Cochlear Implantation Outcomes in Patients With Retrocochlear Pathology: A Systematic Review and Pooled Analysis : Otology & Neurotology

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Cochlear Implantation Outcomes in Patients With Retrocochlear Pathology: A Systematic Review and Pooled Analysis

Schlacter, Jamie A.; Kay-Rivest, Emily; Nicholson, Joseph; Santacatterina, Michele§; Zhang, Yan§; Jethanamest, Daniel; Friedmann, David R.; McMenomey, Sean O.; Roland, J. Thomas Jr

Author Information
doi: 10.1097/MAO.0000000000003648

Abstract

INTRODUCTION

Historically, the presence of retrocochlear pathologies, such as a vestibular schwannoma (VS), was considered a relative contraindication to cochlear implantation (CI). In 1992, the first CI was performed in a patient with neurofibromatosis type 2 (NF2) with a favorable outcome (1). Since this time, increasing evidence suggests that a CI may be considered in these patients, if the cochlear nerve remains anatomically intact and a fluid signal is present within the cochlea (2). Patients with other retrocochlear pathologies may also develop severe to profound hearing loss and benefit from CI, including individuals with other cerebellopontine angle tumors, superficial siderosis, neurosarcoidosis, as well as patients with previous irradiation to the central nervous system (CNS) or skull base in which the cochlea, cochlear nerve, or central auditory processing centers may have been irradiated.

Previous literature reviews have examined the role of CI in patients with sporadic and NF2-associated VS but will often combine patients who were treated with all available modalities: observation, radiation, and surgical resection with either concomitant or delayed CI (3,4). Overall, the outcomes from a CI in small groups of patients with observed and irradiated tumors show favorable results, whereas the outcomes after tumor resection are more variable, even in cases where the cochlear nerve seems to be anatomically intact (5–7). Nonetheless, a CI remains an interesting hearing rehabilitation modality in the context of any retrocochlear pathology, often providing the patient with open-set speech understanding and improved overall quality of life (8–10).

The primary aim of the current study was to systematically review the current literature and extract speech perception scores between 6 months and 1 year after CI in patients with retrocochlear pathologies. A secondary aim was to determine whether certain factors resulted in better outcomes specifically among patients with VS, with a particular focus on nonoperated tumors.

METHODS

A review was performed according to Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidance, and full search strategies are available in the Appendix (11). The systematic review was registered with no further amendments through PROSPERO (ID: CRD42021265439).

Study Inclusion and Exclusion

Included studies were those that evaluated patients 18 years or older diagnosed with retrocochlear pathologies (observed or irradiated VS, meningiomas, CNS or head and neck cancers, neurosarcoidosis, sideroses, NF2) who underwent CI (unilateral or bilateral) and presented with post-CI hearing outcomes with a minimum follow-up of 6 months. Our goal was to focus on observed and irradiated tumors exclusively and therefore if a study combined outcomes of observed, irradiated and operated VS, as long as individual patient data could be extracted, these studies were included. Non-English articles, studies containing aggregated data and conference abstracts were excluded.

Outcome Measures

The primary outcome was speech perception scores beteween 6 and 12 months after CI. Secondary outcomes included daily device use time, rates of device failure, and duration of benefit.

Subgroup Analysis

A subgroup analysis was performed among patients with unoperated VS to assess whether specific factors (age, NF2 status, maximum tumor dimension, and irradiation) led to differences in outcomes.

Search Strategy

A systematic search of the following five databases was performed through March seventh, 2022: PubMed/MEDLINE, Embase and Cochrane CENTRAL via Ovid, CINAHL Complete via Ebsco, and Web of Science Complete Collection. Search strategies were developed iteratively by a librarian experienced in systematic reviews in consultation with the investigators. The searches included both keywords and subject headings to maximize retrieval and reflect the two main concepts: cochlear implants and retrocochlear pathologies. No limits or filters were used for language, date ranges, or study designs in the search strategies.

Study Selection and Data Extraction

Screening and deduplication of results was conducted using Covidence. Screening was conducted in two stages. First, an initial screening of title and abstract for relevance, followed by full-text screening using the predetermined exclusion criteria. Each record was screened independently by two reviewers (J.S. and E.K.R.).

