O178 Correlation between postoperative visual outcome and intraoperative visual evoked potentials during endoscopic transsphenoidal surgery

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Abstracts / Clinical Neurophysiology 128 (2017) e178–e303

Significance: This intraoperative monitoring system (We call as OMNAPP system) for the eOMNs is useful for skull base surgeries including various transcranial approaches. Keywords: Intraoperative ocular movement monitoring, Piezoelectric device, Ocular motor nerves activating piezoelectric potentials doi:10.1016/j.clinph.2017.07.187

O178 Correlation between postoperative visual outcome and intraoperative visual evoked potentials during endoscopic transsphenoidal surgery—Yui Nagata (Kurume University, Department of Neurosurgery, Fukuoka, Japan) Objective: We evaluated intraoperative changes in VEP waveforms to clarify the predictive criteria and limitations of intraoperative monitoring using VEPs. Methods: Between April 2008 and June 2016, we analyzed VEP data obtained from 35 patients who developed visual dysfunction and underwent endoscopic TSS for non-functioning pituitary adenomas. For all patients, we attempted to record intraoperative VEPs for each eye by stimulating with a light-emitting device placed over the eye. Results: We obtained 68 VEP recordings from affected eyes in 35 operations. Along the decompressive surgical stage, N75-P100 amplitude gradually increased, but not P100 latency. N75-P100 amplitude increase greater than 50% correlated with an improvement in postoperative visual acuity. However, visual field recovery did not correlate with the changes in VEP waveform. Discussion: These findings indicate the intraoperative change of N75-P100 amplitude predicted the postoperative improvement of visual acuity. In this study, we obtained stable and reproducible waveforms. Conclusions: Intraoperative VEP monitoring for procedures performed around the anterior visual pathway can detect either visual improvement or deterioration. N75-P100 amplitude changes greater than 50% can indicate changes in visual acuity, but do not predict changes in the visual field. We hypothesized that postoperative visual improvement may correlate with improvement of VEP amplitude before our analysis. These findings can be adapted for transcranial surgery or extended TSS for tumors around the anterior visual pathway. Keywords: Amplitude, Endoscopic, Intraoperative monitoring, Transsphenoidal surgery, Visual evoked potential doi:10.1016/j.clinph.2017.07.188

O179 Intraoperative blink reflex in microvascular decompression for hemifacial spasm. A case report and proposal of a new method to monitor the efficiency of decompression—Dimitrios Kefalas, Frederik Enders, Daniel Haenggi (University Hospital Mannheim, Department of Neurosurgery, Mannheim, Germany) Objectives: To report the utility of blink reflex (BR) monitoring in microvascular decompression (MVD) for hemifacial spasm (HFS). Methods: We report a case of a 64-year-old patient with HFS who underwent MVD with continuous intraoperative neurophysiological monitoring (IONM) of motor, sensory and auditory evoked potentials. The abnormal muscle response (AMR) was monitored with stimulation of zygomatic and buccal branch (zAMR, bAMR) and recording from representative muscles innervated by all facial nerve

(FN) branches. Additionally the BR was utilized to monitor the FN functionality. Results: Before incision, a similar to AMR-spread phenomenon (BR-spread) was observed when the supraorbital branch of trigeminal nerve was stimulated to elicit BR. Both AMRs (zAMR, bAMR) disappeared during MVD, indicating sufficient FN decompression. Concurrently a similar disappearance from BR-spread and FN-MEPs was observed. During closing all responses (AMRs, BR-spread, FNMEPs) reappeared. The HFS was clinically present right after the surgery but the patient was relieved from the symptoms a few hours later. Discussion: The BR-spread and FN-MEPs showed an AMR-like pattern during MVD. The reappearance of AMRs predicted the immediate but not the long term outcome of HFS-MVD. The BR and FN-MEPs are not reliable to monitor the FN integrity in HFS-MVD due to decompression depended responses. We propose further research to investigate the benefits of BR in HFS-MVD. Conclusions: The BR-spread is potentially an alternative IONM tool to determine whether the MVD of HFS is sufficient. Significance: A new IONM method is proposed to monitor HFSMVD. Keywords: Blink reflex, Abnormal muscle response, Hemifacial spasm, Microvascular decompression doi:10.1016/j.clinph.2017.07.189

O181 Usefulness of transcranial motor evoked potential during surgery for gliomas located close to the motor pathway— Nobuyuki Takeshige, Keiko Suematsu, Shinji Nakashima, Yui Nagata, Kiyohiko Sakata, Motohiro Morioka (Kurume University, Neurosurgery, Fukuoka, Japan) Objectives: To determine whether motor evoked potential (MEP) provide reliable monitoring of the motor system during resection of gliomas adjacent to the motor pathway. Method: 74 patients underwent MEP monitoring during surgery (47 males, 27 females; age range, 0–84 years; median age, 58 years). We examined two items. First of all, we evaluated whether the rate of amplitude changes and postoperative motor outcome were correlated. In the next study, we defined the rate of MEP changes in affected hemisphere as ‘A’, and the ratio of MEP changes in unaffected hemisphere as ‘B’. We also researched whether the A/B ratio and postoperative motor outcome were correlated. Result: MEP recordings were stable in amplitude during surgery in 67 patients (90.5%). No postoperative motor deficit was found in 41 out of 67 patients. However, postoperative paresis developed in 26 (38.8%) patients and 15 (22.4%) of them left paralysis after 1 week later. In the paresis developed group, MEP decrease in amplitude (>50%) occurred in 5 patients (33.3%), while decline A/B ratio (<0.6) occurred in 10 patients (66.7%). As predictions of the appearance of postoperative paralysis, the A/B ratio was more reliable than the MEP change rate. Conclusion: During surgery for gliomas close to the motor pathway, we first should pay attention to the MEP change rate. When the amplitude decrease 50% or less, we conclude that operation should be stopped and the A/B ratio (<0.6) should be checked immediately. Keywords: Motor evoked potential, Glioma, Motor pathway doi:10.1016/j.clinph.2017.07.191