Malignant transformation of vestibular schwannoma after radiation therapy

Stereotactic radiosurgery (SRS) is an effective treatment for vestibular schwannomas, offering high rates of tumor control and low neurological risks. Long-term complications of SRS are not fully understood, with several cases of malignant transformation reported in the literature. We report the case of a 50-year-old female with no prior history of neurofibromatosis who presented in 2013 with MRI evidence of a benign vestibular schwannoma. Despite treatment with CyberKnife SRS, she presented 6 years later with new onset neurologic symptoms. Further investigation showed stable lesion size with increasing vasogenic edema and a new area of enhancement in the brainstem, suspicious for malignant transformation. Subsequent treatment with partial craniectomy and histopathologic analysis was consistent with a malignant peripheral nerve sheath tumor diagnosis. Our case adds to a series of 24 similar cases in the literature, details of which have been summarized in our study. Overall, findings support the need for lifelong surveillance following SRS treatment of benign vestibular schwannomas. Patients should be educated on the potential risk of this complication, and clinicians must maintain a high level of suspicion for potential radiation-induced malignancy during the patient's clinical course.

Understanding the Radiobiology of Vestibular Schwannomas to Overcome Radiation Resistance

Vestibular schwannomas (VS) are benign tumors arising from cranial nerve VIII that account for 8-10% of all intracranial tumors and are the most common tumors of the cerebellopontine angle. These tumors are typically managed with observation, radiation therapy, or microsurgical resection. Of the VS that are irradiated, there is a subset of tumors that are radioresistant and continue to grow; the mechanisms behind this phenomenon are not fully understood. In this review, the authors summarize how radiation causes cellular and DNA injury that can activate (1) checkpoints in the cell cycle to initiate cell cycle arrest and DNA repair and (2) key events that lead to cell death. In addition, we discuss the current knowledge of VS radiobiology and how it may contribute to clinical outcomes. A better understanding of VS radiobiology can help optimize existing treatment protocols and lead to new therapies to overcome radioresistance.

Tumor Control Following Stereotactic Radiosurgery in Patients with Vestibular Schwannomas - A Retrospective Cohort Study

BACKGROUND

To better counsel vestibular schwannoma patients, it is necessary to understand the tumor control rates of stereotactic radiosurgery (SRS).

OBJECTIVES

To determine tumor control rates, factors determining control and complication rates following SRS.

METHODS

Tertiary hospital retrospective cohort.

RESULTS

579 tumors (576 patients) were treated with SRS. 477 tumors (474 patients, 82%) had ≥1 year follow up and 60% (344) ≥3 years follow up. 88% of tumors had primary SRS and 6.7% salvage SRS. Median follow up time was 4.6 years. At 3 years, the tumor control rate of primary SRS was 89% (258 of 290) in sporadic tumors compared to 43% in Neurofibromatosis type II (3 of 17) (p < 0.01). Our bivariable survival data analysis showed that Neurofibromatosis type II, documented pre-SRS growth, tumor measured by maximum dimension, SRS given as nonprimary treatment increased hazard of failure to control. There was one case of malignancy and another of rapid change following intra-tumoral hemorrhage. For tumors undergoing surgical salvage (25 of 59), 56% had a total or near-total resection, 16% had postoperative CSF leak, with 12% new facial paralysis (House-Brackmann grade VI) and worsening of facial nerve outcomes (House-Brackmann grade worse in 59% at 12 mo).

CONCLUSIONS

Control of vestibular schwannoma after primary SRS occurs in the large majority. Salvage surgical treatment was notable for higher rates of postoperative complications compared to primary surgery reported in the literature.

Malignant Transformation in Vestibular Schwannoma: Clinical Study With Survival Analysis

Aim

Vestibular schwannomas (VSs) are generally considered benign tumors, and malignant transformation of VSs (MTVSs) are rare findings. The clinical features, treatment strategy, outcomes and prognostic factors remain unclear. We endeavored to analyze the natural history, management, outcomes and prognostic factors of MTVSs.

Materials and Methods

The clinical features, radiologic findings, pathological investigations and surgical outcomes of 4 patients with MTVSs treated at the authors' institution between 2010 and 2019 were retrospectively collected. Related literature published until December 2019 (63 articles, 67 patients) was evaluated. The authors also made a pooled analysis to evaluate the risk factors for overall survival (OS) time.

Results

Of the 4 cases in our series, 3 cases were malignant transformation following previous treatment (surgery and radiosurgery) and 1 was primary MTVS. Of the 71 MTVSs from the literature, 27 were male and 39 were female, with the mean age of 47.2 ± 17.5 years old. Twelve patients (18.5%) were diagnosed with NF2 (15.4%) or NF1 (3.1%). Forty-three (61.4%) patients underwent previous treatment (surgery and/or radiotherapy) prior to the pathological diagnosis of MTVSs. The mean size of the MTVSs was 35.1 ± 13.2mm. The mean Ki-67 index was 30.6% ± 18.8%. Twenty-four (49.0%) patients underwent gross total resection, 25 (51.0%) patients underwent incomplete resection. Twenty-five (44.6%) underwent adjuvant radiotherapy (RT) postoperatively. During the average follow-up of 9.9 ± 9.5 months (range, 0-40 months), 37 (82.2%) patients developed a local recurrence or metastasis. Forty-seven (73.4%) patients died of tumor progression or postoperative complications. The overall 1-year and 2-year survival rate was 42.3% and 18.6% respectively. Log-rank testing for Kaplan-Meier survival analysis identified that size (P = 0.047) and adjuvant radiotherapy (P=0.001) were significant prognostic factors for OS. Multivariate analysis revealed that adjuvant RT was the only prognostic factor for longer OS (P = 0.005).

