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Purpose: For patients with vestibular schwannomas (VS), a conservative observational approach is increasingly used. Therefore, the need for accurate and reliable volumetric tumor monitoring is important. Currently, a volumetric cutoff of 20% increase in tumor volume is widely used to define tumor growth in VS. The study investigates the tumor volume dependency on the limits of agreement (LoA) for volumetric measurements of VS by means of an inter-observer study., Methods: This retrospective study included 100 VS patients who underwent contrast-enhanced T1-weighted MRI. Five observers volumetrically annotated the images. Observer agreement and reliability was measured using the LoA, estimated using the limits of agreement with the mean (LOAM) method, and the intraclass correlation coefficient (ICC)., Results: The 100 patients had a median average tumor volume of 903 mm 3 (IQR: 193-3101). Patients were divided into four volumetric size categories based on tumor volume quartile. The smallest tumor volume quartile showed a LOAM relative to the mean of 26.8% (95% CI: 23.7-33.6), whereas for the largest tumor volume quartile this figure was found to be 7.3% (95% CI: 6.5-9.7) and when excluding peritumoral cysts: 4.8% (95% CI: 4.2-6.2)., Conclusion: Agreement limits within volumetric annotation of VS are affected by tumor volume, since the LoA improves with increasing tumor volume. As a result, for tumors larger than 200 mm 3 , growth can reliably be detected at an earlier stage, compared to the currently widely used cutoff of 20%. However, for very small tumors, growth should be assessed with higher agreement limits than previously thought., (© 2024. The Author(s).)

Objective: To assess the effect of wait and scan (W&S) and stereotactic radiosurgery (SRS) on health-related quality of life (HRQoL) over time in patients with a stable vestibular schwannoma (VS) and growing VS., Study Design: Longitudinal, multicenter, observational study., Setting: Tertiary expert center for VS (Radboudumc Nijmegen) and Gamma-Knife center ETZ Hospital Tilburg., Methods: Changes in HRQoL, measured with the Penn Acoustic Neuroma Quality-of-Life (PANQOL), and the physical and mental component summary scores (PCS and MCS, respectively) derived from the 36-Item Short Form Health Survey (SF-36), were compared among patients managed by W&S and SRS between 2017 and 2022. Second, HRQoL over time in patients with a growing VS was compared between W&S and SRS., Results: Differences in PANQOL total and subdomain scores, PCS and MCS scores over time in the W&S (n = 73) and SRS (n = 170) groups were nonsignificant and on average did not exceed the minimal clinically important differences (mean difference of -2.56 [PANQOL total], 1.22 [PCS], and -1.76 [MCS]; all P > .05). In growing VS, comparison of W&S (n = 29) and SRS (n = 154) also revealed no significant difference (mean difference of 1.19 (PANQOL total), 1.83 (PCS) and -0.12 (MCS); all P > .05)., Conclusion: Differences in HRQoL in patients with VS are minor and not significantly different or clinically relevant between patients managed with W&S or SRS. Similarly, patients with a growing VS managed with W&S or SRS exhibit no significant or clinical relevant difference in HRQoL during follow-up. This can aid clinicians in the counseling of patients regarding HRQoL when deciding on a management strategy after diagnosis or documented growth., (© 2024 The Authors. Otolaryngology–Head and Neck Surgery published by Wiley Periodicals LLC on behalf of American Academy of Otolaryngology–Head and Neck Surgery Foundation.)

Purpose: During counseling and management of patients with vestibular schwannoma (VS), the emphasis is shifting from tumour control and nerve preservation towards maintaining or improving health-related quality of life (HRQoL). Understanding the patients' perspective and impact of VS is, therefore, of utmost importance. The current study aimed to identify treatment outcomes preferred by patients and to explore the patient-reported VS symptoms and management-related side effects and their impact on HRQoL., Methods: Patients with VS were contacted through the Dutch VS association Stichting Hoormij and questioned using a semi-structured, cross-sectional online survey. Patients were asked to report and rank symptoms and side effects, with their impact on HRQoL and frequency of occurrence. Results were structured through qualitative content analysis. Coded symptoms, side effects, impacts, frequencies, and patient-preferred outcomes were analysed and summarized with descriptive statistics., Results: Of the 231 respondents, 71% were actively treated. Hearing (symptoms vs. side effects: 78.8% vs. 63.6%), balance (62.3%; 48.8%), and energy issues (33.8%; 32.6%) were the most frequently mentioned symptoms and management-related side effects. Fatigue, deafness, headaches, and hearing loss had the highest impact on HRQoL. The majority of patients identified hearing preservation (61%), balance preservation (38.5%), and reduced tinnitus (34.6%) to be the patient-preferred outcomes., Conclusion: This qualitative study demonstrates that in this population many patients with VS encounter participation difficulties in their daily physical and social activities and value hearing and balance preservation, reduced tinnitus, and restored energy as preferred outcomes as they are hampered by symptoms and side effects related to hearing, balance, and energy. Healthcare professionals should consider these key points and use these and the patient-preferred outcomes in consultation, shared decision making, treatment, and follow-up to optimize patient-centred care., (© 2023. The Author(s).)

