Schwannoma Patients Research Articles

Erratum. Hearing subclassification may predict long-term auditory outcomes after radiosurgery for vestibular schwannoma patients with good hearing.

Erratum. Hearing subclassification may predict long-term auditory outcomes after radiosurgery for vestibular schwannoma patients with good hearing.

Early Radiosurgery Improves Hearing Preservation in Vestibular Schwannoma Patients With Normal Hearing at the Time of Diagnosis

Vestibular schwannomas (VS) are increasingly diagnosed in patients with normal hearing because of advances in magnetic resonance imaging. We sought to evaluate whether stereotactic radiosurgery (SRS) performed earlier after diagnosis improved long-term hearing preservation in this population. We queried our quality assessment registry and found the records of 1134 acoustic neuroma patients who underwent SRS during a 15-year period (1997-2011). We identified 88 patients who had VS but normal hearing with no subjective hearing loss at the time of diagnosis. All patients were Gardner-Robertson (GR) class I at the time of SRS. Fifty-seven patients underwent early (≤2years from diagnosis) SRS and 31 patients underwent late (>2years afterdiagnosis)SRS. At a median follow-up time of 75months, we evaluated patient outcomes. Tumor control rates (decreased or stable in size) were similar in the early (95%) and late (90%) treatment groups (P=.73). Patients in the early treatment group retained serviceable (GR class I/II) hearing and normal (GR class I) hearing longer than did patients in the late treatment group (serviceable hearing, P=.006; normal hearing, P<.0001, respectively). At 5years after SRS, an estimated 88% of the early treatment group retained serviceable hearing and 77% retained normal hearing, compared with 55% with serviceable hearing and 33% with normal hearing in the late treatment group. SRS within 2years after diagnosis of VS in normal hearing patients resulted in improved retention of all hearing measures compared with later SRS.

The possibility of seeding vestibular schwannomas through surgery: Limited experience with two cases.

Background:We present two exceptional cases of possible tumor seeding in benign vestibular schwannoma (VS) patients occurring years after initial microsurgical resection.Case Description:We retrospectively analyzed the surgical management, histology and documented the growth of new tumor occurrence in close vicinity of the original schwannomas by serial magnetic resonance imaging over a period of 10 years. None of the patients had stigmata of neurofibromatosis, making it a reasonable assumption that the second tumor was due to surgical seeding during the first surgery. Moreover, in the second case, a microsurgical re-exploration showed that the recurrent tumor did not show any adhesion or contact to the caudal cranial nerves as anticipated had this been a new cranial nerve schwannoma.Conclusions:Surgical seeding of VSs is a rare complication but can occur despite benign histology and generous irrigation during surgery.

Perfusion magnetic resonance imaging provides additional information as compared to anatomical imaging for decision-making in vestibular schwannoma

ObjectiveThe added value of perfusion MRI for decision-making in vestibular schwannoma (VS) patients is unknown. MRI offers two perfusion methods: the first employing contrast agent (dynamic susceptibility contrast (DSC)-MRI) that provides information on cerebral blood volume (CBV) and cerebral blood flow (CBF), the second by magnetic labeling of blood (arterial spin labeling (ASL)-MRI), providing CBF-images. The goal of the current study is to investigate whether DSC and ASL perfusion MRI provides complimentary information to current anatomical imaging in treatment selection process of VS. MethodsNine patients with growing VS with extrameatal diameter >9mm were included (>2mm/year and 20% volume expansion/year) and one patient with 23mm extrameatal VS without growth. DSC and ASL perfusion MRI were obtained on 3T MRI. Perfusion in VS was scored as hyperintense, hypointense or isointense compared to the contralateral region. ResultsSeven patients showed hyperintense signal on DSC and ASL sequences. Three patients showed iso- or hypointense signal on at least one perfusion map (1 patient hypointense on both DSC-MRI and ASL; 1 patient isointense on DSC-CBF; 1 patient isointense on ASL). All patients showed enhancement on post-contrast T1 anatomical scan. ConclusionPerfusion MR provides additional information compared to anatomical imaging for decision-making in VS.

