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Clinical Study

Editor's Choice - Free Access

Gamma Knife Radiosurgery for Vestibular Schwannomas and Quality of Life Evaluation

Berkowitz O.a-c · Han Y.-Y.b · Talbott E.O.b · Iyer A.K.a, d · Kano H.a · Kondziolka D.a, e · Brown M.A.c · Lunsford L.D.a

Author affiliations

aLeksell Center for Radiosurgery and Brain Mapping, University of Pittsburgh Medical Center, and bUniversity of Pittsburgh Graduate School of Public Health, Pittsburgh, PA, cBoston University School of Medicine, Boston, MA, dStanford University School of Medicine, Stanford, CA, and eNew York University School of Medicine, New York, NY, USA

Corresponding Author

Oren Berkowitz, PhD, PA-C

Boston University School of Medicine

72 E. Concord St., Suite L801

Boston, MA 02118 (USA)

E-Mail orenberk@bu.edu

Related Articles for ""

Stereotact Funct Neurosurg 2017;95:166-173

Abstract

Background: Further investigation is needed to look at the impact of vestibular schwannoma (VS) on the health-related quality of life (QOL) of participants who undergo Gamma Knife® radiosurgery (GKRS). Objectives: Investigators compared the QOL for VS participants to reported US population norms in order to evaluate disease burden and long-term QOL several years after GKRS. Methods: This cross-sectional study surveyed participants to assess hearing status, tinnitus, imbalance, vertigo, as well as the Short-Form 36-item Health Questionnaire (SF-36). The data were normalized, age adjusted, and functional status was correlated to determine clinically significant differences. Results: A total of 353 participants who underwent GKRS between 1997 and 2007 were included in this study with a median postoperative period of 5 years. SF-36 scores were very similar to population norms, and age-adjusted scores for participants followed the US population curve. Frequent vertigo and balance problems had the largest statistically and clinically significant effect on physical and mental component summary scores followed by nonuseful hearing in the tumor ear. Conclusions: Participants reported a good long-term QOL that was very similar to the QOL of US population norms. Of the common VS symptoms, vertigo had the greatest impact on QOL followed by imbalance and then hearing loss.

© 2017 S. Karger AG, Basel


Introduction

Patients with vestibular schwannomas (VS) are presented with various management options that range from continued observation and microsurgical removal by one of several surgical approaches to stereotactic radiosurgery using one of several methodologies. Few published studies are available to describe the long-term health-related quality of life (QOL) of patients who undergo one or more management options for VS [1,2,3], and most studies have compared various treatment modalities to each other. A different approach is to compare management outcomes to benchmarked population norms. QOL outcomes are increasingly important to VS patients given their choice of treatment options and the recognition of a tumor at earlier stages. Such QOL measures are also of increasing value from a public health standpoint as we try to understand the burden of this disease on society and on everyday functioning. At this institution, it has been noted that most (>80%) patients demonstrate clinical worsening and image-defined tumor growth within a period of 5-10 years without intervention. Previous studies have also confirmed that hearing preservation is better when patients undergo stereotactic radiosurgery earlier [4,5,6].

Early recognition of VS has been facilitated by the widespread use of magnetic resonance imaging (MRI) for patients with symptoms of imbalance or hearing dysfunction. The goal of this study was to take a look at the functional and QOL status of VS patients several years after they had undergone Gamma Knife® radiosurgery (GKRS), and it compares these results by age to normalized US population data.

Methods

This project was part of a comprehensive study of environmental risk factors for the development of VS. The details of that study have been previously described [7]. This study received the approval of the University of Pittsburgh Institutional Review Board for Human Research, and informed consent was obtained from all study participants.

Survey Design

An existing functional status questionnaire was used that has been reported in previous studies [8,9]. The survey assessed the participants' perception of their current hearing status in both ears, tinnitus, balance disorder symptoms, and vertigo. The 36-item Short-Form Health Survey v2.0 (SF-36) was also administered in order to assess health-related QOL [10]. Participants were also queried about their overall satisfaction with the GKRS procedure and whether they would recommend the procedure to somebody else.

