Traditional and emerging indications in cochlear and auditory brainstem implants

Electrical stimulation of the auditory pathway via a cochlear or an auditory brainstem implant has been proved to an effective and safe procedure in the treatment of many patients suffering from a profound sensorineural hearing loss of cochlear and retrocochlear origin. In this paper we will present the impact of experience, technical advances in the design of auditory implants, and improvements in stimulation strategies in traditional criteria for implantation. Besides current indications for cochlear and auditory brainstem implants, we will review a continuously expanding group of potential candidates, namely emerging indications. This review will be exemplified with data from the University of Navarra Cochlear Implant Program, currently accounting for more than 500 patients implanted.     

Activity-dependent developmental plasticity of the auditory brain stem in children who use cochlear implants

OBJECTIVES: 1) To determine if a period of early auditory deprivation influences neural activity patterns as revealed by human auditory brain stem potentials evoked by electrical stimulation from a cochlear implant. 2) To examine the potential for plasticity in the human auditory brain stem. Specifically, we asked if electrically evoked auditory potentials from the auditory nerve and brain stem in children show evidence of development as a result of implant use. 3) To assess whether a sensitive or critical period exists in auditory brain stem development. Specifically, is there an age of implantation after which there are no longer developmental changes in auditory brain stem activity as revealed by electrically evoked potentials? DESIGN: The electrically evoked compound potential of the auditory nerve (ECAP) and the electrically evoked auditory brain stem response (EABR) were recorded repeatedly during the first year of implant use in each of 50 children. The children all had pre- or peri-lingual onset of severe to profound sensorineural hearing loss and received their implants at ages ranging from 12 mo to 17 yr. All children received Nucleus cochlear implant devices. All children were in therapy and in school programs that emphasized listening and required the children to wear their implants consistently. RESULTS: Initial stimulation from the cochlear implant evoked clear responses from the auditory nerve and auditory brain stem in most children. There was no correlation between minimum latency, maximum amplitude, or slope of amplitude growth of initial responses with age at implantation for ECAP eN1, EABR eIII and eV components (p > 0.05). During the first year of implant use, minimum latency of these waves significantly decreased (p < 0.01, p < 0.0001, p < 0.0001, respectively). Neural conduction time, measured using the interwave latency of ECAP eN1-EABR eIII for lower brain stem and EABR eIII-eV for upper brain stem, decreased during the period of 6 to 12 mo of cochlear implant use (p < 0.01 (lower), p < 0.0001(upper)). The ECAP wave eN1 and the EABR wave eV showed significant increases in amplitude during time of implant use (p < 0.05 and p < 0.01, respectively). There were no correlations between the rate of interwave latency decrease and the rate of amplitude increases and the age at which children underwent implantation (p < 0.05). CONCLUSIONS: Activity in the auditory pathways to the level of the midbrain can be evoked by acute stimulation from a cochlear implant. EABR measures are not influenced by any period of auditory deprivation. Auditory development proceeds once the implant is activated and involves improvements in neural conduction velocity and neural synchrony. Underlying mechanisms likely include improvements in synaptic efficacy and possibly increased myelination. The developmental plasticity that we have shown in the human auditory brain stem does not appear from EABR data to be limited by a critical period during childhood.     

Electrically evoked auditory brainstem responses in cochlear implant patients.

Electrically evoked auditory brainstem responses (EABR) were recorded in completely deaf patients implanted with Ineraid multichannel cochlear implants. Clear and reproducible EABR were obtained from all patients. Parametric differences with auditory brainstem responses (ABR) were demonstrated and can be explained by the different natures of both types of stimulations (electric versus acoustic). Evidence is given that other well-known properties of auditory evoked responses, like 'binaural interaction' or suppression of responses in a forward masking paradigm, can be observed in EABR of implanted patients.     

Hearing habilitation with auditory brainstem implantation in two children with cochlear nerve aplasia

Patients with aplasia and hypoplasia of the cochlear nerve have no chance of having their hearing restored by stimulating the periphery of the auditory system using the traditional cochlear implant. A possible approach to auditory rehabilitation may be direct electrical stimulation of the cochlear nuclei with an auditory brainstem implant (ABI). Recently, two children, aged 4 and 3 years, respectively, with bilateral severe cochlear malformations and cochlear nerve aplasia received an ABI. The present paper reports the technique and the preliminary results of this experience. The classic retrosigmoid approach was used. The correct position of the electrodes was estimated with the aid of EABRs and neural response telemetry (NRT). No postoperative complications were observed. High-resolution CT scans with a bone algorithm reconstruction technique were taken postoperatively to evaluate electrode placement before discharge. The ABI was activated 30 days after implantation in both patients. To date 16 and 13 electrodes, respectively, have been activated in the two children. Three months after activation the first patient had achieved good environmental sound awareness, good speech detection and some speech discrimination. The second child, 1 month after activation, had achieved good environmental sound awareness and moderate speech detection. To the best of our knowledge this is the first report of patients with hypoplasia of the cochlea and aplasia of the cochlear nerve, aged below 5 years and treated with an ABI.     

