Molecular biology of familial and sporadic vestibular schwannomas: implications for novel therapeutics

A mechanistic mathematical model of initiation and malignant transformation in sporadic vestibular schwannoma

BACKGROUND

A vestibular schwannoma (VS) is a relatively rare, benign tumour of the eighth cranial nerve, often involving alterations to the gene NF2. Previous mathematical models of schwannoma incidence have not attempted to account for alterations in specific genes, and could not distinguish between nonsense mutations and loss of heterozygosity (LOH).

METHODS

Here, we present a mechanistic approach to modelling initiation and malignant transformation in schwannoma. Each parameter is associated with a specific gene or mechanism operative in Schwann cells, and can be determined by combining incidence data with empirical frequencies of pathogenic variants and LOH.

RESULTS

This results in new estimates for the base-pair mutation rate u = 4.48 × 10^-10 and the rate of LOH = 2.03 × 10^-6/yr in Schwann cells. In addition to new parameter estimates, we extend the approach to estimate the risk of both spontaneous and radiation-induced malignant transformation.

DISCUSSION

We conclude that radiotherapy is likely to have a negligible excess risk of malignancy for sporadic VS, with a possible exception of rapidly growing tumours.

Primary intratracheal schwannoma misdiagnosed as severe asthma in an adolescent: A case report

BACKGROUND

Primary intratracheal schwannoma is an extremely rare type of benign airway tumor, especially in adolescents. The presenting symptoms are typically prolonged cough and wheezing that can be misdiagnosed as asthma in adolescent patients.

CASE

A 16-year-old adolescent girl admitted to a local hospital with symptoms of an irritating cough and wheezing was diagnosed with bronchial asthma and treated with budesonide and formoterol. Over the next year, the patient's wheezing and coughing symptoms gradually worsened and the antiasthma treatment was ineffective. One week prior to this admission, the patient developed dyspnea after catching a cold and was transferred to our hospital with a diagnosis of severe asthma. However, chest computed tomography and bronchoscopy showed a mass in the trachea. Primary intratracheal schwannoma was diagnosed by biopsy. Her symptoms were relieved by endoscopic resection by electrosurgical snaring combined with argon plasma coagulation. No relapse occurred during an 18 mo follow-up.

CONCLUSION

Primary intratracheal schwannoma should be considered in the differential diagnosis in adolescents with recurrent asthma-like attacks.

Analysis of ADAM9 regulation and function in vestibular schwannoma primary cells

Objective

Recently, we described a disintegrin and metalloproteinase 9 (ADAM9) overexpression by Schwann cells of vestibular schwannoma (VS) and suggested that it might be a marker for VS tumor growth and invasiveness. This research note provides additional data utilizing a small cohort of VS primary cultures and tissue samples. We examined whether reconstitution of Merlin expression in VS cells regulates ADAM9 protein expression and performed lentiviral ADAM9 knock down to investigate possible effects on VS cells numbers. Moreover, the co-localization of ADAM9 and Integrins α6 and α2β1, respectively, was examined by immunofluorescence double staining.

Results

ADAM9 expression was not regulated by Merlin in VS. However, ADAM9 knock down led to 58% reduction in cell numbers in VS primary cell cultures (p < 0.0001). While ADAM9 and Integrin α2β1 were co-localized in only 22% (2 of 9) of VS, ADAM9 and Integrin α6 were co-localized in 91% (10 of 11) of VS. Therefore, we provide first observations on possible regulatory functions of ADAM9 expression in VS.

Benign Intracranial Lesions - Radiotherapy: An Overview of Treatment Options, Indications and Therapeutic Results

BACKGROUND

Radiation Therapy (RT) is an established treatment option for benign intracranial lesions. The aim of this study is to display an update on the role of RT concerning the most frequent benign brain lesions and tumors.

METHODS

Published articles about RT and meningiomas, Vestibular Schwannomas (VSs), Pituitary Adenomas (PAs), Arteriovenous Malformations (AVMs) and craniopharyngiomas were reviewed and extracted data were used.

