Cerebellopontine Angle Tumor Surgery Research Articles

Predictive value of Blink reflex and facial corticobulbar motor evoked potential in cerebellopontine angle tumor surgery

ObjectiveThe current study examined the efficacy of the facial corticobulbar motor evoked potentials (FCoMEPs) and blink reflex (BR) on predicting postoperative facial nerve function during cerebellopontine angle (CPA) tumor surgery. MethodsData from 110 patients who underwent CPA tumor resection with intraoperative FCoMEPs and BR monitoring were retrospectively reviewed. The association between the amplitude reduction ratios of FCoMEPs and BR at the end of surgery and postoperative facial nerve function was determined. Subsequently, the optimal threshold of FCoMEPs and BR for predicting postoperative facial nerve dysfunction were determined by receiver operating characteristic curve analysis. ResultsValid BR was record in 103 of 110 patients, whereas only 43 patients successfully recorded FCoMEP in orbicularis oculi muscle. A reduction over 50.3% in FCoMEP (O. oris) amplitude was identified as a predictor of postoperative facial nerve dysfunction (sensitivity, 77.1%; specificity, 83.6%). BR was another independent predictor of postoperative facial nerve deficit with excellent predictive performance, especially eyelid closure function. Its optimal cut-off value for predicting long-term postoperative eyelid closure dysfunction was was 51.0% (sensitivity, 94.4%; specificity, 94.4%). ConclusionsBR can compensate for the deficiencies of the FCoMEPs. The combination of BR and FCoMEPs can be used in CPA tumor surgery. SignificanceThe study first proposed an optimal cut-off value of BR amplitude deterioration (50.0%) for predicting postoperative eyelid closure deficits in patients undergoing CPA tumor surgery.

Facial nerve electrical motor evoked potential in cerebellopontine angle tumors for its anatomical and functional preservation.

Among the technical measures to preserve facial nerve (FN) function, intraoperative neuromonitoring has become mandatory and is constantly being scrutinized. Hence, to determine the efficacy of FN motor evoked potentials (FNMEPs) in predicting long-term motor FN function following cerebellopontine angle (CPA) tumor surgery, an analysis of cases was done. In 37 patients who underwent CPA surgery, FNMEPs through corkscrew electrodes positioned at C5-C6 and C6-C5 (C is the central line of the brain as per 10-20 EEG electrode placement) were used to deliver short train stimuli and recorded from the orbicularis oculi, oris, and mentalis muscles. In 58 patients, triggered electromyography (EMG) was able to identify the FN during resection of tumor, but 8 out of these (4.64%) patients developed new facial weakness, whereas 3 out of 38 (1.11%) patients who had intact FN function MEP (decrement of FN target muscles - CMAPs amplitude peak to peak >50-60%), developed new facial weakness (House and Brackmann grade II to III). The FNMEP has significant superiority over triggered EMG when tumor is giant and envelops the FN.

Unexpected polyuria in a neurosurgical patient undergoing cerebellopontine angle tumor surgery: Can dexmedetomidine be the culprit?

Unexpected polyuria in a neurosurgical patient undergoing cerebellopontine angle tumor surgery: Can dexmedetomidine be the culprit?

Emergent Revascularization After Transposition of an Unexpected Intraosseous Anomalous Subarcuate Loop During Vestibular Schwannoma Surgery: A Case Report

BACKGROUND AND IMPORTANCE: The presence of an anomalous anteroinferior cerebellar artery (AICA) embedded within the subarcuate fossa increases the difficulty of cerebellopontine angle (CPA) tumor surgery. Iatrogenic injury of posterior fossa arteries can result in serious morbidity. CLINICAL PRESENTATION: A 70-year-old man presented with right-sided hearing loss and facial dysesthesia. Magnetic resonance imaging showed a tumor with solid and cystic components and 35-mm maximum diameter in the right CPA. The AICA traveled just dorsal to the tumor and was well-developed because the ipsilateral vertebral artery and posteroinferior cerebellar artery (PICA) were aplastic. During surgery, we unexpectedly encountered an anomalous loop of the AICA-PICA which was embedded in the subarcuate fossa. This loop was mobilized using an ultrasonic bone curette to enable further tumor resection. However, it occluded immediately after mobilization and required open thrombectomy and end-to-end anastomosis. After revascularization, near-complete tumor resection was achieved without causing facial nerve dysfunction or brainstem/cerebellar infarction. Pathological examination of the resected anomalous loop showed abnormal focal hypertrophy of the adventitia and the presence of external elastic lamina. CONCLUSION: Mobilization of an anomalous AICA-PICA loop embedded within the subarcuate fossa during VS resection can result in arterial occlusion which requires thrombectomy and revascularization. Surgeons should be aware of this vascular anomaly and be prepared to deal with its ramifications.

