Multisession Stereotactic Radiosurgery for Vestibular Schwannomas: Single-Institution Experience With 383 Cases

Neurosurgery ◽  
2011 ◽  
Vol 69 (6) ◽  
pp. 1200-1209 ◽  
Author(s):  
Ake Hansasuta ◽  
Clara Y. H. Choi ◽  
Iris C. Gibbs ◽  
Scott G. Soltys ◽  
Victor C. K. Tse ◽  
...  
Keyword(s):  
Stereotactic Radiosurgery ◽  
Tumor Volume ◽  
Medical Center ◽  
Neurofibromatosis Type ◽  
Hearing Preservation ◽  
Additional Treatment ◽  
Vestibular Schwannomas ◽  
Tumor Control ◽  
Complication Rates ◽  
Kaplan Meier

Abstract BACKGROUND Single-session stereotactic radiosurgery (SRS) treatment of vestibular schwannomas results in excellent tumor control. It is not known whether functional outcomes can be improved by fractionating the treatment over multiple sessions. OBJECTIVE To examine tumor control and complication rates after multisession SRS. METHODS Three hundred eighty-three patients treated with SRS from 1999 to 2007 at Stanford University Medical Center were retrospectively reviewed. Ninety percent were treated with 18 Gy in 3 sessions, targeting a median tumor volume of 1.1 cm3 (range, 0.02-19.8 cm3). RESULTS During a median follow-up duration of 3.6 years (range, 1-10 years), 10 tumors required additional treatment, resulting in 3- and 5-year Kaplan-Meier tumor control rates of 99% and 96%, respectively. Five-year tumor control rate was 98% for tumors > 3.4 cm3. Neurofibromatosis type 2–associated tumors were associated with worse tumor control (P = .02). Of the 200 evaluable patients with pre-SRS serviceable hearing (Gardner-Robertson grade 1 and 2), the crude rate of serviceable hearing preservation was 76%. Smaller tumor volume was associated with hearing preservation (P = .001). There was no case of post-SRS facial weakness. Eight patients (2%) developed trigeminal dysfunction, half of which was transient. CONCLUSION Multisession SRS treatment of vestibular schwannomas results in an excellent rate of tumor control. The hearing, trigeminal nerve, and facial nerve function preservation rates reported here are promising.

scholarly journals Stereotactic radiosurgery for vestibular schwannomas: average 10-year follow-up results focusing on long-term hearing preservation

2016 ◽  
Vol 125 (Supplement_1) ◽  
pp. 64-72 ◽  
Author(s):  
Shinya Watanabe ◽  
Masaaki Yamamoto ◽  
Takuya Kawabe ◽  
Takao Koiso ◽  
Tetsuya Yamamoto ◽  
...  
Keyword(s):  
Stereotactic Radiosurgery ◽  
Tumor Volume ◽  
Hearing Preservation ◽  
Interquartile Range ◽  
Vestibular Schwannomas ◽  
Long Term Results ◽  
Tumor Control ◽  
Univariable Analysis

OBJECTIVEThe aim of this study was to reappraise long-term treatment outcomes of stereotactic radiosurgery (SRS) for vestibular schwannomas (VSs). The authors used a database that included patients who underwent SRS with a unique dose-planning technique, i.e., partial tumor coverage designed to avoid excess irradiation of the facial and cochlear nerves, focusing on tumor control and hearing preservation. Clinical factors associated with post-SRS tumor control and long-term hearing preservation were also analyzed.METHODSThis institutional review board–approved, retrospective cohort study used the authors' prospectively accumulated database. Among 207 patients who underwent Gamma Knife SRS for VSs between 1990 and 2005, 183 (who were followed up for at least 36 post-SRS months) were studied. The median tumor volume was 2.0 cm3 (range 0.05–26.2 cm3). The median prescribed dose at the tumor periphery was 12.0 Gy (range 8.8–15.0 Gy; 12.0 Gy was used in 171 patients [93%]), whereas tumor portions facing the facial and cochlear nerves were irradiated with 10.0 Gy. As a result, 72%–99% of each tumor was irradiated with the prescribed dose. The mean cochlear doses ranged from 2.3 to 5.7 Gy (median 4.1 Gy).RESULTSThe median durations of imaging and audiometric follow-up were 114 months (interquartile range 73–144 months) and 59 months (interquartile range 33–109 months), respectively. Tumor shrinkage was documented in 110 (61%), no change in 48 (27%), and enlargement in the other 22 (12%) patients. A further procedure (FP) was required in 15 (8%) patients. Thus, the tumor growth control rate was 88% and the clinical control rate (i.e., no need for an FP) was 92%. The cumulative FP-free rates were 96%, 93%, and 87% at the 60th, 120th, and 180th post-SRS month, respectively. Six (3%) patients experienced facial pain, and 2 developed transient facial palsy. Serviceable hearing was defined as a pure tone audiogram result better than 50 dB. Among the 66 patients with serviceable hearing before SRS who were followed up, hearing acuity was preserved in 23 (35%). Actuarial serviceable hearing preservation rates were 49%, 24%, and 12% at the 60th, 120th, and 180th post-SRS month, respectively. On univariable analysis, only cystic-type tumor (HR 3.36, 95% CI 1.18–9.36; p = 0.02) was shown to have a significantly unfavorable association with FP. Multivariable analysis followed by univariable analysis revealed that higher age (≥ 65 years: HR 2.66, 95% CI 1.16–5.92; p = 0.02), larger tumor volume (≥ 8 cm3: HR 5.36, 95% CI 1.20–17.4; p = 0.03), and higher cochlear dose (mean cochlear dose > 4.2 Gy: HR 2.22, 95% CI 1.07–4.77; p = 0.03) were unfavorable factors for hearing preservation.CONCLUSIONSStereotactic radiosurgery achieved good long-term results in this series. Tumor control was acceptable, and there were few serious complications in patients with small- to medium-sized VSs. Unfortunately, hearing preservation was not satisfactory. However, the longer the observation period, the more important it becomes to compare post-SRS hearing decreases with the natural decline in untreated cases.