Participant Recruitment

Participants were recruited from the University of Pittsburgh GKRS database [11]. In order to capture a long-term follow-up time in participants who underwent GKRS after the integration of MRI for treatment planning, participants were selected who underwent GKRS between the years 1997 and 2007. Participants with neurofibromatosis type 2 and those residing outside the North American continent were excluded. All participants were contacted by written letter via the United States postal service. Participants were given the option to fill out the questionnaire by hand or have it done over the telephone with a trained recruiter.

SF-36 Analysis

SF-36 questionnaire data were analyzed according to the SF-36 v2 user's manual [12] scoring criteria which included summary scores for physical (PCS) and mental health (MCS). The US population scores have been normalized to demonstrate a mean of 50 and a standard deviation of 10 for each of the 8 scales as well as the 2 summary scores [12]. Age groups were stratified and analyzed according to the SF-36 manual [12].

Effect Size Scoring

Cohen's formulation of effect size (ES) scoring [13] was used to benchmark clinically significant differences between SF-36 scores. This was done by dividing the difference in mean scores by the standard deviation of the participant score. The general accepted ranges are: 0.20-0.50 for a “small” effect size; 0.50-0.80 for a “medium” effect size; >0.80 for a “large” effect size. This usually translates to a mean score difference of around 2-5 points for a clinically significant difference [13,14,15].

Statistical Analysis

Descriptive statistics were used to display demographic data including median with range, means, standard deviations, and overall proportions when appropriate. The Student t test was used to explore relationships between univariate items. All data were analyzed using PASW Statistics 18, Release Version 18.0.0 (SPSS Inc., 2009, Chicago, IL, USA; www.spss.com).

Results

A total of 822 VS participants were treated with GKRS from 1997 to 2007, and 712 mailings were sent out based on our inclusion criteria. There were 420 (59%) participants who participated in the survey, and ultimately 353 (50%) had complete data. The mean age of the participants was 60 years (SD 12) at the time of the survey. The mean age at diagnosis of the VS was 53 years (SD 12). The median interval from date of diagnosis to GKRS was 3 months (range 0-265). The median time from GKRS to participation in this study was 63 months (range 18-141). The average tumor volume was 0.5 cm3 (range 0.012-17.3), and the median radiation dose to the tumor margins was 13 Gy (range 7-30) (Table 1).

Table 1

Demographics and tumor descriptives

/WebMaterial/ShowPic/843831

Functional Outcomes

There were 104 (29.7%) participants who reported that they currently maintain useful hearing in the GKRS-treated tumor ear. For our questionnaire, useful hearing was defined as being able to use the ear at least fairly in an everyday conversation. Fifteen participants (4.2%) described their hearing as either poor or deaf in both ears.

Tinnitus was reported by 163 (41.7%) participants either often or continuously. Imbalance symptoms were noted by 121 (34.4%) participants either often or continuously. Vertigo symptoms were reported by 42 (12%) participants either often or continuously (Table 2).

Table 2

Self-reported current functionality

/WebMaterial/ShowPic/843830

Overall Satisfaction

There were 318 (91.1%) participants who reported that they were satisfied with their current overall level of functioning, and 337 (96.8%) noted that they would recommend the GKRS procedure for VS to a friend or relative (Table 2).

SF-36 Outcomes

The physical and mental health component scores were similar to the population normalized score of 50 (PCS = 50.45, MCS = 51.72). The PCS and MCS stratified by age groups also closely resembled the US population normalized scores and followed a similar curve that showed PCS lowering with age (PCS from 56 to 45) but no significant change in MCS with age (MCS from 52 to 53) (Table 3; Fig. 1, 2).

Table 3

Age-adjusted physical component score (PCS) and mental component score (MCS): means ± SD

/WebMaterial/ShowPic/843829

Fig. 1

Age-adjusted SF-36 PCS scores for GKRS cohort and US population.

/WebMaterial/ShowPic/843825

Fig. 2

Age-adjusted SF-36 MCS scores for GKRS cohort and US population.