A standardized form was used to extract data for the following outcomes: study characteristics (author, year of publication, country, study type), patient characteristics (implantation age, sex, duration of deafness, cochlear implant device, laterality of implantation, length of follow-up, history of retrocochlear pathology, previous surgery, radiation history, type and dosage of radiotherapy if available), preoperative and postoperative speech discrimination scores (consonant-nucleus-consonant (CNC) word test, AzBio sentence test), and secondary outcomes (daily usage, need for reprogramming, promontory stimulation outcome, tinnitus suppression and rate of explantation and other adverse events). Benefit from CI was defined as any improvement in speech perception scores from the preoperative condition. Data were reported according to PRISMA guidelines (11).

Level of Evidence and Risk of Bias

Level of evidence was assessed using the Oxford Centre for Evidence Based Medicine grading system (12). Risk of bias was determined by one author using the Risk of Bias in Nonrandomized Studies of Interventions tool based on the Cochrane Risk of Bias tool (13). Studies were assessed for confounding, participant selection, deviations from intended intervention, missing data, outcome measurement, selective reporting, and overall bias.

Data Analysis

A descriptive analysis of speech perception scores before and after CI was performed. Rather than a meta-analysis, individual data from each study were pooled in an unweighted fashion to evaluate overall changes in speech perception within each retrocochlear pathology. In the subgroup analysis of patients with VS, univariate generalized estimated equations (GEE) models with an independent correlation structure were used to evaluate individual factors influencing postoperative CNC word scores and AzBio sentence scores (14). Robust standard errors were used and Wald-type 95% confidence intervals were constructed. A p value less than 0.05 was considered statistically significant.

RESULTS

Search Results and Study Characteristics

A literature search yielded 2,524 publications. Screening by title and abstract excluded 2,345 studies. Full-text review excluded 126 studies, and a total of 53 publications were included in the final analysis (2,5,6,8–10,15–61). A diagram of the search process can be found in Figure 1. The articles included were published between 1996 and 2021 from 17 countries. Supplemental Table 1, https://links.lww.com/MAO/B475, summarizes the descriptive features of all included studies. All studies included were Oxford Centre for Evidence Based Medicine level of evidence 4 (12). Considerable heterogeneity existed in the reporting of speech perception outcomes between studies. The authors attempted to limit this heterogeneity by comparing patients with the same retrocochlear pathology and limiting outcome measures to CNC word scores and AzBio sentence scores. Furthermore, patients were only included if they had a least 6 months of postoperative hearing experience available. The risk of bias across all included studies is summarized in Supplemental Table 2, https://links.lww.com/MAO/B475.

F1
FIG. 1:
PRISMA flowchart of literature review process. From: Page MJ, McKenzie JE, Bossuyt PM, Boutron I, Hoffmann TC, Mulrow CD, et al. The PRISMA 2020 statement: an updated guideline for reporting systematic reviews. BMJ 2021;372:n71. doi: 10.1136/bmj.n71. For more information, visit: http://www.prisma-statement.org/.

Patient Characteristics

Individual data were available for 171 patient cases, and all patients had a minimum follow-up of 6 months. Pathologies included were VS (n = 99, 57.9%), superficial siderosis (n = 39, 22.8%), neurosarcoidosis (n = 11, 6.4%), and previous CNS or skull base irradiation (n = 22, 12.9%). The average patient age was 54.0 years (standard deviation [SD], 16.2) and ranged from 20 to 88.4 years. Male patients comprised 60% of cases. The mean duration of hearing loss before CI was 105.1 months (8.8 years).

Speech Discrimination Outcomes

In the total cohort, the average preoperative CNC word score was 7.3% (SD, 12.7; n = 46), and the average postoperative score was 46.2% (SD, 25.3; n = 58). The change in CNC word scores (mean [SD]) for each individual pathology were: irradiated VS (29.7% [22.6]), observed VS (40.0% [26.6]), superficial siderosis (25.6% [35.3]), neurosarcoidosis (78.0% [2.8]), and previous CNS/skull base irradiation (34.4% [29.8]) (Table 2). Patients with neurosarcoidosis were the best performers overall, whereas patients with a history of irradiation to the CNS or skull base had the most variable and worst postoperative CNC word scores. However, when the change from preoperative to postoperative scores was evaluated, patients with CNS or skull base malignancies had similar levels of improvement in CNC word scores.

