Intraoperative Monitoring of the Cochlear Nerve during Neurofibromatosis Type-2 Vestibular Schwannoma Surgery and Description of a "Test Intracochlear Electrode"

"To implant or not to implant": electrically evoked auditory brainstem response audiometry for decision-making in vestibular schwannoma resection with CI

Vestibular schwannomas (VS) are often associated with debilitating hearing loss. Therefore, preservation and rehabilitation of hearing have become major therapeutic goals of VS management. Recently, cochlear implantation (CI) has been established as an effective treatment option for VS-associated hearing loss. Nevertheless, the integrity and proper function of the cochlear nerve must be evaluated before conducting CI to ensure optimal CI outcomes. Various methods to determine cochlear nerve integrity and functionality have emerged in the last few years. Of these, the use of electrically evoked auditory brainstem response audiometry (eABR) in particular has been proven to be a meaningful tool for monitoring cochlear nerve health during VS surgery. Here, the cochlear nerve can be electrically stimulated using an intracochlear test electrode before, during, and after tumor extirpation. Subsequently, the resulting brainstem responses can be measured and interpreted accordingly to obtain direct information on the cochlear nerve function. This allows for continuous monitoring of cochlear nerve function throughout the course of VS surgery and aids in the decision-making for CI candidacy. Finally, in the case of preserved brainstem responses, CI can be performed instantly after VS extirpation. This simultaneous approach offers several advantages over two-staged procedures and has been shown to be an efficient and safe procedure for restoring hearing after VS removal.

Intraoperative Electrical Stapedius Reflex Testing to Monitor Cochlear Nerve Integrity during Simultaneous Vestibular Schwannoma Resection and Cochlear Implantation

OBJECTIVE

To compare the utility of intraoperative electrically evoked auditory brainstem response (eABR) and electrically evoked stapedial reflex testing (eSRT) for cochlear nerve integrity monitoring during simultaneous translabyrinthine resection of vestibular schwannoma (VS) and cochlear implantation.

STUDY DESIGN

Historical cohort study.

SETTING

Tertiary academic referral center.

PATIENTS

Eleven patients (12 cases) who underwent translabyrinthine tumor resection with simultaneous placement of a standard, unmodified cochlear implant (CI).

INTERVENTION

A CI placed at the beginning of the operation before tumor resection to facilitate intraoperative cochlear nerve monitoring through a CI-delivered electrical stimulus.

MAIN OUTCOME MEASURE

Correlation of intraoperative monitoring outcomes with postoperative CI performance.

RESULTS

Among the 12 cases (median age, 47 years), eABR waveforms were present at the conclusion of tumor resection in 10, including 6 that achieved open set speech perception. Of the 2 cases with negative eABR, 1 achieved open set speech perception. By contrast, of the 8 cases with a positive eSRT response, 7 achieved open set speech perception. Of the 4 cases with a negative eSRT response, none achieved open set speech perception. The 3 cases that did not receive auditory stimulation included 2 with positive and 1 with negative eABR; all 3 had a negative eSRT response.

CONCLUSIONS

Intraoperative eSRT using an unmodified CI is a promising new method for monitoring the integrity of the cochlear nerve during simultaneous VS resection. eSRT response at the conclusion of tumor resection strongly correlated with CI open set speech capacity. Although still useful, eABR was less reliable at predicting postoperative hearing outcomes in this series.

Tympanic Pre-Operative Electrically Evoked Auditory Late Response (TympEALR) as an Alternative to Trans-Tympanic Tests Using Anesthesia in Cochlear Implant Candidacy