Gamma Knife radiosurgery for treatment of growing vestibular schwannomas in patients with neurofibromatosis Type 2: a matched cohort study with sporadic vestibular schwannomas

2018 ◽  
Vol 128 (1) ◽  
pp. 49-59 ◽  
Author(s):  
Ivo J. Kruyt ◽  
Jeroen B. Verheul ◽  
Patrick E. J. Hanssens ◽  
Henricus P. M. Kunst
Keyword(s):  
Gamma Knife ◽  
Tumor Volume ◽  
Gamma Knife Radiosurgery ◽  
Neurofibromatosis Type ◽  
Hearing Preservation ◽  
Vestibular Schwannomas ◽  
Tumor Control ◽  
Nerve Function

OBJECTIVENeurofibromatosis 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.METHODSThe 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.RESULTSActuarial 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 cm3 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.CONCLUSIONSWith 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 cm3 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.

STEREOTACTIC RADIOSURGERY FOR VESTIBULAR SCHWANNOMAS IN PATIENTS WITH NEUROFIBROMATOSIS TYPE 2

Neurosurgery ◽  
2007 ◽  
Vol 60 (3) ◽  
pp. 460-470 ◽  
Author(s):  
David Mathieu ◽  
Douglas Kondziolka ◽  
John C. Flickinger ◽  
Ajay Niranjan ◽  
Richard Williamson ◽  
...  
Keyword(s):  
Stereotactic Radiosurgery ◽  
Tumor Volume ◽  
Gamma Knife Radiosurgery ◽  
Neurofibromatosis Type ◽  
Hearing Preservation ◽  
Neurofibromatosis Type 2 ◽  
Vestibular Schwannomas ◽  
Factors Affecting

Abstract OBJECTIVE Vestibular schwannomas present significant management challenges in patients with neurofibromatosis Type 2 (NF2). We evaluated the results of gamma knife radiosurgery for the management of these tumors, focusing on tumor response, hearing preservation, and other factors affecting outcomes. METHODS Stereotactic radiosurgery was performed to manage 74 schwannomas in 62 patients. Ipsilateral serviceable hearing was present in 35% of tumors before the procedure. The mean tumor volume was 5.7 cm3. The mean margin and maximum dose used were 14 and 27.5 Gy, respectively. Cox regression analyses were performed to identify factors affecting outcomes. RESULTS The median follow-up period was 53 months, and two patients were lost to follow-up. Actuarial local control rates at were 85, 81, and 81% at 5, 10, and 15 years, respectively. Tumor volume was significant as a predictor of local control. Since 1992, using current radiosurgery techniques (magnetic resonance imaging scan targeting and reduced margin dose to 14 Gy or less), the actuarial serviceable hearing preservation rate is 73% at 1 year, 59% at 2 years, and 48% at 5 years after radiosurgery. Facial neuropathy occurred in 8% of tumors, trigeminal neuropathy occurred in 4%, and vestibular dysfunction occurred in 4%. Radiation dose and tumor volume were predictive of development of new deficits. No radiosurgery-associated secondary tumors or atypical or malignant changes were noted. CONCLUSION Stereotactic radiosurgery is a safe and effective management modality for neurofibromatosis Type 2 vestibular schwannomas. Although results do not seem to be as good as for patients with sporadic unilateral tumors, gamma knife radiosurgery results seem favorable and indicate that radiosurgery should be strongly considered for primary tumor management in selected patients.