Conclusions

MTVSs are rare, fatal disease, prone to recur and metastasize rapidly, resulting in death in most of the cases. We found that GTR did not improve the survival in MTVSs but postoperative adjuvant RT can significantly improve the OS, and we recommend early postoperative RT in MTVSs regardless of extent of resection.

High-Grade Sarcoma Arising within a Previously Irradiated Vestibular Schwannoma: A Case Report and Literature Review

BACKGROUND

Vestibular schwannomas are benign tumors of the cerebellopontine angle that are often treated with radiation therapy. Radiation therapy maintains good tumor control rates but involves a small risk of radiation-induced malignancies. We present a case of high-grade sarcoma arising within a previously irradiated vestibular schwannoma and a literature review of this rare but important clinical entity.

METHODS

A 66-year-old woman presented with rapid clinical and radiographic deterioration 17 years after receiving stereotactic radiosurgery for vestibular schwannoma. After resection, pathology revealed a high-grade sarcoma arising within a conventional schwannoma. After further decline and tumor growth, the patient died of her disease 7 months postoperatively. Literature review was performed using PubMed and EMBASE databases and key words "vestibular schwannoma," "acoustic," "triton," "malignant," "sarcoma," "malignant peripheral nerve sheath tumor," "radiation," and "radiosurgery." All previous cases and the clinical circumstances related to these radiation-induced malignancies were assessed and quantified.

RESULTS

The systematic review yielded 20 prior cases of radiation-induced malignant transformation of a vestibular schwannoma in patients without neurofibromatosis. Most tumors (60%) transformed into malignant nerve sheath tumors. At the time of presentation, 70% of patients had new cranial neuropathies, and all had evidence of tumor growth with brainstem compression. Prognosis was poor with mean time to death of 7.6 months.

CONCLUSIONS

Radiation-induced malignant transformation of vestibular schwannomas is a rare but important clinical entity. Given its scarcity, the risk of malignancy should not sway initial management, but rapid clinical deterioration and radiographic growth during follow-up should prompt consideration of malignant transformation.

Glioblastoma multiforme as a secondary malignancy following stereotactic radiosurgery of a meningioma: case report

The documentation and exact incidence of stereotactic radiosurgery (SRS)-induced neoplasia is not well understood, with most literature restricted to single case reports and single-center retrospective reviews. The authors present a rare case of radiosurgery-induced glioblastoma multiforme (GBM) following radiosurgical treatment of a meningioma. A 74-year-old patient with a sporadic meningioma underwent radiosurgery following surgical removal of a WHO grade II meningioma. Eighteen months later she presented with seizures, and MRI revealed an intraaxial tumor, which was resected and proven to be a glioblastoma. As far as the authors are aware, this case represents the third case of GBM following SRS for a meningioma. This report serves to increase the awareness of this possible complication following SRS. The possibility of this rare complication should be explained to patients when obtaining their consent for radiosurgery.

Assessment of costs in open surgery and stereotactic radiosurgery for vestibular schwannomas

OBJECTIVE

Microsurgical resection and radiosurgery remain the most widely used interventions in the treatment of vestibular schwannomas. There is a growing demand for cost-effectiveness analyses to evaluate these two treatment modalities and delineate the factors that drive their total costs. Here, the authors evaluated specific cost drivers for microsurgical and radiosurgical management of vestibular schwannoma by using the Value Driven Outcomes system available at the University of Utah.

METHODS

The authors retrospectively reviewed all cases involving microsurgical and radiosurgical treatment of vestibular schwannomas at their institution between November 2011 and September 2017. Patient and tumor characteristics, subcategory costs, and potential cost drivers were analyzed.

RESULTS

The authors identified 163 vestibular schwannoma cases, including 116 managed microsurgically and 47 addressed with stereotactic radiosurgery (SRS). There were significant differences between the two groups in age, tumor size, and preoperative Koos grade (p < 0.05), suggesting that indications for treatment were markedly different. Length of stay (LOS) and length of follow-up were also significantly different. Facility costs were the most significant contributor to both microsurgical and SRS groups (58.3% and 99.4%, respectively); however, physician professional fees were not specifically analyzed. As expected, microsurgical treatment resulted in an average 4-fold greater overall cost of treatment than for SRS cases (p < 0.05), and there was a greater variation in costs for open cases as well. Costs remained stable over time for both open resection and SRS. Multivariable analysis showed that LOS (β = 0.7, p = 0.0001), discharge disposition (β = 0.2, p = 0.004), nonserviceable hearing (β = 0.1, p = 0.02), and complications (β = 0.2, p = 0.005) affected cost for open surgery, whereas no specifically examined factor could be identified as driving costs for SRS.

CONCLUSIONS

This analysis identified the fact that facility utilization constitutes the majority of total costs for both microsurgery and SRS treatment modalities of vestibular schwannomas. LOS, discharge disposition, nonserviceable hearing, and complications contributed significantly to the total costs for the microsurgical group, whereas none of the factors could be identified as driving total costs for the SRS group. This information may be used to establish policies and protocols to reduce facility costs, with the goal of decreasing the total costs without jeopardizing patient care.

