50 Reporting of Hearing Outcome Data for Vestibular Schwannoma

10.1055/b-0039-169204

50 Reporting of Hearing Outcome Data for Vestibular Schwannoma

Christian A. Bowers and Richard K. Gurgel

50.1 Introduction

Hearing preservation is an important treatment goal for patients with vestibular schwannomas if they have serviceable hearing. The importance of hearing preservation is heightened in younger patients who have many years of potentially good hearing, with smaller tumors which are less technically challenging to treat than larger tumors, in patients with existing hearing loss in the contralateral ear, in patients with threatened hearing in the contralateral ear as with neurofibromatosis type 2, or in patients who depend upon binaural hearing and sound localization for occupational or recreational needs. Of the three primary surgical approaches used for the resection of vestibular schwannoma, only the translabyrinthine approach precludes an attempt at hearing preservation. Therefore, hearing preservation is a key focus for patients undergoing middle fossa or retrosigmoid approaches. Unfortunately, the historical use of various pre- and postoperative hearing measurements and classification schemes has made the comparison of hearing outcomes difficult and complicated.

Management of patients with vestibular schwannoma and serviceable hearing becomes quite complex. In addition to the middle fossa and retrosigmoid approaches, which can preserve inner ear structures and the integrity of the cochlear division of the eighth cranial nerve, nonsurgical management options—namely active surveillance and radiotherapy or radiosurgery—also preserve the anatomic structures critical for hearing. Deciding which of the various strategies to apply to any given patient with functional hearing requires an understanding of the techniques and existing data on the hearing preservation rates of these therapeutic options in addition to balancing other important outcome priorities such as tumor control and facial nerve outcome.

Pre- and postoperative assessment of hearing is fundamental to the diagnostic evaluation of patients with vestibular schwannoma. Hearing is measured by trained clinicians with a background in audiology and is graded according to published standards using calibrated equipment.s. Literatur ^, s. Literatur While conductive and sensorineural hearing loss are commonly measured, in the context of vestibular schwannoma, sensorineural hearing loss is the primary concern. Routine audiometry measures hearing thresholds (dB HL) using pure (single-frequency) tones at predetermined frequencies. At each frequency, the minimum loudness that the person can detect is recorded. Thus, behavioral pure-tone audiometry is a subjective test that requires patient cooperation. Representative frequencies for speech understanding (most commonly 0.5, 1, 2, and 3 or 4 kHz) are then averaged to provide one number that is representative of the average threshold of sound detection—the pure-tone average (PTA). Some studies have used the speech reception threshold (SRT), defined as the lowest intensity level (db HL) at which a patient can correctly identify 50% of common two-syllable words, in place of the PTA since these two measures should be within 5 dB of one another. Another critical component of hearing evaluation is the word recognition (or speech discrimination) score (WRS or SDS), which is a measurement of sound clarity at a volume well above the minimal threshold of hearing. The WRS gives information about the clarity of hearing for a patient, which is often diminished disproportionately more than the PTA in patients with vestibular schwannoma.s. Literatur Of the two basic metrics—PTA and WRS—the WRS has more functional relevance for patients because WRS predicts whether hearing loss is amenable to amplification. Hearing aids can make sound louder, but they do not make sound clearer. Therefore, if patients experience marked WRS deterioration as a result of treatment or tumor progression, they will have functional hearing impairment that cannot be rectified by simply increasing the sound with a hearing aid.

Standardization in reporting hearing outcomes is imperative to comparing the efficacy of different treatment options and understanding the natural history of disease.s. Literatur For example, an omission of either PTA or WRS can mislead a reader who is trying to interpret accurate hearing outcomes for a given therapeutic option. Thus, over the years, several hearing classification systems have been proposed. The objectives of this chapter are to (1) review the evolution and development of the various hearing classification systems used in vestibular schwannoma research and clinical care and (2) discuss unresolved issues and future directions.

50.2 Hearing Measurement and Classification Systems

50.2.1 Gardner–Robertson Scale (1988)

The first hearing metric widely adopted for measuring outcomes in vestibular schwannoma surgery was the Gardner–Robertson (GR) hearing scale derived from the seminal 1988 publication (Table 50‑1 ).s. Literatur The goal of this report was to create a five-class scale that was simple, easy to remember, and clinically relevant.s. Literatur Wade and Houses. Literatur had previously described the “50/50 rule,” which defined serviceable hearing as having a PTA of less than 50 dB HL with a SDS of 50% or better. The GR scale arose from the notion that the “50/50” rule did not provide the important useful clinical information necessary to differentiate and classify the potential variety of hearing outcomes. Therefore, Gardner and Robertson modified a classification system scale of hearing preservation in vestibular schwannoma surgery initially proposed by Silverstein et al.s. Literatur Their modification became the widely standardized hearing scale used for reporting hearing outcomes in vestibular schwannoma surgery for most of the following decade.s. Literatur

Table 50.1 Gardner–Robertson classification for hearing preservation
Grade	PTA or SRT (dB HL)^a	Speech discrimination (%)
I	0–30	70–100
II	31–50	50–69
II	51–90	5–49
IV	91 to max loss	1–4
V	No response	No response
Abbreviations: PTA, pure-tone average; SRT, speech reception threshold. ^aUse better score. If PTA/SRT score and speech discrimination scores do not qualify for same class, use class appropriate for poorer of two scores. Source: Used with permission from Gardner G, Robertson JH.. Hearing preservation in unilateral acoustic neuroma surgery. Ann Otol Rhinol Laryngol. 1988; 97(1):55-66.s. Literatur