RESULTS

In meningiomas RT is applied as an adjuvant therapy, in case of patientrefusing surgery or in unresectable tumors. The available techniques are External Beam RT (EBRT) and stereotactic ones such as Stereotactic Radiosurgery (SRS), Fractionated Stereotactic RT (FSRT), Intensity Modulated RT (IMRT) and proton-beam therapy. The same indications are considered in PAs, in which SRS and FSRT achieve excellent tumor control rate (92-100%), acceptable hormone remission rates (>50%) and decreased Adverse Radiation Effects (AREs). Upon tumor growth or neurological deterioration, RT emerges as alone or adjuvant treatment against VSs, with SRS, FSRT, EBRT or protonbeam therapy presenting excellent tumor control growth (>90%), facial nerve (84-100%), trigeminal nerve (74-99%) and hearing (>50%) preservation. SRS poses an effective treatment modality of certain AVMs, demonstrating a 3-year obliteration rate of 80%. Lastly, a combination of microsurgery and RT presents equal local control and 5-year survival rate (>90%) but improved toxicity profile compared to total resection in case of craniopharyngiomas.

CONCLUSION

RT comprises an effective treatment modality of benign brain and intracranial lesions. By minimizing its AREs with optimal use, RT projects as a potent tool against such diseases.

Surgery of the lateral skull base: a 50-year endeavour

Disregarding the widely used division of skull base into anterior and lateral, since the skull base should be conceived as a single anatomic structure, it was to our convenience to group all those approaches that run from the antero-lateral, pure lateral and postero-lateral side of the skull base as “Surgery of the lateral skull base”. “50 years of endeavour” points to the great effort which has been made over the last decades, when more and more difficult surgeries were performed by reducing morbidity. The principle of lateral skull base surgery, “remove skull base bone to approach the base itself and the adjacent sites of the endo-esocranium”, was then combined with function preservation and with tailoring surgery to the pathology. The concept that histology dictates the extent of resection, balancing the intrinsic morbidity of each approach was the object of the first section of the present report. The main surgical approaches were described in the second section and were conceived not as a step-by-step description of technique, but as the highlighthening of the surgical principles. The third section was centered on open issues related to the tumor and its treatment. The topic of vestibular schwannoma was investigated with the current debate on observation, hearing preservation surgery, hearing rehabilitation, radiotherapy and the recent efforts to detect biological markers able to predict tumor growth. Jugular foramen paragangliomas were treated in the frame of radical or partial surgery, radiotherapy, partial “tailored” surgery and observation. Surgery on meningioma was debated from the point of view of the neurosurgeon and of the otologist. Endolymphatic sac tumors and malignant tumors of the external auditory canal were also treated, as well as chordomas, chondrosarcomas and petrous bone cholesteatomas. Finally, the fourth section focused on free-choice topics which were assigned to aknowledged experts. The aim of this work was attempting to report the state of the art of the lateral skull base surgery after 50 years of hard work and, above all, to raise questions on those issues which still need an answer, as to allow progress in knowledge through sharing of various experiences. At the end of the reading, if more doubts remain rather than certainties, the aim of this work will probably be achieved.

Auditory Brainstem Implants: Recent Progress and Future Perspectives

The auditory brainstem implant (ABI) was first developed nearly 40 years ago and provides auditory rehabilitation to patients who are deaf and ineligible for cochlear implant surgery due to abnormalities of the cochlea and cochlear nerve. The aims of the following review are to describe the history of the ABI and innovations leading up to the modern ABI system, as well as highlight areas of future development in implant design.

Outlook and future of inner ear therapy

Drug delivery to the inner ear is an ideal method to treat a wide variety of otologic conditions. A broad range of potential applications is just beginning to be explored. New approaches combine principles of inner ear pharmacokinetics with emerging technologies of drug delivery including novel delivery systems, drug-device combinations, and new categories of drugs. Strategies include cell-specific targeting, manipulation of gene expression, local activation following systemic delivery, and use of stem cells, viral vectors, and gene editing systems. Translation of these therapies to the clinic remains challenging given the potential risks of intracochlear and intralabyrinthine trauma, our limited understanding of the etiologies of particular inner ear disorders, and paucity of accurate diagnostic tools at the cellular level. This review provides an overview of future methods, delivery systems, disease targets, and clinical considerations required for translation to clinical medicine.

