[Usefulness of Preoperative Simulation: Skull Base Approach].

Preoperative simulation images creates an accurate visualization of a surgical field. The anatomical relationship of the cranial nerves, arteries, brainstem, and related bony protrusions is important in skull base surgery. However, an operator's intention is unclear for a less experienced neurosurgeon. Three-dimensional(3D)fusion images of computed tomography and magnetic resonance imaging created using a workstation aids precise surgical planning and safety management. Since the simulation images allows to perform virtual surgery, a déjà vu effect for the surgeon can be obtained. Additionally, since 3D surgical images can be used for preoperative consideration and postoperative verification, discussion among the team members is effective from the perspective of surgical education for residents and medical students. Significance of preoperative simulation images will increase eventually.

Combined endoscopic endonasal and transcranial approach for internal carotid artery aneurysms: usefulness and safety of endonasal proximal control.

It is necessary to secure both the proximal and distal sides of the parent artery to prevent premature rupture when clipping cerebral aneurysms. Herein, we describe four cases in which the proximal internal carotid artery (ICA), affected by a paraclinoid aneurysm, was secured using an endoscopic endonasal approach. We used various tools, including a surgical video, cadaver dissection picture, artist's illustration, and intraoperative photographs, to elucidate the process. No patient experienced postoperative complications at our institution. Compared to the cervical or cavernous ICA, the ICA adjacent to the clivus (paraclival ICA) can be anatomically safely and easily exposed using an endoscopic endonasal approach because there is no need to consider cerebrospinal fluid leakage or hemorrhage from the cavernous sinus. Securing the proximal side of the parent artery using an endoscopic endonasal approach may be a viable method for clipping selected ICA aneurysms, such as paraclinoid aneurysms especially for upward or outward aneurysms of the C2 portion.

Intraoperative nerve stimulation during vagal nerve stimulator placement.

Background: Vagal nerve stimulation (VNS) is a palliative treatment for refractory epilepsy and intraoperative nerve stimulation is applied to the vagal and other nerves to prevent electrode misplacement. We evaluated these thresholds to establish intraoperative monitoring procedures for VNS surgery. Methods: Forty-six patients who underwent intraoperative nerve stimulation during VNS placement were enrolled. The vagal nerve and other exposed nerves were electrically stimulated during surgery, and muscle contraction was confirmed by electromyography of the vocal cords and visual recognition of cervical muscle contraction. The nerve thresholds and the most sensitive parts of the vagal nerve were analyzed retrospectively. Results: The stimulation of vagal nerves induced vocal cord responses in all 46 patients; the median thresholds of the most sensitive parts and all parts were 0.2 mA (range: 0.05-0.75 mA) and 0.25 mA (range: 0.15-1.5 mA), respectively. The medial middle region was identified as the most sensitive part of the vagal nerve in the majority of participants (82.5%). In 11 patients, other cervical nerves were stimulated and sternohyoid muscle contraction was induced with a median threshold of 0.35 mA (range: 0.1-0.7 mA) in eight patients, while sternocleidomastoid muscle contraction was induced with a median threshold of 0.2 mA (range: 0.1-0.2 mA) in three. Conclusion: Intraoperative stimulation of vagal nerves induces vocal cord responses with locational variations, and the middle part stimulation could minimize the stimulus intensities. The nerves innervating the sternohyoid and sternocleidomastoid muscles may be exposed during the procedure. Knowledge of these characteristics will enhance the effectiveness of this technique in future applications.

Effect of a Low Concentration of Sevoflurane Combined With Propofol on Transcranial Electrical Stimulation Motor Evoked Potential: A Case Series.