/WebMaterial/ShowPic/843824

Each of the participants' 8 SF-36 scale scores were compared to the established US population normalized score of 50 with ES scoring. The vitality category for our participants was better with a small ES of 0.27. Our participants reported outcomes in the remaining categories with effect sizes that were similar to the US population norms and did not exceed a clinically significant ES of at least 0.2 (Table 4).

Table 4

Effect size

/WebMaterial/ShowPic/843828

The influences of functional status on PCS and MCS were evaluated by stratified analyses. Frequent vertigo and imbalance problems were associated with worst PCS and MCS (vertigo PCS: ES -0.73; MCS: ES -0.71, imbalance PCS: ES -0.56; MCS: ES -0.36, p < 0.001). Nonuseful hearing in the tumor ear was associated with a worst PCS (ES = -0.27, p = 0.01) but not MCS (ES = -0.02, p = 0.87). No significant differences were found for tinnitus (Table 5).

Table 5

Functional status effect on summary scores

/WebMaterial/ShowPic/843827

Discussion

This study found that its participants who were treated with GKRS for VS maintained a good, long-term QOL that was comparable to the age-adjusted general US population, overall. More than 90% of participants were satisfied with their current overall functionality and activity level. Three items demonstrated a negative impact on QOL: vertigo, imbalance, and nonuseful hearing. These items were associated with small to moderate ES changes.

Several published studies have evaluated the outcomes of GKRS and indicate that this management strategy is associated with long-term improvement, especially in comparison to outcomes reported after microsurgical management (Table 6) [8,9,16,17,18,19,20,21,22,23,24,25]. Our study compares QOL after GKRS for VS to age-matched US population norms. There are two other studies from the Netherlands and Norway that also compare their GKRS participants with population norms and they found similar results to this study [19,24]. Two additional studies looked at QOL compared with population norms but without surgical intervention. In 2010, Lloyd et al. [26] evaluated QOL in the UK for VS participants who underwent continued observation without intervention and compared them with UK SF-36 population norms, and they did significantly worse than the UK population. In 2008, Vogel et al. [27] did a cross-sectional study to look at baseline SF-36 scores upon initial diagnosis of VS and found that they scored lower than the Dutch population norms prior to intervention. In 2015, Carlson et al. [16] compared several QOL measures with a nontumor control group and found small but clinically insignificant differences between GKRS, microsurgery, conservative management, and even the nontumor controls (Table 6).

Table 6

Literature review of Gamma Knife radiosurgery quality of life outcomes

/WebMaterial/ShowPic/843826

Tinnitus is a commonly reported symptom of participants with VS but the impact of tinnitus is variable among participants, and its presence does not easily correlate with a participant's level of discomfort [28,29,30]. This study did not find any significant association between tinnitus and SF-36 summary score changes. These findings agree with previous studies that also failed to find a significant correlation between summary scores and the tinnitus handicap index [26,31]. Other tinnitus studies have shown that approximately 80% of participants who suffer from chronic tinnitus did not seek treatment for it [28].

Limitations

There is no specific VS QOL questionnaire that has been widely used, and so there is some heterogeneity in the measurement tools of existing research. A publication by Schaffer et al. [32] validated a VS-specific QOL measurement tool named PANQOL, and that may be something researchers begin to use more moving forward. This study used a functional questionnaire that is very similar to one that was developed by the VS Association and one that has been used in previous research [8,33]. This study looked at QOL with a widely validated tool (SF-36) that is generic across many disease processes, has been used in several VS studies, and allows comparisons with age-matched population norms. There were no pretreatment QOL survey data available in this study and therefore we could not compare changes over time. The cross-sectional survey method we used limits our ability to draw conclusions regarding improvement after treatment. Retrospective questioning of QOL status was avoided due to the possibility of poor recollection, misclassification, and recall bias.