The Management and Imaging of Vestibular Schwannomas

Vestibular schwannomas are the most common cerebellopontine angle tumor. During the past century, the management goals of vestibular schwannomas have shifted from total resection to functional preservation. Current treatment options include surgical resection, stereotactic radiosurgery, and observation. Imaging has become a crucial part of the initial screening, evaluation, and follow-up assessment of vestibular schwannomas. Recognizing and understanding the management objectives, various treatment modalities, expected posttreatment findings, and complications allows the radiologist to play an essential role in a multidisciplinary team by providing key findings relevant to treatment planning and outcome assessment. The authors provide a comprehensive discussion of the surgical management, role of radiation therapy and observation, imaging differential, and pre- and posttreatment imaging findings of vestibular schwannomas.

Molecular Genetics of Intracranial Meningiomas with Emphasis on Canonical Wnt Signalling

Research over the last decade recognized the importance of novel molecular pathways in pathogenesis of intracranial meningiomas. In this review, we focus on human brain tumours meningiomas and the involvement of Wnt signalling pathway genes and proteins in this common brain tumour, describing their known functional effects. Meningiomas originate from the meningeal layers of the brain and the spinal cord. Most meningiomas have benign clinical behaviour and are classified as grade I by World Health Organization (WHO). However, up to 20% histologically classified as atypical (grade II) or anaplastic (grade III) are associated with higher recurrent rate and have overall less favourable clinical outcome. Recently, there is emerging evidence that multiple signalling pathways including Wnt pathway contribute to the formation and growth of meningiomas. In the review we present the synopsis on meningioma histopathology and genetics and discuss our research regarding Wnt in meningioma. Epithelial-to-mesenchymal transition, a process in which Wnt signalling plays an important role, is shortly discussed.

Surgical Treatment of Giant Vestibular Schwannomas: Facial Nerve Outcome and Tumor Control

BACKGROUND

Surgical treatment of giant vestibular schwannomas (GVS) is challenging. The philosophy of incomplete tumor resection may balance the preservation of facial nerve function and long-term tumor control.

OBJECTIVE

We aimed to evaluate the outcome of facial nerve function and tumor control in treating GVS via our institutional surgical strategy.

METHODS

From September 2009 to August 2014, 218 patients who underwent surgical treatment of GVS were enrolled in our study. The clinical features, extent of resections, facial nerve outcome, and the tumor regrowth free rate of these patients were retrospectively analyzed. The treatment strategy of this disease was discussed.

RESULTS

All patients had anatomic preservation of the facial nerve. Gross total resection (GTR) was achieved in 58 patients (28.6%), near-total resection (NTR) in 103 (50.7%), and subtotal resection (STR) in 42 (20.7%). Two patients died because of postoperative complications. After a mean follow-up of 39.7 ± 18.3 months, a favorable facial nerve outcome was achieved in 58.6%, 79.6%, and 83.3% of patients who underwent GTR, NTR, and STR, respectively. During follow-up, 20 patients had tumor regrowth and were treated by stereotactic radiosurgery (SRS), and tumor regrowth free rates were 96.6%, 92.2%, and 76.2% in GTR, NTR, and STR, respectively. The extent of resection was the independent risk factor for poor facial nerve function (P = 0.006).

CONCLUSIONS

A surgical philosophy of prioritizing facial nerve preservation over total tumor resection was recommended in treatment of GVS. Favorable facial nerve outcome and tumor control were achieved after NTR of the tumors.

Facial functional outcome in monitored versus not-monitored patients in vestibular schwannomas surgery

Objective:

Even though advances in surgical techniques have improved facial nerve outcomes, functional preservation is still an issue because injury to the facial nerve has significant physical and psychological consequences for the patient. We retrospectively review our data in VS surgery to compare the facial outcome in intraoperative facial monitored versus not-monitored patients.

Materials and Methods:

51 consecutive patients with unilateral vestibular schwannoma in the period from 2005 to 2010 were treated in our Institution. In according to the type of neurophysiological tool used during surgical procedures, two patients groups were identified: Group 1 (facial stimulator only) and Group 2 (stimulator and facial monitoring). Statistical comparison of the two groups was made with the t- test, and facial function results were evaluated with the Fisher's exact test.

Results:

In the Group 1, of the 22 patients with anatomically preserved facial nerves, 3 (13.6%) showed excellent facial nerve function, 14 (63.6%) showed intermediate function, and 5 (22.7%) showed poor function. In the Group 2, all the 27 patients got anatomically preserved facial nerves, and 18 (66.7%) showed excellent facial nerve function, 9 (33.3%) showed intermediate function, and no one showed poor function.

