Cochlear implantation after radiosurgery for vestibular schwannoma

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  • 1 Department of Otolaryngology–Head and Neck Surgery, and
  • | 2 Department of Neurologic Surgery, Mayo Clinic, Rochester, Minnesota
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OBJECTIVE

The object of this study was to ascertain outcomes of cochlear implantation (CI) following stereotactic radiosurgery (SRS) for vestibular schwannoma (VS).

METHODS

The authors conducted a retrospective chart review of adult patients with VS treated with SRS who underwent CI between 1990 and 2019 at a single tertiary care referral center. Patient demographics, tumor features, treatment parameters, and pre- and postimplantation audiometric and clinical outcomes are presented.

RESULTS

Seventeen patients (18 ears) underwent SRS and ipsilateral CI during the study period. Thirteen patients (76%) had neurofibromatosis type 2 (NF2). Median age at SRS and CI were 44 and 48 years, respectively. Median time from SRS to CI was 60 days, but notably, 4 patients underwent SRS and CI within 1 day and 5 patients underwent CI more than 7 years after SRS. Median marginal dose was 13 Gy. Median treatment volume at the time of SRS was 1400 mm3 (range 84–6080 mm3, n = 15 patients). Median post-CI PTA was 28 dB HL, improved from 101 dB HL preoperatively (p < 0.001). Overall, 11 patients (12 ears) exhibited open-set speech understanding. Sentence testing was performed at a median of 10 months (range 1–143 months) post-CI. The median AzBio sentence score for patients with open-set speech understanding was 76% (range 19%–95%, n = 10 ears). Two ears exhibited Hearing in Noise Test (HINT) sentence scores of 49% and 95%, respectively. Four patients achieved environmental sound awareness without open-set speech recognition. Two had no detectable auditory percepts.

CONCLUSIONS

Most patients who underwent CI following SRS for VS enjoyed access to sound at near-normal levels, with the majority achieving good open-set speech understanding. Implantation can be performed immediately following SRS or in a delayed fashion, depending on hearing status as well as other factors. This strategy may be applied to cases of sporadic or NF2-associated VS.

ABBREVIATIONS

AAO-HNS = American Academy of Otolaryngology–Head and Neck Surgery; ABI = auditory brainstem implant; CI = cochlear implantation; CN = cranial nerve; CNC = consonant-nucleus-consonant; CPA = cerebellopontine angle; EPS = electrical promontory stimulation; ESA = environmental sound awareness; HINT = Hearing in Noise Test; IAC = internal auditory canal; NF2 = neurofibromatosis type 2; OSP = open-set speech perception; PTA = pure tone average; SRS = stereotactic radiosurgery; VS = vestibular schwannoma; WRS = word recognition score.

OBJECTIVE

The object of this study was to ascertain outcomes of cochlear implantation (CI) following stereotactic radiosurgery (SRS) for vestibular schwannoma (VS).

METHODS

The authors conducted a retrospective chart review of adult patients with VS treated with SRS who underwent CI between 1990 and 2019 at a single tertiary care referral center. Patient demographics, tumor features, treatment parameters, and pre- and postimplantation audiometric and clinical outcomes are presented.

RESULTS

Seventeen patients (18 ears) underwent SRS and ipsilateral CI during the study period. Thirteen patients (76%) had neurofibromatosis type 2 (NF2). Median age at SRS and CI were 44 and 48 years, respectively. Median time from SRS to CI was 60 days, but notably, 4 patients underwent SRS and CI within 1 day and 5 patients underwent CI more than 7 years after SRS. Median marginal dose was 13 Gy. Median treatment volume at the time of SRS was 1400 mm3 (range 84–6080 mm3, n = 15 patients). Median post-CI PTA was 28 dB HL, improved from 101 dB HL preoperatively (p < 0.001). Overall, 11 patients (12 ears) exhibited open-set speech understanding. Sentence testing was performed at a median of 10 months (range 1–143 months) post-CI. The median AzBio sentence score for patients with open-set speech understanding was 76% (range 19%–95%, n = 10 ears). Two ears exhibited Hearing in Noise Test (HINT) sentence scores of 49% and 95%, respectively. Four patients achieved environmental sound awareness without open-set speech recognition. Two had no detectable auditory percepts.

CONCLUSIONS

Most patients who underwent CI following SRS for VS enjoyed access to sound at near-normal levels, with the majority achieving good open-set speech understanding. Implantation can be performed immediately following SRS or in a delayed fashion, depending on hearing status as well as other factors. This strategy may be applied to cases of sporadic or NF2-associated VS.

ABBREVIATIONS

AAO-HNS = American Academy of Otolaryngology–Head and Neck Surgery; ABI = auditory brainstem implant; CI = cochlear implantation; CN = cranial nerve; CNC = consonant-nucleus-consonant; CPA = cerebellopontine angle; EPS = electrical promontory stimulation; ESA = environmental sound awareness; HINT = Hearing in Noise Test; IAC = internal auditory canal; NF2 = neurofibromatosis type 2; OSP = open-set speech perception; PTA = pure tone average; SRS = stereotactic radiosurgery; VS = vestibular schwannoma; WRS = word recognition score.

In Brief

In this study, patients with vestibular schwannoma underwent radiosurgery to treat the tumor and cochlear implantation for hearing rehabilitation in the ear affected by tumor. This study is important because it comprehensively reports the largest single-institution experience with these patients and, in doing so, offers evidence to support the use of this strategy in the nuanced management of patients with neurofibromatosis type 2–associated or sporadic vestibular schwannoma.

The optimal hearing rehabilitation strategy for patients with vestibular schwannoma (VS) remains largely undefined. In the current era, the decision to intervene when considering small- to medium-sized tumors is often largely dependent on hearing status and options for hearing rehabilitation after treatment. In patients who lose hearing as a result of the natural history or treatment of the tumor, options such as contralateral routing of signal (CROS) hearing aids or bone conduction hearing devices (BCHDs) can be offered. However, only a small proportion of patients with single-sided deafness pursue these options or endorse significant quality-of-life improvement with their use. Unfortunately, in this context, CROS hearing aids and BCHDs do not restore binaural hearing, which is a fundamental requirement for sound localization and enhanced speech understanding in noise.

