Long-term outcomes of stereotactic radiosurgery for intracranial schwannoma in neurofibromatosis type 2: a genetic analysis perspective.

PURPOSE: Neurofibromatosis type 2 (NF2) is intractable because of multiple tumors involving the nervous system and is clinically diverse and genotype-dependent. Stereotactic radiosurgery (SRS) for NF2-associated schwannomas remains controversial. We aimed to investigate the association between radiosurgical outcomes and mutation types in NF2-associated schwannomas. METHODS: This single-institute retrospective study included consecutive NF2 patients with intracranial schwannomas treated with SRS. The patients' types of germline mutations ("Truncating," "Large deletion," "Splice site," "Missense," and "Mosaic") and Halliday's genetic severity scores were examined, and the associations with progression-free rate (PFR) and overall survival (OS) were analyzed. RESULTS: The study enrolled 14 patients with NF2 with 22 associated intracranial schwannomas (median follow-up, 102 months).　The PFRs in the entire cohort were 95% at 5 years and 90% at 10-20 years. The PFRs tended to be worse in patients with truncating mutation exons 2-13 than in those with other mutation types (91% at 5 years and 82% at 10-20 years vs. 100% at 10-20 years, P = 0.140). The OSs were 89% for patients aged 40 years and 74% for those aged 60 years in the entire cohort and significantly lower in genetic severity group 3 than in the other groups (100% vs. 50% for those aged 35 years; P = 0.016). CONCLUSION: SRS achieved excellent PFR for NF2-associated intracranial schwannomas in the mild (group 2A) and moderate (group 2B) groups. SRS necessitates careful consideration for the severe group (group 3), especially in cases with NF2 truncating mutation exons 2-13.

Sporadic vestibular schwannoma in a pediatric population: a case series.

PURPOSE: To describe the characteristics, management, and outcomes of pediatric patients with sporadic vestibular schwannoma (sVS). METHODS: This was a case series at a tertiary care center. Patients were identified through a research repository and chart review. Interventions were microsurgery, stereotactic radiosurgery (SRS), and observation. Outcome measures were tumor control, facial nerve function, and hearing. RESULTS: Eight patients over 2006-2022 fulfilled inclusion criteria (unilateral VS without genetic or clinical evidence of neurofibromatosis type 2 (NF2); age ≤ 21) with a mean age of 17 years (14-20). Average greatest tumor length in the internal auditory canal was 9.7 mm (4.0-16.1). Average greatest tumor dimension (4/8 tumors) in the cerebellopontine angle was 19.1 mm (11.3-26.8). Primary treatment was microsurgery in five (62.5%) patients, observation in two (25%), and SRS in one (12.5%). Four (80%) surgical patients had gross total resections, and one (20%) had regrowth post-near total resection and underwent SRS. One observed patient and the primary SRS patient have remained radiographically stable for 3.5 and 7 years, respectively. The other observed patient required surgery for tumor growth after 12 months of observation. Two surgical patients had poor facial nerve outcomes. All post-procedural patients developed anacusis. Mean follow-up was 3 years (0.5-7). CONCLUSIONS: We describe one of the largest reported cohorts of pediatric sVS in the USA. Diligent exclusion of NF2 is critical. Given the high likelihood of eventually requiring intervention and known adverse effects of SRS, microsurgery remains the preferred treatment. However, observation can be considered in select situations.

An unusual finding of an anaplastic meningioma in NF2-related schwannomatosis.