Conclusions:

We found that retrosigmoid approach associated with continuous EMG facial monitoring combined with the use of bipolar stimulation is a safe and effective treatment for vestibular schwannomas.

Prospect and progress of oncolytic viruses for treating peripheral nerve sheath tumors

INTRODUCTION

Peripheral nerve sheath tumors (PNSTs) are an assorted group of neoplasms originating from neuroectoderm and growing in peripheral nerves. Malignant transformation leads to a poor prognosis and is often lethal. Current treatment of PNSTs is predominantly surgical, which is often incomplete or accompanied by significant loss of function, in conjunction with radiotherapy and/or chemotherapy, for which the benefits are inconclusive. Oncolytic viruses (OVs) efficiently kill tumor cells while remaining safe for normal tissues, and are a novel antitumor therapy for patients with PNSTs.

AREAS COVERED

Because of the low efficacy of current treatments, new therapies for PNSTs are needed. Pre-clinically, OVs have demonstrated efficacy in treating PNSTs and perineural tumor invasion, as well as safety. We will discuss the various PNSTs and their preclinical models, and the OVs being tested for their treatment, including oncolytic herpes simplex virus (HSV), adenovirus (Ad), and measles virus (MV). OVs can be 'armed' to express therapeutic transgenes or combined with other therapeutics to enhance their activity.

EXPERT OPINION

Preclinical testing of OVs in PNST models has demonstrated their therapeutic potential and provided support for clinical translation. Clinical studies with other solid tumors have provided evidence that OVs are safe in patients and efficacious. The recent successful completion of a phase III clinical trial of oncolytic HSV paves the way for oncolytic virotherapy to enter clinical practice.

Novel age-dependent targets in vestibular schwannomas

Background

Schwannomas are the most common neurofibromatosis type 2 (NF2)-associated tumors with significant phenotypic heterogeneity in patients. The most severe subtype has an early and rapid progression and the mild type has a later onset and a less aggressive course. The aim of this study was to elucidate the underlying molecular differences between these groups. We compared the gene expression pattern between patients with early to late age of onset.

Results

A gene signature of 21 genes was constructed to differentiate between early-onset and late-onset patients. We confirmed these results by real-time PCR for SNF1LK2, NGFRAP1L1 (BEX 5), GMNN, and EPHA2.

Conclusion

Genes identified here may be additional aberrations in merlin-depleted cells that govern the disease onset. A significant number of these genes have been suggested as having a role in carcinogenesis and are used as biomarkers for prognosis in several other cancers. The role of these genes in NF2 carcinogenesis and their potential as biomarkers or drug target are worthwhile exploring.

Sporadic vestibular schwannomas associated with good hearing secrete higher levels of fibroblast growth factor 2 than those associated with poor hearing irrespective of tumor size

HYPOTHESIS

We hypothesize that the severity of hearing loss (HL) associated with sporadic vestibular schwannomas (VS) is correlated with tumor secretion of proteins with ototoxic or otoprotective potential.

BACKGROUND

Because the recognition that HL associated with VS is not solely due to compression of the auditory nerve, elucidating the mechanism by which VS cause HL has been an important task. We previously showed that VS stratified by hearing have differential gene expression. We now focus on identifying differentially expressed proteins in tumor secretions.

METHODS

Fresh surgical specimens of VS were incubated in sterile PBS at 37°C to collect secretions. The specimens were divided into a group associated with good hearing (GH, word recognition ≥ 70% and pure-tone average ≤ 30 dB, n = 11) or poor hearing (PH, n = 10). The groups were compared using a customized cytokine array. Statistically significant results were verified with an enzyme-linked immunosorbent assay on a different set of secretions (n = 8 for GH and n = 10 for PH group).

RESULTS

Of the 37 molecules we studied, 9 were significantly expressed in secretions from VS compared with secretions from control nerves. Secretion of fibroblast growth factor 2 (FGF2) was 3.5-fold higher in VS associated with GH versus PH based on cytokine array analysis (p = 0.02), which was validated with enzyme-linked immunosorbent assay.

CONCLUSION

This study highlights FGF2, a mitogen known to protect the auditory nerve, as a potential tumor-secreted mediator of hearing protection in VS. If FGF2's significant role in hearing protection in patients with VS is validated, then FGF2 could be used as a biomarker for HL in VS, and therapeutic targeting of the FGF2 signaling pathway may reduce HL due to VS.

