABI cases with at least 7 different indications other than NF2. ABI should be restricted to those patients who have no other rehabilitation options. Patency of the cochlea and evidence of an intact cochlear nerve should be examined with imaging and electrophysiologic testing. Sometimes a CI trial should be planned prior to proceeding with ABI. We have shown that in many cases a CI is still possible and CI provided better results than ABI. In vestibular schwannoma in the only hearing ear, cochlear otosclerosis, temporal bone fractures, (presumed) bilateral traumatic cochlear nerve disruption, auto-immune inner ear disease and auditory neuropathy primarily CI are indicated. Traumatic bilateral cochlear nerve disruption is exceptionally unlikely. In cochlear nerve aplasia, testing should be performed prior to meeting indications for ABI. In malformations, ABI is indicated only in severe cochlear hypoplasia or cochlear aplasia.

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.

Cochlear implantation in posttraumatic bilateral temporal bone fracture

Temporal bone (TB) fractures can cause loss of audiovestibular function. Four cases of profound hearing impairment following bilateral TB fracture are presented in this report. All patients received a cochlear implant. All 4 patients became regular users of their implants. None of the patients experienced facial nerve stimulation. Implant-aided audiometry demonstrated a hearing threshold of 28 dB HL. The performance in speech understanding was comparable to standard postlingual adult patients implanted. We believe that cochlear implantation in patients suffering from profound sensorineural hearing losses secondary to TB fractures can be an effective tool for rehabilitation.

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

AIM

Hearing preservation is one of the major goals of acoustic neuroma surgery. In NF-2 patients, bilateral hearing loss is frequently caused by the disease or results from its treatment. Several implant devices for electrical stimulation of the cochlear nucleus have been developed to restore serviceable hearing in these patients. We report our experience and results using a high rate continuous interleaved sampling (CIS) auditory brainstem implant (ABI).

METHODS

Between June 1997 and May 2004, 24 NF-2 patients were managed by our group. In 20 patients an ABI was implanted successfully. The cochlear nucleus was located using anatomical landmarks and E-ABR recordings after resection of the neuroma via a retrosigmoid approach in the semi-sitting position. The 12-channel stimulating electrode array was inserted and fixed in the lateral recess. There were no surgical complications related to implantation apart from pseudomeningo that were managed by lumbar drainage.

RESULTS

In one patient the electrode array became dislocated and this necessitated revision surgery which was successful. One patient failed to gain benefit from the implant. Overall, 70% of electrodes were found to be serviceable for auditory stimulation, 5.3% of electrodes were primarily nonauditory, and in 7.8% side effects during stimulation were observed. Lip reading was improved by more than 100% as a result of the additional auditory input. For many patients, comprehension of open speech was restored to a useful level. Almost all patients were able to perceive environmental sounds and tinnitus was masked.

CONCLUSIONS

Restoration of hearing using ABIs in NF-2 patients is a safe and promising procedure for those who would otherwise be totally deaf. The high rate CIS speech processing strategy has proven to be very useful and effective in direct cochlear nucleus stimulation.

Inferior colliculus responses to dual-site intralamina stimulation in the ventral cochlear nucleus

A major limitation of the present auditory brainstem implant (ABI) is its inability to access the tonotopic organization of the ventral cochlear nucleus (VCN). A previous study by our group indicated that stimulation of single sites within a given VCN frequency region did not always elicit frequency-specific responses within the central nucleus of the inferior colliculus (CIC) and in some cases did not elicit a response at all. For this study, we hypothesized that sequential stimulation (with a short interpulse delay of 320 μsec) of two VCN sites in similar frequency regions would enhance responsiveness in CIC neurons. Multiunit neural recordings in response to pure tones were obtained at 58 VCN and 164 CIC sites in anesthetized rats. Among the 58 VCN sites, 39 pairs of sites with similar characteristic frequencies were chosen for electrical stimulation. Each member of a VCN pair was electrically stimulated individually, followed by sequential stimulation of the pair, while recording CIC responses. On average, CIC sites were found to respond to dual-site VCN stimulation with significantly lower thresholds, wider dynamic ranges, a greater extent of activation with increasing current levels, and a higher degree of frequency specificity compared with single-site stimulation. Although these effects were positive for the most part, in some cases dual-site stimulation resulted in increased CIC thresholds and decreased dynamic ranges, extent of activation, and frequency specificity. The results suggest that multisite stimulation within VCN isofrequency laminae using penetrating electrodes could significantly improve ABI stimulation strategies and implant performance.

