Hearing Restoration with Auditory Brainstem Implant

Long-term analysis of ABI auditory performance in patients with neurofibromatosis type 2-related schwannomatosis

PURPOSE

This retrospective monocentric study aimed to evaluate long-term auditory brainstem implant (ABI) function in patients with neurofibromatosis type 2, and to investigate the prognostic factors for ABI use.

METHODS

Between 1997 and 2022, 27 patients with at least five years of follow-up underwent implantation with 32 ABIs. At 1- and 5-years post-implantation and at last follow-up, ABIs were classified as used or non-used and the size of the ipsilateral tumor was recorded. For patients who used their ABIs, we assessed speech perception (disyllabic words, MBAA sentences) in quiet conditions with the ABI only, by lip-reading (LR), and with a combination of the two (ABI + LR). Hearing improvement was calculated as Δ ABI = (ABI + LR)-LR scores. Predictive factors for ABI use were analyzed.

RESULTS

One year post-implantation, 74% patients were ABI-users and 66% of the ABIs were used. Two of these patients were non-users at five years, and another two at last follow-up (14 ± 5.2 years); 54% of the patients were ABI-users at last follow-up. Δ ABI revealed a hearing improvement of 32-41% (disyllabic words) and 28-37% (MBAA sentences). Among 16 ABIs with at least LR improvement at 1-year post-implantation, 4 decreased their performance, coinciding with a large growing ipsilateral tumor in 3/4 ABIs. We identified no significant prognostic factors for ABI use.

CONCLUSIONS

ABIs are indicated in case of bilateral deafness with a non-functional cochlear nerve. Half the patients with ABIs used their implants and auditory performance remained stable over time, except in cases of ipsilateral tumor growth.

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

OBJECTIVE

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

DATA SOURCES

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

REVIEW METHODS

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

RESULTS

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

CONCLUSION

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

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

Purpose

An auditory brainstem implant (ABI) represents an alternative for patients with profound hearing loss who are constrained from receiving a cochlear implant. The positioning of the ABI electrode influences the patient’s auditory capacity and, therefore, quality of life and is challenging even with available intraoperative electrophysiological monitoring. This work aims to provide and assess the feasibility of visual-spatial assistance for ABI positioning.

Methods

The pose of the forceps instrument that grasps the electrode was electromagnetically navigated and interactively projected in the eyepieces of a surgical microscope with respect to a target point. Intraoperative navigation was established with an experimental technique for automated nasopharyngeal patient registration. Two ABI procedures were completed in a human specimen head.

Results

An intraoperative usability study demonstrated lower localization error when using the proposed visual display versus standard cross-sectional views. The postoperative evaluations of the preclinical study showed that the center of the electrode was misplaced to the planned position by 1.58 mm and 3.16 mm for the left and the right ear procedure, respectively.

Conclusion

The results indicate the potential to enhance intraoperative feedback during ABI positioning with the presented system. Further improvements consider estimating the pose of the electrode itself to allow for better orientation during placement.

Supplementary Information

The online version contains supplementary material available at 10.1007/s11548-021-02514-x.

Extended Middle Cranial Fossa Approach for Placement of Auditory Brainstem Implants

OBJECTIVE

Traditionally, auditory brainstem implants (ABIs) have been placed via the translabyrinthine or retrosigmoid approaches. In select patients, a modified extended middle cranial fossa (xMCF) approach with tentorial ligation may be advantageous for vestibular schwannoma (VS) resection and auditory rehabilitation. This manuscript describes the application of this modification of the MCF approach for simultaneous VS resection and ABI placement.

PATIENTS

Patients with neurofibromatosis type 2, profound bilateral sensorineural hearing loss, single functioning sigmoid/jugular venous system, and giant (>4 cm) VS.

INTERVENTIONS

Simultaneous VS resection and ABI placement via a modified xMCF approach with tentorial ligation.

MAIN OUTCOME MEASURES

Extent of tumor removal and brainstem decompression, access to lateral recess of the fourth ventricle, functional hearing improvement, surgical complications.

RESULTS

Two patients met indications and underwent surgery. There were no immediate or delayed surgical complications. Both had subtotal tumor removal with significant decompression of the brainstem and ABI placement. One patient achieved voice and environmental sound awareness at 35 to 55 dbHL across frequencies. The second patient presented with failure to thrive and multiple lower cranial neuropathies in addition to the above-listed indications. She was hospitalized multiple times after surgery due to failure to thrive and recurrent aspiration pneumonia. Her device was never activated, and she expired 1 year after surgery.

CONCLUSIONS

The xMCF with tentorial ligation is an additional approach for tumor resection and ABI placement in selected patients with neurofibromatosis type 2. Future studies will further define when this approach is most applicable as well as the challenges and pitfalls.