Hearing subclassification may predict long-term auditory outcomes after radiosurgery for vestibular schwannoma patients with good hearing

OBJECTIVE In the era of MRI, vestibular schwannomas are often recognized when patients still have excellent hearing. Besides success in tumor control rate, hearing preservation is a main goal in any procedure for management of this population. The authors evaluated whether modified auditory subclassification prior to radiosurgery could predict long-term hearing outcome in this population. METHODS The authors reviewed a quality assessment registry that included the records of 1134 vestibular schwannoma patients who had undergone stereotactic radiosurgery during a 15-year period (1997-2011). The authors identified 166 patients who had Gardner-Robertson Class I hearing prior to stereotactic radiosurgery. Fifty-three patients were classified as having Class I-A (no subjective hearing loss) and 113 patients as Class I-B (subjective hearing loss). Class I-B patients were further stratified into Class I-B1 (pure tone average ≤ 10 dB in comparison with the contralateral ear; 56 patients), and I-B2 (> 10 dB compared with the normal ear; 57 patients). At a median follow-up of 65 months, the authors evaluated patients' hearing outcomes and tumor control. RESULTS The median pure tone average elevations after stereotactic radiosurgery were 5 dB, 13.5 dB, and 28 dB in Classes I-A, I-B1, and I-B2, respectively. The median declines in speech discrimination scores after stereotactic radiosurgery were 0% for Class I-A (p = 0.33), 8% for Class I-B1 (p < 0.0001), and 40% for Class I-B2 (p < 0.0001). Serviceable hearing preservation rates were 98%, 73%, and 33% for Classes I-A, I-B1, and I-B2, respectively. Gardner-Robertson Class I hearing was preserved in 87%, 43%, and 5% of patients in Classes I-A, I-B1, and I-B2, respectively. CONCLUSIONS Long-term hearing preservation was significantly better if radiosurgery was performed prior to subjective hearing loss. In patients with subjective hearing loss, the difference in pure tone average between the affected ear and the unaffected ear was an important factor in long-term hearing preservation.

Fractionated stereotactic radiation therapy for vestibular schwannomas: Dosimetric factors predictive of hearing outcomes

PurposeTo determine dosimetric factors predictive of hearing loss in vestibular schwannoma (VS) patients treated with definitive fractionated stereotactic radiation therapy (FSRT), and to report tumor control, serviceable hearing preservation, and cranial nerve toxicities. Methods and materialsWe identified 45 patients (29 men and 16 women) with unilateral sporadic VS, who underwent definitive FSRT. All patients had serviceable hearing prior to treatment, defined as Gardner-Robertson Class 1 or 2. All patients underwent an audiogram before the start of treatment and serial audiometric assessments after treatment. The median audiometric follow-up time was 35.2 months (range, 5.0-89.7 months). Patients underwent a median of 4.5 (range, 1-9) posttreatment audiograms. The ipsilateral cochlea was contoured retrospectively, and dosimetric data were used to determine factors predictive of losing serviceable hearing. The median clinical follow-up time was 29.9 months (range, 1.5-83.6 months). ResultsAt the time of the last audiometric follow-up, 62% of patients retained serviceable hearing. The actuarial 1-, 2-, and 3-year serviceable hearing preservation rates were 83%, 75%, and 51%, respectively. The estimated median time to loss of serviceable hearing was 42.2 months. On multivariate analysis, cochlear volume <0.15 mL (hazard ratio, 2.849; 95% confidence interval, 1.116-7.270; P = .029) and mean cochlear dose <4000 cGy (hazard ratio, 3.178; 95% confidence interval, 1.116-9.049; P = .030) were statistically significant variables associated with serviceable hearing preservation. The actuarial tumor control was 100%. Three of 39 patients (8%) developed hemifacial spasm after FSRT (House-Brackmann Grade 3), 2 of which completely resolved. No patients experienced deterioration in trigeminal nerve function after FSRT. ConclusionsFractionated stereotactic radiation therapy can provide excellent tumor control with acceptable clinical outcomes. The mean dose to the cochlea is highly predictive of the probability of maintaining serviceable hearing after FSRT.