Proposal for Modification of Cahan's Criteria Utilizing Molecular Genetic Analyses for Cases without Baseline Histopathology: A Unique Method Applicable to Primary Radiosurgery

Background  Cahan's criteria have been utilized since 1948 to establish causality between prior radiation treatment and the development of secondary malignancy. One major criterion specifies that histological and radiographic evidence collected before and after radiation treatment must confirm separate tumor types; however, pretreatment biopsy is rarely obtained prior to radiosurgery for vestibular schwannoma and many other skull base and cranial lesions. Therefore, in these cases Cahan's criteria cannot be validly applied. Objective  This article proposes an update to Cahan's criteria using modern molecular genetic analysis for cases lacking baseline histopathology. Methods  Mate-pair sequencing and whole exome sequencing of a cerebellopontine angle undifferentiated high-grade pleomorphic sarcoma (UHGPS) that developed after stereotactic radiosurgery of a presumed benign vestibular schwannoma. Results  Mate-pair sequencing and whole exome sequencing of the sarcoma revealed complex chromosomal aberrations. Notably, the tumor contained a deletion in the NF2 gene at 22q12 and an in-frame deletion on exon 5 of the remaining copy of NF2 . Biallelic events impacting NF2 are atypical for UHGPS but are characteristic for vestibular schwannoma. These findings help support the conclusion that the UHGPS arose from a benign vestibular schwannoma all along. Conclusions  Next-generation sequencing can be successfully applied to a radiation-induced sarcoma when both the original and malignant tumors harbor separate signature genetic markers. As our understanding of the genetic profile of various tumors expand, we believe that next-generation sequencing and other genomic tools will play an increasingly important role in establishing causality between radiation and the development of secondary malignancy.

Primary undifferentiated sarcoma of the meninges: A case report and comprehensive review of the literature

BACKGROUND AND IMPORTANCE

Sarcomas make up 1% of all cases of adult cancer, with 5-10% of those classified as undifferentiated pleomorphic sarcomas (UPS/PUS) and 0.1-4.3% primary intracranial sarcomas. Intracranial undifferentiated sarcoma is characterized by an earlier age of onset and generally poorer prognosis compared to extracranial undifferentiated sarcomas. Current therapies involve surgical excision with wide margins and radiotherapy, with minimal data available regarding the efficacy of chemotherapy.

CASE DESCRIPTION

A 79-year-old man with a history of remote superficial bladder cancer presented with a large frontal scalp lesion. A biopsy was initially attempted by a dermatologist in the outpatient setting, but a follow-up CT scan revealed a skull-eroding, enhancing soft tissue lesion. Neurosurgical treatment revealed an undifferentiated sarcoma. The patient underwent adjuvant radiation therapy of 59.4 Gy fractionated over 45 days following surgery. Follow-up brain MRIs at 1-, 6-, 9-, 12-, 15-, 21-, and 27 months after surgery have not shown any indications of local recurrence or tumor metastasis. Despite the high propensity that undifferentiated sarcomas have for recurrence and metastasis and the patient's advanced age, this patient remains uniquely disease-free.

CONCLUSION

We provide a description of an unusual case and comprehensive literature review of UPS to clarify the hallmarks of the disease, identify the difficulties in diagnosis, and provide a summary of therapies employed in the literature with their corresponding patient outcomes.

[A malignant peripheral nerve sheath tumor developed from the auditory nerve: a case report and a literature review]

We present a rare clinical case of a patient with a malignant peripheral nerve sheath tumor developed from the auditory nerve as well as a literature review, including 30 reported cases of this disease.

Radiation-induced osteosarcoma after Gamma Knife surgery for vestibular schwannoma: a case report and literature review

We present a rare case of radiation-induced osteosarcoma following Gamma Knife^® surgery (GKS) for a vestibular schwannoma (VS). A 49-year-old female with sporadic VS underwent GKS. Serial follow-up imaging showed that the tumor size decreased. Six years after GKS, magnetic resonance imaging demonstrated regrowth of the tumor. The tumor was removed via the retrosigmoid approach. Interestingly, the final pathology report confirmed osteosarcoma arising in schwannoma with direct transition (osteosarcoma component: 90 %, schwannoma component: 10 %). The osteosarcoma was considered to be a radiation-induced malignancy. The possibility of this rare complication should be explained to the patient before GKS, and the patient should be screened periodically after GKS.

A case of infected schwannoma mimicking malignant tumor

BACKGROUND

Infected schwannoma has been reported, this being one of the four cases published in the literature. Infected schwannoma has proven to be a tough diagnostic challenge to the treating tumor surgeon, mimicking infectious entities and most essentially, a malignant tumor.

CASE PRESENTATION

The authors report the case of a 64-year-old male with a soft tissue mass in his right gluteal area that presented initially with right leg pain, then later with signs of inflammation on the tumor area. Magnetic resonance imaging (MRI), computed tomography (CT), and thallium-201 scintigraphy studies confirm the presence of soft tissue mass which had continuity with sciatic nerve, with subsequent serial MRI findings suggesting tumor enlargement with cystic degeneration. Increased level of C-reactive protein (CRP) was observed before surgery. During an open biopsy upon tissue sampling, exudates with necrotic tissue were seen. Increased level of CRP and necrotic change suggested the possibility of malignant tumor. Histopathological diagnosis was schwannoma, and group B Streptococcus was detected by culture. After the confirmation of infected schwannoma, enucleation of the tumor was performed.

CONCLUSIONS

The report concludes that establishment of a benign pathology is essential when presented with similar clinical findings prior to definitive enucleation of an infected schwannoma.

Late malignant transformation of vestibular schwannoma in the absence of irradiation: case report

Late malignant transformation of vestibular schwannoma (VS) following irradiation has previously been reported 29 times in the literature. Here, the authors report the first late malignant transformation of VS unrelated to neurofibromatosis or radiation exposure. After undergoing a near-total excision of a histologically benign VS, the patient developed malignant regrowth of the tumor remnant 42 months after the primary excision. This case challenges the dogmatic belief of absolute causality between radiation exposure and late malignant transformation of VS, and has important implications regarding future counseling and consent for the treatment of patients with VS.

