Cochlear implant outcomes associated with different treatments of vestibular schwannoma

Introduction

Modern vestibular schwannoma (VS) management employs one of three strategies: observation with serial imaging; stereotactic radiosurgery (SRS); and vestibular schwannoma microsurgical resection (VSMR) (1). Treatment is necessitated when a phase of growth is observed or complications arise and considers both patient and disease factors. Hearing rehabilitation post treatment is important, and largely depends on the size of the VS, symptoms and treatment modality utilised. Importantly, a key consideration is whether the cochlear nerve has been preserved and remains functional. In the majority of patients, VS is unilateral and these patients may lose the benefits of binaural hearing. Only cochlear implantation (CI) allows for the reestablishment of these binaural conditions and has become increasingly utilised in these cases. Neurofibromatosis type 2 (NF2) presents a different issue, as this cohort usually develop bilateral VS (2).

SRS, VSMR and observation with serial imaging of the tumour, all provide the opportunity to preserve the cochlear nerve and so allow for CI. The use of SRS has become more widespread and generally patients with tumours smaller than 25 mm in maximum diameter are potential candidates (1,3). A benefit of SRS is the structural preservation the cochlear nerve, with CI post SRS being performed either immediately, when hearing has been compromised by the disease or treatment or sequentially, for those that lose hearing over time (4,5). VSMR on the other hand places the integrity of the cochlear nerve at risk, but when the cochlear nerve can be preserved, CI is possible. This can be performed as a staged procedure or simultaneously with VSMR. The concurrent surgical paradigm has been referred to in the literature as simultaneous CI with removal of acoustic neuroma (SCIRAN) (6).

Even when the cochlear nerve is preserved surgery may impair neural function to a greater degree than radiosurgery or observation (5). Factors such as mechanical trauma thermal damage or microvascular infarction may play a role (3,7).

The results of CI following both SRS and VSMR have been detailed by several authors with varying success (4-14). The aim of this study was to review the outcomes of patients with VS who were planned for CI, utilising different treatment modalities for the VS (SRS, SCIRAN, observation) from a single program by two surgeons. This information is useful for counselling patients as they consider their treatment options for VS and hearing support.

Methods

A retrospective review of the NextSense (Australia) CI databases was performed. Patients with VS treated by two senior surgeons (C.S.B., R.E.), who underwent ipsilateral CI following observation with serial imaging or SRS as well as those who were evaluated for planned SCIRAN between 2000 and 2024 were included. Demographic data including: gender, age at CI, laterality of disease and year of CI surgery was obtained. Characteristics of patients VS were also recorded, specifically; whether the disease was sporadic or associated with NF2 (diagnosis documented in patient’s medical record), tumour size and the year in which the tumour was treated. The study was conducted in accordance with the Declaration of Helsinki and its subsequent amendments. Ethics approval for the retrospective study was obtained (Sydney Children’s Hospital Network Human Research Ethics Committee, Reference: 2021/ETH00161). Patient confidentiality was maintained by anonymizing data, and individual consent was waived for this retrospective analysis. The study is reported according to the STROBE reporting guidelines (available at https://www.theajo.com/article/view/10.21037/ajo-25-5/rc).

Treatment

Patients with VS who underwent SRS or observation, all underwent CI surgery performed by a single surgeon (C.S.B.). Patients who were considered for SCIRAN all underwent a translabyrinthine VSMR performed by a single surgeon (R.E.).

Pre-CI and post-CI evaluation

Pre-CI evaluation and hearing assessment included pure tone audiometry (PTA), four frequency average (4FAPTA), speech perception including, City University of New York (CUNY) Sentences, Bamford-Kowal-Bench (BKB) sentence testing, speech reception threshold (SRT) or CUNY in noise (+10 dB) and consonant-nucleus-consonant (CNC) word scores. Similar post-CI measures were also gathered at three, six- and 12-month post CI. Due to some missing data, the best scores during this 12-month period were utilised for analysis. Time to CI for those treated with SRS was recorded (months).