NF2-related schwannomatosis (NF2) is a rare autosomal-dominant genetic disorder characterized by bilateral vestibular schwannomas and multiple meningiomas. This case report presents the extremely rare occurrence of an anaplastic meningioma in a 12-year-old male with previously undiagnosed NF2. The patient presented with a history of abdominal pain and episodic emesis, gait unsteadiness, right upper and lower extremity weakness, and facial weakness. He had sensorineural hearing loss and wore bilateral hearing aids. MR imaging revealed a sizable left frontoparietal, dural-based meningioma with heterogeneous enhancement with mass effect on the brain and midline shift. Multiple additional CNS lesions were noted including a homogenous lesion at the level of T5 indicative of compression of the spinal cord. The patient underwent a frontotemporoparietal craniotomy for the removal of his large dural-based meningioma, utilizing neuronavigation and transdural ultrasonography for precise en bloc resection of the mass. Histopathology revealed an anaplastic meningioma, WHO grade 3, characterized by brisk mitotic activity, small-cell changes, high Ki-67 proliferation rate, and significant loss of P16. We report an anaplastic meningioma associated with an underlying diagnosis of NF2 for which we describe clinical and histopathological features.

Evaluation of the non-auditory responses in individuals with auditory brainstem implant.

OBJECTIVES: After auditory brainstem implant (ABI) surgery, stimulation of certain cranial nerves may result in a non-auditory response, and the electrodes that stimulate these nerves may be deactivated. The goals of this study are to compare the number of active electrodes in the initial activation and the last fitting, to investigate non-auditory response types and their frequency as a result of non-auditory stimulation, to compare the placements of deactivated electrodes as a result of non-auditory stimulation in the initial activation and the last fitting. METHODS: The computer software system was used to perform a retrospective analysis of the fitting data of 69 ABI users who underwent auditory brainstem implant surgery between January 1997 and January 2019. The non-auditory response types, deactive electrodes, and the positioning of the deactive electrodes horizontally and vertically were recorded in these users during the initial activation and the last fitting. RESULTS: There was no statistically significant difference between the number of active electrodes in the initial activation and the last fitting. The proportion of the users with deactive electrodes in the initial activation and the last fitting was not statistically significant different. In the horizontal and vertical placement classification, the placement of the deactive electrodes was not statistically different between initial activation and last fitting. The most common type of non-auditory response was facial nerve stimulation at the initial activation and no auditory perception at the last fitting. According to the difference between the number of active and deactive electrodes in the initial activation and the last fitting, as well as the auditory and non-auditory responses, it was found that the ABI users were statistically different between the initial activation and the last fitting. CONCLUSION: The results of this study show that not only auditory but also non-auditory responses occur in most ABI users. In addition, to the best of our knowledge, this study is the first to examine the frequencies of non-auditory response types, and the placement of the electrodes that cause these responses according to horizontal and vertical classifications.

Regression of a spinal schwannoma after Pomalidomide.

A 77-year old female with a history of neurofibromatosis type 2 (NF2) was diagnosed with a spinal schwannoma that was managed conservatively over a decade. During this time, follow up imaging revealed this lesion had been growing and the patient had become symptomatic from it necessitating surgical decompression. However, the patient had been diagnosed with multiple myeloma and underwent treatment with Pomalidomide chemotherapy which delayed surgery for the spinal schwannoma. Further imaging of the spine revealed significant regression in the size of the spinal schwannoma. This phenomenon has not previously been reported and this report aims to explore the implications of Pomalidomide in patients with NF2 related spinal schwannomas.

Bilateral intracochlear schwannomas: histopathological confirmation and outcomes following tumour removal and cochlear implantation with lateral wall electrodes.

Intracochlear schwannomas (ICS) are very rare benign tumours of the inner ear. We present histopathological proof of the extremely rare bilateral occurrence of intracochlear schwannomas with negative blood genetic testing for neurofibromatosis type 2 (NF2). Bilateral schwannomas are typically associated with the condition NF2 and this case is presumed to have either mosaicism for NF2 or sporadic development of bilateral tumours. For progressive bilateral tumour growth and associated profound hearing loss, surgical intervention via partial cochleoectomy, tumour removal, preservation of the modiolus, and simultaneous cochlear implantation with lateral wall electrode carrier with basal double electrode contacts was performed. The right side was operated on first with a 14-month gap between each side. The hearing in aided speech recognition for consonant-nucleus-consonant (CNC) phonemes in quiet improved from 57% to 83% 12 months after bilateral cochlear implantation (CI). Bilateral intracochlear schwannomas in non-NF2 patients are extremely rare but should be considered in cases of progressive bilateral hearing loss. Successful tumour removal and cochlear implantation utilizing a lateral wall electrode is possible and can achieve good hearing outcomes.