Long-term Treatment Response and Patient Outcomes for Vestibular Schwannoma Patients Treated With Hypofractionated Stereotactic Radiation Therapy

Long-term Treatment Response and Patient Outcomes for Vestibular Schwannoma Patients Treated With Hypofractionated Stereotactic Radiation Therapy

Evaluating Radiological Changes in Vestibular Schwannoma Patients Treated With Hypofractionated Stereotactic Radiation Therapy: A Potential Role for a Novel 3-D Quantitative Volumetric Assessment Tool

Evaluating Radiological Changes in Vestibular Schwannoma Patients Treated With Hypofractionated Stereotactic Radiation Therapy: A Potential Role for a Novel 3-D Quantitative Volumetric Assessment Tool

Dose-volume histogram prediction using density estimation

Knowledge of what dose-volume histograms can be expected for a previously unseen patient could increase consistency and quality in radiotherapy treatment planning. We propose a machine learning method that uses previous treatment plans to predict such dose-volume histograms. The key to the approach is the framing of dose-volume histograms in a probabilistic setting.The training consists of estimating, from the patients in the training set, the joint probability distribution of some predictive features and the dose. The joint distribution immediately provides an estimate of the conditional probability of the dose given the values of the predictive features. The prediction consists of estimating, from the new patient, the distribution of the predictive features and marginalizing the conditional probability from the training over this. Integrating the resulting probability distribution for the dose yields an estimate of the dose-volume histogram.To illustrate how the proposed method relates to previously proposed methods, we use the signed distance to the target boundary as a single predictive feature. As a proof-of-concept, we predicted dose-volume histograms for the brainstems of 22 acoustic schwannoma patients treated with stereotactic radiosurgery, and for the lungs of 9 lung cancer patients treated with stereotactic body radiation therapy. Comparing with two previous attempts at dose-volume histogram prediction we find that, given the same input data, the predictions are similar.In summary, we propose a method for dose-volume histogram prediction that exploits the intrinsic probabilistic properties of dose-volume histograms. We argue that the proposed method makes up for some deficiencies in previously proposed methods, thereby potentially increasing ease of use, flexibility and ability to perform well with small amounts of training data.

Factors influencing the growth rate of vestibular schwannoma in patients with neurofibromatosis type 2.

Neurofibromatosis type 2 (NF2) is a devastating disease with no well-accepted management guidelines. Better understanding of the disease process provides the basis for how or when to initiate treatment. Only few studies have addressed the factors influencing the growth rate of NF2-related vestibular schwannomas (VSs), and these studies have reported variable results. This study aimed to assess the clinical factors influencing the growth rate of NF2-related VSs. The medical records of 66 patients (totalling 74 VSs) were retrospectively analysed. The tumours were measured according to a two-component box model. The tumour growth rate was estimated by linear regression analysis of the changes in VS volumes over time. The clinical characteristics of all the patients were recorded. The relationship between the tumour growth rate and clinical factors were analysed. Linear regression, Pearson's correlation and Student's t-test were conducted using the SPSS 19.0 statistical package. The median follow-up duration was 4.9 years. The VSs growth rate was highly correlated with the initial VS volume (r = 0.97, p < 0.01). However, it was inversely correlated with the age at symptom onset (r = -0.41, p < 0.01). The average VS growth rate in patients with spinal tumours was 13.18 cm(3)/year compared with 0.19 cm(3)/year in patients without spinal tumours (p < 0.01). The VS growth rate in patients who had resection of a contralateral VS was slightly higher than that of patients with untreated VSs (p < 0.01). Other factors including sex, vestibular symptom, presence of other cranial schwannomas, family history and dermal abnormalities did not affect the VS growth rate. The potential clinical factors influencing the VS growth rate are the age at symptom onset, initial tumour volume and presence of spinal tumours. Surgical resection of VSs might accelerate the growth rate of contralateral tumours. The effects of these factors require further experimental confirmation.