Background/Objectives: Before a cochlear implant is considered, patients undergo various audiological tests to assess their suitability. One key test measures the auditory brainstem response (ABR) to acoustic stimuli. However, in some cases, even with maximum sound stimulation, no response is detected. Methods: The promontory test involves electrical stimulation near the auditory nerve, allowing patients to associate the sensation. Ideally, the electrode is placed in the middle ear after opening the eardrum. This method, along with trans-tympanic electrically evoked ABR in local anesthesia (LA-TT-EABR) and the cortical equivalent (LA-TT-EALR), helps assess the auditory nerve's existence and excitability. The TympEALR test, utilizing a "tympanic LA-TT-EALR", provides an alternative measurement. Previous research has shown the possibility of deriving brainstem and cortical potentials through trans-tympanic electrical stimulation, allowing for objective assessment of the auditory nerve's integrity and potentially objectifying patient sensations. Results: Sixteen patients have been tested using TympEALR. In seven of these, we found a positive response. The morphology was similar to other electrically evoked cortical auditory responses (EALR), e.g., using cochlear implants or trans-tympanic stimulation electrodes. We observed a higher influence of electrical artifacts than in other EALRs. Conclusions: TympEALR showed positive results in nearly half of the study participants, potentially avoiding invasive procedures. TympEALR can be a valuable alternative to trans-tympanic methods. More research is needed to determine if a negative result suggests against cochlear implantation.

Intraoperative assessment of cochlear nerve functionality in various vestibular schwannoma scenarios: Lessons learned

The use of cochlear implants (CIs) is on the rise for patients with vestibular schwannoma (VS). Besides CI following tumor resection, new scenarios such as implantation in observed and/or irradiated tumors are becoming increasingly common. A significant emerging trend is the need of intraoperative evaluation of the functionality of the cochlear nerve in order to decide if a CI would be placed. The purpose of this paper is to explore the experience of a tertiary center with the application of the Auditory Nerve Test System (ANTS) in various scenarios regarding VS patients. The results are compared to that of the studies that have previously used the ANTS in this condition. Patients with unilateral or bilateral VS (NF2) who were evaluated with the ANTS prior to considering CI in a tertiary center between 2021 and 2023 were analyzed. The presence of a robust wave V was chosen to define a positive electrical auditory brainstem response (EABR). Two patients underwent promontory stimulation (PromStim) EABR previous to ANTS evaluation. Seven patients, 2 NF-2 and 5 with sporadic VS were included. The initial scenario was simultaneous translabyrinthine (TL) tumor resection and CI in 3 cases while a CI placement without tumor resection was planned in 4 cases. The ANTS was positive in 4 cases, negative in 2 cases, and uncertain in one case. Two patients underwent simultaneous TL and CI, 1 patient simultaneous TL and auditory brainstem implant, 3 patients posterior tympanotomy with CI, and 1 patient had no implant placement. In the 5 patients undergoing CI, sound detection was present. There was a good correlation between the PromStim and ANTS EABR. The literature research yielded 35 patients with complete information about EABR response. There was one false negative and one false positive case; that is, the 28 implanted cases with a present wave V following tumor resection had some degree of auditory perception in all but one case. The ANTS is a useful intraoperative tool to asses CI candidacy in VS patients undergoing observation, irradiation or surgery. A positive strongly predicts at least sound detection with the CI.

Brazilian Society of Otology task force - Vestibular Schwannoma ‒ evaluation and treatment

OBJECTIVE

To review the literature on the diagnosis and treatment of vestibular schwannoma.

METHODS

Task force members were educated on knowledge synthesis methods, including electronic database search, review and selection of relevant citations, and critical appraisal of selected studies. Articles written in English or Portuguese on vestibular schwannoma were eligible for inclusion. The American College of Physicians' guideline grading system and the American Thyroid Association's guideline criteria were used for critical appraisal of evidence and recommendations for therapeutic interventions.

RESULTS

The topics were divided into 2 parts: (1) Diagnosis - audiologic, electrophysiologic tests, and imaging; (2) Treatment - wait and scan protocols, surgery, radiosurgery/radiotherapy, and systemic therapy.

CONCLUSIONS

Decision making in VS treatment has become more challenging. MRI can diagnose increasingly smaller tumors, which has disastrous consequences for the patients and their families. It is important to develop an individualized approach for each case, which highly depends on the experience of each surgical team.

