Management of vestibular schwannomas (acoustic neuromas): the value of neurophysiology for evaluation and prediction of auditory function in 420 cases

Trigeminal neuralgia and risk of cancer: A population-based cohort study

BACKGROUND

Evidence of an association between trigeminal neuralgia (TN) and subsequent cancer risk remains sparse. The present study aimed to examine the association between TN and cancer risk in the Danish population.

METHODS

A nationwide population-based cohort study using hospital diagnoses collected routinely and prospectively from Danish population-based registries in 1994-2022.

RESULTS

We identified 7846 individuals with a first-time diagnosis of TN. Within one year of diagnosis, we observed 193 cancer cases (standardized incidence rate (SIR) = 2.45, 95% confidence interval (CI) = 2.11-2.82). Absolute risk (AR) for all cancers within one year of TN diagnosis was 2.5% (95% CI = 2.2-2.9). Cancers of the head, neck and nervous system were most strongly associated with TN (AR 0.9% (95% CI = 0.7-1.1); SIR = 13.5 (95% CI = 10.5-17.0)) and the risk was persistently elevated one year after TN diagnosis. We observed 827 cancer diagnoses beyond one year after TN diagnosis, where smoking related cancers were associated with elevated cancer risk (SIR 1.13 = (95% CI = 0.98-1.29)).

CONCLUSIONS

TN was associated with an elevated risk of cancers of the head, neck and nervous system including site-specific cancers in the area. Our results suggest the potential importance of smoking related tumors in TN, either as a symptom, cause or shared risk factor.

Intraoperative Hearing Monitoring Using ABR and TT-ECochG and Hearing Preservation during Vestibular Schwannoma Resection

Background: Quick and appropriate diagnostics and the use of intraoperative monitoring (IM) of hearing during vestibular schwannoma (VS) resection increase the likelihood of hearing preservation. During surgery, various methods of IM can be used, i.e., auditory brainstem responses (ABRs), transtympanic electrocochleography (TT-ECochG), and direct cochlear nerve action potentials. The aim of the study was to evaluate the prognostic values of IM of hearing using ABR and TT-ECochG in predicting postoperative hearing preservation and to evaluate relationships between them during various stages of surgery. Methods: This retrospective study presents the pre- and postoperative audiological test results and IM of hearing records (TT-ECochG and ABR) in 75 (43 women, 32 men, aged 18-69) patients with diagnosed VS. Results: The preoperative pure tone average hearing threshold was 25.02 dB HL, while after VS resection, it worsened on average by 30.03 dB HL. According to the American Academy of Otolaryngology-Head and Neck Surgery (AAO-HNS) Hearing Classification, before and after (pre/post) surgery, there were 47/24 patients in hearing class A, 9/8 in B, 2/1 in C, and 17/42 in D. In speech audiometry, the average preoperative speech discrimination score at an intensity of 60 dB SPL was 70.93%, and after VS resection, it worsened to 38.93%. The analysis of electrophysiological tests showed that before the tumor removal the I-V ABR interlatencies was 5.06 ms, and after VS resection, it was 6.43 ms. Conclusions: The study revealed correlations between worse postoperative hearing and changes in intraoperatively measured ABR and TT-ECochG. IM of hearing is very useful in predicting postoperative hearing in VS patients and increases the chance of postoperative hearing preservation in these patients.

Pathophysiology of Postoperative Hearing Disorders after Vestibular Schwannoma Resection: Insights from Auditory Brainstem Response and Otoacoustic Emissions

Background: In order to better understand the pathophysiology of surgically induced hearing loss after vestibular schwannoma (VS) surgery, we postoperatively analyzed the hearing status in a series of patients where hearing was at least partially preserved. Methods: Hearing was assessed through tonal audiometry, speech discrimination score, maximum word recognition score (dissyllabic word lists-MaxIS), otoacoustic emissions (OAEs), and auditory brainstem response (ABR). The magnetic resonance imaging (MRI) tumor characterization was also noted. Results: In a series of 24 patients operated on for VS over 5 years, depending on the results of this triple hearing exploration, we could identify, after surgery, patients with either a myelin alteration or partial damage to the acoustic fibers, others with a likely partial cochlear ischemia, and some with partial cochlear nerve ischemia. One case with persisting OAEs and no preoperative ABR recovered hearing and ABR after surgery. Long follow-up (73 ± 57 months) revealed a mean hearing loss of 30 ± 20 dB with a drastic drop of MaxIS. MRI revealed only 25% of fundus invasion. Conclusion: a precise analysis of hearing function, not only with classic audiometry but also with ABR and OEAs, allows for a better understanding of hearing damage in VS surgery.

Electrically evoked auditory responses: A classification for brainstem implant placement in Neurofibromatosis Type 2

OBJECTIVE

In auditory brainstem implant (ABI) surgery, array placement may be optimized by electrophysiological information of adequate brainstem activation gained from electrically evoked auditory brainstem responses (EABR). This study aims 1) to characterize in detail the EABR from ABI implantation, 2) to introduce an EABR Classification Scheme, and 3) to analyze data for their correlation with individual patients' findings.

METHODS

Out of a continuous series of 54 patients who received an ABI between 2005 and 2019, 23 Neurofibromatosis Type 2 patients with complete documentation of 154 recordings were selected for offline analysis and for development and evaluation of a new EABR Classification Scheme comprising Class A: three vertex positive peaks, Class B:two peaks, Class C: a combination of one peak and a second melted double peak, Class D: one sole vertex positive peak and Class E: no peaks.

RESULTS

All 23 subjects showed EABR at final ABI position and experienced auditory sensations at first activation. The most frequent morphology consisted of two peaks, Classes B and C. Identified mean latencies were for P1 0.42 ms (±0.095), P2 1.42 ms (±0.244) and P3 2.41 ms (±0.329). Peak latencies correlated positively with tumor extensions (p < 0.005).

CONCLUSIONS

This study provides clear instructions on optimal EABR performance and evaluation.

SIGNIFICANCE

The new EABR Classification Scheme relies on a fast "online" identification of vertex positive peaks at the estimated post-artifact phase. The variability in EABR morphology provides an individual snapshot of the actual structural and functional status of the brainstem.

Intraoperative brainstem auditory evoked potential monitoring during cerebellopontine angle surgery via retrosigmoid approach

OBJECTIVES

Brainstem auditory evoked potential (BAEP) monitoring was used to identify the influence of auditory function during cerebellopontine angle (CPA) surgery for cranial neuropathy via the retrosigmoid approach.

METHODS

This prospective study included 20 patients who underwent CPA surgery for cranial neuropathy via the retrosigmoid approach with intraoperative BAEP monitoring and pure tone audiometry (PTA). The latency and interpeak latency were analyzed at each surgical step in combination with the pre- and postoperative PTA.

RESULTS

Follow-up data were available for 17 patients. The mean pre- and postoperative PTA values were 25.65 dB and 20.70 dB, respectively. Two patients (2/17, 11.76%) developed hearing loss postoperatively. The latency of wave І significantly changed during direct auditory nerve manipulation and at the end of the surgery, while that of wave III only changed during direct auditory nerve manipulation. The appearance of wave V peak was delayed during CPA surgery.

CONCLUSIONS

CPA surgery for cranial neuropathy via the retrosigmoid approach can cause hearing loss to varying degrees, and intraoperative BAEP monitoring can reduce the occurrence of hearing loss. Intraoperative hearing function can be estimated by the latency of wave I. Hearing loss due to stretching of the brainstem can be estimated by the latency of wave III, and wave V is an early indicator of intraoperative hearing loss. Waves I and III remained stable both pre- and postoperatively, whereas wave V was unstable despite no surgery. Therefore, a precise operation and well-defined operative steps for surgeons during CPA surgery could facilitate maximal preservation of the anatomical structure and function.