Biodistribution of boron after intravenous 4-dihydroxyborylphenylalanine-fructose (BPA-F) infusion in meningioma and schwannoma patients: A feasibility study for boron neutron capture therapy

We studied the uptake of boron after 100mg/kg BPA infusion in three meningioma and five schwannoma patients as a pre-BNCT feasibility study. With average tumour-to-whole blood boron concentrations of 2.5, we discuss why BNCT could, and probably should, be developed to treat severe forms of the studied tumours. However, analysing 72 tumour and 250 blood samples yielded another finding: the plasma-to-whole blood boron concentrations varied with time, suggesting that the assumed constant boron ratio of 1:1 between normal brain tissue and whole blood deserves re-assessment.

Quality of Life in Vestibular Schwannoma Patients Managed by Surgical or Conservative Approaches.

The aim of our study was to assess quality of life (QOL) among patients who underwent microsurgical excision of vestibular schwannoma (VS) compared with those managed conservatively. Retrospective study. Tertiary care center. There was a total sample population of 376 patients diagnosed with a unilateral VS. A total of 223 patients with unilateral VS returned the mailed questionnaires. These were then divided into two groups-78 that had undergone microsurgical excision and 145 that were managed conservatively. Subgroups within these primary groups were created for analysis. The primary outcome measure was the Medical Outcomes Study 36 Items Short Form (SF-36). The Dizziness Handicap Inventory test, Hearing Handicap Inventory test, and Tinnitus Handicap Inventory were also used. The surgically managed group had a worse QOL when compared with the conservatively managed group using SF-36, significantly so in the domains of physical role limitation and social functioning. Trends were seen toward a better QOL in some domains in the subgroups of male patients and patients younger than 65 years. Worse QOL scores in the Tinnitus Handicap Inventory were seen in the subgroups with larger tumor size. Finally, on correlation analysis between all handicap inventories and SF-36, handicap due to disequilibrium had the strongest correlation with worsening of QOL. In SF-36, the vitality domain showed the greatest correlation with otologic handicap overall, whereas the role emotional domain showed the least. This study found that worse QOL scores for surgically managed versus conservatively managed VS patients are most significant in the areas of physical role limitation and social functioning. In some areas, patients who are male and younger report better QOL. Handicap due to disequilibrium seems to have the greatest negative impact on QOL. These factors should be considered when counseling patients regarding approach to VS, in the context of an experienced management program.

Role of cyclins D1 and D3 in vestibular schwannoma.

Vestibular schwannomas in younger patients have been observed to be larger in size and grow more quickly. This study aimed to evaluate the expression of three important cell cycle proteins, cyclin D1, cyclin D3 and Ki-67, in vestibular schwannoma patients separated into two age groups: ≤ 40 years or > 40 years. Immunohistochemical detection of cyclin D1, cyclin D3 and Ki-67 was undertaken in 180 surgically resected vestibular schwannomas. The proliferation index of vestibular schwannomas was statistically higher in the ≤ 40 years age group compared to that in the > 40 years age group (mean of 4.52 vs 3.27, respectively; p = 0.01). Overexpression of cyclin D1 and cyclin D3 was found in 68 per cent and 44 per cent of tumours, respectively. There was an increased Ki-67 proliferation index in the younger age group that appears to correlate with clinical behaviour. Vestibular schwannomas in both age groups show increased expression of cyclin D1 and cyclin D3.