Patient outcomes including CI user status

CI user status as user and non-user status was recorded, including patients who where considered for SCIRAN but unable to undergo CI due to cochlear nerve damage, along with implanted patients that did not use their CI. A CI user was defined as a patient that used their implant for the purpose of hearing. Patients were also stratified into functional performance groups based on open set speech perception (OSP) scores [low (0–33%), intermediate (34–66%) and high (67–100%)] (8,11,15).

Statistical analysis

Descriptive statistics, t-test (tumour size between the two main cohorts (SRS and SCIRAN); speech perception outcomes) and Fisher’s exact test (CI users) were performed using Statistical Package for the Social Sciences software (IBM SPSS Statistics for Mac, version 30, IBM Corp., Armonk, NY, USA) to define and compare differences between treatment groups.

Results

Patient, tumour and disease characteristics

Forty-four patients were identified with VS. Demographic and tumour related data are recorded in Table 1. There was no statistically significant difference between the tumour sizes of the two cohorts, SRS and planned SCIRAN (P=0.33, 95% confidence interval: −6.02 to 9.43).

Treatment groups

Six patients underwent SRS and ipsilateral CI. One patient who underwent observation without tumour treatment received ipsilateral CI. Of the 37 patients planned for SCIRAN, 26 (70.2%) were able to proceed to CI at the time of VSMR. In 11 patients CI surgery was abandoned intraoperatively due to loss of the cochlear nerve and/or loss of auditory brainstem responses during surgery. Of the three patients with NF2, one patient (2.3%) underwent implantation without treatment (only hearing ear, VS not growing) and two underwent SCIRAN. Details of the three patients with NF2 included in this study are included in Table 2.

Preoperative hearing

Using 4FAPTA, the mean preoperative hearing level across all study patients, in the ipsilateral ear was noted to be 60.2 [range, 13.8–120, standard deviation (SD) 29.44] dB and 24.6 dB in the contralateral ear (range, 3.8–120, SD 27.16) dB. Patients who underwent SRS and those who were candidates for SCIRAN had a mean preimplantation 4FAPTA of 82.33 (range, 68–103, SD 12.01) and 54.43 (range, 13.8–120, SD 29.48) dB, respectively.

Postoperative hearing

Cochlear implant user

Twenty-one (47.7%) of the 44 patients were CI users. All SRS patients (n=6) and the one patient who received no treatment were all CI users. Of the potential 37 patients for SCIRAN, 26 (70.2%) were implanted. Of these, 14 (37.8%) were CI users. CI user stats by treatment group is shown in Figure 1. Using Fishers exact test, a significant difference in CI user status (P=0.030, odds ratio 2.64, 95% confidence interval: 1.75–3.99) was noted between the SRS and SCIRAN groups.

Figure 1 CI user status by treatment group. CI, cochlear implantation; SCIRAN, simultaneous cochlear implantation at the time of removal of acoustic neuroma; SRS, stereotactic radiosurgery.

Tumour size did not significantly influence successful cochlear implant outcomes in the planned SCIRAN group.

Two of the three NF2 patients were CI users (one no treatment and one SCIRAN).

Speech perception

Of the 21 CI users, the mean best CUNY and CNC scores were 82.2% (range, 45–100%, SD 23.73) and 37.7% (range, 4–86%, SD 24.79) respectively. When the two cohorts (SRS and SCIRAN) were examined separately, SRS patients had a mean best CUNY sentences of 86.4% (range, 62–99%, SD 14.54) and a mean best CNC words score of 59.2% (range, 36–72%, SD 15.66). One SRS patient has not yet had the three-month post-CI testing, all other implanted patients that received SRS were classified as high performers. The 14 CI users in the SCIRAN group had mean CUNY sentences and CNC word scores of 79.6% (range, 45–100%, SD 26.97) and 28.5% (range, 4–86%, SD 23.62) respectively (Figure 2). Twelve (85.7%) were classified as higher performers. One patient underwent unilateral implantation without treatment and was a high performer with best CUNY and CNC scores of 97% and 40% respectively.

Figure 2 Distribution of CUNY scores for cochlear implant users based on treatment modality. CUNY, City University of New York; SCIRAN, simultaneous cochlear implantation at the time of removal of acoustic neuroma.