Comparing intraoperative hemodynamics and medication use during cranial nerve monitoring with partial muscle relaxants versus without in cerebellopontine angle tumors: a randomized controlled trial

BackgroundThere are many methods used for cranial nerve monitoring in cerebellopontine angle (CPA) tumor excision with or without muscle relaxant which may affect hemodynamics and consumption of drug doses. The partial neuromuscular blockade, on the other hand, appears to be compatible with monitoring in some patients, according to clinical experience. In this study, we evaluated hemodynamic changes and drug consumption differences between partial and without muscle relaxants.Forty patients ages ranging from 18 to 60 years old had CPA surgery and were given either a muscle relaxant to maintain neuromuscular blockade level train-of-four (TOF) count two (group A) or a placebo of normal saline to maintain train-of-four (TOF) count four (group B). Fentanyl was given to both groups. The dose of fentanyl was modified to 0.5–1 mcg\\kg/h, while the dose of propofol was modified to have bi-spectral index between 40 and 60. The total amount of propofol and fentanyl, as well as mean blood pressure and heart rate, are all measured intraoperatively.ResultsThere was a statistically significant difference in propofol and fentanyl doses between both research groups (p = 0.003, p = 0.002) respectively during the intraoperative period. Furthermore, there is a difference in as there were significant differences between two groups in time between stop of anesthesia and eye opening which is shorter in group with partial muscle relaxant reflecting shorter duration of anesthesia and recovery time (stop anesthesia to eye opening time) (p = 0.003, p > 0.001) respectively. Also, there was no statistically significant difference in the incidence of nausea and vomiting, shivering, bradycardia, or hypotension between the two study groups.ConclusionsWe demonstrated that partial muscle relaxant (train of four count 2) has benefits over no muscle relaxant (train of four count 4) for patients undergoing cerebellopontine angle tumor surgery because it can reduce anesthetic duration and generate rabid recovery. Furthermore, partial muscle relaxants exhibit the same hemodynamic stability, side effects, and surgical interruptions as group without muscle relaxants.

Anticipating Facial Nerve Position Using Three-Dimensional Tractography During the Preoperative Assessment of Cerebellopontine Angle Tumors

We aim to evaluate the usefulness of preoperative facial nerve tractography in determining the facial nerve position in cerebellopontine angle tumor resection and its value in helping to preserve facial nerve function during surgery. A prospective study was designed to include patients presenting with cerebellopontine angle tumors. Three-dimensional reconstruction of facial nerve tractography was performed and added to the usual preoperative testing in all patients. Facial nerve position was compared between tractography results and surgical findings. Moreover, facial nerve function was evaluated at baseline and during follow-up. Fifteen patients were included for analysis. Complete resection was obtained in 5 patients, near-total resection was achieved in 8 patients, and partial resection in 2 patients. We found a strong statistically significant concordance between the preoperative facial nerve tractography reconstruction and the intraoperative findings (complete concordance in 86.66% of all the cases; κ= 0.784; P < 0.0001). Facial nerve anatomic structure was preserved in all patients during surgery. At 6 months follow-up, 66.66% of patients had a facial nerve normal function or a mild dysfunction. Preoperative facial nerve tractography reconstruction showed a high correlation with intraoperative findings. Preoperative tractography information regarding facial nerve position and its cisternal course is valuable information and could help the surgeon in increasing the safety of the procedure during cerebellopontine angle tumor surgery.