Objective: Vestibular schwannoma (VS) growth of ≥2 mm during serial MRI observation, irrespective of size, is the benchmark for treatment initiation in almost all centers. Although the probability of less optimal outcomes significantly increases in VS closer to the brainstem, early intervention does not improve long-term quality of life. Moving beyond the recommendation of definitive treatment for all VS after detected growth, we subclassified Koos 2 tumors based on extrameatal extension and relation to the brainstem. The aim of the current study was to evaluate the Koos 2 subclassification's validity and the inter-and intra-rater reliability of the entire Koos classification., Methods: Six experts, including neurosurgeons, otorhinolaryngologists and radiologists from two tertiary referral centers, classified 43 VS MRI scans. Validity of the Koos 2 subclassification was evaluated by the percentage agreement against the multidisciplinary skull base tumor board management advice. Inter- and intra-rater reliability were calculated using the intraclass correlation coefficient (ICC)., Results: Validity was almost perfect in Koos 2a VSs with a 100% agreement and 87.5% agreement for Koos 2b. Inter-rater reliability for all Koos grades was significantly excellent (ICC 0.91; 95%CI 0.866 to 0.944, p= <0.001). Five raters had an excellent intra-rater reliability (ICC > 0.90; p= <0.01) and one rater had a good intra-rater reliability (ICC 0.88; 95% CI 0.742 to 0.949)., Conclusions: Although multiple factors influence decision-making, the classification of Koos 2a and 2b with excellent inter- and intra-rater reliability, can aid in recommending treatment initiation, moving beyond detected tumor growth, aiming to optimize patient centered care., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 The Authors. Published by Elsevier B.V. All rights reserved.)

Anecdotally, cystic vestibular schwannomas (cVSs) are regarded to have unpredictable biologic activity with poorer clinical results, and most studies showed a less favorable prognosis following surgery. While stereotactic radiosurgery (SRS) is a well-established therapeutic option for small- to medium-sized VSs, cVSs are often larger, thus making upfront SRS more complicated. The purpose of this retrospective study was to assess the efficacy and safety of upfront SRS for large cVSs. The authors reviewed the data of 54 patients who received upfront, single-session Gamma Knife radiosurgery (GKRS) with a diagnosis of large cVS (> 4 cm3). Patients with neurofibromatosis type 2, multiple VSs, or recurrent VSs and < 24 months of clinical and neuroimaging follow-up were excluded. Hearing loss (48.1%) was the primary presenting symptom. The majority of cVSs were Koos grade IV (66.7%), and the most prevalent cyst pattern was "mixed pattern of small and big cysts" (46.3%). The median time between diagnosis and GKRS was 12 months (range, 1-147 months). At GKRS, the median cVS volume was 6.95 cm 3 (range, 4.1-22 cm 3 ). The median marginal dose was 12 Gy (range, 10-12 Gy). The mean radiological and clinical follow-up periods were 62.2 ± 34.04 months (range, 24-169 months) and 94.9 ± 45.41 months (range, 24-175 months), respectively. At 2, 6, and 12 years, the tumor control rates were 100%, 95.7%, and 85.0%, respectively. Tumor shrinkage occurred in 92.6% of patients (n = 50), tumor volume remained stable in 5.6% of patients (n = 3), and tumor growth occurred in 1.9% of patients (n = 1). At a median follow-up of 53.5 months, the pre-GKRS tumor volume significantly decreased to 2.35 cm 3 (p < 0.001). While Koos grade 3 patients had a greater possibility of attaining higher volume reduction, "multiple small thick-walled cyst pattern" and smaller tumor volumes decreased the likelihood of achieving higher volume reduction. Serviceable hearing (Gardner-Robertson Scale I-II) was present in 16.7% of patients prior to GKRS and it was preserved in all of these patients following GKRS. After GKRS, 1.9% of patients (n = 1) had new-onset trigeminal neuralgia. There was no new-onset facial palsy, hemifacial spasm, or hydrocephalus. Contrary to what was believed, our findings suggest that upfront GKRS seems to be a safe and effective treatment option for large cVSs., (© 2022. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