全身麻醉对小儿听性脑干反应测试结果的影响

目的　研究应用听性脑干反应 (auditorybrainstemreaction ,ABR)作为监测小儿全身麻醉深度与觉醒的客观指标。方法　选择听力正常的外科择期手术患儿 4 5例 ,按照美国麻醉学家学会表针分为Ⅰ～Ⅱ级 ,分别施行异丙酚静脉麻醉、芬太尼静脉麻醉及异氟醚吸入全身麻醉 ,随机每组 15例 ,应用丹麦Madsen诱发电位反应仪监测并记录麻醉各阶段ABR的Ⅰ、Ⅲ、Ⅴ波潜伏期及Ⅰ Ⅲ、Ⅲ Ⅴ、Ⅰ Ⅴ波间期 ,研究观察潜伏期和波间期随时间推移及麻醉剂量变化之间的关系 ,探讨ABR在异丙酚、芬太尼及异氟醚等不同麻醉中的表现特征和规律。结果　①异丙酚静脉麻醉和异氟醚吸入麻醉与剂量呈良好的正相关 ;②Ⅰ波的潜伏期特性对于控制麻醉深度极为重要 ;③Ⅴ波监测麻醉具有最佳的稳定性及相关性 ;④停用麻醉药一段时间或患儿基本清醒时 ,ABR各波潜伏期和波间期有的仍高于正常值 ,这是滞后 (延迟 )反应 ;⑤ABR对芬太尼术中的觉醒监测不太敏感。结论　ABR各波的潜伏期及波间期变化 ,可判断小儿全身麻醉深度 ,在一定程度上可作为判断觉醒的参考 ,但应考虑有延迟反应的可能     

Peri-operative electrically evoked auditory brainstem response assessment of facial nerve/cochlea interaction at cochlear implantation

Objectives: Dehiscence between the cochlear otic capsule and the facial nerve canal is a rare and relatively newly described pathology. In cochlear implantation (CI), this dehiscence may lead to adverse electric facial nerve stimulation (FNS) already at low levels, rendering its use impossible. Here, we describe an assessment technique to foresee this complication.

Methods: Pre- and postoperative computed tomography (CT) scans and intraoperative electrically evoked auditory brainstem response (e-ABR) measurements were analyzed in two patients with cochlear-facial dehiscence (CFD).

Results: Because of the relatively low resolution, the confirmation of CFD with a clinical CT was difficult. The e-ABR displayed a large potential with 6 and 7.5?ms latency, respectively, which did not occur otherwise.

Discussion: Potential strategies to resolve and manage FNS are described.

Conclusion: Prediction of FNS by assessing the distance between the labyrinthine portion of the facial nerve and the cochlea is difficult using conventional CT scans. A large evoked late myogenic potential at low stimulation levels during intraoperative e-ABR measurement may foresee FNS at CI activation.     

全身麻醉对小儿听性脑干反应测试结果的影响

目的 研究应用听性脑干反应(auditory brainstem reaction，ABR)作为监测小儿全身麻醉深度与觉醒的客观指标。方法 选择听力正常的外科择期手术患儿45例，按照美国麻醉学家学会表针分为I～Ⅱ级，分别施行异丙酚静脉麻醉、芬太尼静脉麻醉及异氟醚吸入全身麻醉，随机每组15例，应用丹麦Madsen诱发电位反应仪监测并记录麻醉各阶段ABR的I、Ⅲ、Ⅴ波潜伏期及I-Ⅲ、Ⅲ-Ⅴ、I-Ⅴ波间期，研究观察潜伏期和波间期随时间推移及麻醉剂量变化之间的关系，探讨ABR在异丙酚、芬太尼及异氟醚等不同麻醉中的表现特征和规律。结果 ①异丙酚静脉麻醉和异氟醚吸入麻醉与剂量呈良好的正相关；②I波的潜伏期特性对于控制麻醉深度极为重要；③Ⅴ波监测麻醉具有最佳的稳定性及相关性；④停用麻醉药一段时间或患儿基本清醒时，ABR各波潜伏期和波间期有的仍高于正常值，这是滞后(延迟)反应；⑤ABR对芬太尼术中的觉醒监测不太敏感。结论 ABR各波的潜伏期及波间期变化，可判断小儿全身麻醉深度，在一定程度上可作为判断觉醒的参考，但应考虑有延迟反应的可能。     