Diagnostic Accuracy of Intracochlear Test Electrode for Acoustic Nerve Monitoring in Vestibular Schwannoma Surgery

OBJECTIVES

Cochlear implants (CIs) are a well-known hearing restoration option for patients with vestibular schwannoma (VS) in cases of neurofibromatosis type-2 and, more recently, for patients with sporadic VS. One of the main limitations when performing CI during VS surgery is the capability to preserve the acoustic nerve (AN) anatomically and functionally. Significant efforts have been directed toward developing an intraoperative testing method for monitoring the AN function to determine if, after tumor removal, it is suitable for conducting stimuli delivered by a CI. However, all these methods have significant limitations, and none of them have documented diagnostic efficacy. To overcome these limitations and to obtain reliable information before CI insertion, a minimally invasive intracochlear test electrode (TE) has been recently developed. This TE has demonstrated to be suitable to test the integrity of the AN before CI in patients without any residual hearing by recording electrically evoked auditory brainstem responses (EABR). The present study constitutes the next phase of this research, which was to determine the usefulness of EABR obtained intraoperatively with the intracochlear TE after the resection of a VS and to calculate its diagnostic accuracy to assess the functionality of the AN for CI.

DESIGN

This was a prospective, multicenter study of diagnostic accuracy. It was conducted in three tertiary referral centers between January 2015 and 2018. This study was designed following the Standards for Reporting of Diagnostic Accuracy Studies (STARD) statement guidelines. The STARD statement are guidelines to improve the completeness and transparency of reports of diagnostic accuracy studies. The diagnostic accuracy of the EABR evoked with the intracochlear TE after tumor removal was studied. Accuracy, sensitivity, specificity, positive predictive value, and negative predictive value were calculated. Patients eligible for the study were consecutive adults undergoing surgery for VS with simultaneous CI. The test under evaluation (index test) was the EABR obtained with the intracochlear TE after resection of the tumor. The reference test (gold standard) was the presence of auditory perception with the CI, defined as the presence of sound detection on an audiogram at 500, 1000, 2000, and 4000 Hz of no greater than 50 dB. In all the cases, auditory perception was verified by the presence of a positive EABR evoked with the CI.

RESULTS

Twenty-one patients were included during the study period; seven patients were excluded from the diagnostic efficacy analysis due to inconclusive EABR results or absence of the gold standard to compare (they did not finally receive the CI). Thus, the outcome of the gold standard was assessed in 14 cases: 9 cases had positive EABR, all of them obtained auditory perception with the CI, and 5 cases had negative EABR, only one case had auditory perception with the CI, which constitutes the only false negative of this study. Accuracy of the TE was 93% (95% confidence interval, 66 to 100%), sensitivity 90% (95% confidence interval, 71 to 100%), specificity 100% (95% confidence interval, 100 to 100%), positive predictive value 100% (95% confidence interval, 100 to 100%), and negative predictive value 80% (95% confidence interval, 45 to 100%).

CONCLUSIONS

EABR elicited with the intracochlear TE had a diagnostic accuracy of 93% for predicting auditory perception with CIs after VS removal. These results suggest that the intracochlear TE can be used intraoperatively after tumor removal to test the integrity of the AN as a useful tool to complement the surgeon's perception for decision-making regarding implantation.

Three-Dimensional Surface Reconstruction of the Human Cochlear Nucleus: Implications for Auditory Brain Stem Implant Design

Objective  The auditory brain stem implant (ABI) is a neuroprosthesis placed on the surface of the cochlear nucleus (CN) to provide hearing sensations in children and adults who are not candidates for cochlear implantation. Contemporary ABI arrays are stiff and do not conform to the curved brain stem surface. Recent advancements in microfabrication techniques have enabled the development of flexible surface arrays, but these have only been applied in animal models. Herein, we measure the surface curvature of the human CN and adjoining regions to assist in the design and placement of next-generation conformable clinical ABI arrays. Three-dimensional (3D) reconstructions from ultrahigh T1-weighted brain magnetic resonance imaging (MRI) sequences and histologic reconstructions based on postmortem adult human brain stem specimens were used. Design  This is a retrospective review of radiologic data and postmortem histologic axial sections. Setting  This is set at the tertiary referral center. Participants  Data were acquired from healthy adults. Main Outcome Measures  The main outcome measures are principal curvature values (Kmin and Kmax) and global radius of curvature. Results  The CN was successfully extracted and rendered as a 3D surface in all cases. Significant curvatures of the CN in both histologic and radiographic reconstructions were found with global radius of curvature ranging from 2.08 to 8.5 mm. In addition, local curvature analysis revealed that the surface is highly complex. Conclusion  Detailed rendering of the human CN is feasible using histology and 3D MRI reconstruction and highlights complex surface topography that is not recapitulated by contemporary stiff ABI arrays.

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSIONS

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