Strategy for the surgical treatment of vestibular schwannomas in patients with neurofibromatosis type 2

ObjectiveGuidelines for appropriate management of vestibular schwannomas in NF2 patients are controversial. In this paper we reviewed our experience with patients with NF2 for the results of surgical treatment with particular reference to hearing and facial nerve preservation. MethodsWe included in the study 30 patients (16 women and 14 men) with the diagnosis of NF2 treated in our department between 1998 and 2014 who underwent surgery for vestibular schwannoma removal with a follow-up for at least 1 year. In 3 cases, the vestibular schwannomas were unilateral. Six patients with bilateral vestibular schwannomas underwent unilateral procedure. Therefore, 51 acoustic tumors were studied in 30 patients. ResultsNo operative death we noted. Significant deterioration to the non-functional level occurred in 19 out of 22 cases with well-preserved preoperative hearing. Only three ears maintained their preoperative good hearing. Hearing was preserved in cases of small schwannoma not exceeding 2cm. Among 21 patients who underwent bilateral operations hearing was preserved in 3 out of 7 cases when smaller tumor or better hearing level side was attempted at first surgery. In contrary none of the 14 patients retained hearing when the first operation concerned the worse-hearing ear. Among 14 tumors up to 2cm there was only one case of moderately severe facial nerve dysfunction (House–Brackmann Grade IV) in the long follow-up. ConclusionEarly surgical intervention for vestibular schwannoma in NF2 patient is a viable management strategy to maintain hearing function and preserve facial nerve function.

Expression and significances of Merlin and mTOR in spinal schwannoma

Objective To clarify the expression and clinicopathological significances of mTOR and Merlin proteins in spinal schwannoma. Methods Immunohistochemical SP method was used to detect the expression levels of mTOR and Merlin proteins in tumor tissues from 21 spinal schwannoma patients. The meaning of the two proteins expression changes on schwannoma was analyzed. Results In 21 cases of schwannoma patients, the mTOR was positive expression in 16 cases, negative expression in 5 cases, while in the normal neural tissue, mTOR was all negative expression. In 21 cases of schwannoma patients, the Merlin protein was negative expression in 18 cases, positive expression in 3 cases, but it was positive in all of normal neural tissue. Merlin protein expression was negatively correlated with mTOR protein expression (r=-0.785, P<0.001). Conclusion The expression level of mTOR proteins in schwannoma is significantly higher than that in normal nerve tissue, while the expression level of Merlin protein in schwannoma tissue is significantly lower than that in normal nerve tissue. There is an internal relationship between mTOR and Merlin. Key words: mTOR; Merlin protein; Schwannoma; Immunohistochemistry

Quality of life in acoustic neuroma patients.

To examine the differences in quality of life for vestibular schwannoma patients undergoing conservative management, gamma knife, and surgery. Vestibular schwannoma patients without a diagnosis of NF2. Vestibular schwannoma treatment or conservative management. Penn Acoustic Neuroma Quality of Life (PANQOL) survey scores (0-100). One hundred eighty-six patients (98 conservative, 49 gamma knife, 39 surgery) were included. Mean patient age (years) of the surgery group (49 ± 14) was significantly younger than both the conservative (58 ± 13) and gamma knife group (59 ± 12) (p < 0.001). Mean follow-up time was 2.6 years.Tumor size (mm) was found to be significantly different between the conservative (8 ± 4.8), gamma knife (18 ± 5.9), and surgery (22 ± 8.3) groups (p < 0.001). Speech recognition threshold and speech discrimination percentage were significantly better for the conservative group compared to the gamma knife or surgery groups (p < 0.001).The hearing domain scores seemed better for the conservative group (62 ± 26) when compared to the surgery group (47 ± 25). The general and total domain scores were similar for all treatment groups, whereas the quality-of-life scores for gamma knife and surgery were similar. Although surgery groups' significantly larger tumors and worse hearing were apparent in specific PANQOL domains, all patients achieved a similar general level of quality of life.

Hearing preservation up to 3 years after gamma knife radiosurgery for Gardner-Robertson class I patients with vestibular Schwannomas.