Pediatric vestibular schwannoma without evidence of neurofibromatosis: consecutive 18 microsurgical experiences.

PURPOSE: Sporadic vestibular schwannoma (VS) is rare in children in contrast to adults, and detailed investigations of case series of these patients using a single fixed protocol are scarce. This study presents our surgical experience of pediatric VSs without clinical evidence of neurofibromatosis type 2 (NF2) at the initial diagnosis. METHODS: Among 1385 consecutive sporadic VS surgeries, 18 pediatric patients (1.3%; 11-18 years old) were retrospectively investigated. RESULTS: The most common initial symptom was hearing disturbance (72.2%), and 6 patients (33.3%) experienced a delayed diagnosis (over 2 years after initial symptom onset). Preoperative image characteristics of these tumors included a solid tumor, hypervascularity, and significant extension into the internal acoustic meatus, when compared with adults. Preoperative embolization was successfully accomplished for 2 recent hypervascular tumors. The tumor resection rate was 95-100% under sufficient intraoperative neuromonitoring, and no additional surgery was required during the follow-up period (average: 57.9 months). No patients experienced permanent facial nerve palsy, and serviceable hearing function was preserved in 6 of 11 patients. Signs of NF2, such as bilateral VSs, were not identified in any patients during the follow-up. CONCLUSION: Safe and sufficient tumor resection was achieved under detailed neuromonitoring in pediatric patients with sporadic VS, although this tends to be difficult owing to hypervascularity, a small cranium, and significant meatal extension. Preoperative embolization may help safe resection of hypervascular tumors. Subsequent development of NF2 has not been observed up to the most recent follow-up, but careful observation is essential for these younger patients.

Cochlear implant in vestibular schwannomas: long-term outcomes and critical analysis of indications.

PURPOSE: To describe our institutional experience in cochlear implantation after vestibular schwannoma (VS) resection, and compare the audiological outcomes between sporadic and neurofibromatosis type 2 (NF2) VS sub-cohorts of patients, and in relation to preoperative contralateral hearing. METHODS: Seventeen patients (8 sporadic and 9 NF2-associated VSs) who had undergone VS resection and cochlear implant (CI) were analyzed retrospectively. Audiological outcomes at 24 months were correlated with preoperative clinical variables. The results according to VS type (sporadic vs. NF2-associated) and contralateral hearing (impaired vs. normal) were compared. RESULTS: Fourteen CIs were actively used by the patients (77.8%). Twenty-four months after CI activation, the median postoperative PTA (pure tone average) was 45.6 dB nHL and a measurable WRS (Word Recognition Score) was achieved by 44.4% of patients (median WRS = 40%). The median postoperative PTA in the implanted ear resulted better in the group with an impaired contralateral hearing (36.3 dB nHL vs. 78.8 dB nHL, p = 0.019). Good preoperative contralateral hearing status (A-B classes of AAO-HNS) was a negative prognostic factor for CI performance on open-set discrimination (OR = 28.0, 95% CI 2.07-379.25, p = 0.012). CONCLUSIONS: CI is a viable rehabilitative option for patients with sporadic or NF2-associated VS. A good contralateral hearing adversely affects CI outcome and should be taken into consideration for patients' selection and rehabilitation programs.

Cochlear Implantation in a Patient with Neurofibromatosis Type 2 and an Intracochlear Schwannoma: A Case Report and Literature Review.

A primary intracochlear schwannoma (ICS) is a unique type of vestibular schwannoma (VS); the tumor originates from the terminal branches of the cochlear nerve and is confined to the cochlea. An ICS is the most common subtype of schwannoma in the inner ear. As an ICS is clinically rare, diagnosis and treatment remain challenging. We report a rare case of cochlear implantation (CI) in a patient with neurofibromatosis type 2 and an ICS. The patient exhibited bilateral, profound, sensorineural hearing loss. The tumor on one side was a common VS treated via tumor and acoustic nerve resection and that on the other side an ICS. To ensure auditory rehabilitation via CI, we performed CI while removing part of the ICS via an enlarged round window. Auditory rehabilitation was satisfactory. Thus, ICS patients, especially those who urgently require auditory rehabilitation, can undergo simultaneous CI and (total or partial) tumor removal. However, the long-term results require close observation.