While nearly all patients with VS demonstrate some degree of hearing loss, the subpopulation with neurofibromatosis type 2 (NF2) is more severely affected. In contrast to those with sporadic VS, patients with NF2-associated VS most commonly experience bilateral cochlear or retrocochlear hearing loss and often have threatened vision from posterior subcapsular lenticular opacities, meningiomas, hydrocephalus, or other intracranial tumors.1 Historically, the only available treatment option for rehabilitation of ipsilateral hearing loss caused by cerebellopontine angle (CPA) tumor(s) has been placement of an auditory brainstem implant (ABI). This technology generally provides patients with sound awareness but offers a wide range of outcomes in open-set speech perception (OSP)—the ability of a listener to repeat a word, phrase, or sentence without knowledge of available responses (i.e., speech in daily life).2

Unlike an ABI, which excites neurons in the dorsal cochlear nucleus, a cochlear implant employs electrical stimulation of the distal cochlear nerve to produce an auditory percept. The device consists of an external sound processor coupled to an internal receiver-stimulator device with a radiofrequency coil. The acoustic signal captured by the microphone in the sound processor is converted to an electrical one that is relayed to the spiral ganglion cells of the cochlear nerve by way of a multichannel electrode array. By taking advantage of the tonotopic organization of the cochlea (with low-frequency sound encoded in the apical region and high-frequency sound located in the basal region), cochlear implants are routinely capable of resolving a broad segment of the audible frequency spectrum in patients with advanced sensorineural hearing loss.

In order to utilize cochlear implantation (CI) as a hearing rehabilitation strategy, the cochlear nerve must not only be anatomically present but of adequate functional integrity to carry the electrical signal elicited by the device. This leaves three options for patients: 1) microsurgical resection with preservation of the cochlear nerve, 2) stereotactic radiosurgery (SRS) or radiotherapy, and 3) observation with serial imaging when clinically appropriate. While microsurgery offers the advantages associated with tumor removal, a challenging situation is presented when the cochlear nerve is anatomically intact, but the patient wakes up with profound hearing loss. Moreover, preservation of the cochlear nerve cannot be ensured in surgery for larger tumors. Electrical promontory stimulation (EPS) offers a noninvasive way of determining the integrity of the cochlear nerve and the central auditory pathway. Electrical stimulation of the cochlear nerve is elicited by a needle electrode placed on the surface of the cochlea. However, this technique is controversial, as some patients with good EPS responses do not benefit from CI and some with poor EPS responses achieve OSP with CI.3

Stereotactic radiosurgery offers a means of achieving tumor control and maintenance of an anatomically intact cochlear nerve regardless of tumor size. At most centers, tumors smaller than 25–30 mm in maximum CPA dimension or a volume less than 14,000 mm3 are potential candidates for SRS. At our center, SRS plus either immediate or delayed CI has become the treatment of choice for growing VSs in this size category in the majority of patients with NF2 as well as those with sporadic VS and threatened or reduced contralateral hearing. The feasibility of this approach has been demonstrated in prior case reports and small case series.

In this report, however, we present the largest single-center experience with CI after SRS for VS. The goal of this study was to use comprehensive pre- and postimplantation audiometry with speech perception testing (in some cases, with many years of follow-up) and patient-reported qualitative assessments of benefit in a population of NF2-associated and sporadic VSs to characterize outcomes of this tumor management and hearing rehabilitation strategy.

Methods

After obtaining Mayo Clinic Institutional Review Board approval, we conducted a retrospective review of all patients who had undergone CI after SRS for VS, either NF2 associated or sporadic, in the period from 1990 to 2019. Demographic data, such as patient age (at radiosurgery and at implantation), sex, ear with CI and treated with radiosurgery, etiology of VS (i.e., NF2 associated or sporadic), and tumor size and location (i.e., CPA or internal auditory canal [IAC] only), were obtained from the medical record. Radiosurgical treatment data, including marginal dose, maximum dose, treatment isodose line, and treatment volume, were obtained by review of operative notes and data maintained in a prospectively maintained database of all patients treated with SRS at our institution.

Stereotactic radiosurgery was performed in a single fraction delivered by the Leksell Gamma Knife unit (Elekta AB) utilizing, in succession, models U, B, C, and Perfexion, with patients under mild oral sedation and a local anesthetic for application of the stereotactic headframe. All tumors were targeted using axial post-Gd T1-weighted or spoiled gradient recalled (SPGR) MRI at a 1- or 3-mm slice thickness with sagittal and coronal reformats. Since 2005, all patients have undergone stereotactic temporal bone CT (1-mm slice thickness axial images) to better visualize inner ear structures and verify stereotactic accuracy. Dose planning was performed using the KULA dose-planning system until 1995 and then successive versions of GammaPlan (both Elekta AB). All procedures were performed on an outpatient basis.

Audiological data, including pure tone average (PTA), word recognition score (WRS), and hearing class, as well as tumor size were reported according to the American Academy of Otolaryngology–Head and Neck Surgery (AAO-HNS) guidelines.4 Pure tone average was defined as the average of hearing thresholds in decibel hearing level (dB HL) at 0.5, 1, 2, and 3 kHz, with appropriate substitution of the 2- and 4-kHz average if necessary.5 Serviceable hearing was defined as a PTA ≤ 50 dB HL and WRS ≥ 50% in accordance with AAO-HNS reporting guidelines. Word and sentence testing for CI candidacy and outcome evaluation included consonant-nucleus-consonant (CNC) word scores, AzBio sentences,6 and Hearing in Noise Test (HINT) sentences. Consonant-nucleus-consonant words are monosyllabic words administered in quiet. Scores are reported as word scores or phoneme scores, the latter of which accounts for errors in repeating distinct sounds, such as saying “bat” instead of “cat.” The AzBio sentences include 1000 sentences recorded from two female and two male talkers. Scores are calculated as the mean of the percent correct for each of the 20 sentences presented (calculated by dividing the number of words correct by the number of words presented).7 The HINT sentences similarly measure the ability of a listener to repeat sentences and can be administered in quiet or with noise from different directions; in the present study, the HINT was administered in quiet. Quantitative performance was grouped according to the method used by Carlson et al.8 In brief, using the highest score on open-set speech testing materials without lip reading or other visual cues, patients were grouped into three categories: 1) high performance (67%–100%), intermediate performance (34%–66%), and low performance (1%–33%). Qualitative outcome measures were 1) ability to attain OSP; 2) use of the device for environmental sound awareness (ESA) per patient reports of hearing sounds such as telephones, alarms, etc.; and 3) no response (NR).

Continuous features were summarized with medians and ranges; categorical features were summarized with frequency counts and percentages. The duration of audiometric follow-up was calculated from the date of CI to the most recent audiometric evaluation. Linear regression was utilized to assess correlation between continuous audiometric and outcome variables where appropriate. Statistical analyses were performed using JMP version 14.1 (SAS Institute). A p value < 0.05 was considered statistically significant.

A review of the available literature from 2006 to the present was conducted to place the results of this study in context. Features abstracted from available reports included number of patients, individual case number within the series, etiology of VS, tumor size, pre-CI performance, best PTA with CI, postimplantation performance scores, and outcome (OSP, ESA, or NR).

Results

A total of 17 patients (18 ears) underwent CI following SRS during the study period. Demographic data are reported in Table 1. All cochlear implants were standard contemporary multichannel devices including both straight and perimodiolar electrode arrays. No device failures occurred during the study period.