Evaluation of Reported Malignant Transformation of Vestibular Schwannoma: De Novo and After Stereotactic Radiosurgery or Surgery

OBJECTIVE

To critically analyze each reported case of malignant transformation of vestibular schwannoma (VS) after either stereotactic radiosurgery (SRS) or microsurgery (MS).

DATA SOURCES

We searched the Pubmed/Medline database using the relevant key words vestibular schwannoma, acoustic neuroma, malignant, transformation, radiation, induced, stereotactic, radiosurgery, malignancy, GammaKnife, and CyberKnife and combinations thereof.

STUDY SELECTION

Inclusion criteria for malignant transformation of VS after SRS included histopathology of initially benign VS, subsequent histopathology confirming malignant VS, reasonable latency period between malignancy and benign diagnoses.

DATA EXTRACTION

A neurotologist and a skull base neurosurgeon independently assessed each case report for quality, entry, exclusion criteria, and comparability of extracted data.

DATA SYNTHESIS

We calculated median age, latency times, and survival times for each case report.

RESULTS

Malignant transformation has been documented to occur after either SRS or MS. Eight cases were included that showed histopathologic evidence of malignant transformation after SRS and MS. Four cases of malignant transformation were included that demonstrated malignant transformation after MS only. Malignant transformation of VS can also occur de novo, and de novo malignant VSs are also encountered, which can confound a causal inference from either SRS or MS. Eighteen cases of primary malignant VS were included. Studies that were identified but not included in the review are summarized and tabulated. We found 12 studies of malignant transformation associated with NF2.

CONCLUSION

The potential mechanism leading to malignant transformation of VS seems more obvious for SRS and is less understood for MS. Given a low incidence of de novo malignant schwannoma, the possibility that these are spontaneous events in either setting cannot be ruled out. Risk of malignant transformation of VS after either SRS or MS is not zero; however, the magnitude of this risk is probably minimal based on the evidence from eight histopathologically confirmed cases.

Malignant peripheral nerve sheath tumors of the eighth cranial nerve arising without prior irradiation

OBJECTIVE Malignant peripheral nerve sheath tumors (MPNSTs) of the eighth cranial nerve (CN) are exceedingly rare. To date the literature has focused on MPNSTs occurring after radiation therapy for presumed benign vestibular schwannomas (VSs), while MPNSTs arising without prior irradiation have received little attention. The objectives of the current study are to characterize the epidemiology, clinical presentation, disease course, and outcome using a large national cancer registry database and a systematic review of the English literature. Additionally, a previously unreported case is presented. METHODS The authors conducted an analysis of the Surveillance, Epidemiology, and End Results (SEER) database, a systematic review of the literature, and present a case report. Data from all patients identified in the SEER database with a diagnosis of MPNST involving the eighth CN, without a history of prior radiation, were analyzed. Additionally, all cases reported in the English literature between January 1980 and March 2015 were reviewed. Finally, 1 previously unreported case is presented. RESULTS The SEER registries identified 30 cases between 1992 and 2012. The average incidence was 0.017 per 1 million persons per year (range 0.000-0.0687 per year). The median age at diagnosis was 55 years, and 16 (53%) were women. Thirteen cases were diagnosed upon autopsy. Of the 17 cases diagnosed while alive, the median follow-up was 118 days, with 3 deaths (18%) observed. When compared with the incidence of benign VS, 1041 VSs present for every 1 MPNST arising from the eighth CN. Including a previously unreported case from the authors' center, a systematic review of the English literature yielded 24 reports. The median age at diagnosis was 44 years, 50% were women, and the median tumor size at diagnosis was 3 cm. Eleven patients (46%) reported isolated audiovestibular complaints typical for VS while 13 (54%) exhibited facial paresis or other signs of a more aggressive process. Treatment included microsurgery alone, microsurgery with adjuvant radiation, or microsurgery with chemoradiation. Sixty-one percent of patients receiving treatment experienced recurrence, 22% of which were diagnosed with drop metastases to the spine. Ultimately, 13 patients (54%) died of progressive disease at a median of 3 months following diagnosis. The ability to achieve gross-total resection was the only feature that was associated with improved disease-specific survival. CONCLUSIONS MPNSTs of the eighth CN are extremely rare and portend a poor prognosis. Nearly half of patients initially present with findings consistent with a benign VS, often making an early diagnosis challenging. In light of these data, early radiological and clinical follow-up should be considered in those who elect nonoperative treatment, particularly in patients with a short duration of symptoms or atypical presentation. These data also provide a baseline rate of malignancy that should be considered when estimating the risk of malignant transformation following stereotactic radiosurgery for VS.

Stereotactic Radiosurgery versus Natural History in Patients with Growing Vestibular Schwannomas

Objective To describe our experience with stereotactic radiosurgery and its efficacy on growing tumors, and then to compare this result with the natural history of a similar cohort of non-radiation-treated lesions. Study Design A retrospective chart review and cohort comparison. Methods The long-term control rates of patients having undergone radiosurgery were collected and calculated, and this population was then compared with a group of untreated patients from the same period of time with growing lesions. Results A total of 61 patients with growing vestibular schwannomas treated with radiosurgery were included. After a mean of 160 months, we observed a control rate of 85.2%. When compared with a group of 36 patients with growing tumors who were yet to receive treatment (previously published), we found a corrected control rate or relative risk reduction of only 76.8%. Conclusion Radiosurgery for growing vestibular schwannomas is less effective than previously reported in unselected series. Although radiosurgery still has a role in managing this disease, consideration should be given to the actual efficacy that may be calculated when the natural history is known. We hope other centers will similarly report their experience on this cohort of patients.