This study was performed with data from a single institution with a survey response rate of 59% and completed data from 50% of surveyed patients, which might raise questions of generalizability and respondent bias. The patient survey was not incentivized, which lowers the expected response rate, and ultimately the respondents in this study were similar to typical patients with VS who are treated with GKRS in the USA based on age, gender, tumor volume, and radiation dose. The overall sample size of this study's cohort is also much larger than that of similar studies done on QOL (Table 6).

Conclusion

Overall, after undergoing GKRS for VS, participants reported a good long-term QOL that was very similar to the QOL of US population norms. Of the common symptoms, vertigo had the greatest impact on QOL followed by imbalance and then hearing loss. Tinnitus did not have a significant impact on QOL. Participants reported that they are satisfied with their current level of functioning and activity.

Acknowledgment

This report was funded by a grant from the Jenny Zoline Foundation.

Disclosure Statement

Dr. L. Dade Lunsford is a stockholder of Elekta.


References

  1. Gouveris HT, Mann WJ: Quality of life in sporadic vestibular schwannoma: a review. ORL 2010;72:69-74.
  2. Godefroy WP, Kaptein AA, Vogel JJ, van der Mey AGL: Conservative treatment of vestibular schwannoma: a follow-up study on clinical and quality-of-life outcome. Otol Neurotol 2009;30:968-974.
  3. Myrseth E, Pedersen P-H, Møller P, Lund-Johansen M: Treatment of vestibular schwannomas. Why, when and how? Acta Neurochir (Wien) 2007;149:647-660.
  4. Lobato-Polo J, Kondziolka D, Zorro O, Kano H, Flickinger JC, Lunsford LD: Gamma knife radiosurgery in younger patients with vestibular schwannomas. Neurosurgery 2009;65:294-301.
  5. Nakaya K, Niranjan A, Kondziolka D, et al: Gamma knife radiosurgery for benign tumors with symptoms from brainstem compression. Int J Radiat Oncol 2010;77:988-995.
  6. Régis J, Carron R, Park MC, et al: Wait-and-see strategy compared with proactive Gamma Knife surgery in patients with intracanalicular vestibular schwannomas. J Neurosurg 2010;113(suppl):105-111.
    External Resources
  7. Berkowitz O, Iyer AK, Kano H, Talbott EO, Lunsford LD: Epidemiology and environmental risk factors associated with vestibular schwannoma. World Neurosurg 2015;84:1674-1680.
  8. Pollock BE, Lunsford LD, Kondziolka D, et al: Outcome analysis of acoustic neuroma management: a comparison of microsurgery and stereotactic radiosurgery. Neurosurgery 1995;36:215-224; discussion 224-229.
  9. Van Roijen L, Nijs HG, Avezaat CJ, et al: Costs and effects of microsurgery versus radiosurgery in treating acoustic neuroma. Acta Neurochir (Wien) 1997;139:942-948.
  10. Ware JE, Sherbourne CD: The MOS 36-item short-form health survey (SF-36). I. Conceptual framework and item selection. Med Care 1992;30:473-483.
    External Resources
  11. Berkowitz O, Kondziolka D, Bissonette D, Niranjan A, Kano H, Lunsford LD: The evolution of a clinical registry during 25 years of experience with Gamma Knife radiosurgery in Pittsburgh. Neurosurg Focus 2013;34:E4.
  12. Ware JE, Kosinski M, Dewey JE: How to Score Version 2 of the SF-36 Health Survey: Standards and Acute Forms. Lincoln, QualityMetric, 2001.
  13. Cohen J: Statistical Power Analysis for the Behavioral Sciences, ed 2. Hillsdale, Erlbaum Associates, 1988.
  14. Walters SJ: Sample size and power estimation for studies with health related quality of life outcomes: a comparison of four methods using the SF-36. Health Qual Life Outcomes 2004;2:26.