Binaural cochlear implantation after bilateral temporal bone fractures

In this clinical note we discuss the indications, feasibility, and outcomes of binaural simultaneous cochlear implantation (CI) following bilateral transverse temporal bone (TB) fractures. A 41-year-old male, totally deaf after a bilateral TB fracture, underwent an audiological, electrophysiological, and imaging investigation in order to assess the integrity of the VIIIth cranial nerves. Five months later he received a simultaneous bilateral CI. Speech perception tests were conducted at different time points. A significant advantage by dichotic listening was observed since the beginning of the habilitation program. The patient achieved a 100% word and sentences recognition in quiet at 12 months. His listening skills in noisy conditions were improved by the use of two implants. A CI in TB fractures is feasible if the VIII nerve is intact and the cochlea is spared by the fracture rim. The early timing of the procedure probably contributed to its success by preventing cochlear fibrosis and ossification.

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.

[Present state of cochlear implant treatment in adults and children]

The technique of cochlear implantation was the first method which allowed replacement of a sense organ by a (partially) implantable electronic prosthesis. By this method the cells of the spiral ganglion of the cochlea are directly stimulated by the electrodes introduced into the cochlea, bypassing the functions of the outer and middle ear as well as the cochlea. Treatment with a cochlear implant (CI) has been established over the last 20-30 years as a reliable method for restoring hearing in adults and children with severe hearing disorders and is now a routine method in many centers. For optimal results in understanding speech and for children in the speech development phase, rehabilitation must be an integral part of the total treatment and follow soon after implantation. To achieve this early diagnosis of hearing difficulties or deafness is necessary, which is simplified by a consistent hearing screening of newborns, now a statutory procedure in Germany.

Progress in restoration of hearing with the auditory brainstem implant

Fifty years ago auditory scientists were very skeptical about the potential of new prosthetic approaches that electrically stimulated the auditory nerve, the cochlear nuclei (CN), and the inferior colliculus (IC). In those decades, the basilar membrane was considered to play a fundamental and irreplaceable role as a fine spectrum analyzer in hearing physiology, and therefore it was thought that electrical stimulation of the auditory system would have never produced functionally useful hearing. Over the last 30 years, cochlear implants (CIs) have improved steadily to the point where the average sentence recognition with modern multichannel devices is better than 90% correct. More recently, similar performance has been observed with electric stimulation of the brainstem with auditory brainstem implants (ABIs). However, it is clear that to fully understand hearing and to design the next generation of prosthetic devices we must better understand the ear-brain relationship. Indeed some aspects of hearing do not require the intricate complexities of cochlear physiological responses, while other auditory tasks rely critically on specialized details of cochlear processing. The progress in electrical stimulation of the central auditory system requires us to reconsider the patient selection criteria for different implant devices, in particular to evaluate the possibility of ABIs for etiologies with poor outcomes with CIs. In the present review, the latest outcomes in restoration of hearing with ABI are presented. New guidelines are proposed for device selection for different etiologies and future research is suggested to further refine the process of matching an individual patient to the most appropriate implant device.

The auditory midbrain implant: effects of electrode location

The auditory midbrain implant (AMI) is a new hearing prosthesis designed for stimulation of the inferior colliculus in patients who do not receive sufficient benefit from cochlear or brainstem prostheses. We have begun clinical trials in which three patients have been implanted with the AMI. Although the intended target was the central nucleus of the inferior colliculus (ICC), the electrode array was implanted into different locations across patients (i.e., ICC, dorsal cortex of inferior colliculus, lateral lemniscus). In this paper, we will summarize the effects of electrical stimulation of these different midbrain regions on various psychophysical properties and speech perception performance. The patient implanted within the intended target, the ICC, exhibited the greatest improvements in hearing performance. However, this patient has not yet achieved open-set speech perception to the performance level typically observed for cochlear implant patients, which we believe is partially due to the location of the array within the ICC. We will present findings from previous AMI studies in guinea pigs demonstrating the existence of spatially distinct functional output regions within the ICC and suggesting that further improvements in performance may be achieved by stimulating within a rostral-ventral region. Remaining questions include if a similar organization exists in the human ICC and if stimulation of its rostral-ventral region with currently available strategies (i.e., those designed for cochlear implants) can restore sufficient speech perception.