TABLE 1.

Summary of patient demographics, tumor characteristics, and radiosurgical treatment parameters

FeatureValue
No. of patients17
No. of ears (%)18 (100)
VS etiology, no. of ears (%)
 NF2-associated14 (78)
 Sporadic4 (22)
Median age at SRS in yrs (range)44 (16–69)
Median age at CI in yrs (range)48 (17–69)
Tumor location, no. of ears (%)
 CPA16 (89)
 IAC2 (11)
Median tumor size in mm (range)12.8 (4.7–18.4)
Time btwn SRS & CI
 Same-day SRS & CI, no. of patients (%)3 (18)
 Next-day CI, no. of patients (%)1 (6)
 Median no. of mos in remaining 13 patients (range)3 (0–236)
Radiosurgical treatment parameters
 Median marginal dose in Gy (range)13 (12–20)
 Median treatment isodose line in % (range)50 (40–50)
 Median treatment vol in mm3 (range)1400 (84–6080)
 No. of fractions1

Table 2 includes a summary of baseline audiometric and speech testing data at the time of SRS and implant evaluation. Of the 16 ears with available audiometric data at the time of SRS, 15 (94%) had AAO-HNS class C or D hearing. One patient (6%) had class A hearing at the time of SRS, but their hearing declined in function over the following 8 years prior to undergoing CI.

TABLE 2.

Baseline audiometric and speech testing data in ear to be implanted

FeatureMedian (range)
At SRS (16 ears)
 PTA in dB HL100 (23–120)
 WRS in %0 (0–100)
At implant evaluation (17 ears)
 PTA in dB HL101 (61–120)
 WRS in %0 (0–70)
 CNCw in %0 (0–32)
 AzBioq in %0 (0–36)

AzBioq = AzBio sentences in quiet; CNCw = CNC word score.

Outcomes

Audiometric and qualitative outcome data are outlined in Table 3. At the conclusion of the study period, 17 of 18 ears (94%) did not require additional treatment. Three ears (17%) have not had follow-up imaging after treatment. One patient experienced tumor growth and required microsurgery, explantation of the implant, and insertion of an ABI and, unfortunately, has lost their OSP ability.

TABLE 3.

Outcomes of CI in 18 ears

Case No.VS EtiologyTumor Size (mm)PTA w/ CI (dB HL)Marginal Dose* (Gy)CNCw (%)HINT (%)AzBioq (%)OutcomePerformance CategoryAudiometric FU (mos)Clinical Tumor Control
1Sporadic8.12812.595OSPHP1NA
2Sporadic10.1121371OSPHP7Y
3LNF217.429138062OSPHP12Y
3RNF217.7291281OSPHP15Y
4NF215.921140ESA3Y
5Sporadic4.719136466OSPIP5NA
6NF21513NB1Y
7NF214.5341404ESA44Y
8NF211.820157287OSPHP143Y
9NF213.1351395OSPHP23N
10NF212.83013.549OSPIP8Y
11NF2NA2620ESA10Y
12NF211.136124453OSPIP26Y
13NF212.313.5ESA65Y
14NF28.116NBNAY
15NF218.426138890OSPHP1NA
16NF27.220147491OSPHP71Y
17Sporadic17.94112.5244019OSPIP3Y

FU = follow-up; HP = high performer (67%–100% score); IP = intermediate performer (34%–66% score); NA = follow-up imaging after SRS not yet available; NB = no benefit.

Prescribed to 50% isodose line.

Patient experienced abrupt decline in CI function thought to be related to SRS.

Notably, 11 patients had OSP with their device. Among these patients, the median CNC word score was 72% (range 24%–88%) and median AzBio sentence score was 76% (range 19%–95%). Two patients with OSP had only HINT scores available for review and were 49% and 95%, respectively. Of the 4 patients with ESA only, median PTA was 26 dB HL (range 21–34 dB HL, n = 3 patients) with the CI, suggesting access to sound in the mild hearing loss range, significantly improved from preoperative levels (median 114 dB, p < 0.001). All but 1 patient in this group are daily cochlear implant users. The remaining patient experienced progressive decline in implant function and succumbed to complications of severe-phenotype NF2.

Linear regression analysis was performed to determine the correlation between tumor size and PTA with CI. A weak correlation between increasing tumor size and increasing PTA (one measure of access to sound with CI) was noted (r2 = 0.22), but this was not statistically significant (p = 0.09).

Notable Cases

Case 16

This patient was diagnosed with NF2 based on a right-sided inner ear schwannoma (intravestibular-cochlear type9) and a left-sided likely VS. She had progressive left-sided hearing loss with poor word understanding and long-standing right-sided profound hearing loss. Given its progressive growth, the left-sided tumor was treated with SRS followed by ipsilateral CI 12 days later. Figure 1 features imaging from the time of SRS and 6 years posttreatment demonstrating durable tumor control and adequate visualization despite a CI magnet artifact. Accompanying audiometric data at SRS and 6 years posttreatment are also shown. The patient has access to sound in the normal to near-normal range and exhibits word and sentence scores in the above-average range as compared to typical cochlear implant recipients.

FIG. 1.
FIG. 1.

Case 16. An NF2 patient with a right-sided intravestibular-cochlear schwannoma and left-sided VS had bilateral profound hearing loss at the time of SRS (A upper) and demonstrated tumor control 6 years after SRS and CI (B upper), normal to near-normal access to sound (A lower, audiometric data at SRS and 6 years posttreatment.), and above-average word and sentence scores (B lower). CL = CI-only thresholds for left-sided implant. Figure is available in color online only.

Case 17

This patient represents an outlier within this group and deserves mention. A patient with severe scleroderma (CREST syndrome) presented to our group with asymmetric advanced sensorineural hearing loss with poor word understanding. Preoperative MRI demonstrated a 1.8-cm left-sided VS. In an effort to maintain a functional cochlear nerve (which was believed to be unlikely if microsurgical tumor removal were pursued), SRS and CI were offered. A slim straight multichannel electrode was placed in the left side without complication approximately 1 month after SRS. At the 3-month programming visit, the patient had attained some OSP, scoring 24% on CNC words and 40% on HINT sentences (compared to 0% on CNC words with a hearing aid). One month later (4 months postimplantation), the patient experienced an abrupt decline in implant performance and House-Brackmann grade III–IV facial weakness, which later recovered incompletely. Implant function did not improve, and the patient eventually underwent right-sided CI. Two months after the right CI, the patient scored 32% on CNC words and 91% on HINT sentences. While the matter has not been specifically studied in the radiosurgical treatment of benign intracranial tumors, anecdotal experience among radiation oncologists suggests that patients with scleroderma may experience greater radiation treatment effect and fibrosis. We speculate that this may have been the mechanism responsible for the dramatic tumor response (Fig. 2), facial weakness (typically extremely rare following SRS for a sporadic VS), and loss of implant function.