Functional outcome and postoperative complications after the microsurgical removal of large vestibular schwannomas via the retrosigmoid approach: a meta-analysis

For large (≥30 mm) or giant (≥40 mm) vestibular schwannomas (VSs) for which microsurgical removal is the main treatment option, complete tumour resection and the preservation of acceptable facial nerve function can be safely and successfully achieved via the retrosigmoid approach. We performed a meta-analysis to provide a reliable estimate of functional outcome and postoperative complications for patients treated surgically for large VSs. We conducted a comprehensive search in Pubmed, Embase and the Chinese National Knowledge Infrastructure (CNKI) databases to identify publications that included only patients in whom the VSs were >3.0 cm in maximal diameter and microsurgically removed by a retrosigmoid approach. Pooled estimates of proportions with corresponding 95 % confidence intervals were calculated using the Freeman-Tukey double arcsine transformation. This meta-analysis revealed that the pooled proportion of gross total resections was 79.1 % (95 % CI, 64.2-90.8 %; I (2) = 95.4 %). By combining microsurgical techniques with continuous electrophysiological monitoring, the anatomical preservation of the facial nerve at the end of surgery was achieved in 88.8 % (95 % CI, 83.6-93.2 %; I (2) = 76.1 %) of the patients. The pooled proportion of good postoperative facial nerve function (House-Brackmann (HB) grades I-II) was 62.9 % (95 % CI, 50.0-74.9 %; I (2) = 91.1 %). Cerebrospinal fluid leakage was reported in 7.8 % (95 % CI, 4.8-11.4 %; I (2) = 49.8 %) of the patients. The mortality rate was 0.87 % (95 % CI, 0.22-1.78 %; I (2) = 4.9 %). Our meta-analysis revealed that for large VSs, very favourable results can be obtained using the retrosigmoid approach with minimal mortality, especially with respect to anatomical and functional facial nerve preservation.

Merlin, the NF2 gene product

Merlin, the protein product of NF2 gene, is one of the most versatile tumor suppressors capable of integrating different mechanisms that regulate cell proliferation, motility, survival and signaling pathways underlying and governing those mechanisms. Merlin is considered a member of the band 4.1 families of cytoskeleton-associated proteins also called ERM family and acts as tumor suppressor. The main cause for transformation of Schwann cells into schwannomas is credited to the inactivation of the neurofibromin 2 (NF2) gene and the consecutive loss of its protein merlin. Recent scientific advances improved our understanding of pathogenic mechanisms involving NF2 gene. The present review brings genetic properties of NF2 gene, molecular characteristics of merlin, summarizes mutational spectra and explains merlin's multifunctional roles regarding its involvement in neurofibromatosis associated tumorigenesis.

Frequency of loss of heterozygosity of the NF2 gene in schwannomas from Croatian patients

Aim

To identify gross deletions in the NF2 gene in a panel of schwannomas from Croatian patients in order to establish their frequencies in Croatian population.

Methods

Changes of the NF2 gene were tested by polymerase chain reaction/loss of heterozygosity (LOH) using two microsatellite markers, D22S444 and D22S929.

Results

The analysis with both markers demonstrated that 43.75% of schwannomas exhibited LOH of the NF2 gene. The D22S444 region exhibited 45.5% of LOHs and the D22S929 region exhibited 14.3% of LOHs. Four LOHs were found in Antoni B, 2 in Antoni A, and 1 in Antoni A and B type tumors.

Conclusion

The frequency of changes observed in Croatian patients is broadly similar to that reported in other populations and thus confirms the existing hypothesis regarding the tumorigenesis of schwannomas and contributes to schwannoma genetic profile helping us to better understand its etiology and treatment.

Neuroanatomical correlation of the House-Brackmann grading system in the microsurgical treatment of vestibular schwannoma

Avoidance of facial nerve injury is one of the major goals of vestibular schwannoma (VS) surgery because functional deficits of the facial nerve can lead to physical, cosmetic, and psychological consequences for patients. Clinically, facial nerve function is assessed using the House-Brackmann grading scale, which also allows physicians to track the progress of a patient's facial nerve recovery. Because the facial nerve is a peripheral nerve, it has the ability to regenerate, and the extent of its functional recovery depends largely on the location and nature of its injury. In this report, the authors first describe the facial nerve anatomy, the House-Brackmann grading system, and factors known to be predictors of postoperative facial nerve outcome. The mechanisms and pathophysiology of facial nerve injury during VS surgery are then discussed, as well as factors affecting facial nerve regeneration after surgery.