A novel intraoperative continuous monitoring method combining dorsal cochlear nucleus action potentials monitoring with auditory nerve test system

Highly accurate real-time cochlear nerve monitoring to preserve cochlear nerve function is essential for simultaneous cochlear implantation and ipsilateral vestibular schwannoma resection. In the present study, we developed a novel real-time monitoring system that combines dorsal cochlear nucleus action potential monitoring with intracochlear stimulating electrodes (Auditory Nerve Test System, ANTS). We used this system for a case with vestibular schwannoma resection via the translabyrinthine approach. The monitoring system developed in this study detected highly reliable evoked potentials from the cochlear nerve every two seconds continuously during tumor resection. Near-total tumor resection was achieved, and cochlear implantation was performed successfully after confirming the preservation of cochlear nerve function in a case. The patient's hearing was well compensated by cochlear implantation after surgery. Our novel method continuously achieved real-time monitoring of the cochlear nerve every two seconds during vestibular schwannoma resection. The usefulness of this monitoring system for simultaneous tumor resection and cochlear implantation was demonstrated in the present case. The system developed in this study is compatible with continuous facial nerve monitoring. This highly accurate and novel monitoring method will broaden the number of candidates for this type of surgery in the future.

Intraoperative Cochlear Nerve Monitoring in Cochlear Implantation after Vestibular Schwannoma Resection

BACKGROUND

The use of a cochlear implant (CI) for hearing rehabilitation after vestibular schwannoma (VS) resection is widely spreading. The procedure is usually performed simultaneously to tumor resection with a translabyrinthine approach. To ensure the best device function, assessing the integrity of the cochlear nerve is of primary importance.

METHODS

A narrative review of the literature on the present topic was carried out up to June 2022. Finally, nine studies were considered.

RESULTS

Electrically evoked auditory brainstem responses (eABR) is the most widely used method of intraoperative monitoring of cochlear nerve (CN) during VS resection, although its limits are known. It can be assessed through the CI electrode array or through an intracochlear test electrode (ITE). Variations of the graph are evaluated during the surgical procedure, in particular the wave V amplitude and latency. As tumor dissection progresses, the parameters may change, informing of the CN status, and the surgical procedure may be modulated.

CONCLUSION

An eABR positive result seems to be reliably correlated with a good CI outcome in those cases in which a clear wave V is recorded before and after tumor removal. On the contrary, in those cases in which the eABR is lost or altered during the surgical procedure, the positioning of a CI is still debatable.

Twelve-Month Outcomes of Simultaneous Translabyrinthine Resection and Cochlear Implantation

OBJECTIVE

Audiometric outcomes at 12 months following simultaneous translabyrinthine (TL) resection of vestibular schwannoma (VS) and cochlear implantation (CI).

STUDY DESIGN

Prospective cohort study.

SETTING

Tertiary referral center.

METHODS

Adult patients undergoing TL resection of sporadic, unilateral VS ≤ 2 cm were prospectively enrolled. Preoperative testing included binaural AZBio in noise and quiet and unilateral Consonant-Nucleus-Consonant (CNC). Tinnitus Handicap Index (THI) and Speech, Spatial, and Qualities of Hearing (SSQ) questionnaires were also completed. Patients underwent TL resection with simultaneous CI. The preoperative test battery was repeated at 1, 3, 6, and 12 months after activation. Statistical analysis was performed to characterize short-term outcomes (preoperative to 3 months), longer-term outcomes (3-12 months), and overall changes during the preoperative to 12-month period.

RESULTS

AZBio, CNC, and THI improved at 3 months with no significant changes thereafter and showed durable improvement at 12 months compared to preoperative testing. While SSQ did not improve at 12 months, a subset of patients showed either recovery or improvement of SSQ-spatial subscores. Patients with cerebellopontine angle tumors had poorer performance, although the impact of tumor size and location could not be deduced based on the small sample size.