Management of Vestibular Schwannoma with Normal Hearing

INTRODUCTION

This work aimed to study the management of vestibular schwannoma (VS) patients with normal hearing (NH).

METHODS

A retrospective study was undertaken in a Quaternary referral center for skull base pathologies. Among 4,000 VS patients 162 met our strict audiological criteria for NH. These patients were divided into 2 management groups, wait and scan (W&S) (45/162, 25%) and operated patients (123/162, 75%), and 6 patients were included in both groups.

RESULTS

Our management strategy achieved the goals for treatment of VS. First goal, all tumors were completely removed except for 2 intentional residuals. Second goal, facial nerve (FN) function preservation (House Brackmann I, II, and III) was 95.9%. Third goal, possible hearing preservation (HP) attempts occurred in (50/122) (40.9%) with an HP rate in 44% of the patients. Additionally, there were only 2 cases of postoperative complications with no CSF leakage. The prospect of HP in NH patients did not differ with respect to tumor size. However, patients with normal preoperative ABR seemed to have better chances of HP and good FN function and vice versa. HP rate was superior for the MCFA as opposed to the RS + RLA. W&S group demonstrated hearing stability in 88.9% of the patients and FN function stability of HB I in 100% of the patients.

CONCLUSIONS

Surgical resection is a reasonable and definitive management option for VS with NH. Nevertheless, choosing to manage cases with observation remains an appropriate management option for NH patients. ABR might be considered as an adjuvant tool indicating better prognosis for HP.

Diagnostic value and prognostic significance of MRI findings in sudden sensorineural hearing loss

Purpose

We evaluated the clinical significance of magnetic resonance imaging (MRI) findings and their prognostic value for initial hearing loss and recovery in patients with sudden sensorineural hearing loss (SSNHL).

Materials and Methods

This retrospective study included consecutive adult patients with unilateral SSNHL, contrast-enhanced MRI and audiometric testing evaluated in our institution between 2005 and 2017. MRI reports, patient data, treatment, and audiometric tests were reviewed, with the relationship between MRI findings and hearing loss/recovery analyzed.

Results

Overall, 266 patients were included. Additional symptoms comprised tinnitus (114/266; 43%), vertigo (45/266; 17%), ear pain (26/266; 10%), and ear pressure (6/266; 2%). At least one cardiovascular risk factor (hypertension, diabetes, hypercholesterolemia, cardiopathy, and active smoking) existed in 167/266 (63%) patients. Corticosteroid treatment was followed by 198/266 (74%) patients while contraindications/refusal/compliance precluded treatment in 68/266(26%). Complete, partial or slight hearing recovery occurred in 167/266 (63%) patients. Three MRI patient groups were identified: a group with normal MRI examinations or incidentalomas (128/266; 48%), a group with peripheral auditory system (PAS) lesions (95/266; 36%), and a group with central nervous system (CNS) lesions (43/266; 16%). PAS lesions included lesions from the cochlea to the brain stem (e.g., schwannoma, meningioma, labyrinthitis, intracochlear hemorrhage, vestibulocochlear neuritis), whereas CNS lesions corresponded in 42/43(98%) of cases to leukoaraiosis and other vascular lesions (e.g., stroke, hemorrhage, aneurysm, venous sinus thrombosis, and cavernoma). Belonging to one of the three MRI groups did not influence the degree of initial hearing loss, affected frequencies or treatment, p > .05. Gender and cardiovascular risk factors did neither affect initial hearing loss nor recovery. However, age > 70 years negatively affected initial hearing loss in all frequencies, as well as recovery in all frequencies except 1000 Hz. Also, poor recovery of initial high-frequency hearing loss (>1000 Hz) was significantly associated with CNS lesions.

Conclusion

Age > 70 years and CNS lesions depicted by MRI independently predicted poor auditory recovery, albeit in different frequencies.

Lay Summary

In patients with sudden hearing loss, older age (above 70 years) predicts poorer hearing recovery than in younger patients in most hearing frequencies. In addition, abnormalities of brain tissue revealed by MRI predict poorer hearing recovery at high frequencies.

Level of Evidence

Level III.

Hearing improvement after vestibular schwannoma surgery in the era of the hearing preservation rule - case report and literature review

OBJECTIVES

Hearing preservation after vestibular schwannoma (VS) surgery remains a surgical challenge. In some patients with preserved inner ear function, hearing improvement is achievable. As it is currently impossible to determine which patients will present this outcome, predictions must rely on previously published reports. Our case report describes a patient who experienced hearing improvement from an unuseful level to a useful one after vestibular schwannoma surgery.

METHODS

Surgery was performed via suboccipital retrosigmoid approach. The patient underwent a basic audiovestibular protocol before and after the surgery - pure tone and speech audiometry, otoacoustic emissions, auditory brainstem responses, electronystagmography - together with a detailed questionnaire study. Usefulness of hearing was evaluated using the AAO-HNS guidelines, supplemented by a frequency of 4 kHz.

RESULTS

Hearing was preserved and even improved from an unuseful level to a useful one. Based on the available literature, the most informative predictive factors for such a result seem to be: sudden sensorineural hearing loss prior to surgery, elicitable otoacoustic emissions and the origin from the superior vestibular nerve.

CONCLUSION

There are a limited number of studies on this topic and it is still impossible to regularly improve hearing in properly selected patients. Furthermore, the importance of postoperative hearing quality compared to other symptoms and complications remains debatable.

Hearing Preservation Microsurgery in Vestibular Schwannomas: Worth Attempting in "Larger" Tumors?

OBJECTIVES/HYPOTHESIS

To review hearing preservation after microsurgical resection of sporadic vestibular schwannomas according to tumor size.

STUDY DESIGN

Retrospective cohort.

METHODS

Baseline, intraoperative, and postoperative patient and tumor characteristics were retrospectively collected for a cohort who underwent hearing preservation microsurgery. Serviceable hearing was defined by a pure tone average ≤50 dB and word recognition score ≥50%.

RESULTS

A total of 243 patients had serviceable hearing preoperatively. Fifty (21%) tumors were confined to the internal auditory canal, and the median tumor size was 16.2 mm (interquartile range [IQR] 11.3-23.2) for tumors with cerebellopontine angle extension. Serviceable hearing was maintained in 64% of patients with tumors confined to the internal auditory canal, 28% with cerebellopontine angle extension <15 mm, and 9% with cerebellopontine angle extension ≥15 mm. On multivariable analysis, the odds ratios of acquiring nonserviceable hearing postoperatively for tumors extending <15 mm and ≥15 mm into the cerebellopontine angle were 5.75 (95% confidence interval [CI] 2.13-15.53; P < .001) and 22.11 (95% CI 7.04-69.42; P < .001), respectively, compared with intracanalicular tumors.

CONCLUSIONS

The strongest predictor of hearing preservation with microsurgery after multivariable adjustment is tumor size. Approximately 10% of patients with tumors ≥15 mm of cerebellopontine angle extension will retain serviceable hearing after microsurgery. Furthermore, hearing preservation techniques offer cochlear nerve preservation and cochlear patency allowing for possible future cochlear implantation. An attempt at hearing preservation, including avoiding surgical approaches that necessarily sacrifice hearing, is worthwhile even in larger tumors if serviceable hearing is present preoperatively.

LEVEL OF EVIDENCE

IV Laryngoscope, 2021.

Evolution in Surgical Treatment of Vestibular Schwannomas

Purpose of Review

Management of vestibular schwannomas (VSs) is multimodal and include watchful observation, radiation treatment, and surgery. Over the past decades, a shift in treatment strategy toward radiation treatment has gradually displaced surgery from the main treatment option for VS. In recent years, however, surgery has been further refined by developments of microsurgical and endoscopic techniques and advances in intraoperative application of neuroprotective drugs. This article presents outcomes of modern surgical treatment of VS in the era of radiosurgery and reviews recent published advancements relevant to VS management.