Isolated hypoglossal schwannoma in a 9-year-old child

The authors report a case of an isolated schwannoma of left hypoglossal nerve in a 9-year-old girl. To the authors' knowledge, this is the first case report of hypoglossal nerve schwannoma in the pediatric population in the absence of neurofibromatosis Type 2. The patient presented with a 2-month history of morning nausea and vomiting with occasional daytime headaches. Magnetic resonance imaging and subsequent CT scanning revealed a dumbbell tumor with a belly in the lower third of the posterior fossa and head underneath the left jugular foramen. Its neck protruded through an expanded hypoglossal canal. Although the lesion bore radiological characteristics of a hypoglossal schwannoma, the absence of hypoglossal palsy and the apparent lack of such tumors in the pediatric population the preoperative diagnosis was not certain. The tumor was approached via a midline suboccipital craniotomy, and gross-total resection was achieved. Pathological examination confirmed the diagnosis of schwannoma. Blood and tumor tests for mutations in the NF2 gene were negative. Postoperative mild hypoglossal palsy recovered by the 3-month follow-up, and an MRI study obtained at 1 year did not show recurrence.

The rise and fall of "biopsy and radiate": a history of surgical nihilism in glioma treatment

Many neurosurgeons take a nihilistic approach to surgical treatment of gliomas, stating the inability to achieve a cure. Where this idea comes from is somewhat nebulous to most neurosurgeons. A review of the scientific studies supporting the commonly held beliefs about gliomas shows that these ideas regarding the surgical treatment of gliomas are based on overgeneralizations of data from older studies. One should avoid the temptation to apply them to the greater concept of what gliomas are, how they behave, and what should be done, but rather we should continue to scientifically evaluate the role of surgical resection in glioma treatment.

Merlin: the wizard requires protein stability to function as a tumor suppressor

Neurofibromatosis type 2 (NF2), characterized by tumors of the nervous system, is a result of functional loss of the NF2 gene. The NF2 gene encodes Merlin (moesin-ezrin-radixin-like protein), an ERM (Ezrin, Radixin, Moesin) protein family member. Merlin functions as a tumor suppressor through impacting mechanisms related to proliferation, apoptosis, survival, motility, adhesion, and invasion. Several studies have summarized the tumor intrinsic mutations in Merlin. Given the fact that tumor cells are not in isolation, but rather in an intricate, mutually sustaining synergy with their surrounding stroma, the dialog between the tumor cells and the stroma can potentially impact the molecular homeostasis and promote evolution of the malignant phenotype. This review summarizes the epigenetic modifications, transcript stability, and post-translational modifications that impact Merlin. We have reviewed the role of extrinsic factors originating from the tumor milieu that influence the availability of Merlin inside the cell. Information regarding Merlin regulation could lead to novel therapeutics by stabilizing Merlin protein in tumors that have reduced Merlin protein expression without displaying any NF2 genetic alterations.

Therapeutic profile of single-fraction radiosurgery of vestibular schwannoma: unrelated malignancy predicts tumor control

Radiosurgery has become an accepted treatment option for vestibular schwannomas. Nevertheless, predictors of tumor control and treatment toxicity in current radiosurgery of vestibular schwannomas are not well understood. To generate new information on predictors of tumor control and cranial nerve toxicity of single-fraction radiosurgery of vestibular schwannomas, we conducted a single-institution long-term observational study of radiosurgery for sporadic vestibular schwannomas. Minimum follow-up was 3 years. Investigated as potential predictors of tumor control and cranial nerve toxicity were treatment technology; tumor resection preceding radiosurgery; tumor size; gender; patient age; history of cancer, vascular disease, or metabolic disease; tumor volume; radiosurgical prescription dose; and isodose line. Three hundred eighty-six patients met inclusion criteria. Treatment failure was observed in 27 patients. History of unrelated cancer (strongest predictor) and prescription dose significantly predicted tumor control. The cumulative incidence of treatment failure was 30% after 6.5 years in patients with unrelated malignancy and 10% after ≥15 years in patients without such cancer (P < .02). Tumor volume was the only predictor of trigeminal neuropathy (observed in 6 patients). No predictor of facial nerve toxicity was found. On the House and Brackmann scale, 1 patient had a permanent one-level drop and 7 a transient drop of 1 to 3 levels. Serviceable hearing was preserved in 75.1%. Tumor hearing before radiosurgery, recurrence, and prescription isodose predicted ototoxicity. Unrelated malignancy is a strong predictor of tumor control. Tumor recurrence predominantly predicts ototoxicity. These findings potentially will aid future clinical decision making in ambiguous cases.

