Martin O'Driscoll

Auditory localization abilities in bilateral cochlear implant recipients.

Objective: To quantify binaural advantage for auditory localization in the horizontal plane by bilateral cochlear implant (CI) recipients. Also, to determine whether the use of dual microphones with one implant improves localization. Methods: Twenty subjects from the UK multicenter trial of bilateral cochlear implantation with Nucleus 24 K/M device were recruited. Sound localization was assessed in an anechoic room with an 11-loudspeaker array under four test conditions: right CI, left CI, binaural CI, and dual microphone. Two runs were undertaken for each of five stimuli (speech, tones, noise, transients, and reverberant speech). Order of conditions was counterbalanced across subjects. Results: Mean localization error with bilateral implants was 24° compared with 67° for monaural implant and dual microphone conditions (chance performance is 65°). Normal controls average 2 to 3° in similar conditions. Binaural performance was significantly better than monaural performance for all subjects, for all stimulus types, and for different sound sources. Only small differences in performance with different stimuli were observed. Conclusions: Bilateral cochlear implantation with the Nucleus 24 device provides marked improvement in horizontal plane localization abilities compared with unilateral CI use for a range of stimuli having different spectral and temporal characteristics. Benefit was obtained by all subjects, for all stimulus types, and for all sound directions. However, binaural performance was still worse than that obtained by normal hearing listeners and hearing aid users with the same methodology. Monaural localization performance was at chance. There is no benefit for localization with dual microphones.

Evaluation of bilaterally implanted adult subjects with the nucleus 24 cochlear implant system.

Objective: To evaluate the speech perception benefits of bilateral implantation for subjects who already have one implant. Study Design: Repeated measures. Patients: Thirty adult cochlear implant users who received their second implant from 1 to 7 years with a mean of 3 years after their first device. Ages ranged from 29 to 82 years with a mean of 57 years. Setting: Tertiary referral centers across the United Kingdom. Main Outcome Measures: Monosyllabic consonant-nucleus-consonant words and City University of New York sentences in quiet with coincident speech and noise and with the noise spatially separated from the speech by ±90°. Results: At 9 months, results showed the second ear in noise was 13.9 ± 5.9% worse than the first ear (p < 0.001); a significant binaural advantage of 12.6 ± 5.4% (p < 0.001) over the first ear alone for speech and noise from the front; a 21 ± 6% (p < 0.001) binaural advantage over the first ear alone when noise was ipsilateral to the first ear; no binaural advantage when noise was contralateral to the first ear. Conclusions: There is a significant bilateral advantage of adding a second ear for this group. We were unable to predict when the second ear would be the better performing ear, and by implanting both ears, we guarantee implanting the better ear. Sequential implantation with long delays between ears has resulted in poor second ear performance for some subjects and has limited the degree of bilateral benefit that can be obtained by these users. The dual microphone does not provide equivalent benefit to bilateral implants.

Predictors of audiological outcome following cochlear implantation in adults.

Abstract The objective of this study was to examine variables that may predict open set speech discrimination following cochlear implantation. It consisted of a retrospective case review conducted in a tertiary referral centre with a cochlear implant programme. The patients were 117 postlingually deafened adult cochlear implant recipients. The main outcome measures were Bench, Kowal, Bamford (BKB) sentence scores recorded nine months following implant activation. The variables studied were age at the time of surgery, sex, duration of hearing loss, aetiology of hearing loss, residual hearing, implant type, speech processor strategy, number of active electrodes inserted. Variables found to have a significant effect on BKB following univariate analysis were entered into a multivariate analysis to determine independent predictors. Multivariate ordinal regression analysis gave an odds ration of 1.09 for each additional year of deafness prior to implantation (confidence interval 1.06–1.13; p<0.001). Duration of deafness prior to implantation is an independent predictor of implant outcome. It accounted for 9% of the variability. Other factors must influence implant performance. Copyright

Ipsilateral cochlear implantation after cochlear nerve preserving vestibular schwannoma surgery in patients with neurofibromatosis type 2.