FIG. 2.
FIG. 2.

Sporadic VS patient with scleroderma. MRI at VS diagnosis (A) demonstrated a 1.8-cm CPA lesion consistent with VS. Six-month post-SRS MRI (B) from the time the patient developed facial weakness and loss of implant function demonstrated marked internal tumor necrosis.

Patients With No Benefit From Implantation

Two patients had no benefit from implantation. Both had severe-phenotype NF2. One patient (case 6) had multiple intracranial schwannomas, spinal tumors, and congenital nystagmus. He had fluctuating, progressively worsening hearing in his right ear that declined to profound sensorineural hearing loss after radiosurgery. Implantation was complicated by a substantial amount of intracochlear tumor that was debulked to facilitate complete insertion of a full-length, straight lateral wall electrode. Unfortunately, the device failed to yield auditory percepts and was removed to facilitate future imaging. Given the rapid growth of his contralateral, previously untreated cranial nerve (CN) VII and VIII tumors, the patient underwent translabyrinthine tumor resection and simultaneous ABI placement. The second patient (case 14) also had multiple intracranial and spinal tumors and underwent radiosurgery for a probable right-sided VS nearly 20 years prior to implantation. The tumor was treated with a marginal dose of 16 Gy (maximum dose 32 Gy), resulting in partial facial weakness and facial numbness. Because of progressive hearing loss in his only hearing (left) ear, implantation in the right side was pursued after his left-sided VS was treated with SRS. Unfortunately, no neural responses or auditory percepts were yielded. The patient succumbed to complications related to impingement and treatment of the cervical spinal cord by a C2 ependymoma approximately 2 years after the cochlear implant had been placed.

Discussion

In this study, the outcomes of CI following SRS for NF2-associated and sporadic VS are presented. Implants were placed in a total of 18 ears in 17 patients. Eleven patients (65%) demonstrated OSP, 8 (47%) of whom are considered to be high performers per the criteria used in the study by Carlson et al.8 Of note, the median word and sentence scores exhibited by the OSP group with available data are similar to those achieved by typical CI recipients without retrocochlear pathology. While quality-of-life outcomes were not assessed in this study, 15 of the 17 patients (88%) who underwent CI are active implant users and have embraced the technology for speech understanding, sound awareness, and assistance with lip reading, among other tasks. The results of this study continue to support the use of CI as a primary auditory rehabilitation strategy (over ABI) in ears affected by VS.

This report expands the initial experience from our institution that was published in 2012.8 In that study, all NF2 patients who had undergone CI were included and separated by treatment modality (observation, radiation therapy, and microsurgery). In the radiotherapy group, 1 patient (case 7 in the prior study, case 8 in the present study) now has nearly 12 years of audiometric follow-up, remains a high performer (with CI: PTA 20 dB HL, 72% of CNC words, 87% of AzBio sentences), and maintains good tumor control 13 years after SRS. The remaining 3 patients in the prior study do not have updated data: 2 unfortunately died from the effects of NF2, and 1 follows up remotely with imaging review only.

The timing of implantation can be approached in several ways and requires a detailed discussion with the patient, CI candidacy test scores, and an audiogram. Patients who meet audiometric criteria for CI and are losing benefit from conventional amplification can be treated with SRS and same-day or next-day CI at our institution. Performing implantation after SRS allows the radiosurgeon to obtain imaging studies adequate for stereotactic localization of the tumor without magnet removal and the replacement that would be required if implantation were performed prior to SRS. If a patient has serviceable hearing at the time of SRS, serial audiograms with speech testing are obtained while the patient uses acoustic hearing. If the patient then experiences a drop into the nonserviceable range, such as a WRS under 50%–60%, CI is considered, and a detailed discussion with the patient occurs to determine whether they have fallen outside the range of benefit of conventional amplification. The interval between SRS and CI can be several years in many cases, but if the patient maintains detectable auditory thresholds at the time of implantation, it is likely that CI would be beneficial. In other words, detectable auditory thresholds on an audiogram would not be present if the functional integrity of the cochlear nerve were compromised. If a patient drops to profound hearing loss after radiation, the outcome may be less predictable, as the auditory nerve may be compromised; however, CI is still offered first rather than promontory stimulation testing or ABI. Finally, patients with observed tumors and progressive hearing decline may undergo implantation and subsequent SRS for tumor progression. In these situations, the magnet must be removed and replaced to facilitate imaging for stereotaxis, but this can be accomplished easily under local anesthesia in most cases.

As mentioned above, surveillance MRI is routinely performed at our institution with the cochlear implant and ABI magnets in place. Some devices include magnets with components that self-align with the field generated by the scanner and require no modification prior to scanning. Others require immobilization of the magnet using a tight head wrap. Our initial experience with 19 ears undergoing a total of 34 studies was published in 2015 and demonstrated a low overall adverse event rate (such as magnet tilt, displacement, or pain).10 An interval update, now with over 100 studies performed, has shown similar results (unpublished data, in press). Monitoring the ipsilateral CPA was feasible in the vast majority of cases. A recent large series summarizing over 400 MRI sessions showed a very low complication rate (3.5%).11 Many centers have safely adopted similar scanning protocols for this burgeoning group of patients through interdisciplinary collaboration among neurosurgery, otolaryngology, and radiology.

The question of the durability of cochlear implant performance in the presence of a VS and ongoing radiation effect remains largely unanswered, as available long-term audiometric follow-up data are limited. Recent systematic reviews have included very few cases with over 2–3 years of performance data.12,13 Figures 3 and 4, respectively, show word and sentence scores for each patient with available data in the present study. Four patients had over 3 years of audiometric follow-up. Two had OSP and maintained AzBio sentence scores in quiet of 87% at 143 months and 91% at 71 months, respectively. One patient treated at our institution developed performance decline related to tumor growth necessitating surgery to remove the tumor, explant the cochlear implant, and place an ABI. Peng et al. reported a case of performance decline over time in a patient treated with SRS; however, a single-channel device was implanted in that patient.14 While extrapolating these data is understandably limited, we counsel patients that cochlear implant performance is likely to be durable as long as tumor growth is absent or minimal and that if decline were to occur, “salvage” ABI remains an option.

FIG. 3.
FIG. 3.

AzBio sentences scores over time (10 ears). Figure is available in color online only.

FIG. 4.
FIG. 4.

CNC word scores over time (8 ears). Figure is available in color online only.