Transcranial electrical motor evoked potential (TCeMEP) is used to monitor the integrity of intraoperative motor function. Total intravenous anesthesia (TIVA) is the preferred method because its effect on MEP is relatively smaller than volatile anesthetics. However, maintaining the balanced anesthesia in long-time surgery using TIVA is challenging and may sometime cause problems including body movement during microsurgery. Such problems can be avoided by intraoperative anesthesia management using a mixture of propofol and a low concentration of sevoflurane. We recorded TCeMEP under a mixture of propofol and low concentration of sevoflurane anesthesia in three cases of neurosurgery. Anesthesia was induced with a 5.0 µg/mL target-controlled infusion of propofol and 0.6 mg/kg rocuronium. General anesthesia was maintained by propofol and 0.1-0.25 µg/kg/min remifentanil infusion. After the recording of control TCeMEP, sequential inhalation of 0.2 minimum alveolar concentration (MAC) and 0.5 MAC of sevoflurane was performed. The duration of each sevoflurane inhalation was 10 minutes, and the MACs were adjusted by the patient's age. In our cases, the combination of propofol and 0.2 MAC sevoflurane suppressed the amplitude of TCeMEP to 38.0±21.7% (379.8±212.0 µV), but the amplitude was high enough for evaluation of motor function monitoring. On the other hand, the combination of 0.5 MAC sevoflurane greatly decreased the amplitude of TCeMEP to 6.3±6.0% (71.9±66.9 µV) resulting in less than 150 µV, and it was difficult to record the change in TCeMEP amplitude over time. The combination of 0.2 MAC sevoflurane with TIVA might enable TCeMEP monitoring with TIVA.

[Assessment of Motor and Language Function during Awake Surgery].

Awake surgery enables the evaluation of neurological functions that are difficult to assess with a conventional electrophysiological examination and is useful in the evaluation of language function. Awake surgery is a team effort involving anesthesiologists and rehabilitation physicians who evaluate motor and language functions, and information sharing during the perioperative period is important. Some points regarding surgical preparation and anesthesia methods are unique and must be well understood. For example, supraglottic airway devices must be used to secure the airway, and ventilation must be checked for availability when positioning the patient. Preoperative neurological evaluation is important in determining the method of intraoperative neurological evaluation, including choosing the simplest possible method of evaluation and sharing the information with the patient prior to surgery. Motor function assessment evaluates small movements that do not affect the surgery. Visual naming and auditory comprehension are useful in the evaluation of language function.

Microbleeds Due to Reperfusion Enhance Early Seizures after Carotid Ligation in a Rat Ischemic Model.

Impaired reperfusion in ischemic brain disease is a condition that we are increasingly confronted with owing to recent advances in reperfusion therapy. In the present study, rat models of reperfusion were investigated to determine the causes of acute seizures using magnetic resonance imaging (MRI) and histopathological specimens. Rat models of bilateral common carotid artery ligation followed by reperfusion and complete occlusion were created. We compared the incidence of seizures, mortality within 24 h, MRI, and magnetic resonance spectroscopy (MRS) to evaluate ischemic or hemorrhagic changes and metabolites in the brain parenchyma. In addition, the histopathological specimens were compared with those observed on MRI. In multivariate analysis, the predictive factors of mortality were seizure (odds ratios (OR), 106.572), reperfusion or occlusion (OR, 0.056), and the apparent diffusion coefficient value of the striatum (OR, 0.396). The predictive factors of a convulsive seizure were reperfusion or occlusion (OR, 0.007) and the number of round-shaped hyposignals (RHS) on susceptibility-weighted imaging (SWI) (OR, 2.072). The incidence of convulsive seizures was significantly correlated with the number of RHS in the reperfusion model. RHS on SWI was confirmed pathologically as microbleeds in the extravasation of the brain parenchyma and was distributed around the hippocampus and cingulum bundle. MRS analysis showed that the N-acetyl aspartate level was significantly lower in the reperfusion group than in the occlusion group. In the reperfusion model, RHS on SWI was a risk factor for convulsive seizures. The location of the RHS also influenced the incidence of convulsive seizures.

Computational Fluid Dynamics Analysis Features in Aneurysm Development in Rats.