TABLE 1 - Description of design (PICOTS)
Population Patients aged 18 yr or older with diagnosed retrocochlear pathology (observed or irradiated VS, neurosarcoidosis, sideroses, and previous radiation to the brain or skull base)
Intervention CI (unilateral or bilateral)
Comparisons Speech perception outcomes among each of the retrocochlear pathologies
Timing 6–12 mo post-CI
Study design Systematic review and pooled analysis
CI indicates cochlear implantation; PICOTS, participants, interventions, comparisons, outcomes, timing and study

TABLE 2 - Speech perception outcomes in different retrocochlear pathologies
Observed VS (n = 53) Irradiated VS (n = 46) Superficial Siderosis (n = 39) Neurosarcoidosis (n = 11) Brain or Skull Base Radiation for Malignancy (n = 22)
CNC words preoperatively, mean (SD) 6.5% (12.3), n = 19 6.2% (10.9), n = 12 13.2% (19.2), n = 8 13.0% (7.1), n = 2 1.6% (3.6), n = 5
CNC words postoperatively, mean (SD) 45.4% (24.2), n = 22 44.4% (20.8), n = 16 43.6% (21.0), n = 10 89.5% (3.0), n = 4 30.0% (30.2), n = 6
Change in CNC words, mean (SD) 40.0% (26.6), n = 19 29.7% (22.6), n = 12 25.6% (35.3), n = 7 78.0% (2.8), n = 2 34.4% (29.8), n = 5
AzBio preoperatively, mean (SD) 6.6% (11.3), n = 12 1.0% (1.4), n = 5 24.5% (0.7), n = 2 NA NA
AzBio postoperatively, mean (SD) 55.9 (28.4), n = 14 62.5% (34.8), n = 6 48.3% (41.9), n = 3 NA NA
Change in AzBio, mean (SD) 48.1% (30.9), n = 12 36.5% (51.6), n = 2 51.0% (NA), n = 1 NA NA
CNC indicates consonant-nucleus-consonant; NA, not available; SD, standard deviation.

Observed vs. Radiated VS

The average preoperative and postoperative CNC word scores for irradiated VS were 6.2 (SD, 10.9) and 44.4% (SD, 20.8), respectively. For observed tumors, preoperative and postoperative scores were 6.5 (SD, 12.3) and 45.4% (SD, 24.2), respectively. There was no statistically significant difference in the average change in CNC word scores for irradiated VS (29.7% [SD, 22.6]) and observed VS (40.0% [SD, 26.6]; p = 0.3).

Factors Affecting Speech Perception Outcomes in VS

Among the 99 implanted patients with a nonoperated VS, we attempted to identify patient and tumor characteristics resulting in better outcomes. On univariate GEE analysis, age, maximal tumor dimension, presence of an NF-2 associated tumor, and previous irradition were not found to significantly impact change in postoperative CNC word scores. A summary of this data can be found in Table 3.

TABLE 3 - Univariate GEE models for evaluating variables influencing change in CNC word scores and AzBio sentence scores in patients with VS
Change in CNC Words Change in AzBio Sentences
Coefficient (95% CI) p Coefficient (95% CI) p
Age at surgery 0.19 (−0.001 to 0.38) NS 0.19 (−0.13 to 0.52) NS
NF-2–associated tumor 14.20 (−13.51 to 41.91) NS NA NA
Maximum tumor dimension −1.07 (−8.18 to 6.03) NS −14.50 (−58.34 to 29.34) NS
Previous irradiation −10.33 (−22.61 to 1.95) NS −11.58 (−57.42 to 34.25) NS
95% CI indicates confidence interval; CNC, consonant-nucleus-consonant; GEE, generalized estimated equation; NA not available because of too few data points; NS, statistically not significant.