At our institution, the use of ABI remains limited with fewer than five implantations performed annually. Certainly, this remains the preferred auditory rehabilitation option for patients with very large tumors that cannot be safely treated with radiosurgery. However, we certainly encounter instances of only nonauditory stimulation despite radiographically ideal electrode placement, as well as mediocre OSP outcomes in those who successfully use their devices. In 2012 Sanna et al. published a single-center series of ABIs in patients with NF2 and a review of the literature.15 In that report, 19 of the 23 patients with follow-up data were users, 8 of whom (42%) had speech recognition. These authors also reported that the majority of patients experienced stimulation of nearby CNs requiring some modification in programming. In 2013 Matthies et al. reported speech perception outcomes among 32 patients with ABIs.16 Among 27 patients who had auditory percepts and were able to undergo stimulation, 37% had some degree of OSP 12 months after implantation.

The optimal radiosurgical dose for VS remains a topic of ongoing debate. In the NF2 population, achieving tumor control with SRS is even more important given the attendant risks of salvage therapy. Specifically, these patients are at risk of bilateral sensorineural hearing loss, facial paralysis, lower CN palsies, and visual deficits; thus, limiting the morbidity of treatment for CPA pathology is vital. Mallory et al. retrospectively analyzed the treatment outcomes for 32 NF2-associated VS cases over a 20-year interval and demonstrated a correlation between improved tumor control and increased radiosurgical dose.17 Specifically, the median marginal dose for tumors that decreased in size during follow-up was 15.5 Gy compared to 13 Gy for the tumors that enlarged after treatment. Anecdotally, we have not observed an increased incidence of facial or trigeminal neuropathy among patients treated with marginal tumor doses of 14–16 Gy. While the median marginal dose in the present series was 13 Gy, doses of 14 Gy or higher were used in 6 patients. Because of our small sample size, no conclusion can be drawn regarding CI outcome and radiosurgical dose. However, especially in rapidly growing tumors, we employ a higher marginal tumor dose (14–15 Gy) to optimize tumor control and continue to evaluate whether cochlear implant performance is affected as a result.

A total of 29 cases (in 28 patients) of CI after radiotherapy for VS were identified in the literature (Table 4).8,14,18–29 As in the current study, the majority of tumors were related to NF2. Though testing was heterogeneous, 16 ears (55%) demonstrated OSP and 5 (21%) demonstrated ESA only. Tumor sizes varied from IAC only to relatively large VSs (3.0 cm or larger), with no observable correlation with performance outcome. Though reported for only 11 ears, access to sound was in the mild hearing loss range for most patients. This is an important indicator of outcome among the patients with ESA only, as hearing environmental sounds, particularly in the bilaterally deafened patient, is important for not only assistance with lip reading but also safety in performing activities of daily living.

TABLE 4.

Literature review of patients who have received CI following ipsilateral VS radiation treatment

Authors & YearNo. of Patients (ears)Case No. in StudyEtiology of VSTumor Size (mm)Pre-CI PerformanceBest PTA w/ CI (dB HL)Post-CI Word or Sentence ScoresOutcome
Amoodi et al., 20121812NF2≈20NDND94% HINT, 52% CNC*ND
Carlson et al., 2012846NF2NDND1846% CNCw, 100% CUNYqOSP
7NF2NDND2086% CNCw, 95% AzBioqOSP
8NF2NDND19NDOSP
9NF2NDNDNDNRNR
Costello et al., 20161911NF2IAC0% CUNYqND36% CUNYqOSP
Lustig et al., 20062024NF2ND0% SDS5546% MTSESA
6NF2ND0% SDS3598% HINTOSP
Mukherjee et al., 20132161NF2150% CUNYq w/ LRNDNDESA
2NF213AnacusisND82% BKBqOSP
3NF2IACAnacusisNDNDESA
4NF21920% BKB w/ LRND68% BKB w/ LRND
5NF2238% BKB w/ LRND36% BKB w/ LRND
6NF237AnacusisNDNDESA
Pai et al., 20132221NF220Anacusis3094% CUNYqOSP
2Sporadic2390 dB HL PTA3661% CUNYqOSP
Peng et al., 20181421NF220AnacusisNDNR
5NF230AnacusisND87% CUNYqOSP
Pimentel et al., 20162311NF2IAC“80 dB threshold,” 30% SDS in bilat best-aided condition100% Ling sentencesND
Pisa et al., 2017242 (3)1, lt earNF2320% WRS, 0% AzBioq2040% CNCw, 45% HINTOSP
1, rt earNF23316% WRS, 2% AzBioq1824% CNCw, 45% HINTOSP
2SporadicIAC2% WRS, 3% AzBioq2228% CNCw, 34% HINTND
Roehm et al., 20112514NF2250% CNCw, 0% CUNYq68% CNCw, 92% CUNYqOSP
Tan et al., 20182614NF2IAC80 dB PTA, 5% WRSNDNDESA
Tran Ba Huy et al., 20092811NF2NDNDND100% “open-set words,” 97% “open-set sentences”OSP
Tolisano et al., 20192716NF217115 dB PTA, 0% AzBioq330% AzBioqND, daily user
Trotter & Briggs, 20102931NF2ND1% CUNYq, 7% CNCpND96% CUNYq, 79% CNCpOSP
2NF2303% CUNYq, 30% CNCpND72% CUNYq, 45% CNCpOSP
3NF2NDNDNDNDOSP
Total28 (29)26 NF2, 2 sporadic22 (18–55, n = 11§)16§ w/ OSP, 5§ w/ ESA
Present study17 (18)13 NF2, 4 sporadic13 (4.7–18.4, n = 17)101 dB HL PTA (61–120 dB HL, n = 17§)28 (12–41, n = 15§)64% CNCw (0%–88%, n = 9); 76% AzBioq (19%–95%, n = 10§)12§ w/ OSP, 4§ w/ ESA, 2§ NR

≈ = approximately equal; BKB = Bamford-Kowal-Bench; BKBq = BKB in quiet; CNCp = CNC phoneme score; CUNYq = City University of New York sentence test in quiet; LR = lip reading; MTS = monosyllable-trochee-spondee; ND = not documented; NR = no response; SDS = speech discrimination score.

Unclear from report whether words or phonemes.

Patient received single-channel cochlear implant, had benefit, and progressively lost implant function following SRS.

Continuous features reported as median (range).

Ears.

We anticipate that the number of cases of CI in VS-affected ears will continue to increase for two reasons. First, many NF2 centers have shifted toward a more conservative approach to tumor management, reserving surgery for very large or rapidly growing tumors and utilizing radiosurgery or observation for smaller lesions. This is primarily attributable to the challenges encountered in the maintenance of hearing with microsurgery (or merely maintaining an anatomically intact cochlear nerve) and the outcomes of ABI.2,15,16,30 Second, and probably of greater impact, the use of CI continues to expand and include patients with larger degrees of ipsilateral and contralateral hearing. One cochlear implant manufacturer obtained US Food and Drug Administration approval in 2019 for implantation in patients with single-sided deafness and asymmetrical sensorineural hearing loss. Since then, increasing numbers of patients with sporadic VS inquire about this option during the pretreatment discussion and in situations in which hearing preservation was attempted but unsuccessful, under the premise that an anatomically intact cochlear nerve may carry a signal generated by a cochlear implant even if acoustic hearing is lost.