Recent Findings

Following VS surgery, excellent tumor resection rates and cranial nerve outcomes were achieved in a consecutive series of 572 adult patients with mean postoperative follow up of 4 years. Innovations in surgical technique include endoscopic technique as additional tool to microsurgery, exploration of semi-sitting position for large tumors, and intraoperative use of vasoactive agents as neuroprotective strategy.

Summary

Despite great developments in radiation treatment of VS, surgery remains the key solution for the majority of the cases in order to achieve cure of the disease, long-term tumor control, and preservation of cranial nerve function at long-term.

Detailed insight into transtympanic electrocochleography (TT-ECochG) and direct cochlear nerve action potential (CNAP) for intraoperative hearing monitoring in patients with vestibular schwannoma - methodology of measurements and interpretation of results

&lt;b&gt;Background:&lt;/b&gt; The aim was to present the methodology and interpretation of intraoperative hearing monitoring with simultaneous Transtympanic Electrocochleography (TT-ECochG) and direct Cochlear Nerve Action Potential (CNAP) measurements during vestibular schwannoma removal. &lt;br&gt;&lt;b&gt;Materials and Methods:&lt;/b&gt; Detailed methodology of measurements and interpretation of results are presented in three exemplary patients who underwent tumor removal via middle fossa approach (MFA) with the use of intraoperative monitoring of hearing with TT-ECochG and direct CNAP performed in real time. In addition, all responses were automatically recorded and stored along with surgical information and subjected to detailed analyses and calculation after surgery. &lt;br&gt;&lt;b&gt;Results:&lt;/b&gt; The following changes in TT-ECochG and direct CNAP responses were observed: Patient #1 - TT-ECochG and CNAP responses with minor, but transient, morphology changes (hearing was preserved); Patient #2 - CNAP responses changed significantly but, temporarily, from triphasic into biphasic responses later, with marked but partially reversible desynchronization of CNAP; changes in TT-ECochG responses were also observed but, at the end, returned to baseline (surgery-related deterioration of hearing); Patient #3 - irreversible changes of TT-ECochG and direct CNAP (complete loss of hearing). &lt;br&gt;&lt;b&gt;Conclusions:&lt;/b&gt; A combination of TT-ECochG and direct CNAP allows for real-time monitoring of auditory function during vestibular schwannoma resection and surgical manipulation which contribute to the risk of hearing loss. Therefore, the surgeon can be instantly informed about changes which could increase the possibility of preserving the patient's hearing.

Risk Stratification for Immediate Postoperative Hearing Loss by Preoperative BAER (Brainstem Auditory Evoked Response) and Audiometry in NF2-Associated Vestibular Schwannomas

Simple Summary

Hearing preservation is one of the major goals in the surgical treatment of Neurofibromatosis Type 2 (NF2) associated vestibular schwannomas (VS) and hearing diagnostics are important monitoring parameters and intraoperative tools to pursue this goal. Our monocentric retrospective analysis aimed to predict postoperative hearing deterioration or loss based on preoperative audiometry and neurophysiological (brainstem auditory evoked potentials, BAEP) findings. In this respect and according to our data evaluation in 100 NF2-associated VS of 72 patients both parameters seem to be prognostic markers, particularly BAEP findings. Large discrepancies between both audiometry and BAEPs which were identified in twenty-one cases of our cohort appear to be at high risk of significant postoperative hearing worsening.

Abstract

Both brainstem auditory evoked potentials (BAEP) and audiometry play a crucial role in neuro-oncological treatment decisions in Neurofibromatosis Type 2 associated (NF2) vestibular schwannoma (VS) as hearing preservation is the major goal. In this study, we investigated the risk of immediate postoperative hearing deterioration (>15 dB and/or 15% loss in pure-tone average [PTA]/ speech discrimination score [SDS] in a cohort of 100 operated VS (ears) in 72 NF2 patients by retrospective analysis of pre- and postoperative hearing data (PTA, SDS, American Association of Otolaryngology–Head and Neck Surgery [AAO-HNS], and brainstem auditory evoked potential [BAEP] class) taking into account relevant influencing factors, particularly preoperative audiometry and BAEP status and the extent of resection. Immediately after surgery, the hearing was preserved in 73% of ears and approximately ~60% of ears kept their hearing classes. Preoperative BAEP (p = 0.015) and resection amount (p = 0.048) significantly influenced postoperative hearing outcome. The prediction model for postoperative hearing deterioration/loss between preoperative BAEP and AAO-HNS class showed increased risk by increasing BAEP class. Twenty-one tumors/ears were identified with large BAEP and AAO-HNS class discrepancies (≥2 points) and were associated with a high (48–100%) risk of deafness after surgery in ears with preoperative available hearing. Overall, the results were heterogeneous but the better both BAEP and audiometry class before surgery, the higher the chance of hearing maintenance afterwards. Large resection amounts (e.g., 100% risk in near-total resections) exhibit a significant (p < 0.05) higher risk compared to smaller amounts (e.g., 10/20% in laser-coagulated/partially resected tumors). Our results emphasized the indispensable role of both hearing monitoring in form of audiometry and neurophysiology (BAEP) in the pre-and perioperative monitoring of NF2-associated VS. Both BAEP and audiometry are good prognostic markers for the postoperative hearing outcome. The extent of resection should be strictly guided by and adjusted to the intraoperative neurophysiological monitoring.

Electrophysiological predictors of hearing deterioration based on AEP monitoring during petroclival meningioma resection

The objective of this study was to calculate the risk of postsurgical hearing deterioration as a function of changes in the amplitude and latency of the most stable components (waves III and V) of the auditory evoked potential (AEP) during petroclival meningioma resection surgery. We retrospectively analyzed intraoperative AEP monitoring results and pre- and postsurgical hearing status in 40 consecutive patients who were surgically treated for petroclival meningiomas. Statistical analyses were conducted to identify the most sensitive and specific way to predict hearing dysfunction after surgery. Patients' mean age was 59 ± 10 years, and 31 (77.5%) were women. Twelve (30%) patients presented with clinically detectable hearing impairment preoperatively. At the first postoperative assessment, four of those 12 patients reported subjective improvement, and eight reported hearing deterioration. Of those eight, four remained stable and four recovered hearing by the last assessment. Wave III latency reached its highest specificity (100%) and sensitivity (71.43%) at x = 143%. Wave V latency, on the other hand, reached its highest sensitivity (71%) and specificity (93%) at x = 124%. Finally, wave V amplitude reached its highest sensitivity (100%) and specificity (79%) at x = 74%. Intraoperative alterations of wave III latency and wave V amplitude seem to be highly sensitive and specific at predicting the risk of auditory dysfunction in patients undergoing petroclival meningioma resection and should be used to determine maximum resection with preservation of function.

Managing NF2-associated vestibular schwannomas in children and young adults: review of an institutional series regarding effects of surgery and bevacizumab on growth rates, tumor volume, and hearing quality

We reviewed our experience in managing of NF2-associated vestibular schwannoma (VS) in children and young adults regarding the effect of surgery and postoperative bevacizumab treatment. A total of 579 volumetric and hearing data sets were analyzed. The effect of surgery on tumor volume and growth rate was investigated in 46 tumors and on hearing function in 39 tumors. Long-term hearing follow-up behavior was compared with 20 non-operated ears in additional 15 patients. Sixteen operated VS were treated with bevacizumab. Mutation analysis of the NF2 gene was performed in 25 patients. Surgery significantly slowed down VS growth rate. Factors associated with a higher growth rate were increasing patient age, tumor volume, and constitutional truncating mutations. Immediately after surgery, functional hearing was maintained in 82% of ears. Deterioration of hearing was associated with initial hearing quality, larger tumor volumes, and larger resection amounts. Average hearing scores were initially better in the group of non-operated VS. Over time, hearing scores in both groups worsened with a similar dynamic. During bevacizumab treatment of residual tumors, four different patterns of growth were observed. Decompression of the internal auditory canal with various degrees of tumor resection decreases the postoperative tumor growth rates. Carefully tailored BAEP-guided surgery does not cause additional hearing deterioration. Secondary bevacizumab treatment showed heterogenous effects both regarding tumor size and hearing preservation. It seems that postoperative tumor residuals, that grow slower, behave differently to bevacizumab than reported for not-operated faster growing VS.

