Preservation of language function by mapping the arcuate fasciculus using intraoperative corticocortical evoked potential under general anesthesia in glioma surgery.

OBJECTIVE: Intraoperative language mapping under general anesthesia is imperative for brain tumor surgery because awake surgery is not always feasible. Monitoring corticocortical evoked potential (CCEP) is known to be a useful method for tracking neuronal connectivity and localizing functional areas. The authors evaluated the clinical benefit of intraoperative CCEP monitoring for language function preservation in patients undergoing glioma surgery. METHODS: Between January 2019 and June 2021, the authors performed a total of 29 consecutive glioma surgeries using CCEP monitoring under general anesthesia because of a risk of speech impairment; these were analyzed. Language area mapping was implemented by the anterior language area to posterior language area CCEP method for arcuate fasciculus mapping, and tumor resection was performed while avoiding the localized language areas. Language function before and after surgery was evaluated by the Controlled Oral Word Association Test (COWAT). RESULTS: Intraoperative CCEP was successfully monitored in 25 patients (86.2%), and a valid signal was undetectable in the other 4 patients. Language function evaluation was possible before and after surgery in a total of 20 patients. Overall, the preservation rate of language function was 65.0%, and the deterioration rate was 35.0% after tumor resection with CCEP monitoring. Among those 8 patients with preoperative COWAT scores ≥ 18, 5 patients (62.5%) successfully preserved their language function, with COWAT scores > 18 after tumor resection. Among the 12 patients with preoperative deteriorated language function (COWAT score < 18), 8 patients (66.7%) showed improvement or preserved language function after surgery. CONCLUSIONS: Intraoperative CCEP monitoring of the arcuate fasciculus is an acceptable technology for the preservation of language function under general anesthesia in glioma surgery in patients in whom awake surgery is not feasible.

Effect of Dexmedetomidine Combined Anesthesia on Motor evoked Potentials During Brain Tumor Surgery.

BACKGROUND: Dexmedetomidine (DEX) is used as an adjunct to total intravenous anesthesia. However, its effect on intraoperative neurophysiologic monitoring (IOM) during brain tumor surgery remains controversial. The aim of this study was to explore the effect of DEX on IOM during brain tumor surgery. METHODS: Seventy-eight consecutive patients (DEX group, n = 40; control group, n = 38), who underwent brain tumor surgery with IOM, were retrospectively reviewed. The outcomes included the predictability, laterality of alterations, and stimulation parameters of transcranial motor evoked potentials (tcMEPs) and somatosensory evoked potentials (SSEPs). RESULTS: The predictability of tcMEPs for postoperative motor outcomes showed a higher false-positive rate in the DEX group than in the control group (27.5% vs. 5.3%, P = 0.047). Bilateral alterations were observed only in the DEX group (31.3%; P = 0.053). Compared with the control group, the DEX group required significantly higher intensity (377.5 ± 48.0 vs. 347.1 ± 30.0 mV; P = 0.001) and repetition rate (6.0 ± 0.2 vs. 5.7 ± 0.5 pulse/train; P = 0.001) of transcranial electric stimulation to evoke adequate tcMEPs. The SSEP results were comparable between both groups. In the DEX group, false-positive tcMEPs changes occurred 222.2 ± 70.5 minutes (range, 95-342 minutes) after the induction of anesthesia. In addition, the patients who were administered DEX under bispectral index monitoring (n = 12) showed a significantly higher false-positive rate than shown by the control group (50.5% vs. 5.3%; P = 0.003). CONCLUSIONS: This study showed that DEX had significant effects on tcMEPs during IOM in brain tumor surgery. Because the high false-positive rate could decrease the accuracy of IOM, outcomes after using DEX should be cautiously interpreted.

Limitation of Intraoperative Transcranial Electrical Stimulation-Motor Evoked Potential Monitoring During Brain Tumor Resection Adjacent to the Primary Motor Cortex.

Transcranial electrical stimulation-motor evoked potential (TES-MEP) is a valuable intraoperative monitoring technique during brain tumor surgery. However, TES can stimulate deep subcortical areas located far from the motor cortex. There is a concern about false-negative results from the use of TES-MEP during resection of those tumors adjacent to the primary motor cortex. Our study reports three cases of TES-MEP monitoring with false-negative results due to deep axonal stimulation during brain tumor resection. Although no significant change in TES-MEP was observed during surgery, study subjects experienced muscle weakness after surgery. Deep axonal stimulation of TES could give false-negative results. Therefore, a combined method of TES-MEP and direct cortical stimulation-motor evoked potential (DCS-MEP) or direct subcortical stimulation should be considered to overcome the limitation of TES-MEP.