Intracranial Undifferentiated Sarcoma Arising from a Low-Grade Glioma: A Case Report and Literature Review

Undifferentiated sarcomas are rarely identified in the intracranial region. A 23-year-old man was admitted with a chief complaint of headache. Initial magnetic resonance images showed signs of low-grade glioma in the frontal lobe. Stereotactic biopsy was performed, and a diagnosis of diffuse astrocytoma was confirmed. Three months later, the patient presented with a high-grade tumor as seen on imaging studies. He underwent total resection of the tumor and histopathological tests identified an undifferentiated sarcoma. The patient died eight months later due to massive tumor bleeding. To the best of our knowledge, this is the first report of undifferentiated sarcoma arising from low-grade glioma without any chemotherapy or radiotherapy.

Management of sporadic vestibular schwannoma

Vestibular schwannomas (VS) comprise 8% of all intracranial tumors and 90% of cerebellopontine angle and internal auditory canal neoplasms. Secondary to the widespread adoption of screening protocols for asymmetrical hearing loss and the increasing use of advanced imaging, the number of VS diagnosed each year continues to rise, while the average size has declined. Microsurgery remains the treatment of choice for large tumors, however the management of small- to medium-sized VS remains highly controversial with options including observation, radiotherapy, or microsurgery. Within this chapter, the authors provide an overview of the contemporary management of VS, reviewing important considerations and common controversies.

Stereotactic radiosurgery in the management of vestibular schwannoma and glomus jugulare: indications, techniques, and results

Gamma Knife stereotactic radiosurgery (GKS) has become an important management strategy for an increasing number of patients with skull base tumors. For select patients with lateral skull base disorders, given the proximity to sensitive critical structures such as the brainstem, cranial nerves, and cochlea, this technology has emerged as a first-line treatment to achieve the paramount goals of long-term tumor control and maintenance of existing neurologic function. This article reviews the indications, technique, and results of GKS for the treatment of vestibular schwannoma and glomus jugulare tumors, and highlights our experience in treating these tumors at the Mayo Clinic.

The incidence of second brain tumors related to cranial irradiation

Secondary brain tumor (SBT) is a devastating complication of cranial irradiation (CI). We reviewed the literature to determine the incidence of SBT as related to specific radiation therapy (RT) treatment modalities. The relative risk of radiation-associated SBT after conventional and conformal RT is well established and ranges from 5.65 to 10.9; latent time to develop second tumor ranges from 5.8 to 22.4 years, depending on radiation dose and primary disease. Theories and dosimetric models suggest that intensity-modulated radiation therapy may result in an increased risk of SBT, but clinical evidence is limited. The incidence of stereotactic radiosurgery-related SBT is low. Initial data suggest that no increased risk from proton therapy and dosimetric models predict a lower incidence of SBT compared with photons. In conclusion, the incidence of SBT related to CI is low. Longer follow-up is needed to clarify the impact of intensity-modulated radiation therapy, proton therapy and other developing technologies.

Malignant transformation in vestibular schwannoma: report of a single case, literature search, and debate

OBJECT

The significance of radiation in the induction of malignancy in vestibular schwannomas (VSs) after radiosurgery is unclear despite an increasing number of case reports. The authors describe a new case of verified malignant transformation in a vestibular schwannoma (MTVS) and provide a new evaluation of such cases previously reported in the literature.

METHODS

A 46-year-old woman underwent subtotal resection of a right-sided VS in 2004. The histological characteristics of the lesion were typical and benign. In early 2007 Gamma Knife surgery (GKS) was performed to treat a residual enlarging remnant. The radiosurgery parameters included the following: target volume 3.5 cm(3), prescription dose 12 Gy, prescription isodose 45%, maximum dose 26.7 Gy, and coverage 97%. At 2 years' follow-up the lesion was enlarged to 5.2 cm(3), but by 5 years it had decreased to 2.3 cm(3). Six months later the lesion was 8.4 cm(3). Repeated surgery was performed, and a histological analysis revealed a malignant peripheral nerve sheath tumor. The case was further managed with repeated GKS performed in the spring of 2013. At that time, the radiosurgery parameters included the following: target volume 3.5 cm(3), prescription dose 16 Gy, prescription isodose 45%, maximum dose 35.6 Gy, and coverage 91%. This Gamma Knife Department has treated a total of 205 patients with VS (local incidence of MTVS 0.49%). A search of the literature published up to and including 2013 was performed using PubMed as well as more informal search methods.

RESULTS

This patient is the 29th reported case of MTVS after radiation therapy. Of these cases, 40.7% were patients with neurofibromatosis (NF). In those cases in which histology showed tumors with previously benign characteristics, totally conforming to the criteria for MTVS, the mean delay to malignant expression was 68 months (median delay 72 months). The authors also retrieved papers reporting 30 cases of malignant VS in patients who had not undergone radiation treatment. Five of those cases were malignant transformation of a benign entity, and in 4 of them histology had verified that the initial disease was benign. In those 4 cases, there was a mean delay to malignant expression of 7.2 months (median delay 8 months).