Gamma Knife surgery for nonvestibular schwannomas: radiological and clinical outcomes

OBJECT

Most intracranial schwannomas arise from cranial nerve (CN) VIII. Stereotactic radiosurgery is a mainstay of treatment for vestibular schwannomas. Intracranial schwannomas arising from other CNs are much less common. We evaluate the efficacy of Gamma Knife surgery on nonvestibular schwannomas including trigeminal, hypoglossal, abducent, facial, trochlear, oculomotor, glossopharyngeal, and jugular foramen tumors.

METHODS

Thirty-six patients with nonvestibular schwannomas were treated at the University of Virginia Gamma Knife center from 1989 to 2008. The median patient age was 48 years (mean 45.6 years, range 10-72 years). Schwannomas arose from the following CNs: CN III (in 1 patient), CN IV (in 1), CN V (in 25), CN VI (in 2), CN VII (in 1), CN IX (in 1), and CN XII (in 3). In 2 patients, tumors arose from the jugular foramen. The median tumor volume was 2.9 cm(3) (mean 3.3 cm(3), range 0.07-8.8 cm(3)). The median margin dose was 13.5 Gy (range 9.3-20 Gy); the median maximum dose was 30 Gy (range 21.7-50.0 Gy).

RESULTS

The mean and median follow-up times of 36 patients were 54 and 37 months, respectively (range 2-180 months). At the last radiological follow-up, the tumor size had decreased in 20 patients, remained stable in 9 patients, and increased in 7 patients. The 2-year actuarial progression-free survival was 91%. Higher maximum dose was statistically related to tumor control (p = 0.027). Thirty-three patients had adequate clinical follow-up. Among them, 21 patients had improvement in their presenting symptoms, 8 patients were stable after treatment with no worsening of their presenting symptoms, 2 patients developed new symptoms, and 1 patient experienced symptom deterioration. Notably, 1 patient with neurofibromatosis Type 2 developed new symptoms that were unrelated to the tumor treated with Gamma Knife surgery.

CONCLUSIONS

Gamma Knife surgery is a reasonably effective treatment option for patients with nonvestibular schwannomas. Patients require careful follow-up for tumor progression and signs of neurological deterioration.

Empirical development of improved diagnostic criteria for neurofibromatosis 2

PURPOSE

Four sets of clinical diagnostic criteria have been proposed for neurofibromatosis 2, but all have low sensitivity at the time of initial clinical assessment for the disease among patients with a negative family history who do not present with bilateral vestibular schwannomas. We have empirically developed and tested an improved set of diagnostic criteria that uses current understanding of the natural history and genetic characteristics of neurofibromatosis 2 to increase sensitivity while maintaining very high specificity.

METHODS

We used data from the UK Neurofibromatosis 2 Registry and Kaplan-Meier curves to estimate frequencies of clinical features at various ages among patients with or without unequivocal neurofibromatosis 2. On the basis of this analysis, we developed the Baser criteria, a new diagnostic system that incorporates genetic testing and gives more weight to the most characteristic features and to those that occur before 30 years of age.

RESULTS

In an independent validation subset of patients with unequivocal neurofibromatosis 2, the Baser criteria increased diagnostic sensitivity to 79% (9-15% greater than previous sets of criteria) while maintaining 100% specificity at the age at onset of the first characteristic sign of neurofibromatosis 2.

CONCLUSION

The Baser criteria permit early diagnosis in a greater proportion of patients with neurofibromatosis 2 than previous sets of diagnostic criteria.