Stereotactic radiosurgery as the primary management for patients with Koos grade IV vestibular schwannomas

2021 ◽  
pp. 1-9
Author(s):  
Akiyoshi Ogino ◽  
L. Dade Lunsford ◽  
Hao Long ◽  
Stephen Johnson ◽  
Andrew Faramand ◽  
...  
Keyword(s):  
Stereotactic Radiosurgery ◽  
Tumor Volume ◽  
Hearing Preservation ◽  
Vestibular Schwannomas ◽  
Tumor Control ◽  
Tumor Diameter ◽  
Single Session ◽  
Lower Margin ◽  
Long Term Outcome

OBJECTIVEWhile extensive long-term outcome studies support the role of stereotactic radiosurgery (SRS) for smaller-volume vestibular schwannomas (VSs), its role in the management for larger-volume tumors remains controversial.METHODSBetween 1987 and 2017, the authors performed single-session SRS on 170 patients with previously untreated Koos grade IV VSs (volumes ranged from 5 to 20 cm3). The median tumor volume was 7.4 cm3. The median maximum extracanalicular tumor diameter was 27.5 mm. All tumors compressed the middle cerebellar peduncle and distorted the fourth ventricle. Ninety-three patients were male, 77 were female, and the median age was 61 years. Sixty-two patients had serviceable hearing (Gardner-Robertson [GR] grades I and II). The median margin dose was 12.5 Gy.RESULTSAt a median follow-up of 5.1 years, the progression-free survival rates of VSs treated with a margin dose ≥ 12.0 Gy were 98.4% at 3 years, 95.3% at 5 years, and 90.7% at 10 years. In contrast, the tumor control rate after delivery of a margin dose < 12.0 Gy was 76.9% at 3, 5, and 10 years. The hearing preservation rates in patients with serviceable hearing at the time of SRS were 58.1% at 3 years, 50.3% at 5 years, and 35.9% at 7 years. Younger age (< 60 years, p = 0.036) and initial GR grade I (p = 0.006) were associated with improved serviceable hearing preservation rate. Seven patients (4%) developed facial neuropathy during the follow-up interval. A smaller tumor volume (< 10 cm3, p = 0.002) and a lower margin dose (≤ 13.0 Gy, p < 0.001) were associated with preservation of facial nerve function. The probability of delayed facial neuropathy when the margin dose was ≤ 13.0 Gy was 1.1% at 10 years. Nine patients (5%) required a ventriculoperitoneal shunt because of delayed symptomatic hydrocephalus. Fifteen patients (9%) developed detectable trigeminal neuropathy. Delayed resection was performed in 4% of patients.CONCLUSIONSEven for larger-volume VSs, single-session SRS prevented the need for delayed resection in almost 90% at 10 years. For patients with minimal symptoms of tumor mass effect, SRS should be considered an effective alternative to surgery in most patients, especially those with advanced age or medical comorbidities.

scholarly journals Gamma Knife Radiosurgery for Large Vestibular Schwannomas: A Canadian Experience

2013 ◽  
Vol 40 (3) ◽  
pp. 342-347 ◽  
Author(s):  
F. A. Zeiler ◽  
M. Bigder ◽  
A. Kaufmann ◽  
P. J. McDonald ◽  
D. Fewer ◽  
...  
Keyword(s):  
Facial Nerve ◽  
Stereotactic Radiosurgery ◽  
Gamma Knife ◽  
Gamma Knife Radiosurgery ◽  
Hearing Preservation ◽  
Vestibular Schwannomas ◽  
Tumor Control ◽  
Complication Rates ◽  
Maximal Diameter

Object:To review our institutional experience with Gamma Knife (GK) stereotactic radiosurgery in treating large vestibular schwannomas (VS) of 3 to 4 cm diameter.Methods:We conducted a retrospective cohort review of all patients treated with GK for VS at our institution between November 2003 and March 2012. Data on age, sex, VS volume, location and maximal diameter, House-Brackmann (HB) facial nerve scores pre and post-GK, Gardner-Robertson (GR) hearing score pre and post-GK, GK treatment parameters, VS response time, complications and clinical outcome was recorded.Results:A total of 28 patients during the defined time period were identified. Three patients were lost to follow-up. Mean follow-up was 34.5 months. Tumor control occurred in 92%, and was maintained in 85.7% at two years. Facial nerve or hearing preservation occurred in all treated compared to pre-GK status, as per HB and GR grading. Transient complications occurred in 80%. Temporary vestibular dysfunction occurred in seven patients (28%). One patient (4%) had the permanent complication of worsening pre-GK hemifacial spasm. Four patients (16%) developed hydrocephalus post-GK.Conclusion:GK stereotactic radiosurgery as a primary treatment modality for large VS can provide acceptable tumor control rates with good facial nerve and hearing preservation, and low complication rates.