Complications, Device Use Time, and Need for Explantation

For all cases combined, the average minimum length of known sustained benefit was 29 months. Limited adverse events were reported. One group described a patient with NF2 who underwent bilateral Gamma Knife SRS (12.5 Gy to the 50% isodose line) (48). The patient then underwent bilateral CI (no noted duration between SRS and surgery), but was found to have bilateral cochlear fibrosis intraoperatively, although a full insertion was achieved with the use of a styleted electrode.

82% of patients with reported CI usage were regular daily users, and overall, 82% of patients demonstrated improvement in speech perception scores after CI. Patients were considered daily users if they used their device more than 8 hours per day, or verbally reported all day cochlear implant use. All available details on patients who did not benefit, or did not have sustained benefit from CI can be found in Supplemental Table 3, https://links.lww.com/MAO/B475. Tinnitus suppression was only mentioned in one report, in which tinnitus suppression was not achieved in a patient implanted with a sporadic VS. Only two cases reported a negative promontory stimulation test before implantation and therefore no conclusions could be drawn regarding the value of this test. One patient with VS who had a negative promontory stimulation test achieved a postoperative pure-tone average of 80, monosyllabic WRS of 0%; disyllabic WRS of 5%, and sentence recognition score of 5%. The patient achieved environment sound awareness and lip reading but could not use the telephone. The patient also reported daily CI usage (54). Another patient with SS had a promontory stimulation test that showed pain sensation in both ears. Six months after CI, he demonstrated 55.0 dB and 30% correct response rate for oral language perception, and he ultimately discontinued CI use after 2 years (60).

Two patients with VS had progressive decline in performance with concomitant tumor growth, requiring device removal (16,21). The first of these patients was a 59-year-old male with a history of bilateral hearing loss (16). Preoperatively, the patient had 40% aided speech discrimination scores bilaterally and a temporal bone CT that was interpreted as normal. The patient underwent a left CI and had initial improvement in speech perception. Nine months after surgery, the patient presented with new onset ataxia and headaches, and an MRI revealed a 3-cm VS on the CI side. Although speech scores remained at 80%, tumor resection was performed because of size and associated hydrocephalus, via a translabyrinthine approach and the device was removed. The second patient was a 50-year-old male with NF2 who previously underwent stereotactic radiosurgery (SRS, 13 Gy at the 50% isodose line) for a 1.4-cm VS and demonstrated immediate and substantial benefit after implantation. He had progressive tumor growth 2.5 years after implantation and subsequently underwent explantation and tumor resection (21).

DISCUSSION

We performed a systematic review of patients with different retrocochlear pathologies who received a cochlear implant. Over 80% of patients demonstrated improvements in speech perception performance with their CI, with the worst performers being individuals previously irradiated for CNS or skull base pathologies, excluding VS. Irradiated VS did not exhibit worse CI performance compared to observed tumors. As the indications for cochlear implants continue to expand, the current study suggests that a retrocochlear pathology should not preclude CI consideration.

Vestibular Schwannomas

Several systematic reviews have assessed the outcomes of CI in both sporadic and NF2-associated VS (3,62). However, these reviews will often combine both operated and observed tumors, making outcome comparisons difficult. Tadokoro et al. (63) reviewed CI in patients with VS and compared outcomes between sporadic and NF2-associated tumors. Fifty-six percent of tumors in their review had undergone resection before CI. West et al. (3) focused on patients who underwent surgical resection with subsequent cochlear implant in the same procedure. Finally, Bartindale et al. (62) reviewed 45 patients with sporadic VS, 86.7% of whom had a surgical resection before CI placement. Our review, therefore, focused on patients undergoing a CI with unoperated retrocochlear pathologies.

We found that irradiated VS did not have worse speech scores compared to observed tumors, similar to a growing body of literature suggesting that irradiation should not preclude a patient from receiving a CI (64). Histologic studies have shown that Gamma Knife radiosurgery, in particular, does not affect the VS cells per say but instead leads to vascular injury that hinders the blood supply to the tumor (65). Furthermore, it is postulated that within the cochlea, radiation-induced injury occurs at the level of the stria vascularis, and a cochlear implant can bypass this pathology. Ideal timing between radiation and CI remains unclear. At our center, CI is usually performed approximately 6 months after treatment, allowing the patient to receive a follow-up MRI without artifact, to assess for an unusually rapid growth pattern.