Adult Auditory Brainstem Implant Outcomes and Three-Dimensional Electrode Array Position on Computed Tomography.

OBJECTIVES: Factors contributing to auditory brainstem implant (ABI) outcomes are poorly understood. The aims of this study are to (1) characterize ABI electrode array position on postoperative imaging and (2) determine if variability in position is related to perceptual outcomes. DESIGN: Retrospective cohort study. Subjects were selected from the adult ABI recipient population at Massachusetts Eye and Ear. Postoperative three-dimensional (3D) computed tomography (CT) reconstruction of the head was used to measure ABI array position in 20 adult ABI recipients (17 with Neurofibromatosis Type 2 (NF2) and three non-NF2 recipients). Three-dimensional electrode array position was determined based on angles from the horizontal using posterior and lateral views and on distances between the proximal array tip superiorly from the basion (D1), laterally (D2P) and posteriorly (D2L) from the midline. Array position was correlated with perceptual data (in 15 of the 20 recipients who used their ABI). Perceptual data included the number of electrodes that provided auditory sensation, location and type of side effects, level of speech perception (from no sound to open-set word recognition of monosyllables) and the amount of charge required for auditory perception. RESULTS: Although the 3D orientation of the ABI array exhibited a variety of angles, all arrays were posteriorly tilted from the lateral view and most were medially tilted from the posterior view. ABI position relative to the basion from posterior showed mean distances of 1.71 ± 0.42 and 1.1 ± 0.29 cm for D1 and D2, respectively, and a mean D2 of 1.30 ± 0.45 cm from the lateral view. A strong linear negative correlation was found between the number of active electrodes and the distance of the proximal array tip laterally from the basion (D2P; rs = -0.73, p = 0.006) when measured in the posterior view. Although side effects were experienced in all recipients and varied in type and location across the array, electrodes in the middle part of the array tended to elicit auditory sensations while the proximal and distal tips of the array tended to elicit nonauditory side effects. Arrays with and without low charge thresholds appeared to generally overlap in position. However, the two recipients with the best (open-set) speech perception had low charge thresholds and had arrays that were tilted superiorly in the posterior view. CONCLUSION: ABI recipients with better speech perception appear to share a profile of arrays that are tilted superiorly as compared to recipients with lower speech perception levels. These ABI recipients have a high number of active electrodes (10 or more) and require less electrical charge on individual electrodes to achieve optimal stimulation.

[Auditory brainstem implantation: current status and prospects].

Auditory brainstem implantation is a hearing restoration technique on the central auditory pathway, which directly stimulates neural tissues of cochlear nucleus by electrode array to produce hearing, so it will not be restricted by abnormalities of the cochlea and cochlear nerve. In the past 30 years since the birth of multi-channel ABI, its indications have expanded from patients with neurofibromatosis type 2 (NF2) to congenital deafness patients with severe inner ear and/or cochlear nerve malformations, and the age of recipients decreases from adults to young children. This article summarizes the principle, indications, surgical techniques, complications and auditory outcomes of ABI.

Options and strategies for hearing restoration in pediatric neurofibromatosis type 2.

PURPOSE: In this article, we will review the mechanisms and natural history of hearing loss in neurofibromatosis type 2 (NF2) and discuss the hearing outcomes with different rehabilitation options. METHODS: Review of the published literature. RESULTS: NF2 is a rare autosomal dominant syndrome characterized by vestibular schwannomas and other intracranial and spinal tumors. Bilateral vestibular schwannomas are the hallmark of the disease which occur in 90 to 95% of the patients. As a result, hearing loss will eventually occur in almost all NF2 patients. Deafness can occur from tumor progression or from treatment of vestibular schwannomas and is among the most debilitating aspects of NF2. A number of surgical and non-surgical rehabilitation options are available for these patients including cochlear and auditory brainstem implants. The audiologic outcomes with surgical rehabilitation options have been variable but most patients are able to achieve sound awareness and benefit from auditory cues in lip reading. CONCLUSION: Early identification and treatment of NF2 patients can help in achieving better hearing outcomes in the pediatric population. An increasing number of NF2 patients are receiving open set word understanding with refinement in surgical techniques.