Stereotactic radiosurgery as the first-line treatment for intracanalicular vestibular schwannomas

2021 ◽  
pp. 1-7
Author(s):  
Akiyoshi Ogino ◽  
L. Dade Lunsford ◽  
Hao Long ◽  
Stephen Johnson ◽  
Andrew Faramand ◽  
...  
Keyword(s):  
Stereotactic Radiosurgery ◽  
Observation Interval ◽  
Univariate Analysis ◽  
Hearing Preservation ◽  
Vestibular Schwannomas ◽  
Tumor Control ◽  
Line Treatment ◽  
First Line ◽  
Additional Intervention ◽  
First Line Treatment

OBJECTIVEThis report evaluates the outcomes of stereotactic radiosurgery (SRS) as the first-line treatment of intracanalicular vestibular schwannomas (VSs).METHODSBetween 1987 and 2017, the authors identified 209 patients who underwent SRS as the primary intervention for a unilateral intracanalicular VS. The median patient age was 54 years (range 22–85 years); 94 patients were male and 115 were female. Three patients had facial neuropathy at the time of SRS. One hundred fifty-five patients (74%) had serviceable hearing (Gardner-Robertson [GR] grades I and II) at the time of SRS. The median tumor volume was 0.17 cm3 (range 0.015–0.63 cm3). The median margin dose was 12.5 Gy (range 11.0–25.0 Gy). The median maximum dose was 24.0 Gy (range 15.7–50.0 Gy).RESULTSThe progression-free survival rates of all patients with intracanalicular VS were 97.5% at 3 years, 95.6% at 5 years, and 92.1% at 10 years. The rates of freedom from the need for any additional intervention were 99.4% at 3 years, 98.3% at 5 years, and 98.3% at 10 years. The serviceable hearing preservation rates in GR grade I and II patients at the time of SRS were 76.6% at 3 years, 63.5% at 5 years, and 27.3% at 10 years. In univariate analysis, younger age (< 55 years, p = 0.011), better initial hearing (GR grade I, p < 0.001), and smaller tumor volumes (< 0.14 cm3, p = 0.016) were significantly associated with improved hearing preservation. In multivariate analysis, better hearing (GR grade I, p = 0.001, HR 2.869, 95% CI 1.569–5.248) and smaller tumor volumes (< 0.14 cm3, p = 0.033, HR 2.071, 95% CI 1.059–4.047) at the time of SRS were significantly associated with improved hearing preservation. The hearing preservation rates of patients with GR grade I VS were 88.1% at 3 years, 77.9% at 5 years, and 38.1% at 10 years. The hearing preservation rates of patients with VSs smaller than 0.14 cm3 were 85.5% at 3 years, 77.7% at 5 years, and 42.6% at 10 years. Facial neuropathy developed in 1.4% from 6 to 156 months after SRS.CONCLUSIONSSRS provided sustained tumor control in more than 90% of patients with intracanalicular VS at 10 years and freedom from the need for additional intervention in more than 98% at 10 years. Patients with initially better hearing and smaller VSs had enhanced serviceable hearing preservation during an observation interval up to 10 years after SRS.

scholarly journals Translabyrinthine microsurgical resection of small vestibular schwannomas

2018 ◽  
Vol 129 (1) ◽  
pp. 128-136 ◽  
Author(s):  
Marc S. Schwartz ◽  
Gregory P. Lekovic ◽  
Mia E. Miller ◽  
William H. Slattery ◽  
Eric P. Wilkinson
Keyword(s):  
Facial Nerve ◽  
Vestibular Schwannoma ◽  
Sinus Thrombosis ◽  
Treatment Options ◽  
Previous Treatment ◽  
Cerebrospinal Fluid Leak ◽  
Neurofibromatosis Type ◽  
Additional Treatment ◽  
Vestibular Schwannomas ◽  
Tumor Control