Vestibular schwannoma patients with Gardner-Robertson (GR) class I hearing seek to maintain high-level hearing whenever possible. To evaluate hearing outcomes at 2 to 3 years in GR class I patients who underwent Gamma Knife radiosurgery (GKRS). Sixty-eight patients with GR class I hearing were identified between 2006 and 2009. Twenty-five patients had no subjective hearing loss (group A) and 43 patients reported subjective hearing loss (group B) before GKRS. The median tumor volume (1 cm) and tumor margin dose (12.5 Gy) were the same in both groups. Serviceable hearing retention rates (GR grade I or II) were 100% for group A compared with 81% at 1 year, 60% at 2 years, and 57% at 3 years after GKRS for group B patients. Group A patients had significantly higher rates of hearing preservation in either GR class I (P < .001) or GR class II (P < .001). Patients with a pure tone average (PTA) <15 dB before GKRS had significantly higher rates of preservation of GR class I or II hearing. At 2 to 3 years after GKRS, patients without subjective hearing loss or a PTA <15 dB had higher rates of grade I or II hearing preservation. Modification of the GR hearing classification into 2 groups of grade I hearing (group A, those with no subjective hearing loss and a PTA <15 dB; and group B, those with subjective hearing loss and a PTA >15 dB) may be useful to help predict hearing preservation rates at 2 to 3 years after GKRS.

Patterns and Predictors of Hearing Loss in Observed Vestibular Schwannoma

Objective: Reliable long-term hearing preservation with vestibular schwannoma remains elusive. The majority of patients will ultimately lose serviceable hearing in the tumor ear as a result of disease or treatment. The primary objective of this study is to characterize long-term hearing loss in a large cohort of conservatively managed vestibular schwannoma patients and to identify predictors of audiometric decline. Patients and Methods: Retrospective review of 89 adult patients from two independent centers who were managed with observation, receiving serial MRI, and audiograms. Only patients with serviceable hearing at the time of diagnosis were included. Patients with neurofibromatosis type 2 and those who have received prior treatment were excluded. Tumor size and hearing capacity were classified according to the 1995 American Academy of Otolaryngology–Head and Neck Surgery reporting guidelines. Results: A total of 89 patients were included in the analysis. The mean age at the time of diagnosis was 56 years, 60% were females, and the average duration of audiometric follow-up was 64 months (range, 11–126 months). Overall, 64% of tumors were purely intracanalicular and 55% were leftsided. Overall, 16% of tumors demonstrated radiologic growth during the period of study. At time of diagnosis, 41 (50%) had class A hearing and 41 (50%) had class B hearing. At the last follow-up, 62% of patients remained within the same hearing class. Overall, at a mean of 64 months, 62% maintained serviceable hearing, whereas31% progressed to class C (8%) or class D (23%) hearing. Patients who started with class A hearing were significantly more likely to retain serviceable hearing at last follow-up, compared with those with class B hearing at diagnosis (85 vs. 46%; p < 0.001). Conclusion: At a mean of 64 months following diagnosis, 62% of observed VS patients with baseline serviceable hearing will maintain class A or class B capacity. Class B hearing at diagnosis and longer duration of audiometric follow-up were the primary predictors of nonserviceable hearing.

Clinical features of vestibular schwannomas in patients who experience hearing improvement after surgery.