In patients who achieved OSP with CI, independent of treatment modality, there was no significant difference between the mean CUNY scores (P=0.238, 95% confidence interval: −16.12 to 33.16). The patient that underwent implantation without treatment and was undergoing observation of their tumour, had best CUNY and CNC scores of 97% and 40% respectively. For patients who obtained OSP, there was no statistically significant difference in speech perception performance group (using Fisher’s exact test) between those treated with SRS and SCIRAN (P=0.544).

Time to implantation

All patients treated with SRS were implanted in a delayed fashion with a mean time to CI of 69.5 (range, 22–146, SD 50.63) months. By definition, all SCIRAN patients were implanted at the time of surgery without delay.

Discussion

This is one of the largest studies in the literature to compare CI outcomes for VS patients treated with three management options: observation with serial imaging; SRS; and SCIRAN. Figure 1 shows that SRS patients had significantly higher CI usage than those planned for SCIRAN. All SRS (6/6, 100%) and observation (1/1, 100%) patients were able to obtain excellent speech perception outcomes and were classified as high performers with the CI. Contrastingly, only 37.8% of patients planned for SCIRAN were CI users, of which 12/14 (85.7%) were high performers. When considering patients who were successfully implanted and achieved OSP, our study showed, that there was no significant difference in CUNY and CNC word scores between patients treated with SRS or SCIRAN. These outcomes are useful for clinicians and patients and importantly, highlight the uncertainty surrounding the possibility of successful CI and the chance of proceeding to OSP following SCIRAN. This information is crucial when counselling between different treatment strategies for VS.

Hearing rehabilitation following the treatment of VS is important. CI gives patients with significant hearing loss the ability to utilise binaural hearing and is indicated when the cochlear nerve is intact and speech perception is poor with conventional hearing aids. Both SRS and VMSR have the capacity to preserve the cochlear nerve and CI surgery has been successful following both treatments (4-16). Our results show that CI user status and speech perception outcomes are more reliable in those who undergo SRS. However, patient’s preference and other factors do influence VS management, and it is crucial to appreciate that the management of larger tumours necessitates surgery.

CI outcomes following SRS showed the implant enabled useful hearing in all patients and gave a reliable outcome of CI user status. Our results are similar to other published studies (4,9,12,16). Young et al. (12) performed a meta-analysis that reported on 17 SRS case series with a total of 57 patients (59 ears). The majority of patients had NF2 (n=44, 74.6%), the remainder had sporadic VS (n=15, 25.4%). Numerous word and sentence scores were employed across the studies with only thirty-eight ears (64%) being able to be assessed. For 94.7% of patients hearing outcomes were improved in at least one hearing measure. Post implantation hearing outcomes were determined for 53 ears (89.8%), with the majority achieving OSP (n=42, 79.2%). These results are similar to our SRS cohort in which all six patients obtained OSP. Similarly, Tian et al. (9) performed a metanalysis including 14 case series, incorporating 33 patients. Numerous outcome measures were used post implantation, they found that the majority of irradiated patients improved their hearing status after CI. Specifically, six patients were assessed post implantation using CUNY sentences and were found to have an average score of 78%, this finding is similar in our study of 86.4%. Tian et al. also noted that despite the wide variability in results, 20 of 21 patients for which subjective hearing data was available, reported improvement in hearing, ranging from environmental sound awareness to telephone use and enjoyment of music.

Timing of CI post SRS varies and requires patient assessment and fulfillment of CI candidacy criteria. Patel et al. reviewed 17 patients at their institution and found that of those who underwent a CI post SRS: three (18%) had same day treatment and CI; one (6%) underwent CI surgery the following day. The remaining 13, underwent CI between 0 and 236 months post-SRS with a mean of 3 months (4). In our study, all patients were implanted in a delayed fashion with a mean time from SRS to CI of 69.5 (range, 22–146) months. Greater delays may be associated with variability in cochlear nerve function, though if there are detectable and useful auditory thresholds, then it can be assumed that the function of the cochlear nerve remains intact (4). This was certainly true of our cohort, in which hearing outcomes were excellent, despite the variable time between SRS and CI.

