Vestibular schwannoma (VS) are benign tumours originating from the Schwann cells of the vestibular nerves. Stereotactic radiosurgery (SRS) is primarily indicated to address the growth of small- to medium-sized tumours, especially in the event of symptom accumulation and deterioration (imbalance, tinnitus, progressive hearing loss, facial palsy) [1], [2]. Gamma knife (GK)-SRS uses fixed Cobalt-60 radiation beams that are collimated to deliver a precise and high radiation dose to a single target. GK-SRS is minimally-invasive and superior to microsurgery regarding cranial nerve and hearing function preservation when treating progressive solitary VS under 3 cm in cisternal diameter [1], [3]. Recently, single-fraction SRS with GK has shown a 5-year tumour control rate of 93% [4] with a low risk of facial nerve damage [1].

The reports on hearing outcomes after SRS are abundant, with a recent systematic review and meta-analysis reporting that 59.4% of cases have preserved hearing after a median of 6.7 years of follow-up [5]. Conversely, there are fewer reports on how GK-SRS affects patient balance and notably objective and quantitative vestibular outcomes. Briefly, key prospective studies have shown no change in patient-reported tinnitus and vertigo, as well as balance platform test results after 2 years [6]. Comparative studies have demonstrated superiority for GK-SRS over microsurgery in terms of patient-reported balance [7] and better questionnaire-based functional outcomes [8] up to 4 years after. One prospective study highlighted a significant improvement in Dizziness Handicap Inventory (DHI) scores among patients >65 years (54 patients with 7–94 months of follow-up) [9]. Findings were based on patient questioning without official questionnaires. Importantly, a retrospective evaluation of 115 patients by Lee et al. [10] has shown a trend for deterioration in vestibular symptoms (imbalance, rotatory vertigo, unsteadiness) 6 months after GK-SRS. Putz et al. [11] also reported a deterioration in objective vestibular function using videonystagmography (VNG) in 17.6% (n = 3/17) of cases. Finally, a cohort study of 353 patients with VS treated with GK-SRS has shown that overall quality of life (QoL) (assessed by the SF36 questionnaire) is comparable to that of the general population, but vertigo is the symptom influencing most QoL [12]. In all, solid conclusions on post-SRS vestibular outcomes cannot yet be drawn [13].

The aim of our study here was thus to determine prospectively how GK-SRS affects the quality of patient balance. To do this, we assessed patient-perceived changes in balance before versus 1-year after treatment. We additionally examined changes in objective vestibular function for the first time.