Objective To investigate the outcomes from ipsilateral simultaneous or sequential cochlear implantation in patients with neurofibromatosis type 2 (NF2) after vestibular schwannoma removal with cochlear nerve preservation. Study Design Retrospective case series. Setting Single tertiary referral NF2 center. Patients Six patients with NF2. Intervention Removal of vestibular schwannoma (VS) with preservation of the cochlear nerve and cochlear implantation. Four patients had their surgery via a translabyrinthine approach. Two patients had a retrosigmoid approach. A cochlear implant was inserted at the same time as tumor removal in 4 cases and sequentially in 2 cases. Main Outcome Measures Surgical and audiometric outcomes using Bamford-Kowal-Bench (BKB) and City of New York University (CUNY) sentence scores. Results The average age at implantation was 24 years (range, 15–36 yr). Follow-up ranged from 5 to 93 months, with an average of 38 months. All patients had useful hearing in the contralateral ear before surgery. One patient gained no benefit from cochlear implantation and proceeded to have an auditory brainstem implant. Of those that had functional cochlear nerves, the average BKB score in quiet was 64%, BKB score in noise was 42%, and CUNY score with lipreading was 97%. Results varied within the group, but all patients gained significant benefit and continue to use their CI at least intermittantly. Conclusion The present series demonstrates that in selected cases, cochlear implantation can be successful after a translabyrinthine approach for VS removal and for restoring hearing after failed retrosigmoid hearing preservation surgery. All patients found the cochlear implant offered useful hearing even in the presence of contralateral hearing.

Vestibular schwannoma in the only hearing ear: cochlear implant or auditory brainstem implant?

Objective: To explore the dilemma faced by neurotologists confronted with the patient who develops a vestibular schwannoma in the only hearing ear, the other having been deaf from birth, and to consider the choice between auditory rehabilitation using a cochlear implant (CI) on the congenitally deaf side and an auditory brainstem implant (ABI) on the tumor side. Study Design: A record review of two patients born deaf in one ear and who developed a vestibular schwannoma in the contra lateral ear, who then received a CI in the congenitally deaf ear. Setting: Tertiary referral center with special experience in vestibular schwannoma surgery, neurofibromatosis type 2 management, and cochlear implantation. Results: Neither patient was a good CI user. At 1 year postimplant, they both scored 0% on abbreviated words and 0% and 7%, respectively, on Bench Kowal Bamford sentences. They scored 54% and 57%, respectively, on City University of New York sentences with lip-reading, and both had fair access to environmental sound scoring at 45% each. Conclusions: The results from cochlear implantation in the congenitally deaf ear in these patients were poor and suggest that stimulus deprivation in the early stages of the maturation of the auditory pathways is important even for a unilateral hearing loss. Unfortunately, the factors that predict a good ABI result are not known. In these circumstances, the authors advocate the insertion of an ABI at the time of tumor removal, retaining the option of CI in the congenitally deaf ear in the event of a poor outcome with the ABI.

English consensus protocol evaluating candidacy for auditory brainstem and cochlear implantation in neurofibromatosis type 2

Objective Hearing loss resulting from bilateral vestibular schwannomas (VSs) has a significant effect on the quality of life of patients with neurofibromatosis Type 2 (NF2). A national consensus protocol was produced in England as a guide for cochlear implantation (CI) and auditory brainstem implantation (ABI) in these patients. Study Design Consensus statement. Setting English NF2 Service. Participants Clinicians from all 4 lead NF2 units in England. Main Outcome Measures A protocol for the assessment, insertion and rehabilitation of CI and ABI in NF2 patients. Results Patients should undergo more detailed hearing assessment once their maximum aided speech discrimination score falls below 50% in the better hearing ear. Bamford-Kowal-Bench sentence testing scores below 50% should trigger assessment for auditory implantation, as recommended by the National Institute for Clinical Excellence guidelines on CI. Where this occurs in patients with bilateral stable VS or a unilateral stable VS where the contralateral cochlear nerve was lost at previous surgery, CI should be considered. Where VS surgery is planned, CI should be considered where cochlear nerve preservation is thought possible, otherwise an ABI should be considered. Intraoperative testing using electrically evoked auditory brainstem responses or cochlear nerve action potentials may be used to determine whether a CI or ABI is inserted. Conclusion The NF2 centers in England agreed on this protocol. Multisite, prospective assessments of standardized protocols for auditory implantation in NF2 provide an essential model for evaluating candidacy and outcomes in this challenging patient population.