Surgical management of collision-tumors between vestibular schwannoma and meningioma in the cerebellopontine angle in patients with neurofibromatosis type 2.

INTRODUCTION: When vestibular schwannoma (VS) collides with meningioma at the cerebellopontine angle (CPA), a particular threat occurs. Sudden acceleration of tumor growth and unpredictable involvement of cranial nerves results in a special environment that aggravates management. The goal of this study was to analyze the extent of resection, postoperative facial and cochlear function, surgical strategy, and survival rates in patients with neurofibromatosis type 2 (NF2) with meningioma-vestibular schwannoma (M-VS) collision tumors. METHODS: A total of 1284 VS, including 165 NF2 VS were operated at our department between January 2004 and May 2018. Out of these cases, a group of six NF2 patients with seven M-VS collision tumors was found following careful analysis of neuroradiological data and pathological and surgical reports. Patients were evaluated for extent of tumor resection and, furthermore, postoperative facial and hearing function. RESULTS: Six patients with NF2 with seven M-VS collision tumors were included in this study. Mean age was 32 ± 8.2 years. A gross total resection (GTR) of both colliding tumors was achieved in only one case, a GTR of the meningioma and a subtotal resection (STR) of the VS in four cases and in two cases only, the meningioma was removed. In five of the cases, facial function was intact or good (House and Brackmann grades I-II) at long-term follow-up (mean follow-up 22 months). No mortality occurred during follow-up. CONCLUSIONS: Collision between M and VS at the CPA is a particular phenomenon in NF2 patients that may aggravate the situation with less favorable surgical outcome than NF-2 VS without meningioma.

Surgical treatment of large vestibular schwannomas in patients with neurofibromatosis type 2: outcomes on facial nerve function and hearing preservation.

Surgical treatment of vestibular schwannoma (VS) in patients with neurofibromatosis type 2 (NF2) along with functional preservation of cranial nerves is challenging. The aim of this study was to analyze the outcomes of hearing and facial nerve function in patients with NF2 who underwent large-size VS (> 2 cm) surgery. From 2006 to 2016, one hundred and forty NF2 patients were included with 149 large-size VS resections using retrosigmoid approach. Hearing function was classified according to the American Academy of Otolaryngology-Head and Neck Surgery (AAO-HNS) criteria. Preoperative and one-year postoperative facial nerve function were both assessed using the House-Brackmann (H-B) grading scale. A multivariate logistic regression was performed to identify preoperative predictors for facial function outcomes. No operative death we noted. Total tumor removal was achieved in 82.6% of the operated VSs. The anatomical integrity of the facial nerve was preserved in 67.8% of surgeries. Good facial nerve function (H-B Grades I-III) was maintained in 49.6% of patients at 12 months after surgery. Tumor size larger than 3 cm and preoperative facial weakness related with worse outcome of facial nerve function (P < 0.001; for both). Hearing preservation surgeries were attempted in 31 ears. Class B or C hearing according to the AAO-HNS criteria was maintained in 7 ears (22.5%), and measurable hearing was maintained 11 ears (35.5%). It is challenging to maintain hearing and facial nerve function in NF2 patients with large VSs. Early surgical intervention is an appropriate choice to decrease the risk of neurological functions deficit.

Surgical anatomy of lateral recess in paediatric auditory brainstem implant patients and its clinical correlates including grades of flocculus.