OBJECTIVETranslabyrinthine resection is one of a number of treatment options available to patients with vestibular schwannomas. Though this procedure is hearing destructive, the authors have noted excellent clinical outcomes for patients with small tumors. The authors review their experience at a tertiary acoustic neuroma referral center in using the translabyrinthine approach to resect small vestibular schwannomas. All operations were performed by a surgical team consisting of a single neurosurgeon and 1 of 7 neurotologists.METHODSData from a prospectively maintained clinical database were extracted and reviewed. Consecutive patients with a preoperative diagnosis of vestibular schwannoma that had less than 1 cm of extension into the cerebellopontine angle, operated on between 2008 and 2013, were included. Patents with neurofibromatosis Type 2, previous treatment, or preexisting facial weakness were excluded. In total, 107 patients were identified, 74.7% of whom had poor hearing preoperatively.RESULTSPathologically, 6.5% of patients were found to have a tumor other than vestibular schwannoma. Excluding two malignancies, the tumor control rates were 98.7%, as defined by absence of radiographic disease, and 99.0%, as defined by no need for additional treatment. Facial nerve outcome was normal (House-Brackmann Grade I) in 97.2% of patients and good (House-Brackmann Grade I–II) in 99.1%. Complications were cerebrospinal fluid leak (4.7%) and sigmoid sinus thrombosis (0.9%), none of which led to long-term sequelae.CONCLUSIONSTranslabyrinthine resection of small vestibular schwannomas provides excellent results in terms of complication avoidance, tumor control, and facial nerve outcomes. This is a hearing-destructive operation that is advocated for selected patients.

scholarly journals Gamma Knife radiosurgery for vestibular schwannomas: evaluation of tumor control and its predictors in a large patient cohort in The Netherlands

2016 ◽  
Vol 124 (6) ◽  
pp. 1619-1626 ◽  
Author(s):  
Stijn Klijn ◽  
Jeroen B. Verheul ◽  
Guus N. Beute ◽  
Sieger Leenstra ◽  
Jef J. S. Mulder ◽  
...  
Keyword(s):  
Gamma Knife ◽  
Tumor Volume ◽  
Gamma Knife Radiosurgery ◽  
Hearing Preservation ◽  
Cox Proportional Hazards Model ◽  
Tumor Control ◽  
Complication Rates ◽  
Tumor Control Rate ◽  
Large Patient

OBJECT The authors of this study sought to assess tumor control and complication rates in a large cohort of patients who underwent Gamma Knife radiosurgery (GKRS) for vestibular schwannoma (VS) and to identify predictors of tumor control. METHODS The records of 420 patients treated with GKRS for VS with a median marginal dose of 11 Gy were retrospectively analyzed. Patients with neurofibromatosis Type 2 or who had undergone treatment for VS previously were excluded. The authors assessed tumor control and complication rates with chart review and used the Cox proportional hazards model to identify predictors of tumor control. Preservation of serviceable hearing, defined as Gardner-Robertson Class I–II, was evaluated in a subgroup of 71 patients with serviceable hearing at baseline and with available follow-up audiograms. RESULTS The median VS tumor volume was 1.4 cm3, and the median length of follow-up was 5.1 years. Actuarial 5-and 10-year tumor control rates were 91.3% and 84.8%, respectively. Only tumor volume was a statistically significant predictor of tumor control rate. The tumor control rate decreased from 94.1% for tumors smaller than 0.5 cm3 to 80.7% for tumors larger than 6 cm3. Thirteen patients (3.1%) had new or increased permanent trigeminal nerve neuropathy, 4 (1.0%) had new or increased permanent facial weakness, and 5 (1.2%) exhibited new or increased hydrocephalus requiring a shunting procedure. Actuarial 3-year and 5-year hearing preservation rates were 65% and 42%, respectively. CONCLUSIONS The 5-year actuarial tumor control rate of 91.3% in this cohort of patients with VS compared slightly unfavorably with the rates reported in other large studies, but the complication and hearing preservation rates in this study were similar to those reported previously. Various factors may contribute to the observed differences in reported outcomes. These factors include variations in treatment indication and in the definition of treatment failure, as well as a lack of standardization of terminology and of evaluation of complications. Last, differences in dosimetric variables may also be an explanatory factor.

Tumor control and hearing preservation after Gamma Knife radiosurgery for vestibular schwannomas in neurofibromatosis type 2

2010 ◽  
Vol 98 (2) ◽  
pp. 265-270 ◽  
Author(s):  
Manish Singh Sharma ◽  
Rakesh Singh ◽  
Shashank S. Kale ◽  
Deepak Agrawal ◽  
Bhawani Shankar Sharma ◽  
...  
Keyword(s):  
Gamma Knife ◽  
Gamma Knife Radiosurgery ◽  
Neurofibromatosis Type ◽  
Hearing Preservation ◽  
Neurofibromatosis Type 2 ◽  
Vestibular Schwannomas ◽  
Tumor Control
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