Objectives: To determine the cost-effectiveness of auditory brainstem response prior to MRI (ABR-MRI) compared to standalone MRI to diagnose vestibular schwannoma., Design: A state transition model was developed to simulate costs and effects (quality-adjusted life years [QALY]) for both diagnostic strategies for patients suspected of a vestibular schwannoma. Model input was derived from literature, hospital databases and expert opinions. Scenario and sensitivity analyses addressed model uncertainty., Results: Over a lifetime horizon, ABR-MRI resulted in a limited cost-saving of €68 or €98 per patient (dependent on MRI sequence) and a health loss of 0.005 QALYs over standalone MRI. ABR-MRI, however, did miss patients with other important pathology (2% of the population) that would have been detected when using standalone MRI. In total, €14 203 or €19 550 could be saved per lost QALY if ABR-MRI was used instead of standalone MRI. The results were sensitive to the detection rate of vestibular schwannoma and health-related quality of life of missed patients., Conclusion: The cost-saving with ABR-MRI does not seem to outweigh the number of missed patients with VS and other important pathologies that would have been detected when using standalone MRI., (© 2021 The Authors. Clinical Otolaryngology published by John Wiley & Sons Ltd.)

This study investigates whether there exist differences in facial emotion detection accuracy in patients suffering from Vestibular Schwannoma (VS) due to their facial paresis. Forty-four VS patients, half of them with, and half of them without a facial paresis, had to classify pictures of facial expressions as being emotional or non-emotional. The visual information of images was systematically manipulated by adding different levels of visual noise. The study had a mixed design with emotional expression (happy vs. angry) and visual noise level (10% to 80%) as repeated measures and facial paresis (present vs. absent) and degree of facial dysfunction as between subjects' factors. Emotion detection accuracy declined when visual information declined, an effect that was stronger for anger than for happy expressions. Overall, emotion detection accuracy for happy and angry faces did not differ between VS patients with or without a facial paresis, although exploratory analyses suggest that the ability to recognize emotions in angry facial expressions was slightly more impaired in patients with facial paresis. The findings are discussed in the context of the effects of facial paresis on emotion detection, and the role of facial mimicry, in particular, as an important mechanism for facial emotion processing and understanding.

Objectives: Patients with a vestibular schwannoma (VS) experience a reduced quality of life (QoL). The main objective of this study was to determine the strongest predictors reducing physical and mental QoL from the disease-specific Penn Acoustic Neuroma Quality of Life (PANQOL) questionnaire in patients with VS., Design: Observational study., Setting: Radboudumc Skull Base Centre, Nijmegen., Participants: Patients newly diagnosed with VS between 2014 and 2017 managed with either observation, stereotactic radiosurgery or microsurgery., Main Outcome Measures: Quality of life was assessed using the disease-specific PANQOL and general Short-Form (36) Health Survey (SF-36). Multiple linear regression models with PANQOL domains as predictors were used to determine the strongest predictors for SF-36 QoL physical and mental health scores. Standardised beta coefficients (β) were used for ranking., Results: A total of 174 patients (50% females, mean age 58.9 years) returned the questionnaires, providing a 69% response rate. Fifteen patients (9%) were treated with microsurgery, 29 (17%) with stereotactic radiosurgery and 130 patients (75%) were observed in a wait and scan strategy. A lack of energy (β = .28; P ≤ .001), lower general health (β = .22; P ≤ .001), headache (β = .16; P ≤ .001), anxiety (β = .15; P ≤ .001) and balance problems (β = .10; P ≤ .001) are the strongest predictors affecting physical health, while mental health is most affected by anxiety (β = .37; P ≤ .001), a lack of energy (β = .34; P ≤ .001), facial nerve dysfunction (β = .07; P ≤ .001), balance problems (β = .04; P ≤ .001) and headaches (β = .04; P ≤ .001)., Conclusion: A lack of energy, anxiety, headache and balance problems are the strongest predictors of both SF-36 physical and mental QoL in patients with VS. More awareness and supportive care regarding energy, anxiety, headache and balance in informing, evaluating and treating patients with VS could improve QoL., (© 2020 The Authors. Clinical Otolaryngology published by John Wiley & Sons Ltd.)