Though a detailed discussion of NF2 management is outside the scope of this report, it is worth discussing how the tumor control and hearing rehabilitation strategy chosen for a patient should fit the overall clinical picture. The phenotypic severity of NF2 in our patient population was quite broad, with some patients diagnosed in late adulthood with relatively indolent tumors and others diagnosed in childhood with Wishart-type disease. In the latter group, life expectancy may be foreshortened by, for example, spinal disease, and providing 5–10 years of tumor control and hearing in a minimally invasive fashion may be appropriate. Radiosurgery and CI, as opposed to microsurgery and ABI, may accomplish this objective with limited morbidity in this most unfortunate cohort.

There are several strengths and limitations to our study, which represents the largest single-center experience with CI following SRS, particularly with comprehensive pre- and posttreatment audiometric data, tumor and treatment characteristics, and follow-up data. The study is limited by its retrospective nature and the potential for selection bias. Specifically, not all patients underwent periodic performance assessments, as many maintain only radiographic follow-up with our institution. Moreover, performance is rarely measured more than annually during programming visits. Patients who are relatively poor performers may not undergo objective performance assessments. This may lead to selection bias, with better performers undergoing more comprehensive word and sentence testing. Finally, given the heterogeneity in the testing performed and the small cohort size, robust statistical analyses to determine predictors of performance outcomes or other subgroup analyses could not be performed. This question would be best addressed by a prospective multicenter study.

Conclusions

Cochlear implantation following SRS for sporadic and NF2-associated VS offers access to sound in the near-normal range and OSP in the majority of cases. Notably, median word and sentence scores are similar to those achieved by conventional CI recipients who do not harbor VS. This strategy offers a minimally invasive, effective, and efficient approach for tumor control and auditory rehabilitation in ears affected by VS.

Disclosures

Dr. Carlson is a consultant for Advanced Bionics, Cochlear Corp., and MED-EL GmbH. Dr. Driscoll is a consultant for Advanced Bionics, Cochlear Corp., and Envoy Medical.

Author Contributions

Conception and design: Driscoll, Patel, Neff, Van Gompel. Acquisition of data: Patel, Carlson, Link. Analysis and interpretation of data: all authors. Drafting the article: Patel, Link. Critically revising the article: all authors. Reviewed submitted version of manuscript: all authors. Approved the final version of the manuscript on behalf of all authors: Driscoll. Statistical analysis: Patel.

Supplemental Information

Previous Presentations

Presented as a podium abstract presentation at the 2020 North American Skull Base Society Meeting held in San Antonio, Texas, on February 7–9, 2020.

Current Affiliations

Dr. Patel: Division of Otolaryngology–Head and Neck Surgery, University of Utah, Salt Lake City, Utah.

References

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    Evans DG . Neurofibromatosis type 2 (NF2): a clinical and molecular review . Orphanet J Rare Dis . 2009 ;4 :16 .

  • 2

    Ramsden RT , Freeman SRM , Lloyd SKW , et al. Auditory brainstem implantation in neurofibromatosis type 2: experience from the Manchester Programme . Otol Neurotol . 2016 ;37 (9 ):1267 1274 .

    • Search Google Scholar
    • Export Citation
  • 3

    Neff BA , Wiet RM , Lasak JM , et al. Cochlear implantation in the neurofibromatosis type 2 patient: long-term follow-up . Laryngoscope . 2007 ;117 (6 ):1069 1072 .

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  • 4

    Committee on Hearing and Equilibrium guidelines for the evaluation of hearing preservation in acoustic neuroma (vestibular schwannoma) . Otolaryngol Head Neck Surg . 1995 ;113 (3 ):179 180 .

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    • Export Citation
  • 5

    Gurgel RK , Popelka GR , Oghalai JS , et al. Is it valid to calculate the 3-kilohertz threshold by averaging 2 and 4 kilohertz? Otolaryngol Head Neck Surg . 2012 ;147 (1 ):102 104 .

    • Search Google Scholar
    • Export Citation
  • 6

    Spahr AJ , Dorman MF . Performance of subjects fit with the Advanced Bionics CII and Nucleus 3G cochlear implant devices . Arch Otolaryngol Head Neck Surg . 2004 ;130 (5 ):624 628 .

    • Search Google Scholar
    • Export Citation
  • 7

    Spahr AJ , Dorman MF , Litvak LM , et al. Development and validation of the AzBio sentence lists . Ear Hear . 2012 ;33 (1 ):112 117 .

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    Carlson ML , Breen JT , Driscoll CL , et al. Cochlear implantation in patients with neurofibromatosis type 2: variables affecting auditory performance . Otol Neurotol . 2012 ;33 (5 ):853 862 .

    • Search Google Scholar
    • Export Citation
  • 9

    Van Abel KM , Carlson ML , Link MJ , et al. Primary inner ear schwannomas: a case series and systematic review of the literature . Laryngoscope . 2013 ;123 (8 ):1957 1966 .

    • Search Google Scholar
    • Export Citation
  • 10

    Carlson ML , Neff BA , Link MJ , et al. magnetic resonance imaging with cochlear implant magnet in place: safety and imaging quality . Otol Neurotol . 2015 ;36 (6 ):965 971 .

    • Search Google Scholar
    • Export Citation
  • 11

    Tam YC , Lee JWY , Gair J , et al. Performing MRI scans on cochlear implant and auditory brainstem implant recipients: review of 14.5 years experience . Otol Neurotol . 2020 ;41 (5 ):e556 e562 .

    • Search Google Scholar
    • Export Citation
  • 12

    Bartindale MR , Tadokoro KS , Kircher ML . cochlear implantation in sporadic vestibular schwannoma: a systematic literature review . J Neurol Surg B Skull Base . 2019 ;80 (6 ):632 639 .

    • Search Google Scholar
    • Export Citation
  • 13

    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 (1 ):9 17 .

    • Search Google Scholar
    • Export Citation
  • 14

    Peng KA , Lorenz MB , Otto SR , et al. Cochlear implantation and auditory brainstem implantation in neurofibromatosis type 2 . Laryngoscope . 2018 ;128 (9 ):2163 2169 .

    • Search Google Scholar
    • Export Citation
  • 15

    Sanna M , Di Lella F , Guida M , Merkus P . Auditory brainstem implants in NF2 patients: results and review of the literature . Otol Neurotol . 2012 ;33 (2 ):154 164 .

    • Search Google Scholar
    • Export Citation
  • 16

    Matthies C , Brill S , Kaga K , et al. Auditory brainstem implantation improves speech recognition in neurofibromatosis type II patients . ORL J Otorhinolaryngol Relat Spec . 2013 ;75 (5 ):282 295 .

