Systematic Review of Hearing Preservation in Observed Vestibular Schwannoma

Abstract

Objective  This is a systematic review of the literature on the spontaneous course of hearing in patients observed with a vestibular schwannoma. Included studies are appraised using the Grading of Recommendations Assessment, Development and Evaluation system.

Design  PubMed, Embase, Medline, Cochrane library, and CINAHL (Cumulative Index to Nursing and Allied Health Literature) were searched for literature on hearing in patients observed with a vestibular schwannoma.

Participants  Of 217 evaluated papers, 15 were included, representing a total of 2,142 patients.

Main Outcome Measures  Hearing according to the AAO-HNS (American Academy of Otorhinolaryngology- Head and Neck Surgery) classification system. Weighted average of the proportion of patients preserving good hearing (>70% discrimination score and pure tone audiometry [PTA] < 30dB) and serviceable hearing (>50% discrimination score and PTA < 50dB) was determined.

Results  Fifty percent of patients presenting with good hearing at diagnosis had preserved this after a mean of 5 years of observation, whereas serviceable hearing was preserved in 54%. Patients with normal discrimination at diagnosis preserve their hearing very well. Very few studies exist on long-term hearing preservation.

Conclusions  After 5 years of observation, around half of patients will have preserved good or serviceable hearing. Patients with normal discrimination at diagnosis are more likely to preserve good hearing.

Introduction

Hearing preservation in patients with vestibular schwannomas (VS) is one of several aspects of managing the disease. Some claim it is the most significant symptom when comparing with other potential symptoms related to VS, for example, dizziness, tinnitus, and facial weakness. ¹ Depending on tumor size or growth of the VS, the potential active treatment options are radiotherapy or surgery. If the hearing on the tumor ear is worth preserving, the surgical approach or the radiotherapeutical strategy may aim to preserve the hearing. In fact, preservation of hearing may itself be an indication to perform surgery, even in smaller or nongrowing tumors, or in the case of an only hearing ear on the tumor side. ^{2 3} However, the hearing results of any active treatment should always be compared with those of the spontaneous course of the disease, documented through repeated audiometry in observed patients.

Over the years, several studies have pointed in different directions with respect to the optimal treatment strategy, increasingly influenced by the fact that an increasing number of papers including larger series of patients report that a significant proportion of VS is not growing after diagnosis. ^{4 5 6 7} Thus, an increasing number of tumors are diagnosed and subsequently observed. ⁸ Importantly, it has also been documented that the hearing at diagnosis is better and better, and an increasing number of patients are presenting with near-normal hearing. ⁹ These facts render an evidence-based strategy for optimal preservation of hearing increasingly important.

The definition of hearing worthy of preservation is debatable. Some authors advocate that as long as the speech discrimination score (SD) is better than 50%, the hearing is serviceable, and thus worthy of preservation, as a hearing aid can be used with at least some benefit. However, most authors use the AAO-HNS class A hearing (pure tone audiometry [PTA] <30dB and SD >70%) as definition of good hearing and class A/B (PTA <50dB and SD >50%) ¹⁰ as definition of serviceable hearing and thus hearing worthy of preservation. Hence, the latter definitions are used in this literature review.

Methods

A search was performed on PubMed, Embase, Medline, Cochrane library, and CINAHL using the keywords “vestibular schwannoma,” “acoustic neuroma,” “growth,” “hearing,” “natural history,” alone and in combination, yielding 115 papers with no early date limit and including publications up to July 2018. All papers were read and their references exhaustively checked for additional papers not occurring in the original search, yielding 102 additional papers.

Pubmed Search Syntax

((“neuroma, acoustic”[MeSH Terms] OR (“neuroma”[All Fields] AND “acoustic”[All Fields]) OR “acoustic neuroma”[All Fields] OR (“vestibular”[All Fields] AND “schwannoma”[All Fields]) OR “vestibular schwannoma”[All Fields]) OR (“neuroma, acoustic”[MeSH Terms] OR (“neuroma”[All Fields] AND “acoustic”[All Fields]) OR “acoustic neuroma”[All Fields] OR (“acoustic”[All Fields] AND “neuroma”[All Fields]))) AND ((“growth and development”[Subheading] OR (“growth”[All Fields] AND “development”[All Fields]) OR “growth and development”[All Fields] OR “growth”[All Fields] OR “growth”[MeSH Terms]) OR (“hearing”[MeSH Terms] OR “hearing”[All Fields])) AND (“natural history”[MeSH Terms] OR (“natural”[All Fields] AND “history”[All Fields]) OR “natural history”[All Fields]) AND (hasabstract[text] AND (“0001/01/01”[PDAT]: “2018/06/31”[PDAT])).

Paper Inclusion Criteria

The 217 identified papers were screened using the following criteria:

1. Clinical articles reporting original data, thus excluding reviews, meta-analyses, and conference abstracts.

2. Observational studies based on case series/cohorts and repeated audiometry.

3. More than 30 patients included.

4. Reported mean/median follow-up.

5. Use of AAO-HNS guidelines for classification of hearing ¹⁰ and reported class A and/or class AB hearing.

6. Sporadic/unilateral VS, excluding neurofibromatosis type 2 (NF2)-associated tumors.

Two hundred and one papers not fulfilling one or more of these inclusion criteria were discarded. This left 16 papers for inclusion. Two of these were disregarded, as they included patients reported on in (two) other included papers. An overview of included papers is given in Table 1 .

Table 1. Included publications on hearing preservation in observed patients with vestibular schwannoma.