CONCLUSIONS

Despite more frequent reports of MTVS after radiation treatment recently, there has been no accurate quantification of the risk, except in patients with NF, in whom the incidence of malignancy is high in relation to the numbers treated. The present analysis indicates that the risk of malignancy over 20 years in cases in which no radiation treatment has occurred is 1.32-2.08 per 100,000, and this risk decreases to 1.09-1.74 per 100,000 if cases of NF are excluded. After radiation treatment, the overall risk over 20 years is 25.1 per 100,000, and this risk decreases to 15.6 per 100,000 if cases of NF are excluded. Radiation treatment increases the risk by approximately 10 times in non-NF cases.

Gamma Knife radiosurgery for vestibular schwannoma: clinical results at long-term follow-up in a series of 379 patients

Object

Since the 1990s, Gamma Knife radiosurgery (GKRS) has become the first-line treatment option for small- to medium-size vestibular schwannomas (VSs), especially in patients without mass effect–related symptoms and with functional hearing. The aim of this study was to assess the safety and efficacy of GKRS, in terms of tumor control, hearing preservation, and complications, in a series of 379 consecutive patients treated for VS.

Methods

Of 523 patients treated at the authors' institution for VS between 2001 and 2010, the authors included 379 who underwent GKRS as the primary treatment. These patients were not affected by Type 2 neurofibromatosis and had clinical follow-up of at least 36 months. Clinical follow-up (mean and median 75.7 and 69.5 months, respectively) was performed for all patients, whereas audiometric and quantitative radiological follow-up examinations were obtained for only 153 and 219 patients, respectively. The patients' ages ranged from 23 to 85 years (mean 59 years). The mean tumor volume was 1.94 ± 2.2 cm3 (median 1.2 cm3, range 0.013–14.3 cm3), and the median margin dose was 13 Gy (range 11–15 Gy). Parameters considered as determinants of the clinical outcome were long-term tumor control, hearing preservation, and complications. A statistical analysis was performed to correlate clinical outcomes with the radiological features of the tumor, dose-planning parameters, and patient characteristics.

Results

Control of the tumor with GKRS was achieved in 97.1% of the patients. In 82.7% of the patients, the tumor volume had decreased at the last follow-up, with a mean relative reduction of 34.1%. The rate of complications was very low, with most consisting of a transient worsening of preexisting symptoms. Patients who had vertigo, balance disorders, or facial or trigeminal impairment usually experienced a complete or at least significant symptom relief after treatment. However, no significant improvement was observed in patients previously reporting tinnitus. The overall rate of preservation of functional hearing at the long-term follow-up was 49%; in patients with hearing classified as Gardner-Robertson (GR) Class I, this value was 71% and reached 93% among cases of GR Class I hearing in patients younger than 55 years.

Conclusions

Gamma Knife radiosurgery is a safe and effective treatment for VS, achieving tumor control in 97.1% of cases and resulting in a very low morbidity rate. Younger GR Class I patients had a significantly higher probability of retaining functional hearing even at the 10-year follow-up; for this reason, the time between symptom onset, diagnosis, and treatment should be shortened to achieve better outcomes in functional hearing preservation.

MPNST after Radiosurgery: A Report and Review of the Literature

OBJECTIVE

To report an unusual case of malignant degeneration in a ganglioneuroma of the jugular foramen post stereotactic radiosurgery as well as to systematically review the pertinent literature involving radiosurgery associated malignancies.

BACKGROUND

Ganglioneuromas are uncommon lesions of the peripheral nervous system and infrequently reported in the head and neck region. There have been no previously described cases of ganglioneuromas occurring in the jugular foramen. Malignant degeneration of these lesions is rarely described, especially in the context of radiosurgery. Radiosurgery associated malignancies overall are exceptionally rare and only a limited number of cases have been reported.

RESULTS/CONCLUSIONS

We describe a case of a ganglioneuroma occurring in the jugular foramen and mimicking the appearance of a jugular foramen schwannoma. This lesion underwent stereotactic radiosurgery and developed a delayed degeneration into a malignant nerve sheath tumor. The occurrence of ganglioneuroma in this region has not been previously described and presumed malignant degeneration is even rarer. This case highlights a previously understated risk associated with stereotactic radiation treatments. To date, 33 previous cases of stereotactic radiosurgery associated malignancies have been reported. We review the pertinent details of these cases. We caution that as follow up periods and awareness increases, reports such as this may become increasingly common.

Tumeurs malignes des gaines nerveuses périphériques après la radiochirurgie : à propos d'un cas et revue de littérature.

Radiation-associated secondary brain tumors after conventional radiotherapy and radiosurgery

Although there is not enough strong molecular evidence for radiation to be a causal factor for the development of secondary brain tumors, a relationship has still been found. There is a slight but significant 2-2.7% increased risk of secondary brain tumors after conventional radiotherapy. However, this risk is small and should not preclude the use of radiotherapy as an effective treatment for uncontrolled pituitary tumors. The risk of radiosurgery-associated secondary brain tumors has not been precisely determined. Taking into account the considerable number of patients who received radiosurgery worldwide and the small number of secondary brain tumors, radiosurgery seems to be a safe treatment modality. This review summarizes the pathogenesis, prevalence and characteristics of secondary brain tumors after conventional radiotherapy and stereotactic radiosurgery for pituitary adenomas.

Secondary neoplasms after stereotactic radiosurgery

OBJECTIVE

The use of medical radiation has increased 6-fold in the past 30 years. Within neurosurgery, the advent of stereotactic radiosurgery (SRS) has significantly altered the treatment paradigm for both benign and malignant central nervous system diseases. With this increased reliance on radiation has come a responsibility to identify the long-term risks, including the potential development of radiation-induced neoplasms. Although the data regarding traditional radiation exposure and its subsequent risks are well-defined, the data for SRS is less developed.