Cochlear Obliteration after Translabyrinthine Resection for Large Cerebellopontine Angle Tumor

Introduction: The aim of this study was to better understand the onset time and factors associated with cochlear obliteration following translabyrinthine approach (TLA) surgery for large cerebellopontine angle tumors. Methods: This retrospective cohort study included 117 patients with large cerebellopontine angle tumor (tumor diameter >2 cm) treated by TLA surgery from June 2011 to March 2019 in a single tertiary referral center. The Kaplan-Meier method with log-rank test was used to estimate cochlear patency survival and the association between survival and covariates, and the Cox proportional hazards regression analysis was used to identify possible factors associated with cochlear obliteration. Results: Of the 117 patients included in our analysis, the median follow-up was 24.8 months. There were 30 (25.6%) patients in the cochlear obliteration group, and 87 (74.4%) in the patent cochlear group. Various degrees of cochlear obliteration was found in 25.6% patients in final MRI scan, comprised of 50% grade I, 30% grade II, and 20% grade III. Cochlear patency survival curves showed 94.0% at 3 months, 73.0% at 18 months, which plateaued after 20 months with a survival rate of 71.6%. In the multivariate Cox proportional hazards model, patients presented with postoperative hyperintense T1W cochlear signal had poorer cochlear patency survival compared to isointense T1W (HR = 4.15). Similarly, postoperative deteriorated facial function (HR = 4.52) and full IAC involvement of tumor (HR = 2.33) demonstrated a higher risks of cochlear obliteration after TLA surgery. Conclusion: The 2-year estimated cochlear patency rate was 71.6% in patients that received TLA. Cochlear obliteration can develop as early as 3 months post-surgery, with no new obliteration 20 months after the surgery and half of these patients got severe obliteration. Three factors associated with cochlear obliteration were identified including full IAC involvement of tumor, postoperative facial function deterioration, and postoperative hyperintense T1W cochlear signal.

Factors Associated with Acute Obstructive Hydrocephalus After Retrosigmoid Approach for Extra-Axial Cerebellopontine Angle Tumors

This study aimed to identify the risk factors for acute obstructive hydrocephalus (AOHCP) after extra-axial cerebellopontine angle (CPA) tumor surgery using the retrosigmoid (RS) approach. This retrospective study assessed 154 patients (100 vestibular schwannomas, 34 CPA meningiomas [MNGs], 9 trigeminal schwannomas, and 11 petroclival MNGs) who underwent surgical resection using the RS approach by a single surgeon between August 2010 and September 2019. AOHCP was defined as postoperative ventricular enlargement due to cerebrospinal fluid flow obstruction caused by surgery-related cerebellar injury within 1week. The radiological characteristics of the tumors were classified, and the surgical outcomes were reviewed. We analyzed the impact of different factors on the development of AOHCP after surgery. AOHCP developed in 17 (11%) patients, all of whom were treated with external ventricular drain insertion. Multivariate analysis showed that CPA MNGs (odds ratio [OR], 37.98), grade of tumor extension beyond the petroclival junction (grade 1: OR, 16.42; grade 2: OR, 17.47), major fourth ventricle compression (OR, 17.77), and surgery-related hemorrhage (OR, 7.64) were associated with AOHCP. Surgery-related hemorrhage was observed in 17 (11%) patients. 9 (6%) patients underwent ventriculoperitoneal shunt surgery because of persistent HCP. An increased risk of AOHCP after the RS approach was observed in patients with extra-axial CPA tumors with clival extension and major fourth ventricle compression. Compulsive and meticulous hemostasis must be achieved because postoperative hemorrhage is associated with AOHCP.

Clinical Studies and Pre-clinical Animal Models on Facial Nerve Preservation, Reconstruction, and Regeneration Following Cerebellopontine Angle Tumor Surgery–A Systematic Review and Future Perspectives