The investigation of how to control the development and growth of cerebral aneurysms is important for the prevention of subarachnoid hemorrhage. Although there have been several types of research studies on computational fluid dynamics (CFD) analysis of brain aneurysm development and growth, there has been no unified interpretation of the CFD analysis results. The purpose of this study is to clarify the characteristics of CFD analysis results related to the development of cerebral aneurysms using an animal model. Nineteen rat models of cerebral aneurysms were created, and the CFD analysis results between the cerebral aneurysm group [n = 10; the aneurysm was observed on magnetic resonance angiography (MRA) within 10 weeks after aneurysm induction surgery] and the nonaneurysm group (n = 9) were compared. All aneurysms were confirmed on the proximal segment of the left cerebral artery (P1), and the cross-sectional area and curvature of the left P1 were evaluated together. In the cerebral aneurysm group, there was a decrease in wall shear stress (WSS) that is consistent with the location of the aneurysm compared to the nonaneurysm group. The cross-sectional area of the left P1 gradually increased in the aneurysm group but not in the nonaneurysm group. The mean curvature in the entire left P1 was higher in the aneurysm group than in the nonaneurysm group. This study revealed that the development of cerebral aneurysms is due to changes in vascular morphology, namely, an increase in vessel diameter and a high curvature, and a decreased WSS consistent with the site of aneurysm development using this animal model.

Transcranial electrical stimulation technique for induction of unilateral motor evoked potentials.

OBJECTIVE: Transcranial electrical stimulation motor evoked potentials (TES-MEP) are widely used to monitor motor function; however, broad current spread and induced body movement are limitations of this technique. We herein report a localized stimulation technique for TES-MEP that induces unilateral MEP responses. METHODS: The stimulation of C1(+)-C4(-) or C2(+)-C3(-) was performed to induce right- or left-sided muscle contraction, respectively, in 70 patients. Electromyography was recorded by placing electrodes on the bilateral abductor pollicis brevis (APB) and abductor hallucis (AH) muscles. Stimulation conditions were regulated in the range to induce unilateral muscle contractions contralateral to the anodal stimulation. The thresholds and amplitudes of TES-MEP were retrospectively analyzed. RESULTS: The thresholds of APB were lower than those of AH in 47 patients, AH thresholds were lower than those of APB in 6 patients, and both APB and AH started to respond at the same intensity in 15 patients. This technical stimulation induced contralateral limb contractions with a suprathreshold stimulation of 129.4 ± 35.6 mA (mean ± standard deviation) in 68 patients (97%). Amplitudes in the suprathreshold stimulation of APB and AH responses were 727.5 ± 695.7 and 403.3 ± 325.7 µV, respectively. CONCLUSIONS: The C1(+)-C4/C2(+)-C3(-) stimulation in TES-MEP enables a localized stimulation to induce unilateral MEP responses. SIGNIFICANCE: Our stimulation technique enables the stable and safe monitoring of unilateral limbs, and contributes to the reliable monitoring of motor function in neurosurgery.

Visual networks: Electric brain stimulation and diffusion tensor imaging.

OBJECTIVE: The present study investigated the networks of visual functional areas using electric brain stimulation (EBS) and diffusion tensor imaging (DTI). METHODS: Thirteen patients with intractable focal epilepsy in which visual functional areas were identified by EBS were enrolled. An electric stimulation at 50Hz was applied to electrodes during several tasks. DTI was used to identify subcortical fibers originating from the visual functional areas identified by EBS. RESULT: The electrical stimulation induced three types of visual symptoms: visual illusions (change of vision), visual hallucinations (appearance of a new object), and blurred vision. Visual illusions were associated with stimulation of lateral temporo-parieto-occipital areas, and visual hallucinations with stimulation of lateral/basal temporal areas, the occipital lobe and the precuneus. Stimulus intensities eliciting visual illusions were significantly higher than those for visual hallucinations. Tractography revealed that the superior fronto-occipital fasciculus was associated with visual illusions and the middle longitudinal fasciculus with visual hallucinations, and both symptoms shared several subcortical fibers such as the vertical occipital fasciculus, inferior fronto-occipital fasciculus, superior longitudinal fasciculus, inferior longitudinal fasciculus, optic radiations, and commissural fibers. CONCLUSION: The present study revealed the characteristic cortical regions and networks of visual functional areas. The results obtained provide information on human visual functions and are a practical guide for electrical cortical stimulation.