Implante auditivo de tronco encefálico: revisão de literatura

OBJETIVO: pesquisar aspectos relevantes sobre implante auditivo de tronco encefálico como conceito, finalidade, métodos de implantação, indicações do procedimento e benefícios. MÉTODOS: realizou-se compilação dos trabalhos disponíveis nas bases de dados LILACS, MEDLINE e SCIELO utilizando os descritores: implante auditivo de tronco encefálico, reabilitação de deficientes auditivos, perda auditiva neurossensorial, procedimentos cirúrgicos otológicos. RESULTADOS: o implante auditivo de tronco encefálico é semelhante ao implante coclear, exceto pela configuração do eletrodo que é projetado para ser colocado no complexo do núcleo coclear, no tronco encefálico. Originalmente foi desenvolvido para restaurar a audição em pacientes com ausência ou lesão no nervo coclear. Hoje é indicado para pacientes que por motivos anatômicos ou funcionais não podem receber estímulos elétricos pela orelha interna, como em casos de malformação/ausência de nervo coclear, ossificação coclear e neuropatia auditiva. Os efeitos relatados são: restabelecimento da audição em pacientes com perda auditiva total, níveis de detecção e discriminação dos sons similares às obtidas com implante coclear e acesso a sons ambientais e da fala. CONCLUSÃO: o implante auditivo de tronco encefálico proporciona o restabelecimento da sensação auditiva em sujeitos não beneficiados pelo uso de próteses auditivas e implante coclear. A quase totalidade dos pacientes implantados obteve algum benefício na comunicação.

Implant auditif du tronc cérébral: indications et résultats

OBJECTIVES

To summarize the indications and evaluate the Auditory Brainstem Implant (ABI) performances in neurofibromatosis type 2 (NF2) and other otologics indications, as postmeningitis ossified cochlea.

MATERIAL AND METHODS

Main and first indication of ABI is NF2. Emergent indications are bilateral total ossified cochlea, vestibular schwannoma with controlateral lesions, cochlear nerve aplasia or inner ear's malformations. The pre-operative evaluation includes clinical, radiological, lipreading, and psychological status. A translabyrinthine or retrosigmoid approach is performed, depending on tumoral or not tumoral status. The auditory perception with the ABI is evaluated by testing, the words recognition in open-set lists, and the speech understanding with usual sentences.

RESULTS

In NF2 patients, best results are obtained in cases of smaller vestibular schwannoma and none, or short term, auditory deprivation. Negative prognostic factors are duration of total hearing loss (>10 years), tumor size (>30 mm), difficulties in electrode array placement, complications during post-operative course and number of active electrodes (<10). In cases of postmeningitis total deafness with totally ossified cochlea, results demonstrate a good benefit reaching these obtained with cochlear implant in post-meningitis deafness.

CONCLUSION

These results show a clear benefit of ABI in NF2 patients, with or without previous tumor removal, in case of small tumor with a short duration of hearing loss. In case of postmeningitis ossified cochlea, results potentially reach those of cochlear implants.

A Model for Auditory Brain Stem Implants: Bilateral Surgical Deafferentation of the Cochlear Nuclei in the Macaque Monkey

BACKGROUND

Patients with extensive bilateral lesions of the auditory nerve have a profound and irreversible sensorineural hearing loss (SNHL), which can only be overcome with individually-fitted auditory brain stem implants that directly stimulate the cochlear nuclei. Despite the enormous potential of this increasingly applied treatment, the auditory performance of many implanted patients is limited, and the variability between cases hinders a complete understanding of the role played by the multiple parameters related to the efficacy of the implant.

OBJECTIVES

To mimic the condition of patients who have bilateral lesions of the auditory nerve, we developed an experimental model of bilateral deafferentation of the cochlear nuclei by surgical transection of the cochlear nerves of adult primates.