Flexible endoscopic assistance in the surgical management of vestibular schwannomas

Endoscopic-assisted techniques have extensively been applied to vestibular schwannoma (VS) surgery allowing to increase the extent of resection, minimize complications, and preserve facial nerve and auditory functions. In this paper, we retrospectively analyze the effectiveness of flexible endoscope in the endoscopic-assisted retrosigmoid approach for the surgical management of VS of various sizes. The authors conducted a retrospective analysis on 32 patients who underwent combined microscopic and flexible endoscopic resection of VS of various sizes over a period of 16 months. Flexible endoscopic-assisted retrosigmoid approach was performed in all cases, and in 6 cases, flexible and rigid endoscopic control were used in combination to evaluate the differences between the two surgical instruments. The surgical results were additionally compared with a previous case series of 141 patients operated for VS of various sizes without endoscopic assistance. Gross-total resection was achieved in 84% of the cases and near-total resection was accomplished in the rest of them. Excellent or good facial nerve function was observed in all except one case with a preoperative severe facial palsy. Hearing preservation surgery (HPS) was attempted in 11 cases and accomplished in 9 (81.8%). A tumor remnant was endoscopically identified in the fundus of the IAC in all cases (100%). Endoscopic assistance increased the rate of total removal and no intrameatal residual tumor was seen at radiological follow-up. Comparative analysis with a surgical cohort of patients operated with the sole microsurgical technique showed a significative association between endoscopic assistance and intracanalicular extent of resection. Combined microsurgical and flexible endoscopic assistance provides remarkable advantages in the pursuit of maximal safe resection of VS and preservation of facial nerve and auditory functions, minimizing the risk of post-operative complications.

Impact of Surgery on Long-Term Results of Hearing in Neurofibromatosis Type-2 Associated Vestibular Schwannomas

Hearing preservation is a major goal in the treatment of neurofibromatosis type 2 (NF2) associated vestibular schwannoma (VS), particularly in children and adolescents. In this study, we retrospectively reviewed hearing and volumetry data sets of 39 operated tumors (ears) in 23 patients under the age of 25 and in a follow-up period of 21 to 167 months. Hearing data over a compatible period on 20 other tumors, which did not receive surgery due to their less aggressive nature, were included for comparison. Surgery was carried out via a retrosigmoid approach with the brainstem auditory evoked potential (BAEP) guide. Immediately after surgery, functional hearing was maintained in 82% of ears. Average hearing scores were better in the non-surgery ears. However, the hearing scores in both groups worsened gradually with a similar dynamic during the 42-month postoperative follow-up period. No accelerated impairment of hearing was evident for the operated cases. Rather, the gap between the two hearing deterioration lines tended to close at the end of the follow-up period. Our result suggested that the BAEP-guided surgery did not cause additional hearing deterioration in the long-term and seemed to slow down hearing deterioration of those tumors that were initially more aggressive.

The prediction of the tumor size of a vestibular schwannoma by clinical performance and vestibular function tests

PURPOSE

To investigate the relationship between vestibular schwannoma (VS) size and the dysfunction and compensation of the vestibular system.

METHODS

One hundred fifty-two patients with unilateral VS were investigated using multiple auditory-vestibular function tests such as audiometry, sensory organization test (SOT), caloric test, cervical vestibular-evoked myogenic potential (cVEMP) test, and ocular VEMP (oVEMP) test.

RESULTS

In this study, 89% of patients with unilateral VS had mild to severe hearing loss on the involved side. All patients showed higher threshold values or no response in the cVEMP and oVEMP tests, which both exhibited a lower response rate on the affected side than on the unaffected side. Patients with a tumor size ≥ 30 mm had significantly lower equilibrium scores for condition 5 and condition 6 of the SOT, which were associated with vestibular dysfunction, higher rates of canal paresis in the caloric test, and lower response rates in the cVEMP and oVEMP tests on the affected sides, compared with the results of patients with a tumor size ≤ 14 mm and patients with a tumor size of 15-29 mm.

CONCLUSIONS

A diameter > 30 mm may be the critical threshold at which vestibular function is affected and vestibular compensation is interfered with by a VS tumor. Functional performance of the vestibular system can help clinicians predict the size of a tumor and provide a basis for the development of treatment protocols.

Electrophysiology of Cranial Nerve Testing: Auditory Nerve

The electrocochleogram and brainstem auditory evoked potentials (BAEPs) are electrophysiologic signals used to assess the auditory nerve. The electrocohleogram includes the cochlear microphonic, the cochlear summating potential, and the eighth nerve compound action potential. It is used predominantly for hearing assessment and for diagnosis of Ménière disease and auditory neuropathy. Brainstem auditory evoked potentials are used for hearing assessment, diagnosis of dysfunction within the cochlea, the auditory nerve, and the brainstem auditory pathways up to the level of the mesencephalon, and intraoperative monitoring of these structures. The earliest BAEP component, wave I, and the eighth nerve compound action potential reflect the same process-the initial depolarization in the distal auditory nerve. Brainstem auditory evoked potential wave II receives contributions from the region of the cochlear nucleus and from the second depolarization in the distal auditory nerve. Wave III and later components are entirely generated rostral to the auditory nerve. Interpretation of BAEP studies is based on waves I, III, and V; auditory nerve dysfunction is manifested as prolongation of the I-III interpeak interval or absence of waves III and V. Eighth nerve tumors can cause a variety of BAEP abnormalities depending on which structures they affect. Adverse intraoperative BAEP changes can have many etiologies, including direct mechanical or thermal injury of tissue, ischemia (including cochlear ischemia or infarction due to compromise of the internal auditory artery), eighth nerve stretch, systemic or localized hypothermia, and artifactual BAEP changes due to technical factors.

Postoperative Tinnitus After Vestibular Schwannoma Surgery Depends on Preoperative Tinnitus and Both Pre- and Postoperative Hearing Function

Objective

Tinnitus is one of the most common symptoms before and/or after the surgical removal of a vestibular schwannoma (VS) affecting almost half of the patients. Although there is increasing evidence for the association of hearing impairment and VS-associated tinnitus, the effect of hearing deterioration due to surgery and its relation to the postoperative tinnitus (postTN) is poorly investigated. This knowledge, however, might (i) enlighten the pathophysiology of VS-associated tinnitus (i.e., peripheral or central origin) and (ii) improve preoperative patient counseling. The aim of this study was to understand the predisposition factors for a postTN in relation to hearing outcome after surgery.

Methods

This retrospective study analyzed the presence of tinnitus in 208 patients with unilateral VS before and after surgical removal. A binomial logistic regression was performed to ascertain the effect of pre- and postoperative hearing as well as age, gender, tumor side, and size, and intraoperative cochlear nerve resection (CNR) on the likelihood of postoperative VS-associated tinnitus.

Results

Preoperative tinnitus was the strongest predictor of postTN. In addition, deterioration of functional hearing was increasing, while functional deafferentation (i.e., postoperative hearing loss) of non-functional hearing was reducing the risk of postTN. At the same time, patients with no preoperative tinnitus but complete hearing loss had the lowest risk to suffer from postTN. Patient age, gender, tumor side, and size as well as CNR played a subordinate role.

Conclusion

While the presence of preoperative tinnitus was the strongest predictor of postTN, there is a distinct relationship between hearing outcome and postTN depending on the preoperative situation. Functional or anatomical deafferentation due to surgical tumor removal does not prevent postTN per se.