    • Search Google Scholar
    • Export Citation
  • 17

    Mallory GW , Pollock BE , Foote RL , et al. Stereotactic radiosurgery for neurofibromatosis 2-associated vestibular schwannomas: toward dose optimization for tumor control and functional outcomes . Neurosurgery . 2014 ;74 (3 ):292 301 .

    • Search Google Scholar
    • Export Citation
  • 18

    Amoodi HA , Makki FM , Cavanagh J , et al. Cochlear implant rehabilitation for patients with vestibular schwannoma: report of two cases . Cochlear Implants Int . 2012 ;13 (2 ):124 127 .

    • Search Google Scholar
    • Export Citation
  • 19

    Costello MS , Golub JS , Barrord JV , et al. Cochlear implantation after radiation therapy for acoustic neuroma . J Radiosurg SBRT . 2016 ;4 (1 ):69 74 .

    • Search Google Scholar
    • Export Citation
  • 20

    Lustig LR , Yeagle J , Driscoll CL , et al. Cochlear implantation in patients with neurofibromatosis type 2 and bilateral vestibular schwannoma . Otol Neurotol . 2006 ;27 (4 ):512 518 .

    • Search Google Scholar
    • Export Citation
  • 21

    Mukherjee P , Ramsden JD , Donnelly N , et al. Cochlear implants to treat deafness caused by vestibular schwannomas . Otol Neurotol . 2013 ;34 (7 ):1291 1298 .

    • Search Google Scholar
    • Export Citation
  • 22

    Pai I , Dhar V , Kelleher C , et al. Cochlear implantation in patients with vestibular schwannoma: a single United Kingdom center experience . Laryngoscope . 2013 ;123 (8 ):2019 2023 .

    • Search Google Scholar
    • Export Citation
  • 23

    Pimentel PS , Ramos DS , Muniz L , et al. Cochlear implant in a patient with neurofibromatosis type 2 undergoing radiotherapy . Rev Bras Otorrinolaringol (Engl Ed). 2016 ;82 (2 ):242 243 .

    • Search Google Scholar
    • Export Citation
  • 24

    Pisa J , Sulkers J , Butler JB , et al. Stereotactic radiosurgery does not appear to impact cochlear implant performance in patients with neurofibromatosis type II . J Radiosurg SBRT . 2017 ;5 (1 ):63 71 .

    • Search Google Scholar
    • Export Citation
  • 25

    Roehm PC , Mallen-St Clair J , Jethanamest D , et al. Auditory rehabilitation of patients with neurofibromatosis Type 2 by using cochlear implants . J Neurosurg . 2011 ;115 (4 ):827 834 .

    • Search Google Scholar
    • Export Citation
  • 26

    Tan H , Jia H , Li Y , et al. Impact of cochlear implantation on the management strategy of patients with neurofibromatosis type 2 . Eur Arch Otorhinolaryngol . 2018 ;275 (11 ):2667 2674 .

    • Search Google Scholar
    • Export Citation
  • 27

    Tolisano AM , Baumgart B , Whitson J , Kutz JW Jr . Cochlear implantation in patients with neurofibromatosis type 2 . Otol Neurotol . 2019 ;40 (4 ):e381 e385 .

    • Search Google Scholar
    • Export Citation
  • 28

    Tran Ba Huy P , Kania R , Frachet B , et al. Auditory rehabilitation with cochlear implantation in patients with neurofibromatosis type 2 . Acta Otolaryngol . 2009 ;129 (9 ):971 975 .

    • Search Google Scholar
    • Export Citation
  • 29

    Trotter MI , Briggs RJS . Cochlear implantation in neurofibromatosis type 2 after radiation therapy . Otol Neurotol . 2010 ;31 (2 ):216 219 .

    • Search Google Scholar
    • Export Citation
  • 30

    Matthies C , Brill S , Varallyay C , et al. Auditory brainstem implants in neurofibromatosis Type 2: is open speech perception feasible? J Neurosurg . 2014 ;120 (2 ):546 558 .

    • Search Google Scholar
    • Export Citation
Illustrations from Marx and Schroeder (pp 318–326). Copyright Henry W. S. Schroeder. Published with permission.

Contributor Notes

Correspondence Colin L. W. Driscoll: Mayo Clinic, Rochester, MN. driscoll.colin@mayo.edu.

INCLUDE WHEN CITING Published online July 24, 2020; DOI: 10.3171/2020.4.JNS201069.

Disclosures Dr. Carlson is a consultant for Advanced Bionics, Cochlear Corp., and MED-EL GmbH. Dr. Driscoll is a consultant for Advanced Bionics, Cochlear Corp., and Envoy Medical.

  • View in gallery

    Case 16. An NF2 patient with a right-sided intravestibular-cochlear schwannoma and left-sided VS had bilateral profound hearing loss at the time of SRS (A upper) and demonstrated tumor control 6 years after SRS and CI (B upper), normal to near-normal access to sound (A lower, audiometric data at SRS and 6 years posttreatment.), and above-average word and sentence scores (B lower). CL = CI-only thresholds for left-sided implant. Figure is available in color online only.

  • View in gallery

    Sporadic VS patient with scleroderma. MRI at VS diagnosis (A) demonstrated a 1.8-cm CPA lesion consistent with VS. Six-month post-SRS MRI (B) from the time the patient developed facial weakness and loss of implant function demonstrated marked internal tumor necrosis.

  • View in gallery

    AzBio sentences scores over time (10 ears). Figure is available in color online only.

  • View in gallery

    CNC word scores over time (8 ears). Figure is available in color online only.

  • 1

    Evans DG . Neurofibromatosis type 2 (NF2): a clinical and molecular review . Orphanet J Rare Dis . 2009 ;4 :16 .

  • 2

    Ramsden RT , Freeman SRM , Lloyd SKW , et al. Auditory brainstem implantation in neurofibromatosis type 2: experience from the Manchester Programme . Otol Neurotol . 2016 ;37 (9 ):1267 1274 .

    • Search Google Scholar
    • Export Citation
  • 3

    Neff BA , Wiet RM , Lasak JM , et al. Cochlear implantation in the neurofibromatosis type 2 patient: long-term follow-up . Laryngoscope . 2007 ;117 (6 ):1069 1072 .

    • Search Google Scholar
    • Export Citation
  • 4

    Committee on Hearing and Equilibrium guidelines for the evaluation of hearing preservation in acoustic neuroma (vestibular schwannoma) . Otolaryngol Head Neck Surg . 1995 ;113 (3 ):179 180 .

    • Search Google Scholar
    • Export Citation
  • 5

    Gurgel RK , Popelka GR , Oghalai JS , et al. Is it valid to calculate the 3-kilohertz threshold by averaging 2 and 4 kilohertz? Otolaryngol Head Neck Surg . 2012 ;147 (1 ):102 104 .