INTRODUCTION: Auditory brainstem implant (ABI), a standard technique in treatment of profound sensorineural hearing loss in patients with neurofibromatosis 2, is now being increasingly employed in children with congenital bilateral sensorineural hearing loss, as in Michele's deformity. A detailed knowledge of the relevant surgical anatomy of the lateral recess and its anatomical landmarks including the flocculus, the choroid plexus and the root entry zones of facial-vestibulocochlear and glossopharyngeal-vagus nerve complexes and their anatomical variants is mandatory, as it is the conduit for electrode array placement. The placement of electrode may be eased or impeded by these variations. MATERIALS AND METHODS: Thirty-two children with congenital bilateral hearing loss underwent surgery through retromastoid suboccipital approach for placement of auditory brainstem implant. The preoperative anatomy was reviewed in detail during procedure and again later in the operative videos. RESULTS: The flocculus was classified into four grades based on its anatomy and relations. Among these, grade II (11 children) was the commonest while grade IV (five children) was least common. Choroid plexus was variable in size across grades of flocculus. Difficulty in defining the anatomy was significantly more (p value = 0.003) in the group with higher grade flocculus (grade III and IV) than in lower grade flocculus (grade I and II). CONCLUSION: The flocculus in these patients is classifiable into one of the four grades and the surgical nuances such as difficulty in defining the anatomy for placement of ABI are dependent on the characteristics exhibited by the floccular anatomy and relations.

A new experience of auditory brainstem implantation in Malaysia.

Auditory brainstem implantation (ABI) is the only solution to restore hearing when cochlear nerves are disrupted together with the pathologies where bilateral cochleae do not provide a suitable location for cochlear implantation. We reported first two successful auditory brainstem implantation cases in patients with neurofibromatosis Type II (NF2) with bilateral acoustic neuroma causing bilateral profound sensorineural hearing loss in Malaysia. A good candidate selection, dedicated surgeons and rehabilitation team as well as strong family support are the crucial factors in achieving the best possible surgical, audiological and speech outcomes.

Endoscopic approach via the interhemispheric fissure: the role of an endoscope in a surgical case of multiple falcine lesions.

BACKGROUND: For treating a patient with multiple falcine and parasagittal lesions, we believe that it is beneficial to resect the maximum possible number of lesions during one operation, even if some lesions are asymptomatic. This practice can potentially reduce the total number of operations during a patient's lifetime. METHODS: We provide an introduction of a concurrent endoscopic approach via the interhemispheric fissure. CONCLUSIONS: Applying this endoscopic approach concurrently with conventional microscopic surgery can enable the safe resection of as many lesions as possible during one operation.

[Intramedullary spinal cord tumors and neurofibromatosis]. / Intramedullyarnye opukholi spinnogo mozga i neirofibromatoz.

The article addresses the issue of a combination and relationship between intramedullary spinal cord tumors (IMSCTs) and neurofibromatosis (NF). AIM: To study, based on large clinical material, features of the prevalence and biological nature of intramedullary spinal cord tumors in neurofibromatosis patients in different age groups. MATERIAL AND METHODS: We analyzed the data of the largest series of patients from all age groups who underwent surgery for spinal cord intramedullary tumors (541 patients; 586 surgeries; age, 2 months to 72 years). RESULTS: Our findings support a potential pathogenetic relationship between intramedullary tumors and neurofibromatosis. Astrocytoma was a predominant intramedullary tumor in patients with NF-1, while ependymoma predominated in patients with NF-2. IMSCTs combined with NF-1 occur predominantly in children and adolescents, while a combination with NF-2 is typical of young adults. Our findings confirm the fact that IMSCT surgery is required for a small number of NF patients.

Electrically Evoked Auditory Event-Related Responses in Patients with Auditory Brainstem Implants: Morphological Characteristics, Test-Retest Reliability, Effects of Stimulation Level, and Association with Auditory Detection.