Brain stem responses evoked by stimulation with an auditory brain stem implant in children with cochlear nerve aplasia or hypoplasia.

Objectives: The inclusion criteria for an auditory brain stem implant (ABI) have been extended beyond the traditional, postlingually deafened adult with Neurofibromatosis type 2, to include children who are born deaf due to cochlear nerve aplasia or hypoplasia and for whom a cochlear implant is not an option. Fitting the ABI for these new candidates presents a challenge, and intraoperative electrically evoked auditory brain stem responses (EABRs) may assist in the surgical placement of the electrode array over the dorsal and ventral cochlear nucleus in the brain stem and in the postoperative programming of the device. This study had four objectives: (1) to characterize the EABR by stimulation of the cochlear nucleus in children, (2) to establish whether there are any changes between the EABR recorded intraoperatively and again just before initial behavioral testing with the device, (3) to establish whether there is evidence of morphology changes in the EABR depending on the site of stimulation with the ABI, and (4) to investigate how the EABR relates to behavioral measurements and the presence of auditory and nonauditory sensations perceived with the ABI at initial device activation. Design: Intra- and postoperative EABRs were recorded from six congenitally deaf children with ABIs, four boys and two girls, mean age 4.2 yrs (range 3.2 to 5.0 yrs). The ABI was stimulated at nine different bipolar sites on the array, and the EABRs recorded were analyzed with respect to the morphology and peak latency with site of stimulation for each recording session. The relationship between the EABR waveforms and the presence or absence of auditory electrodes at initial device activation was investigated. The EABR threshold levels were compared with the behavioral threshold (T) and comfortably loud (C) levels of stimulation required at initial device activation. Results: EABRs were elicited from all children on both test occasions. Responses contained a possible combination of one to three peaks from a total of four identifiable peaks with mean latencies of 1.04, 1.81, 2.61, and 3.58 msecs, respectively. The presence of an EABR was a good predictor of an auditory response; however, the absence of the EABR was poor at predicting a site with no auditory response. The morphology of EABRs often varied with site of stimulation and between EABR test occasions. Postoperatively, there was a trend for P1, P3, and P4 to be present at the lateral end of the array and P2 at the medial end of the array. Behavioral T and C levels showed a good correlation with postoperative EABR thresholds but a poor correlation with intraoperative EABR thresholds. Conclusions: The presence of an intraoperative EABR was a good indicator for the location of electrodes on the ABI array that provided auditory sensations. The morphology of the EABR was often variable within and between test sessions. The postoperative EABR thresholds did correlate with the behavioral T and C levels and could be used to assist with initial device fitting.

Brain stem responses evoked by stimulation of the mature cochlear nucleus with an auditory brain stem implant