The molecular biology and novel treatments of vestibular schwannomas

Vestibular schwannomas are histopathologically benign tumors arising from the Schwann cell sheath surrounding the vestibular branch of cranial nerve VIII and are related to the NF2 gene and its product merlin. Merlin acts as a tumor suppressor and as a mediator of contact inhibition. Thus, deficiencies in both NF2 genes lead to vestibular schwannoma development. Recently, there have been major advances in our knowledge of the molecular biology of vestibular schwannomas as well as the development of novel therapies for its treatment. In this article the authors comprehensively review the recent advances in the molecular biology and characterization of vestibular schwannomas as well as the development of modern treatments for vestibular schwannoma. For instance, merlin is involved with a number of receptors including the CD44 receptor, EGFR, and signaling pathways, such as the Ras/raf pathway and the canonical Wnt pathway. Recently, merlin was also shown to interact in the nucleus with E3 ubiquitin ligase CRL4(DCAF1). A greater understanding of the molecular mechanisms behind vestibular schwannoma tumorigenesis has begun to yield novel therapies. Some authors have shown that Avastin induces regression of progressive schwannomas by over 40% and improves hearing. An inhibitor of VEGF synthesis, PTC299, is currently in Phase II trials as a potential agent to treat vestibular schwannoma. Furthermore, in vitro studies have shown that trastuzumab (an ERBB2 inhibitor) reduces vestibular schwannoma cell proliferation. With further research it may be possible to significantly reduce morbidity and mortality rates by decreasing tumor burden, tumor volume, hearing loss, and cranial nerve deficits seen in vestibular schwannomas.

Neurofibromatosis-2 and spinal cord ependymomas: Report of two cases and review of the literature

OBJECT

The incidence of ependymoma in patients with neurofibromatosis-2 (NF-2) is low and information regarding treatment and prognosis is lacking. We present two cases of cervicomedullary tumors in patients with NF-2 from our institution, and we provide a review of the literature in order to summarize the known clinical information about this rare occurrence.

PATIENTS AND METHODS

Patient #1 had histological confirmation of ependymoma and was treated with subtotal resection followed by observation and has had no evidence of progression for 11 months. Patient #2 has been observed for 4 1/2 years without treatment for a cervicomedullary tumor, which appears to be an ependymoma by imaging. Although it has increased in size very slowly, there have been no clinical symptoms. Among the additional 21 cases of NF-2 and ependymoma from the literature, the most common location is the cervical spine (70%), and the median age at diagnosis is 15 years. Surgical resection was performed in 85% of the cases and subtotal resection in 64% of cases. Fifteen patients (75%) were reported alive at the time of the published reports, with survival ranging from 0.1 to 10 years, and the 8-year survival estimated as 51%. Survival was related to the location of the tumor.

CONCLUSIONS

We conclude from our two cases and review of the existing literature that NF-2 associated spinal ependymomas have an indolent course and typically can be observed or treated by surgical excision alone.

Factors associated with preservation of facial nerve function after surgical resection of vestibular schwannoma

Avoidance of facial nerve palsy is one of the major goals of vestibular schwannoma (VS) microsurgery. In this study, we examined the significance of previously implicated prognostic factors (age, tumor size, the extent of resection and the surgical approach) on post-operative facial nerve function. We selected all VS patients from prospectively collected database (1984–2009) who underwent microsurgical resection as their initial treatment for histopathologically confirmed VS. The effect of variables such as surgical approach, tumor size, patient age and extent of resection on rates facial nerve dysfunction after surgery, were analyzed using multivariate logistic regression. Patients with preoperative facial nerve dysfunction (House-Brackman [HB] score 3 or higher) were excluded, and HB grade of 1 or 2 at the last follow-up visit was defined as “facial nerve preservation.” A total of 624 VS patients were included in this study. Multivariate logistic regression analysis found that only pre-operative tumor size significantly predicted poorer facial nerve outcome for patients followed-up for ≥6 and ≥12 months (OR 1.27, 95% CI 1.09–1.49, p < 0.01; OR 1.35, 95% CI 1.10–1.67, P < 0.01, respectively). We found no significant relationship between facial nerve function and age, extent of resection, surgical approach, or tumor size (when extent of resection and surgical approach were included in the regression analysis). Because facial nerve palsy is a debilitating and psychologically devastating condition for the patient, we suggest altering surgical aggressiveness in patients with unfavorable tumor anatomy, particularly in cases with large tumors where overaggressive resection might subject the patient to unwarranted risk. Residual disease can be followed and controlled with radiosurgery if interval growth is noted.