Multivariate study of auditory perception using multi-electrode cochlear implants]

The goal of this study was to determine the influence of auditory and cognitive factors in hearing or listening mechanisms with the Nucleus multielectrode cochlear implant. Accordingly, hearing sensitivity, psycho-acoustical masking functions and measures of temporal resolution were obtained from 14 adults with acquired deafness. In addition, six measures of open-set speech discrimination were introduced to represent a possible contribution of cognitive factors. Results indicated the contribution of both auditory and cognitive factors to speech understanding. Cognitive factors were most influential. Differences were also found in the relative importance of various cognitive factors, both before and after an intensive aural rehabilitation program. Initially, subjects relied more heavily on their ability to make efficient use of the linguistic redundancy of speech. At the end of the program, they paid more attention to speech acoustics, as a result of enhanced auditory spectral analysis and temporal resolution at about 2 kHz.     

Abnormal timing delays in auditory brainstem responses evoked by bilateral cochlear implant use in children.

HYPOTHESIS: A period of unilateral implant use before bilateral implantation affects timing of brainstem processes measured by the electrically evoked auditory brainstem response (EABR). BACKGROUND: EABR latencies decrease with unilateral implant use potentially disrupting binaural timing cues important in auditory brainstem processing of bilateral input. METHODS: EABRs were evoked by electrical pulses from the left, right, and both implants simultaneously in 3 groups of children. All were initially implanted at ages younger than 3 years and had the following: 1) a long delay (>2 yr [n = 16]), 2) a short delay (<1 yr [n = 15]), or 3) no delay (n = 15) between left and right ear implantation. Responses were recorded on the first day of bilateral implant use and 3 and 9 months thereafter. RESULTS: Relative to responses evoked in the experienced ear, the naive ear showed prolonged latency in both the EABR peaks and the binaural difference response. After 3 and 9 months of bilateral implant use, the relative prolongation decreased in the long and short delay groups, but significant differences persisted in the former. No clear differences in latencies evoked by the left versus right implant were found at any time point in children receiving bilateral implants simultaneously. CONCLUSION: Results suggest potential disruptions to binaural brainstem processing based on timing cues in children receiving a second cochlear implant after more than 2 years of unilateral implant use that persist through at least the first 9 months of bilateral implant use.     

Usefulness of measuring electrically evoked auditory brainstem responses in children with inner ear malformations during cochlear implantation

Conclusions: EABR is a reliable and effective way of objectively confirming device function and implant-responsiveness of the peripheral auditory neurons up to the level of the brainstem in cases of inner ear malformation. Objective: To investigate the usefulness of measuring the intra-operative electrically evoked compound action potential (ECAP) and electrically evoked auditory brainstem response (EABR) in patients with and without congenital inner ear anomalies during cochlear implantation. Method: Thirty-eight consecutive children (40 ears) aged 5 or younger with congenital profound hearing loss. Twenty-four (25 ears) lacked congenital inner ear anomalies. The 14 patients (15 ears) with a malformation had common cavities (four ears), incomplete partition type I (three ears), cochlea hypoplasia type III (three ears), enlarged vestibular aqueduct (four ears), and cochlear nerve canal stenosis (one ear). Main outcome measures are ECAP and EABR responses. Results: Of the 25 ears lacking any malformation, 21, three, and one showed ‘Good’, ‘Variable’, and ‘No’ ECAP responses, respectively, and 24 and one showed ‘Good’ and ‘Variable’ intra-cochlear responses, respectively. Of the 15 ears with a malformation, two showed ‘Good’ ECAP responses, nine had ‘Variable’ ECAP responses, and four showed ‘No’ ECAP responses. Moreover, five showed ‘Good’ EABR responses and 10 showed ‘Variable’ EABR responses.     