Background and purpose: Tumorous lesions developing in the cerebellopontine angle (CPA) get into close contact with the 1st (cisternal) and 2nd (meatal) intra-arachnoidal portion of the facial nerve (FN). When surgical damage occurs, commonly known reconstruction strategies are often associated with poor functional recovery. This article aims to provide a systematic overview for translational research by establishing the current evidence on available clinical studies and experimental models reporting on intracranial FN injury.Methods: A systematic literature search of several databases (PubMed, EMBASE, Medline) was performed prior to July 2020. Suitable articles were selected based on predefined eligibility criteria following the Preferred Reporting Items for Systematic Reviews and Meta Analyses (PRISMA) guidelines. Included clinical studies were reviewed and categorized according to the pathology and surgical resection strategy, and experimental studies according to the animal. For anatomical study purposes, perfusion-fixed adult New Zealand white rabbits were used for radiological high-resolution imaging and anatomical dissection of the CPA and periotic skull base.Results: One hundred forty four out of 166 included publications were clinical studies reporting on FN outcomes after CPA-tumor surgery in 19,136 patients. During CPA-tumor surgery, the specific vulnerability of the intracranial FN to stretching and compression more likely leads to neurapraxia or axonotmesis than neurotmesis. Severe FN palsy was reported in 7 to 15 % after vestibular schwannoma surgery, and 6% following the resection of CPA-meningioma. Twenty-two papers reported on experimental studies, out of which only 6 specifically used intracranial FN injury in a rodent (n = 4) or non-rodent model (n = 2). Rats and rabbits offer a feasible model for manipulation of the FN in the CPA, the latter was further confirmed in our study covering the radiological and anatomical analysis of perfusion fixed periotic bones.Conclusion: The particular anatomical and physiological features of the intracranial FN warrant a distinguishment of experimental models for intracranial FN injuries. New Zealand White rabbits might be a very cost-effective and valuable option to test new experimental approaches for intracranial FN regeneration. Flexible and bioactive biomaterials, commonly used in skull base surgery, endowed with trophic and topographical functions, should address the specific needs of intracranial FN injuries.

Intraoperative transcranial facial motor evoked potential monitoring in surgery of cerebellopontine angle tumors predicts early and late postoperative facial nerve function

ObjectiveWe propose a novel method that predicts facial nerve function (FNF) calculated from the drop and recovery of facial motor evoked potential (FMEP) amplitude ratio during the surgery of cerebellopontine angle tumors. MethodsWe enrolled 73 patients with cerebellopontine angle tumor, and used a biphasic, constant current, and suprathreshold stimulation (BCS) protocol to record FMEP of the orbicularis oris. We measured the intraoperative minimum-to-baseline amplitude ratio (MBR), the final-to-baseline amplitude ratio (FBR), and the recovery value (RV). RV was measured by subtracting MBR from FBR. Using those values, we evaluated FNF both at early postoperative (EP) and late postoperative (LP) periods. ResultsWe successfully obtained 62 FMEP readings. Facial palsies occurred in 22 patients during the EP period, and 14 patients recovered during the LP period. Both MBR and FBR showed a significant correlation with FNF in the EP period. RV showed a good predictive power of FNF recovery during the LP period for the first time. ConclusionsRV is a new and useful predictor of FNF recovery. MBR can be an intraoperative predictor of FNF in the EP period. SignificanceFNF outcome in the early and late postoperative periods can be predicted by FMEP.

Natural History of Facial Weakness Following Surgery of the Cerebellopontine Angle: A Tertiary Care Cohort.

Facial function is a key outcome in surgery of the cerebellopontine angle (CPA). This study describes the natural history of facial weakness after CPA surgery. Retrospective study of two tertiary centers. Patients undergoing surgery for CPA tumors from 2003 to 2017 with preoperatively normal facial function and without subsequent surgical or adjuvant therapy. Serial facial nerve examinations using the House-Brackmann (HB) scale. Of 301 patients examined, 149 (49.5%) had facial weakness postoperatively and 74.5% of these occurred within 24 hours. Of patients with HB-1 function within 24 hours after surgery, 95.3% had HB-1 function and 100% had HB-3 or better function at last follow-up. Of patients with HB-4 or worse function within 24 hours after surgery, 22.6% ultimately achieved HB-1 function and 83.9% ultimately achieved HB-3 or better function. By 180 days postoperatively, 83.7% of patients' facial function had stabilized. At last follow-up, 3.0% of patients had facial function poorer than HB-3, which was associated with subtotal resections (12.9% vs. 4.4% for near total and 0.6% for gross total resections, p = 0.002), aspirin use (10.6% vs. 1.6%, p = 0.001), larger tumors (p < 0.0005), longer surgery (p < 0.002), and immediate versus delayed postoperative facial weakness (p = 0.002). Facial function over time after CPA surgery is presented. While facial function immediately after surgery correlates with future function, delayed weakness or improvement is common. These data inform patient counseling both preceding and following surgery.

Prognostic value of a bilateral motor threshold criterion for facial corticobulbar MEP monitoring during cerebellopontine angle tumor resection.