Intraoperative Monitoring of Hypoglossal Nerve Using Hypoglossal Motor Evoked Potential in Infratentorial Tumor Surgery: A Report of Two Cases.

The hypoglossal nerve (CN XII) may be placed at risk during posterior fossa surgeries. The use of intraoperative monitoring (IOM), including the utilization of spontaneous and triggered electromyography (EMG), from tongue muscles innervated by CN XII has been used to reduce these risks. However, there were few reports regarding the intraoperative transcranial motor evoked potential (MEP) of hypoglossal nerve from the tongue muscles. For this reason, we report here two cases of intraoperative hypoglossal MEP monitoring in brain surgery as an indicator of hypoglossal deficits. Although the amplitude of the MEP was reduced in both patients, only in the case 1 whose MEP was disappeared demonstrated the neurological deficits of the hypoglossal nerve. Therefore, the disappearance of the hypoglossal MEP recorded from the tongue, could be considered a predictor of the postoperative hypoglossal nerve deficits.

Delayed facial palsy after microvascular decompression for hemifacial spasm: friend or foe?

OBJECTIVE The authors investigated the incidence, clinical course, and predisposing factors associated with delayed facial palsy (DFP) following microvascular decompression (MVD). METHODS The authors reviewed the records of 310 patients (311 cases) who were followed after MVD for hemifacial spasm (HFS). Of these patients, 45 (14.5%) developed DFP after MVD. The clinical characteristics and predisposing factors of the patients with HFS were investigated to identify prognostic factors that predicted the development of DFP after MVD. Log-rank tests were used to compare times to symptom disappearance, and a logistic regression analysis was performed to compare clinical characteristics between patients who developed DFP and those who did not. RESULTS HFS was completely resolved immediately after MVD in 158 cases (50.8%), and HFS eventually disappeared in 289 (92.9%) of the cases. Of the 45 patients with DFP, 17 were men and 28 were women. DFP occurred between postoperative Days 1 and 44 (mean 9.67 days). Finally, 44 patients (97.8%) completely recovered. The average time to recovery was 3.9 months (range 1-24 months). Patients who had experienced an immediate disappearance of HFS experienced a significantly higher occurrence of DFP than those who did not (odds ratio 0.383, 95% confidence interval 0.183-0.802; p = 0.011). In addition, preoperative botulinum neurotoxin injections negatively influenced the occurrence of DFP (p = 0.016). CONCLUSIONS In this study, the incidence rate of DFP was slightly higher than previously reported values. Moreover, DFP can occur even when spasms disappear immediately after MVD, but the patients with DFP can fully recover within weeks.

An Electrode Configuration for Recording Muscle Motor Evoked Potentials in the Upper Extremities during Intraoperative Neurophysiological Monitoring.

OBJECTIVE: The main aim of the present study is to examine the electrode configurations used to record the muscle motor evoked potential (mMEP) in the upper extremities during surgery with the goal of producing a high and stable mMEP signal, in particular among the abductor pollicis brevis (APB), abductor digiti minimi (ADM), and across the APB-ADM muscles, which have been widely used for the mMEP in the upper extremities. METHODS: Thirty right-handed patients were recruited in this prospective study. No patients showed any adverse events in their mMEP signals of the upper extremities during surgery. The mMEPs were recorded independently from the signals for the APB and ADM and for those across the APB-ADM. RESULTS: The mMEP amplitude from across the APB-ADM was statistically higher than those recorded from the APB and ADM muscles. Moreover, the coefficient of variation of the mMEP amplitude from across the APB-ADM was smaller than those of mMEP amplitude recorded from the APB and ADM muscles. CONCLUSION: The mMEP from across the APB-ADM muscles showed a high yield with high stability compared to those in each case from the APB and ADM muscles. The configuration across the APB-ADM muscles would be best for mMEP recordings from the upper extremities for intraoperative neurophysiological monitoring purposes.

Intraoperative Motor-Evoked Potential Disappearance versus Amplitude-Decrement Alarm Criteria During Cervical Spinal Surgery: A Long-Term Prognosis.