Objectives: To develop a prediction model to predict vestibular schwannoma (VS) growth for patients in a wait and scan (W&S) strategy., Design: Retrospective cohort study., Setting: Tertiary hospital (Radboud university medical center, Nijmegen, the Netherlands)., Participants: Patients with unilateral VS, entering a W&S strategy and at least one follow-up MRI available. Data on demographics, symptoms, audiometry and MRI characteristics at time of diagnosis were collected from medical records., Main Outcome Measures: Following multiple imputation, a multivariable Cox regression model was used to select variables, using VS growth (≥2 mm) as outcome. Decision curve analyses (DCA) were performed to compare the model to the current strategy., Results: Of 1217 analysed VS patients, 653 (53.7%) showed growth during follow-up. Balance complaints (HR 1.57 (95% CI: 1.31-1.88)) and tinnitus complaints in the affected ear (HR 1.36 (95% CI: 1.15-1.61)), Koos grade (Koos 1 is reference, Koos 2 HR 1.03 (95% CI: 0.80-1.31), Koos 3 HR 1.55 (95% CI: 1.16-2.06), Koos 4 HR 2.18 (95% CI: 1.60-2.96)), time since onset of symptoms (IQR HR 0.83 (95% CI: 0.77-0.88) and intrameatal diameter on MRI (IQR HR 1.67 (95% CI: 1.42-1.96)) were selected as significant predictors. The model's discrimination (Harrell's C) was 0.69 (95% CI: 0.67-0.71), and calibration was good. DCA showed that the model has a higher net benefit than the current strategy for probabilities of VS growth of >12%, 15% and 21% for the first consecutive 3 years, respectively., Conclusions: Patients with balance and tinnitus complaints, a higher Koos grade, short duration of symptoms and a larger intrameatal diameter at time of diagnosis have a higher probability of future VS growth. After external validation, this model may be used to inform patients about their prognosis, individualise the W&S strategy and improve (cost-)effectiveness., (© 2020 The Authors. Clinical Otolaryngology published by John Wiley & Sons Ltd.)

Objective: Stereotactic radiosurgery (SRS) is one of the treatment modalities for vestibular schwannomas (VSs). However, tumor progression can still occur after treatment. Currently, it remains unknown how to predict long-term SRS treatment outcome. This study investigates possible magnetic resonance imaging (MRI)-based predictors of long-term tumor control following SRS., Study Design: Retrospective cohort study., Setting: Tertiary referral center., Patients: Analysis was performed on a database containing 735 patients with unilateral VS, treated with SRS between June 2002 and December 2014. Using strict volumetric criteria for long-term tumor control and tumor progression, a total of 85 patients were included for tumor texture analysis., Intervention(s): All patients underwent SRS and had at least 2 years of follow-up., Main Outcome Measure(s): Quantitative tumor texture features were extracted from conventional MRI scans. These features were supplied to a machine learning stage to train prediction models. Prediction accuracy, sensitivity, specificity, and area under the receiver operating curve (AUC) are evaluated., Results: Gray-level co-occurrence matrices, which capture statistics from specific MRI tumor texture features, obtained the best prediction scores: 0.77 accuracy, 0.71 sensitivity, 0.83 specificity, and 0.93 AUC. These prediction scores further improved to 0.83, 0.83, 0.82, and 0.99, respectively, for tumors larger than 5 cm., Conclusions: Results of this study show the feasibility of predicting the long-term SRS treatment response of VS tumors on an individual basis, using MRI-based tumor texture features. These results can be exploited for further research into creating a clinical decision support system, facilitating physicians, and patients to select a personalized optimal treatment strategy.

Objective: This study investigates whether there exist differences in lateralization of facial emotion processing in patients suffering from Vestibular Schwannoma (VS) based on the presence of a facial paresis and their degree of facial functioning as measured by the House Brackmann Grading scale (HBG)., Methods: Forty-four VS patients, half of them with a facial paresis and half of them without a facial paresis, rated how emotive they considered images of faces showing emotion in the left versus right visual field. Stimuli consisted of faces with a neutral half and an emotional (happy or angry) half. The study had a mixed design with emotional expression (happy vs. angry) and emotional half (left vs. right visual field) of the faces as repeated measures, and facial paresis (present vs. absent) and HBG as between subjects' factors. The visual field bias was the main dependent variable., Results: In line with typical findings in the normal population, a left visual field bias showed in the current sample: patients judged emotional expressions shown in the left visual field as more emotive than those shown in the right visual field. No differences in visual field bias showed based on the presence of a facial paresis nor based on patients' HBG., Conclusion: VS patients show a left visual field bias when processing facial emotion. No differences in lateralization showed based on the presence of a facial paresis or on patients' HBG. Based on this study, facial paresis thus does not affect the lateralization of facial emotion processing in patients with VS., (© 2020 The Authors. Brain and Behavior published by Wiley Periodicals LLC.)