In intraoperative neuromonitoring (IONM), facial nerve motor function (FaNMF) is assessed by facial muscle corticobulbar motor evoked potentials (FMcoMEP). Mostly only amplitude decrease is used as warning criterion. We related a refined criterion for FMcoMEP consisting of a bilateral final-to-baseline motor threshold ratio with standard criteria and postoperative FaNMF. 79 patients (45 females; 48 ± 16years) undergoing IONM-guided cerebellopontine angle tumor surgery were retrospectively analyzed. An intraoperative final-to-baseline motor threshold increase ≥ 20% ipsi- versus contralaterally (bFBMT20) was correlated to postoperative FaNMF at day 1 (D1), 7 (D7) and 3months (3M). An ipsilateral-only final-to-baseline motor threshold increase ≥ 20mA (iAMT20) and amplitude decrement ≥ 50% (iAR50) served as reference. Tumors included vestibular schwannomas (68%), meningiomas (19%) and others (13%). Mean tumor diameter was 2.7 ± 1.1cm. Postoperatively, HB-increase ≥ 2 was seen in 27% (D1), 17% (D7), and 6% (3M) of patients, respectively. FMcoMEP were obtained in 75/79 cases. Pathological bFBMT20, iAMT20 and iAR50 were seen in 17, 17, and 46 cases, respectively. Area under the ROC curve for bFBMT20 (iAMT20) was 0.894 (0.868) at D1; 0.903 (0.822) at D7 and 0.941 (0.959) at 3M. iAR50 performed worse at all time points. Diagnostic odds ratios were highest for bfBMT20 compared to iAMT20 and iAR50 for D1 (172.5 vs. 8.7 vs. 0.45) and D7 (51.4 vs. 6.1 vs. 0.8). The refined parameter bFBMT20 provides a valuable contribution to the prognostic assessment of FaNMF. Due to its bihemispheric character, it might thus circumvent false-positive events which affect FMcoMEP bilaterally.

Correlation of Preoperative Cranial Nerve Diffusion Tensor Tractography with Intraoperative Findings in Surgery of Cerebellopontine Angle Tumors

Imaging to visualize nerves around tumors preoperatively could help the surgeon to plan the surgery and excise the tumor with preservation or improvement in patients' quality of life. In the present prospective study, we attempted to correlate the preoperative cranial nerves (i.e., trigeminal, abducens, facial, and vestibulocochlear diffusion tensor tractography and anatomic magnetic resonance imaging [MRI] findings) with intraoperative findings during cerebellopontine angle (CPA) tumor surgery. The 40 enrolled patients had CPA tumors (31 vestibular schwannomas, 5 epidermoid tumors, 2 meningiomas, 2 trigeminal schwannomas). All the patients were undergoing microsurgery for the first time. They underwent preoperative MRI for anatomic and diffusion tensor imaging (DTI) data. The imaging series were postprocessed, and 3-dimensional images were obtained. The location of the involved nerves around the tumors was recorded during surgery by the senior surgeon, who was kept unaware of the results of the fiber tracking, and a correlation was performed. We evaluated the correlation between the DTI and intraoperative findings for the nerve location in relation to the tumor in the CPA. The correlation between the DTI and intraoperative findings for the facial, trigeminal, and vestibulocochlear nerves was 85% (34 of 40), 85% (34 of 40), and 75% (12 of 16), respectively. The modified technical parameters proposed could lead to better preservation of cranial nerve function, especially for patients with large tumors. To the best of our knowledge, the present study is the first systematic study of relevant cranial nerves in 40 patients with demonstration of the vestibulocochlear bundle by preoperative MRI in the most common CPA tumors using advanced MRI sequences such as diffusion tensor tractography and capturing the data in a multiplanar format.

Evaluation of balance after surgery for cerebellopontine angle tumor.