METHODS

We reviewed the published literature to more accurately define the risk of developing secondary neoplasms after stereotactic radiosurgery.

RESULTS

A total of 36 cases of SRS-induced neoplasms were identified. More than half of the cases had an initial diagnosis of vestibular schwannoma. Overall, the risk of developing an SRS-induced neoplasm is approximately 0.04% at 15 years.

CONCLUSION

The risk of developing an SRS-induced neoplasm is low but not zero. Thus, long-term surveillance imaging is advised for patients treated with SRS.

Long-term safety and efficacy of stereotactic radiosurgery for vestibular schwannomas: evaluation of 440 patients more than 10 years after treatment with Gamma Knife surgery

Object

Little is known about long-term outcomes, including tumor control and adverse radiation effects, in patients harboring vestibular schwannomas (VSs) treated with stereotactic radiosurgery > 10 years previously. The aim of this study was to confirm whether Gamma Knife surgery (GKS) for VSs continues to be safe and effective > 10 years after treatment.

Methods

A total of 440 patients with VS (including neurofibromatosis Type 2) treated with GKS between May 1991 and December 2000 were evaluable. Of these, 347 patients (79%) underwent GKS as an initial treatment and 93 (21%) had undergone prior resection. Three hundred fifty-eight patients (81%) had a solid tumor and 82 (19%) had a cystic tumor. The median tumor volume was 2.8 cm3 and the median marginal dose was 12.8 Gy.

Results

The median follow-up period was 12.5 years. The actuarial 5- and ≥ 10-year progression-free survival was 93% and 92%, respectively. No patient developed treatment failure > 10 years after treatment. According to multivariate analysis, significant factors related to worse progression-free survival included brainstem compression with a deviation of the fourth ventricle (p < 0.0001), marginal dose ≤ 13 Gy (p = 0.01), prior treatment (p = 0.02), and female sex (p = 0.02). Of 287 patients treated at a recent optimum dose of ≤ 13 Gy, 3 (1%) developed facial palsy, including 2 with transient palsy and 1 with persistent palsy after a second GKS, and 3 (1%) developed facial numbness, including 2 with transient and 1 with persistent facial numbness. The actuarial 10-year facial nerve preservation rate was 97% in the high marginal dose group (> 13 Gy) and 100% in the low marginal dose group (≤ 13 Gy). Ten patients (2.3%) developed delayed cyst formation. One patient alone developed malignant transformation, indicating an incidence of 0.3%.

Conclusions

In this study GKS was a safe and effective treatment for the majority of patients followed > 10 years after treatment. Special attention should be paid to cyst formation and malignant transformation as late adverse radiation effects, although they appeared to be rare. However, it is necessary to collect further long-term follow-up data before making conclusions about the long-term safety and efficacy of GKS, especially for young patients with VSs.

Vestibular schwannomas in the modern era: epidemiology, treatment trends, and disparities in management

OBJECT

There are a variety of treatment options for the management of vestibular schwannomas (VSs), including microsurgical resection, radiotherapy, and observation. Although the choice of treatment is dependent on various patient factors, physician bias has been shown to significantly affect treatment choice for VS. In this study the authors describe the current epidemiology of VS and treatment trends in the US in the modern era. They also illustrate patient and tumor characteristics and elucidate their effect on tumor management.

METHODS

Patients diagnosed with VS were identified through the Surveillance, Epidemiology, and End Results database, spanning the years 2004-2009. Age-adjusted incidence rates were calculated and adjusted using the 2000 US standard population. The chi-square and Student t-tests were used to evaluate differences between patient and tumor characteristics. Multivariate logistic regression was performed to determine the effects of various patient and tumor characteristics on the choice of tumor treatment.

RESULTS

A total of 6225 patients with VSs treated between 2004 and 2009 were identified. The overall incidence rate was 1.2 per 100,000 population per year. The median age of patients with VS was 55 years, with the majority of patients being Caucasian (83.16%). Of all patients, 3053 (49.04%) received surgery only, with 1466 (23.55%) receiving radiotherapy alone. Both surgery and radiation were only used in 123 patients (1.98%), with 1504 patients not undergoing any treatment (24.16%). Increasing age correlated with decreased use of surgery (OR 0.95, 95% CI 0.95-0.96; p<0.0001), whereas increasing tumor size was associated with the increased use of surgery (OR 1.04, 95% CI 1.04-1.05; p<0.0001). Older age was associated with an increased likelihood of conservative management (OR 1.04, 95% CI 1.04-1.05; p<0.0001). Racial disparities were also seen, with African American patients being significantly less likely to receive surgical treatment compared with Caucasians (OR 0.50, 95% CI 0.35-0.70; p<0.0001), despite having larger tumors at diagnosis.

CONCLUSIONS

The incidence of vestibular schwannomas in the US is 1.2 per 100,000 population per year. Although many studies have demonstrated improved outcomes with the use of radiotherapy for small- to medium-sized VSs, surgery is still the most commonly used treatment modality for these tumors. Racial disparities also exist in the treatment of VSs, with African American patients being half as likely to receive surgery and nearly twice as likely to have their VSs managed conservatively despite presenting with larger tumors. Further studies are needed to elucidate the reasons for treatment disparities and investigate the nationwide trend of resection for the treatment of small VSs.