OBJECTIVE: This study aimed to (1) characterize morphological characteristics of the electrically evoked cortical auditory event-related potentials (eERPs) and explore the potential association between onset eERP morphology and auditory versus nonauditory stimulation; (2) assess test-retest reliability of onset eERPs; (3) investigate effects of stimulation level on onset eERPs; and (4) explore the feasibility of using the onset eERP to estimate the lowest stimulation level that can be detected for individual stimulating electrodes in patients with auditory brainstem implants (ABIs). DESIGN: Study participants included 5 children (S1 to S5) and 2 adults (S6 to S7) with unilateral Cochlear Nucleus 24M ABIs. Pediatric ABI recipients ranged in age from 2.6 to 10.2 years (mean: 5.2 years) at the time of testing. S6 and S7 were 21.2 and 24.6 years of age at the time of testing, respectively. S6 and S7 were diagnosed with neurofibromatosis II (NF2) and implanted with an ABI after a surgical removal of the tumors. All pediatric subjects received ABIs after being diagnosed with cochlear nerve deficiency. The lowest stimulation level that could be detected (behavioral T level) and the estimated maximum comfortable level (C level) was measured for individual electrodes using clinical procedures. For electrophysiological measures, the stimulus was a 100-msec biphasic pulse train that was delivered to individual electrodes in a monopolar-coupled stimulation mode at stimulation levels ranging from subthreshold to C levels. Electrophysiological recordings of the onset eERP were obtained in all subjects. For studies evaluating the test-retest reliability of the onset eERP, responses were measured using the same set of parameters in two test sessions. The time interval between test sessions ranged from 2 to 6 months. The lowest stimulation level that could evoke the onset eERP was defined as the objective T level. RESULTS: Onset eERPs were recorded in all subjects tested in this study. Inter- and intrasubject variations in morphological characteristics of onset eERPs were observed. Onset eERPs with complex waveforms were recorded for electrodes that evoked nonauditory sensations, based on feedback from subjects, as well as for electrodes without any indications of nonauditory stimulations. Onset eERPs in patients with ABIs demonstrated good test-retest reliability. Increasing stimulation levels resulted in increased eERP amplitudes but showed inconsistent effects on response latencies in patients with ABIs. Objective and behavioral T levels were correlated. CONCLUSIONS: eERPs could be recorded in both non-NF2 and NF2 patients with ABIs. eERPs in both ABI patient groups show inter- and intrasubject variations in morphological characteristics. However, onset eERPs measured within the same subject in this study tended to be stable across study sessions. The onset eERP can potentially be used to estimate behavioral T levels in patients with ABIs. Further studies with more adult ABI recipients are warranted to investigate whether the onset eERP can be used to identify electrodes with nonauditory stimulations.

Clinical outcome of neurofibromatosis type 2-related vestibular schwannoma: treatment strategies and challenges.

To discuss the appropriate treatment strategy for NF2-related vestibular schwannoma (VS) according to our experiences, we analyzed long-term clinical and radiological data focusing on NF2-related VS patients. Seventeen NF2-related VS patients were included. Based on their first management modality for VS, we classified these patients into the following four groups: microsurgery (MS), fractionated gamma knife radiosurgery (f-GKS), single session gamma knife radiosurgery (s-GKS), and conservative management (CM). Each patient was assessed for each separate ear. Changes of tumor volume and hearing status for 32 ears in 17 patients according to their first treatment modality were evaluated. The mean follow-up duration and tumor volume of the MS (4 ears, 4 patients), f-GKS (12 ears, 10 patients), s-GKS (8 ears, 7 patients), and CM (8 ears, 7 patients) groups were 3.9 years and 1.6 mL; 5.1 years and 11.1 mL; 8.4 years and 5.6 mL; and 6.1 years and 1.6 mL, respectively. Relatively lower local control rates were observed in the MS and the CM group (0 and 12.5 %, respectively). On the other hand, better local control rates for follow-up periods of 5.1 and 8.4 years were achieved in the f-GKS and the s-GKS groups (75 and 50 %, respectively). However, hearing preservation in all treatment modalities could not be achieved effectively. Long-term preservation of hearing in at least one serviceable ear as well as tumor control should be considered for each patient. Therefore, a proper treatment option should be selected at the appropriate time according to clinical characteristics of individual patients.