The origin of about 10% of tumors located in the intracranial region is the cerebellopontine angle. Therefore Cerebellopontine Angle (CPA) tumors affect patients' balance. The aim of this study was to compare the balance in individuals who underwent surgery for CPA tumors with healthy individuals. Thirty patients who were being followed-up by the Department of Neurosurgery and had been operated on CPA tumor and 31 healthy individuals were included in the study as group 1 and group 2, respectively. The participants were evaluated using Romberg Test, Sharpened Romberg Test, One-leg Stance (OLS), Tandem Walking, Walk Across, Berg Balance Scale (BBS), Dizziness Handicap Inventory (DHI) and Short Form 36 (SF-36). In comparison of the groups, OLS tests (p< 0.001), BBS (p< 0.05) and DHI (p< 0.05) were significantly different in favor of healthy group. SF-36 results revealed a significant difference between the groups, except for Bodily Pain and Vitality (p< 0.05). The results of this study demonstrated a decrease in balance parameters and quality of life in individuals who underwent CPA tumor surgery in comparison to healthy individuals. Evaluation of balance in the preoperative and postoperative period should not be ignored in these patients and they are suggested to start rehabilitation in the early postoperative period.

Continuous and Dynamic Facial Nerve Mapping During Surgery of Cerebellopontine Angle Tumors: Clinical Pilot Series

To evaluate a new surgical tool combining suction and monopolar neurostimulation (stimulation sucker) for cerebellopontine angle (CPA) tumors. The usefulness for continuous (time) and dynamic (space) facial nerve mapping was studied. Patients operated on with the stimulation sucker for a CPA tumor between April 2016 and May 2017 in a tertiary care center were identified. Clinical charts were retrospectively evaluated. The minimum follow-up time of patients was 12 months. The study population included 17 patients with tumor (6 women and 11 men). The age range was from 2 to 77 years (mean age, 45.7 years; standard error of the mean, 22.7 years). Most CPA tumors were large (Koos grade 4) vestibular schwannomas (n= 10); other pathologies included petrous meningioma (n= 1), metastasis (n= 1), medulloblastoma (n= 2), ependymoma (n= 2), and pilocytic astrocytoma (n= 1). One patient with trigeminal neuralgia served as the normal control subject. No complications because of the stimulation sucker were encountered. Clinical and radiologic outcomes compared favorably with institutional experience and literature. The stimulation sucker allowed for continuous (time) mapping of the facial nerve at the site of resection (space). This real-time feedback allowed early identification of the facial nerve. Handling and ergonomy were excellent and workflow improved. The shortcomings compared with a bayonet-shaped bipolar probe were decreased visibility of neurovascular structures and lower spatial discrimination. The new device did not simplify delicate at the brainstem and on the nerve. We think it should be considered as a complementary tool in the surgeon's armamentarium. Until now, nerve damage as assessed by neuromonitoring (e.g., facial nerve electromyography, motor evoked potential) served as surrogate for nerve function. This concept should be challenged. The studied stimulation sucker detected the facial nerve earlier than conventional techniques, preventing harm by surgical trauma. A larger, prospective study is warranted to better define its role in CPA surgery.

PB6. A new motor threshold criterion for intraoperative corticobulbar MEP can predict postoperative facial nerve function

Objective Intraoperatively, facial nerve (FN) function is assessed with corticobulbar Motor Evoked Potentials (FN-coMEP). MEP-amplitude decrement and increase in motor threshold (MT) serve as warning criteria. A novel threshold criterion for extremity muscle MEP compares final-to-baseline motor threshold levels (BFB-MT) between the operated versus non-operated side. We applied BFB-MT for FN-coMEP with regard to postoperative FN-function. Methods 79 patients (45f; 48 ± 16 yrs., 68% vestibular schwannoma) undergoing cerebellopontine angle tumor surgery were analysed. FN-function was assessed with the House-Brackmann score (HB) pre- and postoperatively at day 1 (d1), 7 (d7), 3 months (3 m) and grouped in mild (HB score increase ⩽ 1) or marked deterioration (HB score increase ⩾ 2). FN-coMEP were elicited with anodal transcranial electric stimulation at C4;C3 referenced to Cz, and recorded from oris and mentalis muscles. A BFB-MT difference ⩾ 20% (operated vs. non-operated side) was considered significant. MT-increase of ⩾ 20 mA and amplitude decrement ⩾ 50% on the operated side served as reference criteria. FN function was correlated to all 3 criteria. Results At d1, 22% of patients (17/79) showed mild HB deterioration, 27% (21/79) marked. At d7, 25% (20/79) showed mild and 16% (13/79) marked deterioration. At 3 m follow-up (available in 68 patients), 94% showed recovery (64/68). Only 4/68 patients showed residual marked FN function deterioration. FN-coMEP were obtained in 95% cases (75/79). Changes according to BFB-MT (35 ± 17 mA) occurred in 17 patients, 16 of these patients suffered a marked deterioration of FN function at d1. BFB-MT correlated significantly with FN function at d1 and d7. The correlation was stronger using the BFB-MT (Spearman correlation: d1: p = 0.726; d7: p = 0.559; 3 m: p = 0.265) compared to absolute threshold increase ⩾ 20 mA (Spearman correlation: d1: p = 0.675; d7: p = 0.528; 3 m: p = 0.275) and amplitude reduction ⩾ 50% (Spearman correlation: d1: p = 0.305; d7: p = 0.378; 3 m: p = 0.118). Conclusion An increase of BFB-MT ⩾ 20% between the operated vs. non-operated side serves as a better predicator for postoperative FN function than absolute mA increase and amplitude reduction. Further studies have to validate this criterion intraoperatively for its real time applicability.