Whether gamma knife radiosurgery is really necessary for treatment of patients with vestibular schwannomas

The present study was directed at establishing the role of Gamma Knife radiosurgery (GKS) in the management of vestibular schwannomas (VSs), particularly those that are large. We analyzed a consecutive series of 222 tumors operated on by a single neurosurgeon (T. Hori) at Tottori University (1981-1998) and Tokyo Women's Medical University (1998-2011). The surgical strategy for sporadic unilateral VSs was typically total or nearly total tumor removal with facial nerve preservation, whereas in some cases of neurofibromatosis type 2 intentional subtotal resection was performed. In all, 15 patients (8.6 %) in the series underwent GKS before (4 cases), after (9 cases), or before and after (2 cases) tumor removal. Overall, 211 patients (95 %) were cured by microsurgery alone. Of note, six patients underwent primary radiosurgery but were operated later on for regrowth of the neoplasm, and in four of them near-total resection led to good long-term tumor control. GKS was required in only 5 % of cases for management of residual VS or, more frequently, its regrowth. Radiosurgery resulted in volume reduction in one-third of these tumors. In other cases it stabilized the lesion, preventing further progression. Thus, GKS is considered a reasonable management option for residual or regrowing small VSs to obtain maximum tumor growth control after initially attempting complete surgical removal.

What intervention is best practice for vestibular schwannomas? A systematic review of controlled studies

OBJECTIVE

Largely, watchful waiting is the initial policy for patients with small-sized or medium-sized vestibular schwannoma, because of slow growth and relatively minor complaints, that do not improve by an intervention. If intervention (microsurgery, radiosurgery or fractionated radiotherapy) becomes necessary, the choice of intervention appears to be driven by the patient's or clinician's preference rather than by evidence based. This study addresses the existing evidence based on controlled studies of these interventions.

DESIGN

A systematic Boolean search was performed focused on controlled intervention studies. The quality of the retrieved studies was assessed based on the Sign-50 criteria on cohort studies.

DATA SOURCES

Pubmed/Medline, Embase, Cochrane Central Register of Controlled Trials and reference lists.

STUDY SELECTION

Six eligibility criteria included a controlled intervention study on a newly diagnosed solitary, vestibular schwannoma reporting on clinical outcomes. Two prospective and four retrospective observational, controlled studies published before November 2011 were selected.

DATA ANALYSIS

Two reviewers independently assessed the methodological quality of the studies and extracted the outcome data using predefined formats.

RESULTS

Neither randomised studies, nor controlled studies on fractionated radiotherapy were retrieved. Six studies compared radiosurgery and microsurgery in a controlled way. All but one were confined to solitary tumours less than 30 mm in diameter and had no earlier interventions. Four studies qualified for trustworthy conclusions. Among all four, radiosurgery showed the best outcomes: there were no direct mortality, no surgical or anaesthesiological complications, but better facial nerve outcome, better preservation of useful hearing and better quality of life.

CONCLUSIONS

The available evidence indicates radiosurgery to be the best practice for solitary vestibular schwannomas up to 30 mm in cisternal diameter.

Radiation therapy and radiosurgery for vestibular schwannomas: indications, techniques, and results

This article describes in detail the uses of and distinctions between stereotactic radiosurgery (SRS) and stereotactic radiotherapy (SRT) for vestibular schwannoma (VS). The authors discuss devices and techniques used in SRS and SRT and, additionally, present readers the approach used by surgeons at Mayo Clinic. They discuss indications and results for both approaches in patients with vestibular schwannoma. Treatment of small and large tumors is discussed, along with cystic tumors and NF2-associated VS. Repeating SRS for vestibular schwannoma is also mentioned.

Long-term tumor control and cranial nerve outcomes following Gamma Knife surgery for larger-volume vestibular schwannomas

Object

Gamma Knife surgery (GKS) for vestibular schwannoma (VS) is an accepted treatment for small- to medium-sized tumors, generally smaller than 2.5 cm in the maximum posterior fossa dimension. The purpose of this study was to evaluate the efficacy and toxicity of GKS for larger tumors.

Methods

Prospectively collected data were analyzed for 22 patients who had undergone GKS for VSs larger than 2.5 cm in the posterior fossa diameter between 1997 and 2006. No patient had symptomatic brainstem compression at the time of GKS. The median treated tumor volume was 9.4 cm3 (range 5.3–19.1 cm3). The median maximum posterior fossa diameter was 2.8 cm (range 2.5–3.8 cm). The median tumor margin dose was 12 Gy (range 12–14 Gy). Serial imaging, audiometry (10 patients with serviceable hearing pre-GKS), and clinical follow-up were available for a median of 66 months (range 26–121 months). Tumor control failure was defined as either a progressive increase in tumor diameter of at least 2 mm in any dimension or a later resection.

Results

Four patients met the criteria for GKS failure, including 1 patient who demonstrated sarcomatous degeneration more than 7 years after GKS and died 3 months after microsurgical debulking. An enlarging cystic component was the surgical indication in 1 of the 2 patients who required resection, although 27% of tumors (6 lesions) were cystic before GKS. The 3-year actuarial rate of tumor control, freedom from new facial neuropathy, and preservation of functional hearing were 86%, 92%, and 47%, respectively. At 5 years post-GKS, these rates decreased to 82%, 85%, and 28%, respectively. At the most recent follow-up, 91% of tumors were smaller than at the time of GKS and the median maximum posterior fossa diameter reduction was 26%. On multivariate analysis, none of the following factors was associated with GKS failure, new facial weakness, new trigeminal neuropathy, or loss of serviceable hearing: patient age, tumor volume, tumor margin dose, and preoperative cranial nerve dysfunction.

Conclusions

Single-session radiosurgery is a successful treatment for the majority of patients with larger VSs. Although tumor control rates are lower than those for smaller VSs managed with GKS, the cranial nerve morbidity of GKS is significantly lower than that typically achieved via resection of larger VSs.