Prediction of Early Postoperative Language Function by Quantitative Evaluation with Visual and Auditory Naming Tasks during Awake Craniotomy for Brain Tumor Resection: Significance of Auditory Naming Task.

Language tasks for monitoring intraoperative language symptoms have not yet been established. This study aimed to examine whether the quantitative evaluation of language function with visual and auditory naming during awake craniotomy predicts early postoperative language function in patients. Thirty-seven patients with brain tumors in the language-dominant hemisphere were included. They underwent visual and auditory naming preoperatively and at the end of tumor resection for intraoperative evaluation. Using the Western Aphasia Battery, their overall language functions were evaluated preoperatively, early postoperatively (within 1 week), and late postoperatively (after 1 month). The preoperative and intraoperative changes in the visual and auditory naming scores were significantly correlated with most of the Western Aphasia Battery score changes between the preoperative and early postoperative evaluations, which was more remarkable for auditory naming. Multiple linear regression analysis showed that changes in the auditory naming score predicted the preoperative to early postoperative changes in the aphasia quotient of the Western Aphasia Battery. Receiver operating characteristics analysis showed a higher area under the curve or discriminative power for auditory than visual naming in predicting the development or exacerbation of aphasia in the early postoperative period. Considering the analyses applied separately for low- and high-grade glioma, auditory naming, which taps into a wider range of linguistic functions, may be more informative than visual naming as language evaluation in awake craniotomy for the early postoperative development of aphasia, especially for patients with high-grade glioma.

Deep learning for the diagnosis of mesial temporal lobe epilepsy.

OBJECTIVE: This study aimed to enable the automatic detection of the hippocampus and diagnose mesial temporal lobe epilepsy (MTLE) with the hippocampus as the epileptogenic area using artificial intelligence (AI). We compared the diagnostic accuracies of AI and neurosurgical physicians for MTLE with the hippocampus as the epileptogenic area. METHOD: In this study, we used an AI program to diagnose MTLE. The image sets were processed using a code written in Python 3.7.4. and analyzed using Open Computer Vision 4.5.1. The deep learning model, which was a fine-tuned VGG16 model, consisted of several layers. The diagnostic accuracies of AI and board-certified neurosurgeons were compared. RESULTS: AI detected the hippocampi automatically and diagnosed MTLE with the hippocampus as the epileptogenic area on both T2-weighted imaging (T2WI) and fluid-attenuated inversion recovery (FLAIR) images. The diagnostic accuracies of AI based on T2WI and FLAIR data were 99% and 89%, respectively, and those of neurosurgeons based on T2WI and FLAIR data were 94% and 95%, respectively. The diagnostic accuracy of AI was statistically higher than that of board-certified neurosurgeons based on T2WI data (p = 0.00129). CONCLUSION: The deep learning-based AI program is highly accurate and can diagnose MTLE better than some board-certified neurosurgeons. AI can maintain a certain level of output accuracy and can be a reliable assistant to doctors.

Effect of remimazolam on intraoperative neurophysiology monitoring of visual-evoked potential: a case series.

There are very few reports on the effects of benzodiazepines such as midazolam and diazepam on intraoperative visual-evoked potential (VEP), and there is no report on the effect of remimazolam at all. Five patients underwent neurosurgery using VEP monitoring for avoiding surgical injury to the optic nerve. In all cases, drug administration was based on actual body weight. General anesthesia was induced with propofol and remifentanil, and then maintained with propofol at target concentrations of 2.7-3.5 µg/ml for maintaining bispectral index (BIS) between 40 and 60. After resection of the tumor under stable VEP, we discontinued propofol immediately followed by infusion of remimazolam at 12 mg/kg/h for a few seconds, then reduced to 1 mg/kg/h. After a time, when blood levels of remimazolam appeared to be stable, VEP was monitored again and compared to controls. In all cases, we were able to confirm that there was reproducibility. Remimazolam may provide a comparable quality of anesthesia to that of existing drugs for VEP in neurosurgery.