Predictive value of neurophysiological monitoring in facial nerve function after cerebellopontine angle tumor surgery

Objective To investigate the predictive value of preoperative and intraoperative electrophysiological parameters in facial nerve (FN) function after cerebellopontine angel (CPA) tumor surgery. Methods A total of 58 patients with CPA tumor underwent operations from August 2016 to March 2017 at Department of Neurosurgery, Beijing Tiantan Hospital, Capital Medical University and were enrolled into this retrospective study. Preoperative blink reflex (BR) and FN F wave response were tested in all patients. The R1 component latency and mean F wave latency were determined. Intraoperative facial motor evoked potentials (FMEP) was applied to monitor the FN function and the amplitude ratio of FMEP was documented. According to the House-Brackmann (H-B) grading system, the functional classification of FN was determined preoperatively, at 1 week, 3 months and 6 months postoperatively. Multiple logistic regression analysis was applied to explore the predictor of postoperative FN function. Results A total of 58 cases of CPA tumor underwent microsurgical excisions by retrosigmoid approach. Total and subtotal resections were performed in 55 (94.8%) and 3 cases, respectively. Single factor Logistic regression analysis showed that the results of blink reflex in patients with good FN outcome were better than those in the group with poor outcome at 3 follow-up time points (P<0.05). The results of F wave response in patients with good FN outcome were better than those in poor outcome group at 6 months post operation (P<0.05). At 3 and 6 months post surgery, the maximal tumor diameters in the good outcome group were (31.9±10.2) mm and (31.9±9.3) mm, respectively, which were smaller than those in the poor outcome group [(37.8±9.7) mm and (40.0±10.0) mm, respectively] (both P<0.05). At 1 week, 3 and 6 months post surgery, the FMEP amplitude ratios in the good outcome group were (84.6±21.3)%, (83.0±19.0)% and (81.0±19.1)%, respectively, which were higher than those in the poor outcome group [(66.2±27.0)%, (63.4±29.0)% and (59.6±31, 2)%] (all P<0.05). Multivariate Logistic regression analysis showed that FMEP amplitude ratio was the independent predictor of FN outcome at 1 week, 3 and 6 months post operation (P<0.05). The maximal tumor diameter was the independent predictor of FN outcome at 3 and 6 months post operation (P<0.05). BR classification was the independent predictor of FN outcome at 6 months after operation (P<0.05). ROC (receiver operating characteristic) curve analysis showed that the FMEP amplitude ratio cut-off values of 89.2% [AUC (area under the curve)=0.709], 58.2% (AUC=0.706) and 58.2% (AUC=0.713) predicted good FN function at 1 week, 3 and 6 months after surgery, respectively. Conclusions BR and maximal tumor diameter have certain predictive values for postoperative FN function. The FMEP amplitude ratio is a valuable predictor for postoperative FN function and its value of at least 60% is predictive of favorable long-term postoperative FN function. Key words: Cerebellopontine angle; Brain neoplasms; Facial nerve; Electrophysiology; Forecasting

The relation between flocculus volume and tinnitus after cerebellopontine angle tumor surgery