CONCLUSION

Patients undergoing simultaneous CI and TL resection of VS had durable improvements in speech perception and tinnitus severity 12 months following surgery. Subjective improvements in localization were not observed. Additional studies are needed to determine which VS patients are optimal candidates for CI.

Cochlear implantation: an effective modality for hearing restoration following vestibular schwannoma resection

PURPOSE OF REVIEW

Preservation of hearing is one of the tenets of vestibular schwannoma management. In recent years, cochlear implants have been employed with increasing use in patients who have suffered profound sensorineural hearing loss due to the natural history of vestibular schwannoma or due to injury to neurovascular anatomy at time of surgical resection.

RECENT FINDINGS

Cochlear implantation has been found to be an effective modality for hearing restoration following vestibular schwannoma. Simultaneous cochlear implantation has been employed by an increased number of centers around the world and has been shown to provide restoration of open set speech perception and return of binaural hearing. Ongoing use of electrically evoked auditory brainstem response (ABR) has improved our detection of viable cochlear nerves and provided insight into those who would benefit from this procedure. Finally, minimally invasive approaches to the internal auditory canal and intralabyrinthine tumors have been described. These methods frequently employ simultaneous cochlear implantation and have emphasized that hearing preservation remains possible with surgical excision despite the location of the tumor.

SUMMARY

Cochlear implantation is an effective modality for hearing restoration following vestibular schwannoma excision.

Intraoperative Use of Electrical Stapedius Reflex Testing for Cochlear Nerve Monitoring During Simultaneous Translabyrinthine Resection of Vestibular Schwannoma and Cochlear Implantation

OBJECTIVE

To report the novel use of intraoperative electrically evoked stapedial reflex (eSR) for cochlear nerve monitoring during simultaneous translabyrinthine resection of vestibular schwannoma (VS) and cochlear implantation.

STUDY DESIGN

Clinical capsule report with video demonstration.

SETTING

Tertiary academic referral center.

PATIENT

A 58-year-old female presented with a small right intracanalicular VS with associated asymmetrical right moderate to severe sensorineural hearing loss, poor word recognition, tinnitus, and disequilibrium. Based on patient symptomatology and goals, simultaneous CI with translabyrinthine resection of the VS was performed.

INTERVENTION

Cochlear implantation before the tumor was resected facilitated intraoperative eSRs by delivering repeated single-electrode stimulations through the cochlear implant (CI) electrode during tumor resection. A pulse duration of 50-us and a current amplitude of 200-CL or 648-us was used to elicit eSRs visible through the facial recess. Intraoperative eSR was monitored in conjunction with electrically evoked compound action potentials via neural response telemetry and electrical auditory brainstem response.

RESULTS

Despite the transient evoked compound action potentials amplitude and electrical auditory brainstem response latency changes, the visually observed eSR was preserved and remained robust throughout tumor dissection, indicating an intact cochlear nerve. Four weeks postoperatively, the patient exhibited open-set speech capacity (14% CNC and 36% AzBio in quiet).

CONCLUSION

The current study demonstrates the feasibility of using intraoperative eSR via a CI electrode to monitor cochlear nerve integrity during VS resection, which may indicate successful CI outcomes. These preliminary findings require further substantiation in a larger study.

Cochlear Implantation in Vestibular Schwannoma: A Systematic Literature Review

Objective  Ipsilateral cochlear implantation (CI) in vestibular schwannoma (VS) has been an emerging trend over the last two decades. We conducted the first systematic review of hearing outcomes comparing neurofibromatosis 2 (NF2) and sporadic VS undergoing CI. A comparison of the two populations and predictor of outcome was assessed. This is an update to a previously presented study. Data Sources  Systemic data searches were performed in PubMed NCBI and Scopus by an academic librarian. No restrictions based on the year of publication were used. Study Selection  Studies were selected if patients had a diagnosis of NF2 and a CI placed in the affected side with reports of hearing outcome. Two independent reviewers screened each abstract and full-text article. Data Extraction  Studies were extracted at the patient level, and the assessment of quality and bias was evaluated according to the National Institutes of Health Quality Assessment Tool. Main Outcome Measures  Outcome predictors were determined by using the chi-square test and Student's t -test. Results  Overall, most CI recipients functioned in the high-to-intermediate performer category for both sporadic and NF2-related VS. Median AzBio (Arizona Biomedical Institute Sentence Test) was 72% (interquartile range [IQR]: 50) in NF2 patients and 70% (IQR: 7.25) in sporadic patients. Larger tumor size predicted a poorer final audiometric outcome. Conclusions  Categorization of hearing outcome into superior performance and inferior performance based on sentence recognition revealed a generally good hearing outcome regardless of treatment or patient population. Select patients with sporadic and NF2 VS may benefit from CI.

