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Commentary: Long-Term Hearing Outcomes Following Stereotactic Radiosurgery in Vestibular Schwannoma Patients-A Retrospective Cohort Study.

Copyright C © 2018 by the Congress of Neurological Surgeons V estibular schwannoma (VS), colloquially known as acoustic neuroma, is a rare tumor of the vestibulocochlear nerve with a prevalence of approximately 3300 in the United States1 and incidence of approximately 10 to 25 cases per million.1-3 VS has a benign natural history, with a mean growth rate of <2 mm/yr.4,5 However, with close proximity to the vestibulocochlear apparatus and cerebellopontine angle, even small lesions may lead to such symptoms as hearing loss, tinnitus, vertigo, facial numbness, and otalgia. Options in the management of VS include observation, surgical intervention, and radiation therapy. Since the seminal work of Leksell demonstrating excellent outcomes with stereotactic radiosurgery (SRS),6 this has been the preferred radiation-based technique whether by Gamma Knife radiosurgery (GKRS; Elekta AB, Stockholm, Sweden) or linear accelerator-based methods, such as Cyberknife (Accuray Inc, Sunnyvale, California).7 Utilization of different treatment approaches varies by geography and institution with numerous factors influencing the decision to intervene and the modality that is applied. Given the rarity of the tumor and long-term follow-up required to assess outcomes, Level I evidence is lacking to help standardize management, which makes observational and high-quality retrospective data of great value. Santa Maria et al8 provide a rigorous assessment of their institutional experience with SRS for VS. In this retrospective study, 473 tumors treated with Cyberknife SRS over a span of 21 yr were included and had an average follow-up of 5.5 yr. The authors are commended on their efforts to collate and analyze this database as well as adhere to reporting standards for this type of work with the inclusion of individual patient data that may advance future investigations. A wealth of information may be deduced from this investigation, but the primary conclusion—that SRS is associated with a high rate of hearing decline—and what it means for treatment recommendations deserves special considerations. Hearing may decline in patients with VS in the absence of treatment and, in some patients, even in the absence of tumor growth. In a prospective study of conservative management with MRI surveillance for VS, the subgroup of patients who demonstrated no growth or growth <1 mm/yr still experienced a 40% decline in speech discrimination scores and a mean decline in pure tone average of 36 dB after a median follow-up of 10 yr.9 Another prospective study employed close observation in an effort to avoid empiric treatment for VS.10 Over one-third of patients failed observation, consistent with other reports,4,5,11 and patients who had less than perfect speech discrimination scores at diagnosis had only a 55% chance of maintaining good hearing at the end of the 10-yr follow-up period. In another study of observation, audiometry analyses showed the mean rate of hearing decline was numerically worse during the surveillance period (5.39 dB/yr) than after SRS (3.77 dB/yr) though the difference was not statistically significant.12 In the same way that clinicians must use caution when recommending empiric treatment for VS, these data remind us that conservative management also carries risks. A valid argument for conservative management is that, although observation may be associated with hearing decrements, the timecourse of decline is likely protracted relative to the adverse effects of treatment. To be sure, while surgical intervention may acutely impair hearing and SRS may lead to a steady decline over many months to a few years, the negative effects of close observation typically develop only after many years of follow-up. As with most controversies in oncology, the essence of the matter is patient selection, and this highlights the strength of Santa Maria and colleague’s data.8