Author (reference)	Year	Study design	Patients (number)	Mean follow-up (years)	Preservation of good hearing (%) >30% DS <30dB PTA	Preservation serviceable hearing (%) >50%DS <50dB PTA	Grade quality of evidence	Grade strength of recommendation
Kirchmann et al 12	2017	Pro cohort	156 IAC	9.5	17	34	Moderate	Strong
Tveiten et al 13	2015	Retro cohort	148	8.3	62	67	Moderate	Strong
Stangerup et al 9	2010	Pro cohort	932	4.7	51	56	Moderate	Strong
Stangerup et al 14	2008	Pro cohort	548	3.9	52	55	Moderate	Disregarded
Breivik et al 7	2012	Pro cohort	186	3.6	NR	63	Moderate	Strong
Caye-Thomasen et al 15	2007	Pro cohort	156 IAC	4.6	47	47	Moderate	Disregarded
Breivik et al 16	2013	Pro cohort	124	4.6	NR	24	Moderate	Strong
Grayeli et al 4	2005	Retro cohort	105	2.8	52	57	Low	Weak
Lin et al 17	2005	Retro cohort	86	6.8	NR	43	Low	Weak
Godefroy et al 18	2009	Pro cohort	70	3.6	NR	57	Moderate	Strong
Quaranta et al 19	2007	Retro cohort	70	2.8	71	60	Low	Weak
Ferri et al 20	2008	Pro cohort	56	3.6	NR	73	Moderate	Strong
Roehm and Gantz 21	2007	Retro cohort of elderly >65	48	3.0	33	38	Very low	Weak
Pennings et al 22	2011	Retro cohort	47 IAC	3.6	65	74	Moderate	Strong
Régis et al 23	2010	Pro cohort	40 IAC	3.3	69	68	Low	Weak
Lee et al 24	2014	Retro cohort	31 IAC	2.6	45	NR	Very low	Weak
All studies	–	–	2142	5.0	50.4%	54.3%

Abbreviations: DS, discrimination score (speech discrimination); IAC, intracanalicular; NR, not reported; PTA, pure tune audiometry.

All papers were scored using the Grading of Recommendations Assessment, Development and Evaluation (GRADE) system ¹¹ (see Table 1 ).

Results

Data on the natural history of hearing exist from more than 2,100 patients, as reported in 14 papers ( Table 1 ). Almost half the patients are presented in the 2010 paper by Stangerup et al. ⁹ Even though it is listed in Table 1 , the 2008 paper by Stangerup et al ¹⁴ is disregarded, as the patients in this paper are included in the 2010 article. ⁹ The same applies to the 2007 paper by Caye-Thomasen et al ¹⁵ which is disregarded, as the patients are part of the same prospective cohort included in the most recent paper from 2017 by Kirchmann et al. ¹²

Weighted calculation based on the number of included patients in each paper showed a mean follow-up of 5.0 years, ranging from 2.6 to 9.5 years. Only three papers, representing a total of 390 (86 + 148 + 156) patients, had more than 5 years follow-up (6.8, 8.3, and 9.5 years). ^{12 13 17}

Weighted calculation on the preservation of hearing showed that on average 50% of patients diagnosed with a unilateral/sporadic VS and presenting with good hearing at diagnosis will preserve this within 5 years of observation, whereas 54% of patients presenting with serviceable hearing at diagnosis will preserve this within the same period of observation ( Table 1 ).

A few larger studies show that normal SD at diagnosis indicates that good hearing will be maintained for many years, ^{9 14 15 25} and some studies show a faster decline in hearing acuity in patients with growing tumors, ^{12 15 26} while others do not.

All papers are subject to selection bias concerning tumor size, as larger tumors were excluded (and typically operated). All but four papers ^{9 12 14 15} involved referral bias (patients may not be representative for the general VS population) and the majority of papers involved some degree of patient selection bias concerning age and co-morbidity. Most studies do not distinguish between purely intracanalicular tumors and tumors with an extrameatal extension, whereas some do.

Discussion and Conclusion

We performed a systematic review of the spontaneous course of hearing in patients observed with a sporadic VS. We chose to include clinical articles reporting original data on sporadic tumors (excluding NF2 cases), thus excluding reviews, meta-analyses, and conference abstracts. Only studies with more than 30 patients and reporting mean/median follow-up, using the AAO-HNS classification of hearing, ¹⁰ and reporting class A and/or class AB hearing were included. The latter choice was made, as the majority of published studies use the AAO-HNS classification system, thus allowing comparisons and overall conclusions to be made. It should be noted, however, that an international consensus on the reporting of hearing does not exist for these patients, although warranted and overdue. Good international studies using other classification systems (e.g., the Gardner–Robertson system) are still published. ^{27 28} By the choice above, such studies were not included in this review, thus introducing a potential bias to our conclusion. Optimally, an international consensus on the use of one classification system of hearing and what constitutes good and/or serviceable hearing should be reached.

Using the GRADE system evaluation, it is evident that the level of evidence according to this system is on average moderate (see Table 1 ), which is the highest level achievable for observed case series. The quality of several studies is, however, relatively high, leading to strong recommendation concerning study conclusions (see Table 1 ), and thus adding to the overall validity of the present review.

Based on this review comprising more than 2,100 unique patients, we conclude that after 5 years of observation, on average around half the patients will have preserved good and/or serviceable hearing. Patients with normal discrimination at diagnosis are more likely to preserve good hearing. As a reference, these data on conservative management should be considered when evaluating and reporting hearing preservation outcomes using active treatment (i.e., microsurgery or radiotherapy).