Simultaneous Cochlear Implantation After Translabyrinthine Vestibular Schwannoma Resection: A Report of 41 Cases

OBJECTIVE

To study the auditory outcome of simultaneous translabyrinthine vestibular schwannoma (VS) resection and cochlear implantation (CI) after successful cochlear nerve preservation.

STUDY DESIGN

A retrospective case series and patient questionnaire.

SETTING

Quaternary referral center for skull base pathologies.

PATIENTS

Patients with small (<2 cm) sporadic or neurofibromatosis 2 related tumors were included in this study.

INTERVENTION

Vestibular schwannoma resection + simultaneous cochlear implantation.

MAIN OUTCOME MEASURE

Audiological performance postimplantation and perceived patients' benefits.

RESULTS

Forty-one patients were included. Thirty-three were sporadic VS and eight were neurofibromatosis 2. Auditory perception postimplantation was achieved in 33 patients (80.5%). At the last follow-up, 20 patients (48.8%) were users and 21 (51.2%) were nonusers. In the users' group, and after 1 year of implant activation, vowel identification was 75.3%, disyllabic word recognition 54%, sentence recognition 60.7%, and common phrase comprehension 61%, whereas in the nonusers' group and after 1 year of implant activation, vowel identification was 22.9%, disyllabic word recognition 14.8%, sentence recognition 15.3%, and common phrase comprehension 14%. Sixteen users were classified into 10 high performers, three intermediate performers, and three poor performers. In the user' group, the mean postimplantation pure tone average was 63.4 dB and the mean speech discrimination score was 63.7%.

CONCLUSIONS

Simultaneous CI and VS resection is a viable option with many patients achieving auditory perception and nearly half the patients are CI users at long follow-up.

Intraoperative Cochlear Nerve Monitoring for Vestibular Schwannoma Resection and Simultaneous Cochlear Implantation in Neurofibromatosis Type 2: A Case Series

BACKGROUND

Neurofibromatosis type 2 (NF2) often results in profound hearing loss and cochlear implantation is an emerging hearing rehabilitation option. However, cochlear implant (CI) outcomes in this population vary, and intraoperative monitoring to predict cochlear nerve viability and subsequent outcomes is not well-established.

OBJECTIVE

To review the use of intraoperative electrically evoked cochlear nerve monitoring in patients with NF2 simultaneous translabyrinthine (TL) vestibular schwannoma (VS) resection and cochlear implantation.

METHODS

A retrospective review was performed of 3 patients with NF2 that underwent simultaneous TL VS resection and cochlear implantation with electrical auditory brainstem response (eABR) measured throughout tumor resection. Patient demographics, preoperative assessments, surgical procedures, and outcomes were reviewed.

RESULTS

Patients 1 and 3 had a reliable eABR throughout tumor removal. Patient 2 had eABR pretumor removal, but post-tumor removal eABR presence could not be reliably determined because of electrical artifact interference. All patients achieved auditory percepts upon CI activation. Patients 1 and 2 experienced a decline in CI performance after 1 yr and after 3 mo, respectively. Patient 3 continues to perform well at 9 mo. Patients 2 and 3 are daily users of their CI.