PurposeChronic tinnitus is a common symptom after cerebellopontine angle (CPA) tumor removal. Sometimes, the tinnitus is gaze-modulated. In that case, patients can change the loudness or pitch of their tinnitus by ocular movements. During tumor removal by a retrosigmoid craniotomy, the cerebellar flocculus is manipulated by the surgical approach to access the tumor. The flocculus has been associated with tinnitus in rats, and is involved in eye-gaze control. This suggests that the flocculus may have a role in gaze-modulated tinnitus after CPA tumor removal. In order to investigate this hypothesis, the relation between the flocculus volume and the characteristics of postoperative tinnitus was studied. ResultsA single-center cohort of 51 patients completed a questionnaire after CPA tumor removal. The questionnaire asked for the effect of eye movements on tinnitus and included the Tinnitus Functional Index (TFI). Tinnitus was present in 36 patients (71% of 51), of which 29 (81% of 36) described gaze-modulation. The median TFI was 22 (range 0–85). A postoperative MRI-scan of sufficient quality was available in 34 cases. The volumes of the (para)flocculi ipsilateral and contralateral to the surgery, and the ratio of these volumes were similar between patients with and without tinnitus. The TFI correlated with the volume of both ipsi- and contralateral (para)flocculus (rs(23) = .516, p = .008 and rs(23) = .430, p = .032). The ipsilateral-to-contralateral volume ratio of the (para)flocculi volumes was significantly lower in patients that could modulate the loudness of their tinnitus by eye gaze, compared to patients that could not (t(23) = 3.337, p = .003). ConclusionsThe lack of a relation between flocculus volumes and the presence of tinnitus, combined with the significant correlation between tinnitus severity and flocculus volumes, suggests that the flocculus may not be the primary source of tinnitus, but is likely to mediate tinnitus severity. The reduced ipsi-to-contralateral volume ratio in patients with gaze-modulated tinnitus suggests that atrophy of the flocculus on the surgery side triggers cross-modal interactions leading to modulation of tinnitus.

Level Specific CE-Chirp® BAEP's: A new faster technique in neuromonitoring cochlear nerve during cerebello-pontine angle tumor surgery

Abstract Background Level Specific (LS) CE-Chirp® Brainstem Auditory Evoked Potentials (BAEP's) are the most recent evolution of classical Click BAEP's, performed both in clinical studies and in intraoperative neuromonitoring (IONM) of acoustic pathways during several neurosurgical procedures. LS CE-Chirp® is a new group of acoustic stimuli, latter evolution of Broadband CE-Chirp®, designed by Claus Elberling to provide faster recording of larger amplitude BAEP's V waves in infants. While the original Broadband CE-Chirp® was conceived for optimal response amplitude of V wave at low and medium stimulation intensities, the LS CE-Chirp® provides clearer I–III–V waves at high intensities. Material and method We report a consecutive series of 31 cases in which the new LS CE-Chirp® BAEP's were performed during different skull base surgery procedures during the last 24 months: 25 vestibular schwannomas, 3 cerebello-pontine angle (CPA) meningiomas and 3 CPA epidermoid tumors. Results Using LS-CE-Chirp® BAEP's monitoring, neurosurgeon was alerted in 10–15 s about variation of conduction parameters of acoustic pathways. At the end of surgery, BAEP's were normal in 11 patients, showed deconstructed waves in 14, and elongated waves in 6. At a minimum clinical and BAEP's follow-up of 6 months, hearing function was preserved in 19 cases (61,3%). Conclusions We herein confirm that LS CE-Chirp® BAEP's provide a fast feedback to surgeons regarding acoustic pathways function, helping them during skull base tumor removal in the attempt to hearing preservation when it is socially useful in the preoperative evaluation.

Diffusion tensor tractography in the preoperative precise identification of the course of facial nerve in a meningioma of the cerebellopontine angle – Technical implications

Abstract Background Facial paralysis remains as one of the major morbidities of surgery of cerebellopontine angle tumors. The preoperative standard Magnetic Resonance Image does not identify, with precision, the path of the facial nerve. Case description The authors describe a case of a 56 years-old female with a cerebellopontine angle meningioma, submitted to preoperative Diffusion Tensor Tractography to identification of the course of the facial nerve, and correlate its position with the intraoperative findings. There was an accurate correlation between the path of the facial nerve revealed by preoperative DTT and the route of the nerve identified during surgery. Conclusion The preoperative identification of the facial nerve seems to be possible by tractography in meningiomas of the cerebellopontine angle. It is possible that this technique may have utility in larger tumors, where the intraoperative identification of the facial path can be more difficult.