  15. Samsa G, Edelman D, Rothman ML, Williams GR, Lipscomb J, Matchar D: Determining clinically important differences in health status measures: a general approach with illustration to the Health Utilities Index Mark II. Pharmacoeconomics 1999;15:141-155.
  16. Carlson ML, Tveiten OV, Driscoll CL, et al: Long-term quality of life in patients with vestibular schwannoma: an international multicenter cross-sectional study comparing microsurgery, stereotactic radiosurgery, observation, and nontumor controls. J Neurosurg 2015;122:833-842.
  17. Kim HJ, Roh KJ, Oh HS, Chang WS, Moon IS: Quality of life in patients with vestibular schwannomas according to management strategy. Otol Neurotol 2015;36:1725-1729.
  18. McLaughlin EJ, Bigelow DC, Lee JY, Ruckenstein MJ: Quality of life in acoustic neuroma patients. Otol Neurotol 2015;36:653-656.
  19. Myrseth E, Møller P, Pedersen P-H, Vassbotn FS, Wentzel-Larsen T, Lund-Johansen M: Vestibular schwannomas: clinical results and quality of life after microsurgery or gamma knife radiosurgery. Neurosurgery 2005;56:927-935; discussion 927-935.
    External Resources
  20. Myrseth E, Møller P, Pedersen P-H, Lund-Johansen M: Vestibular schwannoma: surgery or gamma knife radiosurgery? A prospective, nonrandomized study. Neurosurgery 2009;64:654-663.
  21. Pollock BE, Driscoll CLW, Foote RL, et al: Patient outcomes after vestibular schwannoma management: a prospective comparison of microsurgical resection and stereotactic radiosurgery. Neurosurgery 2006;59:77-85.
  22. Régis J, Pellet W, Delsanti C, et al: Functional outcome after gamma knife surgery or microsurgery for vestibular schwannomas. J Neurosurg 2002;97:1091-1100.
  23. Sandooram D, Grunfeld EA, McKinney C, Gleeson MJ: Quality of life following microsurgery, radiosurgery and conservative management for unilateral vestibular schwannoma. Clin Otolaryngol Allied Sci 2004;29:621-627.
  24. Timmer FCA, van Haren AEP, Mulder JJS, et al: Quality of life after gamma knife radiosurgery treatment in patients with a vestibular schwannoma: the patient's perspective. Eur Arch Otorhinolaryngol 2010;267:867-873.
  25. Wangerid T, Bartek J, Svensson M, Förander P: Long-term quality of life and tumour control following gamma knife radiosurgery for vestibular schwannoma. Acta Neurochir (Wien) 2014;156:389-396.
  26. Lloyd SKW, Kasbekar AV, Baguley DM, Moffat DA: Audiovestibular factors influencing quality of life in patients with conservatively managed sporadic vestibular schwannoma. Otol Neurotol 2010;31:968-976.
  27. Vogel JJ, Godefroy WP, van der Mey AGL, le Cessie S, Kaptein AA: Illness perceptions, coping, and quality of life in vestibular schwannoma patients at diagnosis: Otol Neurotol 2008;29:839-845.
  28. Henry JA, Dennis KC, Schechter MA: General review of tinnitus: prevalence, mechanisms, effects, and management. J Speech Lang Hear Res 2005;48:1204.
  29. Henry JA, Meikle MB: Psychoacoustic measures of tinnitus. J Am Acad Audiol 2000;11:138-155.
    External Resources
  30. Sullivan MD, Katon W, Dobie R, Sakai C, Russo J, Harrop-Griffiths J: Disabling tinnitus. Association with affective disorder. Gen Hosp Psychiatry 1988;10:285-291.
  31. Myrseth E, Møller P, Wentzel-Larsen T, Goplen F, Lund-Johansen M: Untreated vestibular schwannomas: vertigo is a powerful predictor for health-related quality of life: Neurosurgery 2006;59:67-76.
    External Resources
  32. Shaffer BT, Cohen MS, Bigelow DC, Ruckenstein MJ: Validation of a disease-specific quality-of-life instrument for acoustic neuroma: the Penn Acoustic Neuroma Quality-of-Life Scale. Laryngoscope 2010;120:1646-1654.
  33. Wiegand DA, Fickel V: Acoustic neuroma - the patient's perspective: subjective assessment of symptoms, diagnosis, therapy, and outcome in 541 patients. Laryngoscope 1989;99:179-187.