    • Search Google Scholar
    • Export Citation
  • 6

    Spahr AJ , Dorman MF . Performance of subjects fit with the Advanced Bionics CII and Nucleus 3G cochlear implant devices . Arch Otolaryngol Head Neck Surg . 2004 ;130 (5 ):624 628 .

    • Search Google Scholar
    • Export Citation
  • 7

    Spahr AJ , Dorman MF , Litvak LM , et al. Development and validation of the AzBio sentence lists . Ear Hear . 2012 ;33 (1 ):112 117 .

  • 8

    Carlson ML , Breen JT , Driscoll CL , et al. Cochlear implantation in patients with neurofibromatosis type 2: variables affecting auditory performance . Otol Neurotol . 2012 ;33 (5 ):853 862 .

    • Search Google Scholar
    • Export Citation
  • 9

    Van Abel KM , Carlson ML , Link MJ , et al. Primary inner ear schwannomas: a case series and systematic review of the literature . Laryngoscope . 2013 ;123 (8 ):1957 1966 .

    • Search Google Scholar
    • Export Citation
  • 10

    Carlson ML , Neff BA , Link MJ , et al. magnetic resonance imaging with cochlear implant magnet in place: safety and imaging quality . Otol Neurotol . 2015 ;36 (6 ):965 971 .

    • Search Google Scholar
    • Export Citation
  • 11

    Tam YC , Lee JWY , Gair J , et al. Performing MRI scans on cochlear implant and auditory brainstem implant recipients: review of 14.5 years experience . Otol Neurotol . 2020 ;41 (5 ):e556 e562 .

    • Search Google Scholar
    • Export Citation
  • 12

    Bartindale MR , Tadokoro KS , Kircher ML . cochlear implantation in sporadic vestibular schwannoma: a systematic literature review . J Neurol Surg B Skull Base . 2019 ;80 (6 ):632 639 .

    • Search Google Scholar
    • Export Citation
  • 13

    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 (1 ):9 17 .

    • Search Google Scholar
    • Export Citation
  • 14

    Peng KA , Lorenz MB , Otto SR , et al. Cochlear implantation and auditory brainstem implantation in neurofibromatosis type 2 . Laryngoscope . 2018 ;128 (9 ):2163 2169 .

    • Search Google Scholar
    • Export Citation
  • 15

    Sanna M , Di Lella F , Guida M , Merkus P . Auditory brainstem implants in NF2 patients: results and review of the literature . Otol Neurotol . 2012 ;33 (2 ):154 164 .

    • Search Google Scholar
    • Export Citation
  • 16

    Matthies C , Brill S , Kaga K , et al. Auditory brainstem implantation improves speech recognition in neurofibromatosis type II patients . ORL J Otorhinolaryngol Relat Spec . 2013 ;75 (5 ):282 295 .

    • Search Google Scholar
    • Export Citation
  • 17

    Mallory GW , Pollock BE , Foote RL , et al. Stereotactic radiosurgery for neurofibromatosis 2-associated vestibular schwannomas: toward dose optimization for tumor control and functional outcomes . Neurosurgery . 2014 ;74 (3 ):292 301 .

    • Search Google Scholar
    • Export Citation
  • 18

    Amoodi HA , Makki FM , Cavanagh J , et al. Cochlear implant rehabilitation for patients with vestibular schwannoma: report of two cases . Cochlear Implants Int . 2012 ;13 (2 ):124 127 .

    • Search Google Scholar
    • Export Citation
  • 19

    Costello MS , Golub JS , Barrord JV , et al. Cochlear implantation after radiation therapy for acoustic neuroma . J Radiosurg SBRT . 2016 ;4 (1 ):69 74 .

    • Search Google Scholar
    • Export Citation
  • 20

    Lustig LR , Yeagle J , Driscoll CL , et al. Cochlear implantation in patients with neurofibromatosis type 2 and bilateral vestibular schwannoma . Otol Neurotol . 2006 ;27 (4 ):512 518 .

    • Search Google Scholar
    • Export Citation
  • 21

    Mukherjee P , Ramsden JD , Donnelly N , et al. Cochlear implants to treat deafness caused by vestibular schwannomas . Otol Neurotol . 2013 ;34 (7 ):1291 1298 .

    • Search Google Scholar
    • Export Citation
  • 22

    Pai I , Dhar V , Kelleher C , et al. Cochlear implantation in patients with vestibular schwannoma: a single United Kingdom center experience . Laryngoscope . 2013 ;123 (8 ):2019 2023 .

    • Search Google Scholar
    • Export Citation
  • 23

    Pimentel PS , Ramos DS , Muniz L , et al. Cochlear implant in a patient with neurofibromatosis type 2 undergoing radiotherapy . Rev Bras Otorrinolaringol (Engl Ed). 2016 ;82 (2 ):242 243 .

    • Search Google Scholar
    • Export Citation
  • 24

    Pisa J , Sulkers J , Butler JB , et al. Stereotactic radiosurgery does not appear to impact cochlear implant performance in patients with neurofibromatosis type II . J Radiosurg SBRT . 2017 ;5 (1 ):63 71 .

    • Search Google Scholar
    • Export Citation
  • 25

    Roehm PC , Mallen-St Clair J , Jethanamest D , et al. Auditory rehabilitation of patients with neurofibromatosis Type 2 by using cochlear implants . J Neurosurg . 2011 ;115 (4 ):827 834 .

    • Search Google Scholar
    • Export Citation
  • 26

    Tan H , Jia H , Li Y , et al. Impact of cochlear implantation on the management strategy of patients with neurofibromatosis type 2 . Eur Arch Otorhinolaryngol . 2018 ;275 (11 ):2667 2674 .

    • Search Google Scholar
    • Export Citation
  • 27

    Tolisano AM , Baumgart B , Whitson J , Kutz JW Jr . Cochlear implantation in patients with neurofibromatosis type 2 . Otol Neurotol . 2019 ;40 (4 ):e381 e385 .

    • Search Google Scholar
    • Export Citation
  • 28

    Tran Ba Huy P , Kania R , Frachet B , et al. Auditory rehabilitation with cochlear implantation in patients with neurofibromatosis type 2 . Acta Otolaryngol . 2009 ;129 (9 ):971 975 .

    • Search Google Scholar
    • Export Citation
  • 29

    Trotter MI , Briggs RJS . Cochlear implantation in neurofibromatosis type 2 after radiation therapy . Otol Neurotol . 2010 ;31 (2 ):216 219 .

    • Search Google Scholar
    • Export Citation
  • 30

    Matthies C , Brill S , Varallyay C , et al. Auditory brainstem implants in neurofibromatosis Type 2: is open speech perception feasible? J Neurosurg . 2014 ;120 (2 ):546 558 .

    • Search Google Scholar
    • Export Citation

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