[Surgical indications and complications management in vestibular schwannoma]

BACKGROUND

Recent surgical treatment concepts for patients with vestibular schwannoma (VS) require an interdisciplinary approach as well as recognition and mastering of complications.

OBJECTIVE

This paper provides an overview of indications, as well as possible options for function preservation and management of complications in the surgical resection of these tumors.

METHODS

Up-to-date treatment concepts and surgical indications were differentiated according to size and extent of tumors. The frequency of important complications was extracted from the literature. Technical options to avoid and correct complications were compiled from personal experience and review of the literature.

RESULTS

Complications unrelated to cranial nerves are not infrequent, particularly in older patients. Small and medium-sized tumors that do not reach the fundus and cochlear fossa can be completely removed with good chances of hearing preservation. As long as these tumors do not grow, patients benefit from observation. Large tumors are overrepresented in surgical series compared to their prevalence. Postoperative facial nerve function correlates to tumor volume. Hearing preservation in these tumors is rare. Intraoperative electrophysiological techniques are valuable for attempted preservation of cranial nerve function. Persistent facial palsies can be remedied by dynamic and static interventions for facial rehabilitation.

CONCLUSION

Mortality and morbidity associated with surgical treatment of VS are very acceptable. Surgical concepts should be custom-tailored to the individual patient in order to ensure high quality of life.

Non-invasive intraoperative monitoring of cochlear function by cochlear microphonics during cerebellopontine-angle surgery

In vestibular-schwannoma (VS) surgery, hearing-preservation rate remains low. Besides damage to the cochlear nerve, intraoperative cochlear ischemia is a potential cause of hearing loss. Here, we used non-invasive cochlear microphonic (CM) recordings to detect the cochlear vascular events of VS surgery. Continuous intraoperative CM monitoring, in response to 80-95 dB SPL, 1-kHz tone-bursts, was performed in two samples of patients undergoing retrosigmoid cerebellopontine-angle surgery: one for VS (n = 31) and one for vestibular neurectomy or vasculo-neural conflict causing intractable trigeminal neuralgia, harmless to hearing (n = 19, control group). Preoperative and postoperative hearings were compared as a function of intraoperative CM changes and their chronology. Monitoring was possible throughout except for a few tens of seconds when drilling or suction noises occurred. Four patterns of CM time course were identified, eventless, fluctuating, abrupt or progressive decrease. Only the VS group displayed the last two patterns, mainly during internal-auditory-canal drilling and the ensuing tumor dissection, always with postoperative loss of hearing as an end result. Conversely, eventless and fluctuating CM patterns could be associated with postoperative hearing loss when the cochlear nerve had been reportedly damaged, an event that CM is not meant to detect. Cochlear ischemia is a frequent event in VS surgery that leads to deafness. The findings that CM decrease raised no false alarm, and that CM fluctuations, insignificant in control cases, were easily spotted, suggest that CM intraoperative monitoring is a sensitive tool that could profitably guide VS surgery.

Auditory Monitoring in Vestibular Schwannoma Surgery: Intraoperative Development and Outcome

OBJECTIVE

The auditory brainstem response (ABR) may be a predictor of postoperative cochlear nerve function. In this study, the course of intraoperative ABR monitoring was analyzed to find predictive markers for postoperative hearing function.

PATIENTS AND METHODS

From 2010 to 2012, 46 patients who had had vestibular schwannoma surgery were investigated by intraoperative ABR monitoring. The type of ABR development was identified: type A, improved or stable ABR; type B, fluctuating or deteriorated ABR; and type C, slow or sudden ABR loss. Hearing function was correlated with ABR monitoring.

RESULTS

The different types of ABR development showed a strong correlation with postoperative hearing (P < 0.001). ABR quality after 60% tumor removal was independently significant for hearing outcome. Possible interpretations are: 1) Independent of positive factors at the start of surgery at the final phase of tumor resection, what mattered for hearing outcome was the ABR quality (P < 0.001). 2) Dependence on ABR quality in the last phase might be a result of what the cochlear nerve has endured during resection. 3) The importance of ABR quality in the last phase might be because the tumor capsule is dissected from the nerves in that final phase.

ANALYSIS

of critical actions with incidence of ABR impairment showed that dissection in the internal auditory canal and drilling were most critical.

CONCLUSIONS

Intraoperative ABR development is a predictive factor for postoperative hearing outcome. Deterioration should be avoided, because ABR improvement as a result of good status at the beginning of surgery could not be assumed.

When Does Hearing Loss Occur in Vestibular Schwannoma Surgery? Importance of Auditory Brainstem Response Changes in Early Postoperative Phase

OBJECTIVE

Some patients suffer postoperative hearing loss even when the intraoperative auditory brainstem response (ABR) is preserved during vestibular schwannomas surgery. This study was conducted to evaluate whether there are dynamic changes of the ABR after surgery.

PATIENTS AND METHODS

In a prospective study from 2010-2012, 46 patients (24 female and 22 male) with vestibular schwannomas were investigated by intraoperative and postoperative ABR monitoring. Development of ABR quality during and after surgery (Class 1 normal, Class 5 complete loss) was correlated to auditory outcome.

RESULTS

At the end of surgery, 17 patients had an ABR Class 1-4 and 29 had Class 5. Four hours after surgery, 9 of 23 (39%) patients showed an ABR quality change, and 24 hours after surgery, 15 of 30 (50%) had undergone ABR quality changes. Four different types of postoperative ABR courses could be distinguished-Course 1: stable with reproducible ABR, Course 2: unstable with reproducible ABR, Course 3: unstable with ABR loss, and Course 4: stable with ABR loss. These courses correlated highly significantly with the intraoperative development (P < 0.001) and with hearing outcome (P = 0.003).

CONCLUSION

The study identifies ongoing changes of ABR quality and hearing function after the end of vestibular schwannoma surgery. Therefore it seems worthwhile to continue ABR monitoring in the postoperative phase in order to identify patients who are at risk of a secondary hearing deterioration and start therapeutic interventions in a timely manner.

Probabilistic Fiber-Tracking Reveals Degeneration of the Contralateral Auditory Pathway in Patients with Vestibular Schwannoma

BACKGROUND AND PURPOSE

Vestibular schwannomas cause progressive hearing loss by direct damage to the vestibulocochlear nerve. The cerebral mechanisms of degeneration or plasticity are not well-understood. Therefore, the goal of our study was to show the feasibility of probabilistic fiber-tracking of the auditory pathway in patients with vestibular schwannomas and to compare the ipsi- and contralateral volume and integrity, to test differences between the hemispheres.

MATERIALS AND METHODS

Fifteen patients with vestibular schwannomas were investigated before surgery. Diffusion-weighted imaging (25 directions) was performed on a 3T MR imaging system. Probabilistic tractography was performed for 3 partial sections of the auditory pathway. Volume and fractional anisotropy were determined and compared ipsilaterally and contralaterally. The laterality ratio was correlated with the level of hearing loss.

RESULTS

Anatomically reasonable tracts were depicted in all patients for the acoustic radiation. Volume was significantly decreased on the hemisphere contralateral to the tumor side for the acoustic radiation and diencephalic section, while fractional anisotropy did not differ significantly. Tracking did not yield meaningful tracts in 3 patients for the thalamocortical section and in 5 patients for the diencephalic section. No statistically significant correlations between the laterality quotient and classification of hearing loss were found.

CONCLUSIONS

For the first time, this study showed that different sections of the auditory pathway between the inferior colliculus and the auditory cortex can be visualized by using probabilistic tractography. A significant volume decrease of the auditory pathway on the contralateral hemisphere was observed and may be explained by transsynaptic degeneration of the crossing auditory pathway.

Management of vestibular schwannoma: A pilot case series with postoperative ABR monitoring

OBJECTIVE

Auditory brainstem response (ABR) monitoring is regularly used in surgery of vestibular schwannoma to achieve hearing preservation. Despite ABR preservation at the end of surgery, there are cases with postoperative deafness. To date it is unclear whether these are false positive ABR data or cases of secondary hearing loss. In this pilot study, we focused on the early postoperative phase and possible ABR changes in this period.