Author Contacts

Oren Berkowitz, PhD, PA-C

Boston University School of Medicine

72 E. Concord St., Suite L801

Boston, MA 02118 (USA)

E-Mail orenberk@bu.edu


Article / Publication Details

First-Page Preview
Abstract of Clinical Study

Received: October 25, 2016
Accepted: March 20, 2017
Published online: May 23, 2017
Issue release date: July 2017

Number of Print Pages: 8
Number of Figures: 2
Number of Tables: 6

ISSN: 1011-6125 (Print)
eISSN: 1423-0372 (Online)

For additional information: https://www.karger.com/SFN


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References

  1. Gouveris HT, Mann WJ: Quality of life in sporadic vestibular schwannoma: a review. ORL 2010;72:69-74.
  2. Godefroy WP, Kaptein AA, Vogel JJ, van der Mey AGL: Conservative treatment of vestibular schwannoma: a follow-up study on clinical and quality-of-life outcome. Otol Neurotol 2009;30:968-974.
  3. Myrseth E, Pedersen P-H, Møller P, Lund-Johansen M: Treatment of vestibular schwannomas. Why, when and how? Acta Neurochir (Wien) 2007;149:647-660.
  4. Lobato-Polo J, Kondziolka D, Zorro O, Kano H, Flickinger JC, Lunsford LD: Gamma knife radiosurgery in younger patients with vestibular schwannomas. Neurosurgery 2009;65:294-301.
  5. Nakaya K, Niranjan A, Kondziolka D, et al: Gamma knife radiosurgery for benign tumors with symptoms from brainstem compression. Int J Radiat Oncol 2010;77:988-995.
  6. Régis J, Carron R, Park MC, et al: Wait-and-see strategy compared with proactive Gamma Knife surgery in patients with intracanalicular vestibular schwannomas. J Neurosurg 2010;113(suppl):105-111.
    External Resources
  7. Berkowitz O, Iyer AK, Kano H, Talbott EO, Lunsford LD: Epidemiology and environmental risk factors associated with vestibular schwannoma. World Neurosurg 2015;84:1674-1680.
  8. Pollock BE, Lunsford LD, Kondziolka D, et al: Outcome analysis of acoustic neuroma management: a comparison of microsurgery and stereotactic radiosurgery. Neurosurgery 1995;36:215-224; discussion 224-229.
  9. Van Roijen L, Nijs HG, Avezaat CJ, et al: Costs and effects of microsurgery versus radiosurgery in treating acoustic neuroma. Acta Neurochir (Wien) 1997;139:942-948.
  10. Ware JE, Sherbourne CD: The MOS 36-item short-form health survey (SF-36). I. Conceptual framework and item selection. Med Care 1992;30:473-483.
    External Resources
  11. Berkowitz O, Kondziolka D, Bissonette D, Niranjan A, Kano H, Lunsford LD: The evolution of a clinical registry during 25 years of experience with Gamma Knife radiosurgery in Pittsburgh. Neurosurg Focus 2013;34:E4.
  12. Ware JE, Kosinski M, Dewey JE: How to Score Version 2 of the SF-36 Health Survey: Standards and Acute Forms. Lincoln, QualityMetric, 2001.
  13. Cohen J: Statistical Power Analysis for the Behavioral Sciences, ed 2. Hillsdale, Erlbaum Associates, 1988.
  14. Walters SJ: Sample size and power estimation for studies with health related quality of life outcomes: a comparison of four methods using the SF-36. Health Qual Life Outcomes 2004;2:26.
  15. Samsa G, Edelman D, Rothman ML, Williams GR, Lipscomb J, Matchar D: Determining clinically important differences in health status measures: a general approach with illustration to the Health Utilities Index Mark II. Pharmacoeconomics 1999;15:141-155.
  16. Carlson ML, Tveiten OV, Driscoll CL, et al: Long-term quality of life in patients with vestibular schwannoma: an international multicenter cross-sectional study comparing microsurgery, stereotactic radiosurgery, observation, and nontumor controls. J Neurosurg 2015;122:833-842.