CONCLUSION

Cochlear implantation is attainable in cases of NF2-associated VS resection. Intraoperative eABR may facilitate cochlear nerve preservation during tumor removal, though more data and long-term outcomes are needed to refine eABR methodology and predictive value for this population.

Early Outcomes of Simultaneous Translabyrinthine Resection and Cochlear Implantation

OBJECTIVES/HYPOTHESIS

Hearing rehabilitation after translabyrinthine resection of a vestibular schwannoma (VS) has largely been based on the transfer of acoustic stimulus to the contralateral ear, typically through a contralateral routing of signal hearing aid or bone-anchored hearing aid (BAHA). Cochlear implant, either as a subsequent surgery or simultaneously, has become a more common treatment option; however, there is still relatively limited data available on its success. The purpose of this study is to evaluate the early outcomes of simultaneous cochlear implantation in patients with sporadic VS undergoing translabyrinthine resection.

STUDY DESIGN

Prospective, nonrandomized study.

METHODS

A prospective study of nonrandomized patients was completed at a tertiary care neurotology center. Audiologic outcomes, primarily based on AzBIO in quiet and background noise, as well as consonant-nucleus-consonant (CNC) testing of the affected ears were utilized. Tinnitus, dizziness, and spatial hearing questionnaries were also completed. Audiologic outcomes and questionnaires were compared between the pre- and postoperative groups.

RESULTS

Ten patients were included in the study with 3 month follow-up data. There was statistically significant improvement in AzBO with +10 and +5 signal to noise ratio and in quiet, as well as in CNC testing (P < .05). There was a significant improvement in Tinnitus Handicap Inventory between the two groups.

CONCLUSIONS

Simultaneous cochlear implantation is a viable treatment for hearing loss after translabyrinthine approach to VS. These patients have improved hearing in background noise and tinnitus compared to their preoperative state. Further prognostic data are required to determine which patients are the best candidates.

LEVEL OF EVIDENCE

4 Laryngoscope, 131:E2312-E2317, 2021.

Monitoring Cochlear Nerve Integrity During Vestibular Schwannoma Microsurgery in Real-Time Using Cochlear Implant Evoked Auditory Brainstem Response and Streaming Neural Response Imaging

OBJECTIVE

Intraoperative far-field auditory brainstem response (ABR) and direct cochlear nerve action potential monitoring using neural response imaging (NRI) are techniques for monitoring the cochlear nerve during vestibular schwannoma (VS) surgery. A new paradigm has developed where the cochlear nerve is anatomically preserved during tumor removal to facilitate cochlear implantation in select circumstances. This report describes the use of an unmodified commercial cochlear implant (CI) to elicit electrically-evoked direct cochlear nerve and far-field ABR monitoring to evaluate the status of the cochlear nerve during tumor resection in real time.

PATIENTS

Adult female with unilateral, sporadic VS.

INTERVENTION(S)

Cochlear implantation followed by translabyrinthine resection of VS in single operation.

MAIN OUTCOME MEASURES

During tumor resection intra-cochlear electrodes were used to deliver electrical stimulation and measure NRI or the cochlear nerve action potential. Electrically-evoked ABR (eABR) was measured using surface electrodes and wave V was monitored (far-field ABR) during surgery.

RESULTS

A 61-year-old female was evaluated for a unilateral, enlarging intracanalicular VS with asymmetric SNHL. The patient opted for microsurgery and due to her bilateral hearing loss was a candidate for CI. Cochlear implantation with an unmodified, commercially available lateral wall electrode was performed. The remainder of the approach and tumor resection was performed under continuous eABR and NRI monitoring. Gross total resection was achieved with intact eABR and NRI at the conclusion of the case. Changes in ABR and NRI consistently recovered after modifying dissection strategy. The patient reported auditory percepts with her cochlear implant postoperatively.

CONCLUSIONS

This report demonstrates the feasibility of using real-time NRI and eABR with a CI to facilitate preservation of the cochlear nerve during VS microsurgery. Using this method to mitigate cochlear nerve trauma during microsurgery may preserve the option of CI for hearing rehabilitation.