PATIENT AND METHOD

In a prospective study from March 2008 to April 2009, eleven patients (5 female and 6 male) with vestibular schwannoma and preoperative residual hearing were investigated by repeated postoperative ABR investigation at seven dates during the first week. ABR results, hearing function and tumor extension were categorized according to Hannover classification system. The postoperative developments of the first week after surgery are described.

RESULTS

Hearing preservation was achieved in 55% (6 of 11) of the patients. In the early postoperative phase, three patients with an ABR loss at the end of surgery showed some kind of recovery. In one case, a permanent recovery could be reproduced and developed step by step during the early postoperative phase. Three patients showed a postoperative deterioration resulting in a complete ABR loss. In one of these cases, it was probably a technical problem, but in the two other cases it was a real impairment. In 8 of 11 ABR, quality changed considerably during the early postoperative phase.

CONCLUSION

This pilot study identifies considerable change of ABR formation occurring in a considerable proportion of patients early after vestibular schwannoma resection. Obviously, in some patients, the endoperative state of the ABR is not the final state. Some patients show a postoperative improvement and some a deterioration towards a complete loss of all ABR components. Whether secondary hearing loss could be presented by early detection, will be a matter of further studies.

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

OBJECTIVE

Guidelines for appropriate management of vestibular schwannomas in NF2 patients are controversial. In this paper we reviewed our experience with patients with NF2 for the results of surgical treatment with particular reference to hearing and facial nerve preservation.

METHODS

We included in the study 30 patients (16 women and 14 men) with the diagnosis of NF2 treated in our department between 1998 and 2014 who underwent surgery for vestibular schwannoma removal with a follow-up for at least 1 year. In 3 cases, the vestibular schwannomas were unilateral. Six patients with bilateral vestibular schwannomas underwent unilateral procedure. Therefore, 51 acoustic tumors were studied in 30 patients.

RESULTS

No operative death we noted. Significant deterioration to the non-functional level occurred in 19 out of 22 cases with well-preserved preoperative hearing. Only three ears maintained their preoperative good hearing. Hearing was preserved in cases of small schwannoma not exceeding 2 cm. Among 21 patients who underwent bilateral operations hearing was preserved in 3 out of 7 cases when smaller tumor or better hearing level side was attempted at first surgery. In contrary none of the 14 patients retained hearing when the first operation concerned the worse-hearing ear. Among 14 tumors up to 2 cm there was only one case of moderately severe facial nerve dysfunction (House-Brackmann Grade IV) in the long follow-up.

CONCLUSION

Early surgical intervention for vestibular schwannoma in NF2 patient is a viable management strategy to maintain hearing function and preserve facial nerve function.

Preoperative balance control compensation in patients with a vestibular schwannoma: does tumor size matter?

OBJECTIVE

The influence of tumor size on postural control of patients with vestibular schwannoma (VS) remains to be determined. This study aimed to compare the postural performances of VS patients, according to the size of the tumor, with healthy subjects.

METHODS

The six conditions (C1-C6) of the sensory organization test (SOT) were carried out in 87 patients, split into four groups according to the Koos classification (stage I-IV), and in 72 aged-matched controls to evaluate postural control. The vestibular reflectivity and compensation were estimated with videonystagmography.

RESULTS

Among patients, lower C5 and C6 scores were found in stage I and IV patients than in stage II and III patients, whereas vestibular compensation did not impact the tumor size influence on the postural control. The scores were significantly (p<0.001) lower for all the groups of patients than the controls in the vestibular-related SOT conditions (C5-C6).

CONCLUSIONS

Patients with an unilateral VS displayed altered postural performances compared to the control subjects and tumor size had a bell-like pattern effect on balance control.

SIGNIFICANCE

The tumor size could be seen as a determining factor in the implementation of adaptive mechanisms that lead to the postural compensation and might be dissociated from vestibular compensation.

Superiority of tympanic ball electrodes over mastoid needle electrodes for intraoperative monitoring of hearing function

Object

Recording the auditory brainstem response (ABR) is a common method for monitoring the integrity of auditory pathways during surgery in the cerebellopontine angle. Electrocochleography (ECochG) is an alternative means of intraoperative neuromonitoring. In the present study the authors compared the practicability and prognostic significance of these two methods by performing simultaneous recordings in the operating room.

Methods

Between 2006 and 2011, 125 patients (mean age 55 years) underwent surgery in the cerebellopontine angle. Seventy-one percent of the patients presented with a hearing deficit, and 37% had useful hearing but with slight functional impairment. Auditory brainstem response was recorded with a subdermal needle electrode at the mastoid. For ECochG recording, a noninvasive ball electrode was attached to the tympanic membrane. Amplitudes obtained from both ECochG and ABR audiometry were compared and correlated to pre- and postoperative hearing deficits.

Results

Simultaneous intraoperative monitoring via ABR and ECochG was possible in 114 cases (91%). Postoperatively, 42% of patients showed some degree of new hearing deficit, whereas 4% had improvement. The mean amplitudes in ECochG monitoring were significantly higher (0.18 ± 0.04 μV) than the ABR potentials (0.08 ± 0.006 μV; p < 0.05). All waves recorded at the mastoid needle electrode could be recognized in the potentials of the tympanic ball electrode. Hearing outcome correlated more reliably with the relative amplitude changes in Waves III and V in ECochG (III: p = 0.0008, V: p = 0.0015) than in ABR monitoring (III: p = 0.2075, V: p = 0.0398).

Conclusions

Intraoperative monitoring of the auditory system by recording with noninvasive tympanic ball electrodes is more practicable than with subcutaneous needle electrodes at the tragus. Since there is also a reliable correlation between ECochG and clinical outcome, the method can replace common ABR recording during surgery in the cerebellopontine angle.

Interaural Difference of Wave V Predicting Postoperative Hearing in Gardner-Robertson Class II Acoustic Neuroma Patients

Patients with acoustic neuroma classified in Gardner and Robertson (GR) Class II should be considered to have useful hearing, and patients classified in Class III should be considered to have not-useful hearing. Therefore, it is important for acoustic neuroma surgery to distinguish between postoperative GR Class II and Class III patients by brainstem auditory evoked potentials (BAEPs). We evaluate which BAEP parameter is the best for predicting postoperative GR Class II or III in 36 preoperative GR Class II patients with unilateral acoustic neuroma. Delay in wave V latency, reduction ratio in wave V amplitude, and interaural difference of wave V (IT5) are evaluated by a receiver-operating characteristic (ROC) curve in this study. IT5 is the best distinguishing parameter between postoperative Class II and Class III. IT5 below 1.12 millisecond (msec) should be a good marker to preserve postoperative useful hearing. Thus, comparing the latency of wave V on both sides is important, and surgeons would be able to make more informed decisions during surgery by checking IT5 on BAEPs.

Preoperative characteristics of auditory brainstem response in acoustic neuroma with useful hearing: importance as a preliminary investigation for intraoperative monitoring

We classified the results of preoperative auditory brainstem response (ABR) in 121 patients with useful hearing and considered the utility of preoperative ABR as a preliminary assessment for intraoperative monitoring. Wave V was confirmed in 113 patients and was not confirmed in 8 patients. Intraoperative ABR could not detect wave V in these 8 patients. The 8 patients without wave V were classified into two groups (flat and wave I only), and the reason why wave V could not be detected may have differed between the groups. Because high-frequency hearing was impaired in flat patients, an alternative to click stimulation may be more effective. Monitoring cochlear nerve action potential (CNAP) may be useful because CNAP could be detected in 4 of 5 wave I only patients. Useful hearing was preserved after surgery in 1 patient in the flat group and 2 patients in wave I only group. Among patients with wave V, the mean interaural latency difference of wave V was 0.88 ms in Class A (n = 57) and 1.26 ms in Class B (n = 56). Because the latency of wave V is already prolonged before surgery, to estimate delay in wave V latency during surgery probably underestimates cochlear nerve damage. Recording intraoperative ABR is indispensable to avoid cochlear nerve damage and to provide information for surgical decisions. Confirming the condition of ABR before surgery helps to solve certain problems, such as choosing to monitor the interaural latency difference of wave V, CNAP, or alternative sound-evoked ABR.