MATERIALS AND METHODS

We performed bilateral transection of the cochlear nerves of six adult, healthy, male captive-bred macaques (Macaca fascicularis). Before surgery, brain stem auditory evoked potentials were recorded. The histological material obtained from these animals was compared with similarly processed sections from seven macaques with intact cochlear nerves. The surgical technique, similar to that used in human neuro-otology, combined a labyrinthectomy and a neurectomy of the cochlear nerves, and caused deafness. We analyzed immunocytochemically the expression in cochlear nerve fibers of neurofilaments (SMI-32), and cytosolic calcium binding proteins calretinin, parvalbumin and calbindin, and also applied a histochemical reaction for acetylcholinesterase.

RESULTS

None of the primates had any major complications due to the surgical procedure. The lesions produced massive anterograde degeneration of the cochlear nerves, evidenced by marked gliosis and by loss of both type I fibers (which in this species are immunoreactive for calretinin, parvalbumin and neurofilaments) and type II fibers (which are acetylcholinesterase positive). The model of surgical transection described herein causes extensive damage to the cochlear nerves while leaving the cochlea intact, thus mimicking the condition of patients with profound SNHL due to bilateral cochlear nerve degeneration.

CONCLUSIONS

The phylogenetic proximity of primates to humans, and the paramount advantage of close anatomical and physiological similarities, allowed us to use the same surgical technique applied to human patients, and to perform a thorough evaluation of the consequences of neurectomy. Thus, bilateral surgical deafferentation of the macaque cochlear nuclei may constitute an advantageous model for study of auditory brain stem implants.

Rebuilding lost hearing using cell transplantation

OBJECTIVE

The peripheral auditory nervous system (cochlea and auditory nerve) has a complex anatomy, and it has traditionally been thought that once the sensorineural structures are damaged, restoration of hearing is impossible. In the past decade, however, the potential to restore lost hearing has been intensively investigated using molecular and cell biological techniques, and we can now part with such a pessimistic view. In this review, we examine an important field in hearing restoration research: cell transplantation.

METHODS

Most efforts in this field have been directed to the replacement of hair cells by transplantation to the cochlea. Here, we focus on transplantation to the auditory nerve, from the side of the cerebellopontine angle rather than the cochlea.

RESULTS

Delivery of cells to the cochlea is potentially damaging, and nerve cells transplanted distally to the Schwann-glial transitional zone (cochlear side) may become inhibited when they reach the transitional zone. The auditory nerve is probably the most suitable route for cell transplantation.

CONCLUSION

The auditory nerve occupies an important position not only in neurosurgery but also in various diseases in other disciplines, and several lines of recent evidence indicate that it is a key target for hearing restoration. It is familiar to most neurosurgeons, and the recent advances in the molecular and cell biology of inner-ear development are of direct importance to neurorestorative medicine. In this article, we review the anatomy, development, and molecular biology of the auditory nerve and cochlea, with emphasis on the advances in cell transplantation.

Auditory Midbrain Implant

HYPOTHESIS

The lateral suboccipital approach is a well-established route for safe removal of vestibular schwannomas in neurofibromatosis Type 2 (NF2) patients. The goal of this study was to assess if this approach can be extended to a lateral supracerebellar infratentorial approach to enable insertion of an auditory midbrain implant (AMI) penetrating array along the tonotopic gradient of the inferior colliculus central nucleus (ICC).

BACKGROUND

The AMI is a new auditory prosthesis designed for penetrating stimulation of the ICC in patients with neural deafness. The initial candidates are NF2 patients who, because of the growth and/or surgical removal of bilateral acoustic neuromas, develop neural deafness and are unable to benefit from cochlear implants. The ideal surgical approach in NF2 patients must first enable safe removal of vestibular schwannomas and then provide sufficient exposure of the midbrain for AMI implantation.

METHODS

This study was performed on formalin-fixed and fresh cadaver specimens. Computed tomography scan and magnetic resonance imaging were used to study the heads of the specimens and for surgical navigation.