Object: Surgery of tumours in the cerebellopontine angle (CPA) can lead to loss of facial nerve function. Different methods of intra-operative nerve monitoring (IOM) (including free-running EMG, direct nerve stimulation and transcranial motor evoked potentials (TcMEP)) have been used to predict facial nerve outcome during surgery. Recent research has shown TcMEP threshold increase and the occurrence of A-trains on the EMG to have great potential in doing so. This study compares these two methods and correlates them to House-Brackmann (HB) scores post-op in patients with tumours in the cerebellopontine angle., Method: Forty-three patients (one was operated twice) with large CPA tumours treated surgically in the Radboud University Medical Center between 2015 and 2019 were included in this study. During surgery, TcMEP threshold increases and A-train activity were measured. Because our treatment paradigm aims at facial nerve preservation (accepting residual tumour), TcMEP threshold increase of over 20 mA or occurrence of A-trains were considered as warning signs and used as a guide for terminating surgery. HB scores were measured post-op, at 6 weeks, 6 months and 1 year after surgery. Spearman's correlation was calculated between the IOM-values and the HB scores for a homogeneous subgroup of 30 patients with vestibular schwannoma (VS) without neurofibromatosis type II (NF-II) and all patients collectively., Results: TcMEP threshold was successfully measured in 39 (90.7%) procedures. In the homogeneous VS non-NFII group, we found a statistically significant moderate-to-strong correlation between TcMEP threshold increase and House Brackmann score immediately post-op, at 6 weeks, 6 months and 1 year after surgery (Spearman's rho of 0.79 (p < 0.001), 0.74 (p < 0.001), 0.64 (p < 0.001) and 0.58 (p = 0.002), respectively). For A-trains, no correlation was found. Similar results were found when including all patients with CPA tumours. A threshold increase of < 20 mA was a predictor of good facial nerve outcome., Conclusion: These results show that TcMEP threshold increases are strongly correlated to post-operative HB scores, while A-trains are not. This suggests TcMEP threshold increases can be a valuable predictor for facial nerve outcome in patients with large tumours when facial nerve preservation is prioritized over total resection. In this study, we found no use for A-trains to prevent facial nerve deficits.

Objectives: To assess the cost-effectiveness of frequently used monitoring strategies for vestibular schwannoma (VS)., Design: A state transition model was developed to compare six monitoring strategies for patients with VS: lifelong annual monitoring; annual monitoring for the first 10 years after diagnosis; scanning at 1-5, 7, 9, 12, 15 years after diagnosis and subsequently every 5 years; a personalised monitoring strategy for small and large tumours; scanning at 1, 2 and 5 years after diagnosis and no monitoring. Input data were derived from literature and expert opinion. Quality-adjusted life years (QALYs) and healthcare costs of each strategy were modelled over lifetime. Net monetary benefits (NMBs) were calculated to determine which strategy provided most value for money. Sensitivity analyses were performed to address uncertainty., Results: Omitting monitoring is least effective with 18.23 (95% CI 16.84-19.37) QALYs per patient, and lifelong annual monitoring is most effective with 18.66 (95% CI 17.42-19.65) QALYs. Corresponding costs were €6526 (95% CI 5923-7058) and €9429 (95% CI 9197-9643) per patient, respectively. Lifelong annual monitoring provided the best value with a NMB of €363 765 (339 040-383 697), but the overall probability of being most cost-effective compared to the other strategies was still only 23%. Sensitivity analysis shows that there is large uncertainty in the effectiveness of all strategies, with largely overlapping 95% confidence intervals for all strategies., Conclusions: Due to the largely overlapping 95% confidence intervals of all monitoring strategies for VS, it is unclear which monitoring strategy provides most value for money at this moment., (© 2019 The Authors. Clinical Otolaryngology Published by John Wiley & Sons Ltd.)