Trotter and Briggs (13) described their experience with three NF2 patients who underwent CI following SRS for VS. All three were daily CI users and an improvement in OSP was noted two of the three cases. The third case was unable to complete testing for unrelated reasons but reported a dramatic improvement in communication and is a daily implant user. Three patients in our study with NF2 were reported: one underwent unilateral implantation after established VS quiescence during observation and serial imaging, and two underwent SCIRAN. The patient undergoing observation for the VS had excellent post-CI speech perception, along with one NF2 patient undergoing SCIRAN. The other SCIRAN patient obtained no benefit, with CUNY and CNC scores of 0, and elected to have their device explanted. Table 2 shows that his patient had a large tumour (35 mm). However, both Carlson et al. (11) in a systematic review and Grenier et al. (17) found no association between tumour size and OSP capacity in NF2 patients.

The single patient in our series undergoing observation of their VS, with no treatment on the ipsilateral side prior to CI, had an excellent CI outcome and was a high performer regarding speech perception. This outcome is consistent with the findings of Mukherjee et al. (14) who reported on five VS patients (2 sporadic, 3 NF2) who receive no prior treatment prior to CI. All obtained OSP and experienced marked improvement in their BKB and CUNY scores. Similarly, Borsetto et al. (16), in their systematic review, examined 50 patients across 12 studies treated with observation or SRS for VS. They determined that CI sentence outcomes between SRS and observation groups were similar, with 64% and 60% of patients in the SRS and observation groups achieving OSP respectively. These findings echo our own, however our mean outcome (for SRS and the observed patient) were all in the high performer range rather than intermediate. Borsetto’s study suggest that in patients with truly stable tumours that show little to no growth on serial scanning, that CI without treatment may be preferential from an audiological perspective—consistent with the outcome of the patient who was under surveillance in our series. Importantly, this approach also does not preclude treatment by either SRS or microsurgery in the future, should the need arise.

Like SRS, SCIRAN has been shown to be an effective means of hearing rehabilitation following VSMR (6) for both extra and intracochlear schwannomas (18). Gadenstaetter et al. (19) prospectively examined 25 patients undergoing VSMR who were candidates for SCIRAN. Only 15 (60%) had positive cochlear nerve responses allowing for CI. Of these 15, 14 (93.3%) were regular implant users. Overall, the implanted patients showed improvement in WRS and four frequency PTA. In our study, 70.2% of patients planned for possible SCIRAN were able to proceed at the time of surgery, with the remainder being abandoned due to loss of the cochlear nerve or poor intraoperative CI electrically evoked auditory brainstem response (eABR) results. Despite, the majority of patients proceeding to CI, these data highlight the potential uncertainty VSMR poses to CI. Additionally, most of the patients planned for SCIRAN in our series had tumours that, based on size, would have been candidates for SRS, potentially allowing for staged implantation. While there are numerous factors that go into the shared decision making with patients, the uncertain potential to be able to meaningfully implant these patients should be reinforced during preoperative counselling.

Following successful SCIRAN good speech outcomes have been reported. In a study of early outcomes following SCIRAN, Conway et al. (8) showed a statistically significant improvement in the +10 and +5 dB signal to noise ratio, and in quiet AzBIO as well as CNC testing compared to the preoperative testing (P<0.05). Similarly, Sana et al. showed that patients who were implanted had improved sentence scores at 12 months post implantation and better sound localisation in the aided setting compared with the unaided setting (20). These findings are echoed in the current study, in which the 14 SCIRAN patients who were CI users had a mean CUNY sentence score of 79.6%, with twelve (85.7%) classified as high performers.

Patient selection for SCIRAN can be difficult and is critical in those with smaller tumours who may also be candidates for SRS. To determine the factors associated with better outcomes post SCIRAN, West et al. (21) performed a systematic review across 29 studies with 86 patients. Patients were categorised into high or low performers based on post-operative speech outcomes. High performance status was associated with tumour size, with a mean of tumour size of 7 mm being associated with better outcomes and a mean size of 10 mm being associated with low performance. Interestingly, in our series, SCIRAN patients that were high performers had a mean tumour size of 9.70 mm. West et al. also showed that patients with preoperative American Academy of Otolaryngology – Head and Neck Surgery (AAO-HNS) hearing class A and B were more likely to fall into the high performance category than those with class C and D results preoperatively. They also showed no significant differences between NF2 and sporadic cases. During VSMR eABR can be used to predict the potential success of SCIRAN (19,22), however, West et al. found the use of eABR did not affect outcomes (21).