BACKGROUND AND PURPOSE: We studied the clinical significance of amplitude-reduction and disappearance alarm criteria for transcranial electric muscle motor-evoked potentials (MEPs) during cervical spinal surgery according to different lesion locations [intramedullary (IM) vs. nonintramedullary (NIM)] by evaluating the long-term postoperative motor status. METHODS: In total, 723 patients were retrospectively dichotomized into the IM and NIM groups. Each limb was analyzed respectively. One hundred and sixteen limbs from 30 patients with IM tumors and 2,761 limbs from 693 patients without IM tumors were enrolled. Postoperative motor deficits were assessed up to 6 months after surgery. RESULTS: At the end of surgery, 61 limbs (2.2%) in the NIM group and 14 limbs (12.1%) in the IM group showed MEP amplitudes that had decreased to below 50% of baseline, with 13 of the NIM limbs (21.3%) and 2 of the IM limbs (14.3%) showing MEP disappearance. Thirteen NIM limbs (0.5%) and 5 IM limbs (4.3%) showed postoperative motor deficits. The criterion for disappearance showed a lower sensitivity for the immediate motor deficit than did the criterion for amplitude decrement in both the IM and NIM groups. However, the disappearance criterion showed the same sensitivity as the 70%-decrement criterion in IM (100%) and NIM (83%) surgeries for the motor deficit at 6 months after surgery. Moreover, it has the highest specificity for the motor deficits among diverse alarm criteria, from 24 hours to 6 months after surgery, in both the IM and NIM groups. CONCLUSIONS: The MEP disappearance alarm criterion had a high specificity in predicting the long-term prognosis after cervical spinal surgery. However, because it can have a low sensitivity in predicting an immediate postoperative deficit, combining different MEP alarm criteria according to the aim of specific instances of cervical spinal surgery is likely to be useful in practical intraoperative monitoring.

Multimodal intraoperative monitoring during intramedullary spinal cord tumor surgery.

BACKGROUND: The aim of this work is to evaluate the utility of multimodal intraoperative monitoring (IOM) during intramedullary spinal cord tumor (IMSCT) surgery in our institution, and to investigate which IOM events are likely to be encountered during critical surgical phases. METHODS: Twenty-five patients who underwent IMSCT surgery with IOM were included in this study. Our multimodal IOM assessment included SSEP, mMEP, and fEMG monitoring. Positive predictive value (PPV), negative predictive value (NPV), sensitivity, and specificity were assessed 24 h and 1 month after surgery. The IOM events during three main surgical phases were also investigated. For mMEP assessment, two warning criteria (>50 % decrease in mMEP amplitude and all-or-none mMEP amplitude presence) were employed. RESULTS: Long-term outcome prediction was better when the all-or-none criterion was applied than when the >50 % amplitude decrease criterion was applied. Based on the all-or-none criterion, the PPV, NPV, sensitivity, and specificity were 60, 100, 100, and 91 %. Frequent IOM events were observed during the three major main surgical phases. Seven (29 %) patients showed SSEP events during opening of the spinal cord. During tumor removal, 21 of 25 patients (84 %) had IOM events, and 13 of 18 (72 %) of the fEMG events occurred prior to the mMEP events. CONCLUSIONS: Based on the association of fEMG events with upcoming mMEP events during tumor removal, we recommend inclusion of fEMG monitoring in IOM. Multimodal IOM provides useful electrophysiological information during IMSCT surgery, especially during the main surgical phases.

A new measure for monitoring intraoperative somatosensory evoked potentials.

OBJECTIVE: To propose a new measure for effective monitoring of intraoperative somatosensory evoked potentials (SEP) and to validate the feasibility of this measure for evoked potentials (EP) and single trials with a retrospective data analysis study. METHODS: The proposed new measure (hereafter, a slope-measure) was defined as the relative slope of the amplitude and latency at each EP peak compared to the baseline value, which is sensitive to the change in the amplitude and latency simultaneously. We used the slope-measure for EP and single trials and compared the significant change detection time with that of the conventional peak-to-peak method. When applied to single trials, each single trial signal was processed with optimal filters before using the slope-measure. In this retrospective data analysis, 7 patients who underwent cerebral aneurysm clipping surgery for unruptured aneurysm middle cerebral artery (MCA) bifurcation were included. RESULTS: We found that this simple slope-measure has a detection time that is as early or earlier than that of the conventional method; furthermore, using the slope-measure in optimally filtered single trials provides warning signs earlier than that of the conventional method during MCA clipping surgery. CONCLUSION: Our results have confirmed the feasibility of the slope-measure for intraoperative SEP monitoring. This is a novel study that provides a useful measure for either EP or single trials in intraoperative SEP monitoring.