Steady-State Cortico-Cortical Evoked Potential.

PURPOSE: The present study evaluated the utility of the steady-state responses of cortico-cortical evoked potentials (SSCCEPs) and compared them with the responses of conventional CCEPs. METHODS: Eleven patients with medically intractable focal epilepsy who underwent the implantation of subdural electrodes or stereoelectroencephalography were enrolled. Conventional CCEPs were obtained by averaging responses to alternating 1-Hz electrical stimuli, and 5-Hz stimuli were delivered for recording SSCCEPs. The distribution of SSCCEPs was assessed by a frequency analysis of fast Fourier transform and compared with conventional CCEPs. RESULTS: Steady-state responses of cortico-cortical evoked potentials were successfully recorded in areas consistent with conventional CCEPs in all patients. However, SSCCEPs were more easily disturbed by the 5-Hz stimulation, and small responses had difficulty generating SSCCEPs. CONCLUSIONS: Steady-state responses of cortico-cortical evoked potentials may be a useful alternative to conventional CCEPs.

The intraoperative motor-evoked potential when propofol was changed to remimazolam during general anesthesia: a case series.

Remimazolam is a short-acting benzodiazepine that was approved for clinical use in 2020. We report three patients who underwent surgery for cerebral and spinal cord tumors, in whom transcranial electrical stimulation-motor-evoked potential (TES-MEP) was successfully monitored under general anesthesia with remimazolam. During total intravenous anesthesia with propofol at a target concentration of 2.7 - 3.5 µg/mL and 0.1 - 0.35 µg/kg/min of remifentanil, delayed awakening, bradycardia, and hypotension during propofol anesthesia were expected in all three cases. With patient safety as the top priority, we considered changing the anesthetic agent. Propofol was replaced with remimazolam at a loading dose of 12 mg/kg/h for a few seconds (case 3), followed by 1 mg/kg/h for maintenance (cases 1-3). TES-MEP was recorded during propofol and remimazolam administration in all three patients. Amplitudes of TES-MEP during anesthesia with propofol and remimazolam were 461.5 ± 150 µV and 590.5 ± 100.9 µV, 1542 ± 127 µV and 1698 ± 211 µV, and 581.5 ± 91.3 µV and 634 ± 82.7 µV sequentially from Case 1. Our findings suggest that intraoperative TES-MEP could be measured when anesthesia was managed with remimazolam at 1 mg/kg/h.

Usefulness of Intraoperative Electrocorticography for the Localization of Epileptogenic Zones.

Intraoperative electrocorticography (iECoG) is widely performed to identify irritative zones in the cortex during brain surgery; however, several limitations (e.g., short recording times and the effects of general anesthesia) reduce its effectiveness. The present study aimed to evaluate the utility of iECoG for localizing epileptogenic zones. We compared the results of iECoG and chronic electrocorticography (cECoG) in 25 patients with refractory epilepsy. Subdural electrodes were implanted with iECoG under general anesthesia (2% sevoflurane). cECoG recordings were performed for 3-14 days. The distribution of iECoG spikes was compared with cECoG spike, seizure onset zone, and resection areas. The concordance patterns of each distribution were classified into four patterns: Group 1: No spike in iECoG, Group 2: concordant (2a: iECoG smaller, 2b: iECoG larger, Group 3: discordant >50%). The concordance rate of interictal spikes, seizure onset zones, and resection areas were 88.0% (Group 2a: 72.0%, Group 2b: 16.0%), 70.0% (Group 2a: 25.0%, Group 2b: 45.0%), and 81.0% (Group 2a: 42.9%, Group 2b: 38.1%), respectively. The resection of iECoG spike areas significantly correlated with good surgical outcomes. The indication and limitations of iECoG need to be realized, and the complementary use of iECoG and cECoG may enhance clinical utility.