Similar outcomes were noted between sporadic and NF2-related tumors, which differs from previous literature (58). We hypothesize that the similar outcomes in this review may be related to the fact that operated tumors were excluded. CI consideration in observed or irradiated VS will usually occur for smaller, more dormant tumors. This may also be the reason why maximal tumor dimension did not affect speech perception outcomes in this study. Deep et al. (5) reported that tumors 1.5 cm or less had better speech understanding after CI, however only small numbers of resected, irradiated, and observed tumors were included. Our findings suggest that when possible, a CI should be considered in a stable tumor with hearing loss, particularly before considering an auditory brainstem implant, as a CI will always outperform the auditory brainstem implant (66,67). In fact, some groups may suggest that a CI in a patient with a VS, who may subsequently undergo a systemic drug trial, may represent a paradigm shift in the management of NF2 (64).

Other Retrocochlear Pathologies

Patients with other retrocochlear pathologies showed good CI performance in this review, with the best performers being individuals with neurosarcoidosis. Hearing loss associated with neurosarcoidosis is thought to be caused by either perivascular lymphocytic intraneural invasion of the eighth cranial nerve or due to ischemia secondary to vasculitis of the inner ear neuroepithelium (68). Overall, less than 10% of patients with neurosarcoidosis are thought to develop hearing loss and among those who do, there is an important rate of spontaneous recovery with corticosteroid treatment (69). One study suggested waiting over a year to ensure that the hearing will not recover (2), but to remain vigilant and perform serial imaging as cochlear ossification has been reported in this group of patients. Overall, excellent CI outcomes are reported in several small studies in the context of neurosarcoidosis, and these outcomes were stable over time (2,25,52,70).

Patients with superficial siderosis also demonstrated good speech perception outcomes. The pathophysiology of hearing loss in these patients is related to the deposition of hemosiderin within the leptomeninges and subpial layer (71). Modest et al. (42) reviewed their own cohort of seven ears implanted and performed a literature review of cochlear implants in patients with known superficial siderosis. Similar to our findings, all but two patients in their group gained significant benefit from their implant. The two who did not benefit had important disease progression resulting in poorer outcomes. One observation made when reviewing the granular individual SS data was that almost every small case series had at least one patient whose disease progressively worsened with concomitant decline in speech performance (15,17,29,42,59).

Finally, patients with a history of CNS or skull base radiation in the context of malignancy were the worst and most unpredictable performers. The mechanism of hearing loss after radiotherapy is not completely understood, but likely secondary to hair-cell injury within the cochlea and possible damage to the cochlear nerve or even the cochlear nucleus (especially if the brainstem was radiated) (72,73). Certain groups suggest performing preoperative CNS imaging to identify radiation-induced pathologic changes of the CNS, including gliosis and demyelination, which could lead to a more guarded prognosis (74). Despite this variability in outcomes, previous radiation therapy should not deter clinicians from offering CI to patients, as some may receive great benefit (2).

LIMITATIONS

The included publications were entirely retrospective, and thus, risk of biased reporting is high. Furthermore, notable heterogeneity exists in the tests used for reporting speech discrimination outcomes, which resulted in a limited sample size because only CNC word and AzBio sentence scores were included. Lastly, it is known that some patients display delayed benefit from CI after 6 months of follow-up. Because both 6-month and 12-month results were combined due to limited available data, the post-CI hearing outcomes may be an underestimation of the benefit provided by CI.

CONCLUSION

In conclusion, the current review suggests that CI in patients with concomitant retrocochlear pathology generally results in improved speech discrimination scores. In patients with VS, previous irradiation and NF2 status did not seem to affect speech outcomes.

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Keywords:

Central nervous system malignancy; Cochlear implants; Neurosarcoidosis; Retrocochlear pathology; Superficial siderosis; Vestibular schwannoma

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