When comparing outcomes of CI associated with different treatments for VS, Dornhoffer et al. (5) conducted a retrospective review of 49 patients (52 ears). Of these, 19 had microsurgery [9 (47%) underwent SCIRAN and 10 (53%) underwent subsequent CI], 22 radiotherapy and 11 were observed. They found a significant difference in speech perception outcomes, with 53% of the microsurgical cohort the 100% SRS and observation cohorts obtaining OSP. This finding is similar to the current study in which 54% of patients who underwent successful SCIRAN were cochlear implant users. Furthermore, they suggested that SCIRAN may be a superior strategy to delayed CI due to better speech perception outcomes between these microsurgical options (5).

The limitations of our study include the small number of SRS and observation cases, however we highlight a large SCIRAN cohort. Not all patients had speech perception testing at all timepoints necessitating using the best result available. Having said that, our study shows clear outcomes for different cohorts from a single CI program.

Conclusions

CI following the treatment of VS may provide useful hearing to the affected ear. While SRS, observation and VSMR all potentially allow for CI post treatment, patients treated with radiotherapy had more reliable outcomes with better CI user outcomes and OSP at higher rates than those who were planned for SCIRAN. The patient who was being observed also achieved excellent speech perception outcomes with the CI. However, when open set speech can be established following SCIRAN, speech perception results can be equivalent to patients treated with radiotherapy. This information is important for counselling of patients with regards to hearing outcomes when selecting between the different treatment options for VS.

Acknowledgments

None

Footnote

Reporting Checklist: The authors have completed the STROBE reporting checklist. Available at https://www.theajo.com/article/view/10.21037/ajo-25-5/rc

Data Sharing Statement: Available at https://www.theajo.com/article/view/10.21037/ajo-25-5/dss

Peer Review File: Available at https://www.theajo.com/article/view/10.21037/ajo-25-5/prf

Funding: None.

Conflicts of Interest: All authors have completed the ICMJE uniform disclosure form (available at https://www.theajo.com/article/view/10.21037/ajo-25-5/coif). The authors have no conflicts of interest to declare.

Ethical Statement: The authors are accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved. The study was conducted in accordance with the Declaration of Helsinki and its subsequent amendments. Ethics approval for the retrospective study was obtained (Sydney Children’s Hospital Network Human Research Ethics Committee, Reference: 2021/ETH00161). Patient confidentiality was maintained by anonymizing data, and individual consent was waived for this retrospective analysis.

Open Access Statement: This is an Open Access article distributed in accordance with the Creative Commons Attribution-NonCommercial-NoDerivs 4.0 International License (CC BY-NC-ND 4.0), which permits the non-commercial replication and distribution of the article with the strict proviso that no changes or edits are made and the original work is properly cited (including links to both the formal publication through the relevant DOI and the license). See: https://creativecommons.org/licenses/by-nc-nd/4.0/.