A-trains for intraoperative monitoring in patients with recurrent vestibular schwannoma

BACKGROUND

Second surgery of recurrent vestibular schwannoma (VS) after previous surgery, stereotactic radiosurgery (SR) or fractionated radiotherapy (FR) carries an increased risk for deterioration of facial nerve function, e.g., due to adhesions, underlining the need for intraoperative monitoring. Facial “Atrain” EMG activity (“traintime”) correlates with the degree of postoperative facial palsy. Studies investigating A-trains in VS patients with previous surgery, SR or FR are missing. We therefore investigated the value of A-train monitoring in patients undergoing second surgery for VS.

METHOD

Intraoperative EMG data from patients who underwent second surgery for VS after previous surgery, SR and/or FR at our institution between 2006 and 2012 were retrospectively analyzed. Ten patients were selected (5 male): Seven had previous SR/RT and MS, three previous surgery only. Traintime values and distribution was compared to published thresholds and to 77 patients who underwent first surgery for VS during the same time period.

RESULTS

A-trains were recorded early after opening of the dura, before facial nerve preparation. Mean traintime was 46.9 s (18.51 s – 80.82 s) in patients with previous SR/RT. In patients with previous MS only, traintime was 0.06 s, 0.99 s and 22.46 s. Compared to the literature, traintime was higher than expected in six patients (four with previous SR/RT, two without), respectively seven compared to the 77 patients with first surgery (5 SR/RT). Seven patients with previous SR/RT and none with previous surgery showed diffuse A-train distributions without significant percentages in single channels, compared to 60 of 77 patients with first surgery (p <0.02).

CONCLUSIONS

Especially SR/RT, but also previous surgery seems to induce changes in the facial nerve leading to hyperexcitability and exceedingly high traintime values. Based on these findings, A-train monitoring in this specific patient group should be interpreted with caution.

Positive auditory cortical responses in patients with absent brainstem response

OBJECTIVE

To compare the detectability of the different auditory evoked responses in patients with retrocochlear lesion.

METHODS

The 40-Hz auditory steady state response (ASSR) and the N1m auditory cortical response were examined by magnetoencephalography in 4 patients with vestibular schwannoma, in whom the auditory brainstem response (ABR) was absent.

RESULTS

Apparent N1m responses were observed despite total absence of the ABR or absence except for small wave I in all patients, although the latency of N1m was delayed in most patients. On the other hand, clear ASSFs could be observed only in one patient. Very small 40-Hz ASSFs could be detected in 2 patients (amplitude less than 1fT), but no apparent ASSFs were observed in one patient, in whom maximum speech intelligibility was extremely low and the latency of N1m was most prolonged.

CONCLUSION

The N1m response and 40-Hz ASSR could be detected in patients with absent ABR, but the N1m response appeared to be more detectable than the 40-Hz ASSR.

SIGNIFICANCE

Combined assessment with several different evoked responses may be useful to evaluate the disease conditions of patients with retrocochlear lesions.

Facial nerve schwannoma arising from the cerebellopontine angle

A 74-year-old female suffered hearing disturbance in the right ear persisting for several years, followed by sudden onset of right facial nerve palsy. Her symptoms gradually worsened and neuroradiological imaging revealed a 4-cm cerebellopontine angle (CPA) tumor. Intraoperatively, the tumor was found to originate from the facial nerve. Total removal of the tumor was achieved, followed by a split hypoglossal-facial nerve anastomosis. Facial nerve schwannomas are rare and extremely difficult to preoperatively distinguish from vestibular schwannomas, especially if arising from the CPA and the internal auditory canal. However, preoperative diagnosis of facial nerve schwannomas is important because functional preservation of the facial nerve is more challenging than for vestibular schwannomas. Facial nerve palsy is one of the most unique symptoms in patients with facial nerve schwannomas, but is rare with vestibular schwannomas. Facial nerve schwannomas should be included in the differential diagnosis of CPA tumors with atypical clinical manifestations, and patients should be informed before surgery of the possibility of facial nerve dysfunction and the consequent need for facial nerve graft or reconstruction.

Intraoperative neuromonitoring techniques in the surgical management of acoustic neuromas

Unfavorable outcomes such as facial paralysis and deafness were once unfortunate probable complications following resection of acoustic neuromas. However, the implementation of intraoperative neuromonitoring during acoustic neuroma surgery has demonstrated placing more emphasis on quality of life and preserving neurological function. A modern review demonstrates a great degree of recent success in this regard. In facial nerve monitoring, the use of modern electromyography along with improvements in microneurosurgery has significantly improved preservation. Recent studies have evaluated the use of video monitoring as an adjunctive tool to further improve outcomes for patients undergoing surgery. Vestibulocochlear nerve monitoring has also been extensively studied, with the most popular techniques including brainstem auditory evoked potential monitoring, electrocochleography, and direct compound nerve action potential monitoring. Among them, direct recording remains the most promising and preferred monitoring method for functional acoustic preservation. However, when compared with postoperative facial nerve function, the hearing preservation is only maintained at a lower rate. Here, the authors analyze the major intraoperative neuromonitoring techniques available for acoustic neuroma resection.

Meningiomas, nerve sheath tumors, and pituitary tumors: diagnosis and treatment

This article gives an overview of meningiomas, pituitary tumors, and intracranial nerve sheath tumors as regards epidemiology, diagnosis, and treatment. Discussion includes the definition of these tumors and their symptomatology, diagnostic procedures, treatment options, surgical techniques, and outcomes.

Tracking the expression of excitatory and inhibitory neurotransmission-related proteins and neuroplasticity markers after noise induced hearing loss

Excessive exposure to loud noise can damage the cochlea and create a hearing loss. These pathologies coincide with a range of CNS changes including reorganisation of frequency representation, alterations in the pattern of spontaneous activity and changed expression of excitatory and inhibitory neurotransmitters. Moreover, damage to the cochlea is often accompanied by acoustic disorders such as hyperacusis and tinnitus, suggesting that one or more of these neuronal changes may be involved in these disorders, although the mechanisms remain unknown. We tested the hypothesis that excessive noise exposure increases expression of markers of excitation and plasticity, and decreases expression of inhibitory markers over a 32-day recovery period. Adult rats (n = 25) were monaurally exposed to a loud noise (16 kHz, 1/10(th) octave band pass (115 dB SPL)) for 1-hour, or left as non-exposed controls (n = 5). Animals were euthanased at either 0, 4, 8, 16 or 32 days following acoustic trauma. We used Western Blots to quantify protein levels of GABA(A) receptor subunit α1 (GABA(A)α1), Glutamic-Acid Decarboxylase-67 (GAD-67), N-Methyl-D-Aspartate receptor subunit 2A (NR2A), Calbindin (Calb1) and Growth Associated Protein 43 (GAP-43) in the Auditory Cortex (AC), Inferior Colliculus (IC) and Dorsal Cochlear Nucleus (DCN). Compared to sham-exposed controls, noise-exposed animals had significantly (p<0.05): lower levels of GABA(A)α1 in the contralateral AC at day-16 and day-32, lower levels of GAD-67 in the ipsilateral DCN at day-4, lower levels of Calb1 in the ipsilateral DCN at day-0, lower levels of GABA(A)α1 in the ipsilateral AC at day-4 and day-32. GAP-43 was reduced in the ipsilateral AC for the duration of the experiment. These complex fluctuations in protein expression suggests that for at least a month following acoustic trauma the auditory system is adapting to a new pattern of sensory input.