Postoperative improvements in hearing in patients with vestibular schwannoma are extremely rare. We reviewed nine cases retrospectively to investigate the clinical features of these cases. Hearing improvement was defined as an improvement in hearing class according to American Academy of Otolaryngology-Head and Neck Surgery (AAO-HNS) criteria. The nine patients comprised five men and four women with a mean age of 40.4 years. Of the nine tumors, three were solid and six cystic; mean tumor size was 29.7 mm. Mean pure tone average (PTA) and mean speech discrimination scores (SDS) were 47.5 dB and 22.8%, respectively, preoperatively and 29.6 dB and 83.9%, respectively, postoperatively. AAO-HNS class distribution was class B:1 and D:8, preoperatively, and class A: 5 and B:4, postoperatively. A lateral suboccipital retrosigmoid approach with a lateral (park bench) position was used in all nine patients. Clinical features of these vestibular schwannomas included (1) large cystic tumors, (2) sudden onset hearing loss, (3) the presence of a valley shape in the middle-pitch area on preoperative audiograms, (4) almost intact preoperative inner ear function, (5) a low SDS relative to PTA preoperatively, (6) surgical treatment via a lateral suboccipital approach within 6 months of the most recent exacerbation of hearing loss, (7) observation of I waves in preoperative, intraoperative, and postoperative auditory brainstem response (ABR) recordings, and (8) postoperative improvement in mainly the middle-pitch range and SDS. For surgical treatment of vestibular schwannomas with the above clinical features, a translabyrinthine approach and cochlear nerve section (unless the I wave on the intraoperative ABR trace disappears) should be avoided, regardless of the patient's preoperative hearing level, if a surgeon hopes to maximize the chances of preserving or improving hearing.

Long-term follow-up studies of Gamma Knife surgery for patients with neurofibromatosis Type 2.

The aim of this study was to evaluate long-term clinical outcomes after Gamma Knife surgery (GKS) for patients with neurofibromatosis Type 2 (NF2) and the role of GKS in the management of NF2. From December 1994 through December 2008, a total of 46 patients (21 male, 25 female) with NF2 underwent GKS and follow-up evaluation for at least 5 years at the Gamma Knife Center of the Beijing Neurosurgical Institute. GKS was performed using the Leksell Gamma Knife Models B and C. The mean age of the patients was 30 years (range 13-59 years). A family history of NF2 was found for 9 (20%) patients. The NF2 phenotype was thought to be Wishart for 20 (44%) and Feiling-Gardner for 26 (56%) patients. Among these 46 patients, GKS was performed to treat 195 tumors (73 vestibular schwannomas and 122 other tumors including other schwannomas and meningiomas). For vestibular schwannomas, the mean volume was 5.1 cm(3) (median 3.6 cm(3), range 0.3-27.3 cm(3)), the mean margin dose was 12.9 Gy (range 10-14 Gy), and the mean maximum dose was 27.3 Gy (range 16.2-40 Gy). For other tumors, the mean volume was 1.7 cm(3) (range 0.3-5.5 cm(3)), the mean margin dose was 13.3 Gy (range 11-14 Gy), and the mean maximum dose was 26.0 Gy (range 18.0-30.4 Gy). The median duration of follow-up was 109 months (range 8-195 months). For the 73 vestibular schwannomas that underwent GKS, the latest follow-up MR images demonstrated regression of 30 (41%) tumors, stable size for 31 (43%) tumors, and enlargement of 12 (16%) tumors. The total rate of tumor control for bilateral vestibular schwannomas in patients with NF2 was 84%. Of the 122 other types of tumors that underwent GKS, 103 (85%) showed no tumor enlargement. The rate of serviceable hearing preservation after GKS was 31.9% (15/47). The actuarial rates for hearing preservation at 3 years, 5 years, 10 years, and 15 years were 98%, 93%, 44%, and 17%, respectively. Of the 46 patients, 22 (48%) became completely bilaterally deaf, 17 (37%) retained unilateral serviceable hearing, and 7 (15%) retained bilateral serviceable hearing. The mean history of the disease course was 12 years (range 5-38 years). GKS was confirmed to provide long-term local tumor control for small- to medium-sized vestibular schwannomas and other types of tumors, although vestibular schwannomas in patients with NF2 responded less well than did unilateral sporadic vestibular schwannomas. Phenotype is the most strongly predictive factor of final outcome after GKS for patients with NF2. The risk for loss of hearing is high, whereas the risk for other cranial nerve complications is low.