RESULTS

The lateral suboccipital craniotomy enabled sufficient exposure of the cerebellopontine angle and internal auditory canal for tumor removal. It could then be extended to a lateral supracerebellar infratentorial approach that provided good exposure of the dorsolateral aspect of the tentorial hiatus and mesencephalon for implantation of the AMI along the tonotopic gradient of the ICC. This approach did not endanger the trochlear nerve or any major midline venous structures in the quadrigeminal cistern.

CONCLUSION

This modified lateral suboccipital approach ensures safe removal of large vestibular schwannomas and provides sufficient exposure of the inferior colliculus for ideal AMI implantation.

Favorable Outcome of Cochlear Implant in VIIIth Nerve Deficiency

OBJECTIVE

To report on the outcomes of cochlear implantation (CI) in a child with cochleovestibular nerves (CVN) hypoplasia.

STUDY DESIGN

Retrospective case review.

SETTING

Tertiary referral center, University hospital.

PATIENTS

An 18-month-old child with profound bilateral congenital hearing loss and bilateral hypoplasia of the CVN at imaging.

INTERVENTION

Left CI at age 29 months with a Nucleus Contour device (Cochlear Ltd., Lane Cove, New South Wales, Australia) after unsatisfactory results of hearing aid use for 10 months.

MAIN OUTCOME MEASURES

Speech perception tests, behavioral observation, electrophysiologic tests, and cognitive evaluation.

RESULTS

Although the child scores poorly in every perceptive category with the CI alone, the device greatly enhances his speech understanding with the hearing aid in the opposite ear. In the bimodal condition, his words and sentences identification, recognition, and comprehension far exceed the monaural figures. The Meaningful Auditory Integration Scale (MAIS) tests reaches a score of 26/40, and the MacArthur's questionnaires confirm the improvement of language production and comprehension. These results became noticeable after 5 to 6 months and continued to improve up to the 10th month. The child's cognitive scores and overall performance competences greatly benefit from the CI, with the mental age overcoming the chronological age.

CONCLUSION

We can confirm the chance of achieving satisfactory results by CI even when the imaging of CVN is doubtful and the electrophysiological tests are disappointing. In our experience, a CI in Type IIb dysplasia of the CVN is a feasible option, provided that the candidate shows some responses at aided audiogram and at least minimal signs of language development. Adequate counseling is necessary for these children because the expected outcome is somewhat lower than that of their deaf peers with normal appearance of the nerves.

Auditory brainstem implant (ABI): new frontiers in adults and children

Previous studies have considered only patients with neurofibromatosis type 2 (NF2) older than 12 years as candidates for an auditory brainstem implant (ABI). Our study expands the potential criteria to include both children and adult subjects with other cochlear or cochlear nerve malfunctions who either would not benefit at all from a cochlear implant (eg, cochlear nerve aplasia or avulsion) or whose benefit was or would be severely compromised (eg, cochlear ossification, cochlear fracture).

STUDY DESIGN

In our department, over the period from April 1997 to September 2002, 29 patients, 20 adults and 9 children, were fitted with ABIs. Their ages ranged from 14 months to 70 years. Thirteen subjects had tumors, 10 NF2 and 3 solitary vestibular schwannoma, and 16 patients had a variety of nontumor (NT) cochlear or cochlear nerve diseases. A retrosigmoid-transmeatal approach was used in T and a retrosigmoid approach in NT patients. The electrode array was inserted into the lateral recess of the fourth ventricle and correct electrode positioning was monitored with the aid of electrically evoked auditory brainstem responses (EABRs).

RESULTS

Correct implantation was achieved in all patients. No complications were observed due to implantation surgery or related to ABI activation or long-term use. Auditory sensations were induced in all patients with various numbers of electrodes (from 5 to 15). Different pitch sensations were identifiable with different electrode stimulation. Closed-set word recognition, open-set sentence recognition, and speech tracking scores achieved by the patients are reported in detail. The auditory performance of the patients showed significantly better outcomes than controls (Multicentric European clinical investigations on ABI with NF2).

CONCLUSION

We have shown that the indications for the ABI can be extended to include NT patients with severe cochlear and/or cochlear nerve abnormalities. The degree of auditory benefit varies as a function of the underlying pathological conditions, with NT subjects exhibiting significantly better outcomes than the T patients.