  17. Kim HJ, Roh KJ, Oh HS, Chang WS, Moon IS: Quality of life in patients with vestibular schwannomas according to management strategy. Otol Neurotol 2015;36:1725-1729.
  18. McLaughlin EJ, Bigelow DC, Lee JY, Ruckenstein MJ: Quality of life in acoustic neuroma patients. Otol Neurotol 2015;36:653-656.
  19. Myrseth E, Møller P, Pedersen P-H, Vassbotn FS, Wentzel-Larsen T, Lund-Johansen M: Vestibular schwannomas: clinical results and quality of life after microsurgery or gamma knife radiosurgery. Neurosurgery 2005;56:927-935; discussion 927-935.
    External Resources
  20. Myrseth E, Møller P, Pedersen P-H, Lund-Johansen M: Vestibular schwannoma: surgery or gamma knife radiosurgery? A prospective, nonrandomized study. Neurosurgery 2009;64:654-663.
  21. Pollock BE, Driscoll CLW, Foote RL, et al: Patient outcomes after vestibular schwannoma management: a prospective comparison of microsurgical resection and stereotactic radiosurgery. Neurosurgery 2006;59:77-85.
  22. Régis J, Pellet W, Delsanti C, et al: Functional outcome after gamma knife surgery or microsurgery for vestibular schwannomas. J Neurosurg 2002;97:1091-1100.
  23. Sandooram D, Grunfeld EA, McKinney C, Gleeson MJ: Quality of life following microsurgery, radiosurgery and conservative management for unilateral vestibular schwannoma. Clin Otolaryngol Allied Sci 2004;29:621-627.
  24. Timmer FCA, van Haren AEP, Mulder JJS, et al: Quality of life after gamma knife radiosurgery treatment in patients with a vestibular schwannoma: the patient's perspective. Eur Arch Otorhinolaryngol 2010;267:867-873.
  25. Wangerid T, Bartek J, Svensson M, Förander P: Long-term quality of life and tumour control following gamma knife radiosurgery for vestibular schwannoma. Acta Neurochir (Wien) 2014;156:389-396.
  26. Lloyd SKW, Kasbekar AV, Baguley DM, Moffat DA: Audiovestibular factors influencing quality of life in patients with conservatively managed sporadic vestibular schwannoma. Otol Neurotol 2010;31:968-976.
  27. Vogel JJ, Godefroy WP, van der Mey AGL, le Cessie S, Kaptein AA: Illness perceptions, coping, and quality of life in vestibular schwannoma patients at diagnosis: Otol Neurotol 2008;29:839-845.
  28. Henry JA, Dennis KC, Schechter MA: General review of tinnitus: prevalence, mechanisms, effects, and management. J Speech Lang Hear Res 2005;48:1204.
  29. Henry JA, Meikle MB: Psychoacoustic measures of tinnitus. J Am Acad Audiol 2000;11:138-155.
    External Resources
  30. Sullivan MD, Katon W, Dobie R, Sakai C, Russo J, Harrop-Griffiths J: Disabling tinnitus. Association with affective disorder. Gen Hosp Psychiatry 1988;10:285-291.
  31. Myrseth E, Møller P, Wentzel-Larsen T, Goplen F, Lund-Johansen M: Untreated vestibular schwannomas: vertigo is a powerful predictor for health-related quality of life: Neurosurgery 2006;59:67-76.
    External Resources
  32. Shaffer BT, Cohen MS, Bigelow DC, Ruckenstein MJ: Validation of a disease-specific quality-of-life instrument for acoustic neuroma: the Penn Acoustic Neuroma Quality-of-Life Scale. Laryngoscope 2010;120:1646-1654.
  33. Wiegand DA, Fickel V: Acoustic neuroma - the patient's perspective: subjective assessment of symptoms, diagnosis, therapy, and outcome in 541 patients. Laryngoscope 1989;99:179-187.
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