The auditory performance in children using cochlear implants: effects of mental function

OBJECTIVE: Mental function is considered to affect the post-operative outcomes of deaf children with cochlear implants. The purpose of this study is to evaluate the effect of mental function on the auditory performance in children with cochlear implants. METHODS: In a retrospective review of data, 26 pre-lingual deafened children received pre-operative evaluation of mental function and were divided into normal and retarded groups. Categories of auditory performance scale (CAP) was conducted at 1-year intervals after implantation. ANCOVA was used for statistic analysis. RESULTS: The average scores of auditory performance in normal group (n=14) were 3.93 (S.D. 1.07) and 5.86 (S.D. 0.95) at 1- and 2-year post-implantation. While the average scores in the retarded group were 2.5 (S.D. 1.51) and 4.17 (S.D. 1.85), both groups demonstrated obvious improvement in speech perception (F 103.12, P<0.001) during the first 2 post-operative years. The auditory performance in the normal group was significantly superior to the retarded group (F 8.67, P<0.01). However, the interaction between the duration of the device use and mental status showed no significant difference in the auditory perception performance (F 1.575, P=0.222). CONCLUSIONS: The results revealed the mental function plays as one of the predictive parameters of auditory performance in profoundly hearing impaired children after cochlear implantation.     

Comparison of electrically evoked whole-nerve action potential and electrically evoked auditory brainstem response thresholds in nucleus CI24R cochlear implant recipients

In this study, differences between electrically evoked whole-nerve action potential (EAP) and electrically evoked auditory brainstem response (EABR) measurements within Nucleus CI24R cochlear implant recipients were evaluated. Precurved modiolus-hugging internal electrode arrays, such as the CI24R, are designed to provide more direct stimulation of neural elements of the modiolus. If the electrode array is closer to the modiolus, electrically evoked and behavioral levels might be lower than were previously recorded for the straight electrode array, the CI24M. EAP and EABR growth functions and behavioral levels were obtained for 10 postlingually deafened adults. Results revealed no significant differences between EAP and EABR threshold levels, and these levels were not significantly lower than those obtained using the CI24M.     

Central auditory development in children with bilateral cochlear implants

OBJECTIVE: To examine the time course of maturation of P1 latencies in infant sequential and simultaneous bilateral cochlear implant recipients. DESIGN: Retrospective case series. SETTING: Pediatric collaborative cochlear implant program. PATIENTS: Four children who received bilateral cochlear implants prior to age 2 years. INTERVENTION: Cortical auditory evoked potential was completed to determine the latency of the P1 response in 4 children with bilateral cochlear implants. MAIN OUTCOME MEASURES: Longitudinal development of the latency of the P1 cortical auditory evoked potential in children who received bilateral cochlear implants prior to age 2 years. RESULTS: In 2 patients who received sequential bilateral implants, P1 latencies recorded from the first implanted ear were within normal limits after 3 to 6 months of implant use. By comparison, P1 latencies from the second implanted ear reached normal limits as early as 1 month after implant use. In 2 patients who received simultaneous bilateral implants, P1 latencies from both ears were also within normal limits in a very short time frame (ie, by 1 month poststimulation). CONCLUSIONS: Our data suggest a high degree of plasticity of the central auditory pathways after early bilateral implantation. We find that P1 latencies provide a clinically useful biomarker of central auditory system development in children after cochlear implantation.     

Electrically evoked compound action potential (ECAP) in cochlear implant children: Changes in auditory nerve response in first year of cochlear implant use

AimRecording of the electrically evoked compound action potential (ECAP) of the auditory nerve in cochlear implant (CI) patients represents an option to assess changes in auditory nerve responses and the interaction between the electrode bundle and the neural tissue over time. The aim of the present work is to assess ECAP changes during the first year of cochlear implant for the purpose of predicting thresholds and adjustment of the patients’ programs over time.MethodData were collected from 25 children using Cochlear Nucleus 24 implants. ECAP thresholds were examined at the time of surgery, at initial stimulation, and 3, 6 and 12 months post-stimulation. Five electrodes located at basal, middle, and apical positions in the cochlea were tested at each time interval and ECAP thresholds were analyzed and compared.ResultsThere was a significant decrease in ECAP thresholds between the intraoperative measure and fitting time at all electrode sites. Mean ECAP thresholds measured at 3, 6 and 12 months post-stimulation remained similar to initial stimulation levels. Although there was no significant difference in ECAP thresholds recorded at fitting time and 12 months follow up session, there was significant increase in behavioral T and C levels from initial stimulation to the 12 months’ time point.ConclusionMost electrodes undergo non-significant change in ECAP thresholds over time, and therefore thresholds obtained on the day of initial stimulation can be used to estimate the patients’ map levels at any time. On the other hand, intraoperative thresholds demonstrated significant change relative to postoperative recording times, limiting the ability to use intraoperatively recorded ECAP thresholds to predict postoperative measurements.