OBJECTIVE Gamma Knife radiosurgery (GKRS) has become an accepted treatment for vestibular schwannoma, with a high rate of tumor control and good clinical outcome. In a small number of cases, additional treatment is needed. This retrospective study examines the clinical outcome, reproducibility of volumetric response patterns, and tumor control rate after administering a second GKRS to treat vestibular schwannomas. METHODS A total of 38 patients were included: 28 patients underwent a radiosurgical procedure as the initial treatment (Group 1), and 10 patients underwent microsurgical resection with adjuvant radiosurgery on the tumor remnant as the initial treatment (Group 2). The indication for a second GKRS treatment was growth observed on follow-up imaging. The median margin dose was 11.0 Gy for the first procedure and 11.5 Gy for the second procedure. Tumor control after retreatment was assessed through volumetric analysis. Clinical outcome was assessed through medical chart review. RESULTS Median tumor volume at retreatment was 3.6 cm 3 , with a median treatment interval of 49 months. All patients showed tumor control in a median follow-up period of 75 months after the second radiosurgical procedure. Volumetric tumor response after the second procedure did not correspond to response after the first procedure. After retreatment, persisting House-Brackmann Grade II facial nerve dysfunction was observed in 3 patients (7.9%), facial spasms in 5 patients (13%), and trigeminal nerve hypesthesia in 3 patients (7.9%). Hearing preservation was not evaluated because of the small number of patients with serviceable hearing at the second procedure. CONCLUSIONS Repeat GKRS after a failed first treatment appears to be an effective strategy in terms of tumor control. The volumetric response after a repeat procedure could not be predicted by the volumetric response observed after first treatment. This justifies considering repeat GKRS even for tumors that do not show any volumetric response and show continuous growth after first treatment. An increased risk of mild facial and trigeminal nerve dysfunction was observed after the second treatment compared with the first treatment.

OBJECTIVE Neurofibromatosis Type 2 (NF2) is a tumor syndrome characterized by an autosomal dominant pattern of inheritance. The hallmark of NF2 is the development of bilateral vestibular schwannomas (VSs), generally by 30 years of age. One of the first-line treatment options for small to medium-large VSs is radiosurgery. Although radiosurgery shows excellent results in sporadic VS, its use in NF2-related VS is still a topic of dispute. The aim of this study was to evaluate long-term tumor control, hearing preservation rates, and factors influencing outcome of optimally dosed, contemporary Gamma Knife radiosurgery (GKRS) for growing VSs in patients with NF2 and compare the findings to data obtained in patients with sporadic VS also treated by means of GKRS. METHODS The authors performed a retrospective analysis of 47 growing VSs in 34 NF2 patients who underwent GKRS treatment performed with either the Model C or Perfexion Leksell Gamma Knife, with a median margin dose of 11 Gy. Actuarial tumor control rates were estimated using the Kaplan-Meier method. For patient- and treatment-related factors, a Cox proportional hazards model was used to identify predictors of outcome. Trigeminal, facial, and vestibulocochlear nerve function were assessed before and after treatment. NF2-related VS patients were matched 1:1 with sporadic VS patients who were treated in the same institute, and the same indications for treatment, definitions, and dosimetry were used in order to compare outcomes. RESULTS Actuarial tumor control rates in NF2 patients after 1, 3, 5, and 8 years were 98%, 89%, 87%, and 87%, respectively. Phenotype and tumor volume had significant hazard rates of 0.086 and 22.99, respectively, showing that Feiling-Gardner phenotype and a tumor volume not exceeding 6 cm 3 both were associated with significantly better outcome. Actuarial rates of serviceable hearing preservation after 1, 3, 5, and 7 years were 95%, 82%, 59%, and 33%, respectively. None of the patients experienced worsening of trigeminal nerve function. Facial nerve function worsened in 1 patient (2.5%). No significant differences in tumor control, hearing preservation, or complications were found in comparing the results of GKRS for NF2-related VS versus GKRS for sporadic VS. CONCLUSIONS With modern GKRS, the use of low margin doses for treating growing VSs in patients with NF2 demonstrates good long-term tumor control rates. Feiling-Gardner phenotype and tumor volume smaller than 6 cm 3 seem to be independently associated with prolonged progression-free survival, highlighting the clinical importance of phenotype assessment before GKRS treatment. In addition, no significant differences in tumor control rates or complications were found in the matched-control cohort analysis comparing GKRS for VS in patients with NF2 and GKRS for sporadic VS. These results show that GKRS is a valid treatment option for NF2-related VS, in addition to being a good option for sporadic VS, particularly in patients with the Feiling-Gardner phenotype and/or tumors that are small to medium in size. Larger tumors in patients with the Wishart phenotype appear to respond poorly to radiosurgery, and other treatment modalities should therefore be considered in such cases.