References

1. Carlson ML, Link MJ. Vestibular Schwannomas. N Engl J Med 2021;384:1335-48. [Crossref] [PubMed]
2. Evans DG. Neurofibromatosis type 2 (NF2): a clinical and molecular review. Orphanet J Rare Dis 2009;4:16. [Crossref] [PubMed]
3. Neff BA, Wiet RM, Lasak JM, et al. Cochlear implantation in the neurofibromatosis type 2 patient: long-term follow-up. Laryngoscope 2007;117:1069-72. [Crossref] [PubMed]
4. Patel NS, Carlson ML, Link MJ, et al. Cochlear implantation after radiosurgery for vestibular schwannoma. J Neurosurg 2021;135:126-35. [Crossref] [PubMed]
5. Dornhoffer JR, Haller T, Lohse CM, et al. Cochlear Implant Outcomes between Patients with Sporadic and Neurofibromatosis Type 2-Associated Vestibular Schwannoma. Otol Neurotol 2023;44:791-7. [Crossref] [PubMed]
6. Roberts S, Levin B, Sanli H, et al. Simultaneous cochlear implantation and removal of acoustic neuroma: implications for hearing. J Laryngol Otol 2020;134:519-25. [Crossref] [PubMed]
7. Sorrentino F, Tealdo G, Cazzador D, et al. Cochlear implant in vestibular schwannomas: long-term outcomes and critical analysis of indications. Eur Arch Otorhinolaryngol 2022;279:4709-18. [Crossref] [PubMed]
8. Conway RM, Tu NC, Sioshansi PC, et al. Early Outcomes of Simultaneous Translabyrinthine Resection and Cochlear Implantation. Laryngoscope 2021;131:E2312-7. [Crossref] [PubMed]
9. Tian L, West N, Cayé-Thomasen P. Cochlear Implantation After Radiotherapy of Vestibular Schwannomas. J Int Adv Otol 2021;17:452-60. [Crossref] [PubMed]
10. Dahm V, Auinger AB, Honeder C, et al. Simultaneous Vestibular Schwannoma Resection and Cochlear Implantation Using Electrically Evoked Auditory Brainstem Response Audiometry for Decision-making. Otol Neurotol 2020;41:1266-73. [Crossref] [PubMed]
11. Carlson ML, Breen JT, Driscoll CL, et al. Cochlear implantation in patients with neurofibromatosis type 2: variables affecting auditory performance. Otol Neurotol 2012;33:853-62. [Crossref] [PubMed]
12. Young K, Grewal MR, Diaz RC, et al. Cochlear Implantation after Stereotactic Radiosurgery for Vestibular Schwannoma: Initial Hearing Improvement and Longevity of Hearing Restoration. Otol Neurotol 2023;44:201-8. [Crossref] [PubMed]
13. Trotter MI, Briggs RJ. Cochlear implantation in neurofibromatosis type 2 after radiation therapy. Otol Neurotol 2010;31:216-9. [Crossref] [PubMed]
14. Mukherjee P, Ramsden JD, Donnelly N, et al. Cochlear implants to treat deafness caused by vestibular schwannomas. Otol Neurotol 2013;34:1291-8. [Crossref] [PubMed]
15. DeHart AN, Broaddus WC, Coelho DH. Translabyrinthine vestibular schwannoma resection with simultaneous cochlear implantation. Cochlear Implants Int 2017;18:278-84. [Crossref] [PubMed]
16. Borsetto D, Hammond-Kenny A, Tysome JR, et al. Hearing rehabilitation outcomes in cochlear implant recipients with vestibular schwannoma in observation or radiotherapy groups: A systematic review. Cochlear Implants Int 2020;21:9-17. [Crossref] [PubMed]
17. Grenier B, Mosnier I, Ferrary E, et al. Cochlear Implantation in Neurofibromatosis Type 2-Related Schwannomatosis: Long-Term Hearing Outcomes. Otolaryngol Head Neck Surg 2024;171:218-30. [Crossref] [PubMed]
18. Di Micco R, Salcher R, Lesinski-Schiedat A, et al. Long-Term Hearing Outcome of Cochlear Implantation in Cases with Simultaneous Intracochlear Schwannoma Resection. Laryngoscope 2024;134:1854-60. [Crossref] [PubMed]
19. Gadenstaetter AJ, Auinger AB, Gerlitz M, et al. Functional Outcome After Simultaneous Vestibular Schwannoma Resection and Cochlear Implantation With Intraoperative Cochlear Nerve Monitoring. Otolaryngol Head Neck Surg 2023;168:1502-10. [Crossref] [PubMed]
20. Sanna M, Medina MD, Macak A, et al. Vestibular Schwannoma Resection with Ipsilateral Simultaneous Cochlear Implantation in Patients with Normal Contralateral Hearing. Audiol Neurootol 2016;21:286-95. [Crossref] [PubMed]
21. West N, Sass H, Cayé-Thomasen P. Sporadic and NF2-associated vestibular schwannoma surgery and simultaneous cochlear implantation: a comparative systematic review. Eur Arch Otorhinolaryngol 2020;277:333-42. [Crossref] [PubMed]
22. Dahm V, Gadenstaetter AJ, Arnoldner C. “To implant or not to implant”: electrically evoked auditory brainstem response audiometry for decision-making in vestibular schwannoma resection with CI. HNO 2025;73:22-8. [Crossref] [PubMed]