Objectives: The Nucleus auditory brain stem implant (ABI) has been used in the hearing rehabilitation of totally deaf individuals for whom a cochlear implant is not an option such as in the case of neurofibromatosis type 2 (NF2). Intraoperative electrically evoked auditory brain stem responses (EABRs) are recorded to assist in the placement of the electrode array over the dorsal and ventral cochlear nuclei in the lateral recess of the IVth ventricle of the brain stem. This study had four objectives: (1) to characterize EABRs evoked by stimulation with an ABI in adolescents and adults with NF2, (2) to evaluate how the EABR morphology relates to auditory sensations elicited from stimulation by an ABI, (3) to establish whether there is evidence of morphology changes in the EABR with site of stimulation by the ABI, and (4) to investigate how the threshold of the EABR relates to behavioral threshold and comfortably loud sensations measured at initial device activation. Design: Intraoperative EABRs were recorded from 34 subjects with ABIs: 19 male and 15 female, mean age 27 yrs (range 12 to 52 yrs). ABI stimulation was applied at seven different sites using either wide bipolar stimulation across the array or in subsections of the array from medial to lateral and inferior to superior. The EABRs were analyzed with respect to morphology, peak latency, and changes in these characteristics with the site of stimulation. In a subset of eight subjects, additional narrow bipolar sites were stimulated to compare the intraoperative EABR threshold levels with the behavioral threshold (T) and comfortably loud (C) levels of stimulation required at initial device activation. Results: EABRs were elicited from 91% of subjects. Morphology varied from one to four vertex-positive peaks with mean latencies of 0.76, 1.53, 2.51, and 3.64 msecs, respectively. The presence of an EABR from stimulation by electrodes across the whole array had a high predictive value for the presence of auditory electrodes at initial device activation. When examining subsections of the array, the absence of an EABR was a poor predictor for the absence of auditory electrodes. The morphology of the EABRs varied with site of stimulation in 16 cases, but there was no consistent pattern of change with stimulation site. There was a trend for more auditory electrodes to be present in stimulation sites that evoked EABRs with a higher number of peaks in the waveform. The EABR threshold was closer to the behavioral C level than the T level, but there was no overall correlation between the intraoperative EABR threshold level and the behavioral T and C levels. Conclusions: The presence of an intraoperative EABR corresponded well to the presence of auditory electrodes. The absence of an EABR from stimulating subsections of the array was not; however, a good indicator for the absence of auditory electrodes and the EABR from such stimulation would not be of assistance in identifying the nonauditory sections of the array to exclude in behavioral fitting of the device. The morphology of the EABR did not relate to site of stimulation. More peaks in the EABR was associated with a greater number of electrodes with auditory sensations, suggesting that correct positioning of the ABI activated more auditory subsystems within the cochlear nucleus. The intraoperative EABR thresholds did not correlate with the behavioral T and C levels and could not be used to assist in device fitting.

Explanatation of a nucleus multichannel cochlear implant and re-implantation into the contralateral ear. A case report of a new strategy

We present a unique case in which a multichannel cochlear implant device was explanted and the same device was re-implanted into the contralateral ear. A patient with bilateral total deafness secondary to head injury received an implant in his left ear but developed severe facial nerve stimulation. Because this stimulation could not be eliminated effectively with change of programming, it was decided to implant the contralateral ear. Since the device itself was functioning well, it was explanted from the left ear and re-implanted successfully into the right ear. Facial nerve stimulation was minimal in this ear and the patient demonstrated very good speech discrimination. To our knowledge, this is the first description of this strategy.

Cochlear implantation in children with auditory neuropathy spectrum disorders

Abstract Aim To present the outcomes of cochlear implantation (CI) in children with auditory neuropathy spectrum disorders (ANSD). Materials and methods The pre- and post-CI hearing outcomes in children with ANSD were retrospectively evaluated. Performance was assessed with categories of auditory performance (CAP) and the Manchester spoken language development scale (MSLDS). Results Full data were available in 27 implanted children with ANSD with average age at implantation 35.4 months (range 19–68 months). Nine children were implanted bilaterally, while 13 were bimodal. The pre-CI CAP and MSLDS scores were 2.5 (range 0–5) and 2.5 (range 0–6), while the post-CI scores 5.8 (range 2–9) and 7.7 (range 3–10), respectively. Conclusions Although the outcome of CI in children with ANSD might vary, it is favourable in most of the cases. CI seems a justified hearing rehabilitation option for children with ANSD and limited benefits from conventional hearing aids.