Use of piezosurgery for internal auditory canal drilling in acoustic neuroma surgery

BACKGROUND

Piezosurgery is based on microvibrations generated by the piezoelectrical effect and has a selective bone-cutting ability with preservation of soft tissue. This study examined the applicability of Piezosurgery compared to rotating drills (RD) for internal auditory canal (IAC) opening in acoustic neuroma (AN) surgery.

MATERIALS AND METHODS

Piezosurgery was used in eight patients for IAC drilling in AN surgery. After exposition of the IAC and tumor, the posterior wall of the IAC was drilled using Piezosurgery instead of RD. Piezosurgery was evaluated with respect to practicability, safety, preciseness of bone cutting, preservation of cranial nerves, influences on neurophysiological monitoring, and facial nerve and hearing outcome.

RESULTS

Piezosurgery was successfully used for selective bone cutting, while cranial nerves were structurally and functionally preserved, which could be measured by means of neuromonitoring. Piezosurgery guaranteed a safe and precise cut by removing bone layer by layer in a shaping way. Compared to RD, limited influence on neurophysiological monitoring attributable to Piezosurgery was noted, allowing for continuous neuromonitoring. No disadvantage due to microvibrations was noticed concerning hearing function. The angled tip showed better handling in right-sided than in left-sided tumors in the hands of a right-handed surgeon. The short, thick handpiece may be improved for more convenient handling.

CONCLUSION

Piezosurgery is a safe tool for selective bone cutting for opening of the IAC with preservation of facial nerve and hearing function in AN surgery. Piezosurgery has the potential to replace RD for this indication because of its safe and precise bone-cutting properties.

Quantitative parameters of facial motor evoked potential during vestibular schwannoma surgery predict postoperative facial nerve function

BACKGROUND

Facial motor evoked potential (FMEP) amplitude ratio reduction at the end of the surgery has been identified as a good predictor for postoperative facial nerve outcome. We sought to investigate variations in FMEP amplitude and waveform morphology during vestibular schwannoma (VS) resection and to correlate these measures with postoperative facial function immediately after surgery and at the last follow-up.

METHODS

Intraoperative orbicularis oculi and oris muscles FMEP data from 35 patients undergoing surgery for VS resection were collected, then analysed by surgical stage: initial, dural opening, tumour dissection (TuDis), tumour resection (TuRes) and final.

FINDINGS

Immediately after surgery, postoperative facial function correlated significantly with the FMEP amplitude ratio during TuDis, TuRes and final stages in both the orbicularis oculi (p = 0.003, 0.055 and 0.028, respectively) and oris muscles (p = 0.002, 0.104 and 0.014, respectively). At the last follow-up, however, facial function correlated significantly with the FMEP amplitude ratio only during the TuDis (p = 0.005) and final (p = 0.102) stages for the orbicularis oris muscle. At both time points, postoperative facial paresis correlated significantly with FMEP waveform deterioration in orbicularis oculi during the final stage (immediate, p = 0.023; follow-up, p = 0.116) and in orbicularis oris during the TuDis, TuRes and final stages (immediate, p = 0.071, 0.000 and 0.001, respectively; follow-up, p = 0.015, 0.001 and 0.01, respectively).

CONCLUSIONS

FMEP amplitude ratio and waveform morphology during VS resection seem to represent independent quantitative parameters that can be used to predict postoperative facial function. Event-to-baseline FMEP monitoring is quite useful to dictate when intraoperative changes in surgical strategy are warranted to reduce the chances of facial nerve injury.

Intraoperative brainstem auditory evoked potential observations after trigeminocardiac reflex during cerebellopontine angle surgery

BACKGROUND

The occurrence of trigeminocardiac reflex (TCR) is known to be a negative prognostic factor for hearing preservation in cerebellopontine angle tumor surgery. Our study was conducted to investigate brainstem auditory evoked potential (BAEP) changes after this reflex in cerebellopontine angle tumor surgery and to evaluate their impact on postoperative hearing function.

METHODS

Five of 102 consecutive patients had an intraoperative TCR (4.9%) and were retrospectively evaluated for the intraoperative BAEP changes after TCR and postoperative auditory function (7 to 10 d after surgery). One of the 5 patients was preoperatively deaf and therefore excluded from this analysis.

RESULTS

Four patients with preoperative functional hearing developed one or more episodes of TCR. Intraoperative BAEP was maintained in 1 patient, whereas in 3 cases an acute intraoperative BAEP deterioration occurred within 2:04 to 3:27 minutes (mean 2:44 min) after TCR with increased wave latency, decreased wave amplitude, and even wave loss. Two patients had deteriorated BAEP waves until the surgical completion and were postoperatively deaf.

CONCLUSIONS

Although no direct cause-effect relationship has yet been shown, we suggest TCR as an additional event that may cause BAEP changes. The observed BAEP alterations occurred minutes rather than seconds after the TCR incident leading to both temporary and permanent wave deterioration. This association of BAEP deterioration and TCR occurrence, however, remains yet to be proven justifying further study in the field.

Transcranial Electrocortical Stimulation to Monitor the Facial Nerve Motor Function During Cerebellopontine Angle Surgery

OBJECTIVE

This study was conducted to investigate the success rate of using the facial motor evoked potential (FMEP) of orbicularis oculi and oris muscles for facial nerve function monitoring with use of a stepwise protocol, and its usefulness in predicting facial nerve outcome during cerebellopontine angle (CPA) surgeries.

METHODS

FMEPs were recorded intraoperatively from 60 patients undergoing CPA surgeries. Transcranial electrocortical stimulation (TES) was performed using corkscrew electrodes positioned at hemispheric montage (C3/C4 and CZ). The contralateral abductor pollicis brevis muscle was used as the control response. Stimulation was always applied contralaterally to the affected side using 1, 3, or 5 rectangular pulses ranging from 200 to 600 V with 50 μs of pulse duration and an interstimulus interval of 2 ms. Facial potentials were recorded from needles placed in the orbicularis oculi and oris muscles.

RESULTS

FMEP from the orbicularis oris and oculi muscles could be reliably monitored in 86.7% and 85% of the patients, respectively. The immediate postoperative facial function correlated significantly with the FMEP ratio in the orbicularis oculi muscle at 80% amplitude ratio (P = .037) and orbicularis oris muscle at 35% ratio (P = .000). FMEP loss was always related to postoperative facial paresis, although in different degrees.

CONCLUSION

FMEPs can be obtained reliably by using TES with 3 to 5 train pulses. Stable intraoperative FMEPs can predict a good postoperative outcome of facial function. However, further refinements of this technique are necessary to minimize artifacts and to make this method more reliable.

An anatomical assessment of the supracerebellar midline and paramedian approaches to the inferior colliculus for auditory midbrain implants using a neuronavigation model on cadaveric specimens

The inferior colliculus (IC) is an alternative site for electrode placement in neural deafness due to its surgical accessibility and its well-known tonotopic stratification. In patients where tumor surgery has already occurred and the cerebellopontine angle contains scar tissue or tumor-remnants, midline and paramedian supracerebellar approaches are alternative routes. They are often avoided due to concerns regarding the venous drainage of the cerebellum, the electrode trajectory and the course of the electrode cable. We studied these surgical routes in five neuronavigated fixed cadaveric specimens. For paramedian and midline approaches, the transverse sinus was exposed 5.8mm on average. A mean of 1.6 cerebellar veins, with an average diameter of 2.0mm, draining to the tentorium were transected to reach the tentorial notch. Only 0.4 arterial branches were met. We conclude that the supracerebellar midline and paramedian approaches provide a good exposure of the IC and offer safe and viable alternative routes to the IC. Additionally, they provide a wider angle of action for optimal electrode placement.