Male sex and presence of preoperative symptoms are associated with early recurrence of WHO grade I meningiomas after surgical resection: analysis from the nationwide Brain Tumor Registry of Japan.

This study aimed to assess the risk factors for the recurrence of WHO grade I intracranial meningiomas using the Brain Tumor Registry of Japan (BTRJ) database. We extracted the data of 4641 patients with intracranial WHO grade I meningiomas treated only by surgical resection between 2001 and 2008. We conducted complete data analysis (n = 3690) and multiple imputation analysis (n = 4641) to adjust for missing data on tumor size. The influence of factors including age, sex, size, extent of resection, location, and preoperative symptoms on PFS was assessed. Univariate analyses of the complete data set showed that age did not affect PFS; however, male sex (p < 0.001), tumor size ≥ 30 mm (p < 0.001), low extent of resection, tumor location at the skull base (p < 0.001), and the presence of preoperative symptoms (p < 0.001) were risk factors for a significantly shorter PFS. Multivariate analysis demonstrated that male sex (p < 0.001) and presence of preoperative symptoms (p = 0.027) were independent risk factors for shorter PFS alongside large tumor size (p < 0.001) and non-gross total resection (p < 0.001). These results were confirmed for the imputed dataset. While most previous large nationwide studies of meningiomas have evaluated overall survival, progression-free survival has yet to be thoroughly examined. This study suggests that even histologically benign meningiomas may have a sex difference in postoperative behavior. This observation may provide clues to understanding the mechanism of meningioma cell proliferation.

A Case of Perimesencephalic Subarachnoid Hemorrhage with Cerebral Venous Sinus Thrombosis due to Stenosis of the Junction of the Vein of Galen and Rectus Sinus.

Perimesencephalic subarachnoid hemorrhage (PMSAH) is a group of diseases characterized by bleeding around the brainstem. In recent years, it has been suggested that PMSAH is associated with the venous system. We report a case of PMSAH caused by stenosis of the junction of the vein of Galen (VG) and the rectus sinus (RS). A 39-year-old man presented with restlessness at work. He was administered diazepam, and a few minutes later, his consciousness became clear. Imaging showed subarachnoid hemorrhage (SAH) around the right midbrain, occlusion of the right sigmoid sinus and the right transverse sinus, stenosis of the junction of the VG and RS, T2 hyperintensity in the right middle temporal gyrus, and obstruction of the right vein of Labbe. The location of the SAH coincided with stenosis of the junction of the VG and RS. PMSAH was diagnosed due to the increase in intracranial venous pressure caused by the patient's sinus obstruction in addition to the stenosis of the junction of the VG and RS. It is necessary to pay attention to venous return when PMSAH is observed.

Validity of Preoperative Screening Before Open-Heart Surgery in Reduction of Perioperative Ischemic Stroke.

OBJECTIVES: Cerebrovascular event after open-heart surgery is a critical complication and contributes to poor prognosis, including increased mortality. The purpose of this study is to investigate the appropriate preoperative risk assessment and monitoring for reducing the risk of ischemic stroke after open-heart surgery. MATERIALS AND METHODS: 184 patients who underwent surgery for valvular heart disease were included in this study. Near-infrared oxygen saturation monitoring (INVOS system) was performed during open-heart surgery. For the purpose of perioperative stroke risk assessment, we evaluated the clinical and radiological factors of the group that underwent preoperative consultation and the group that did not, and of the patients with and without postoperative ischemic stroke. RESULTS: Preoperative consultation was performed in 60 cases. Large vessel steno-occlusive disease was found in nine cases, of which three had undergone revascularization surgery. Cerebral infarction developed in four cases, all of which had no large vessel steno-occlusive disease. There was no significant association between the development of postoperative ischemic stroke and presence of large vessel steno-occlusive disease. Preoperative baseline INVOS value was significantly low in the ischemic stroke group (49.5 ± 12.5) compared to the non-ischemic stroke group (66.8 ± 10.0), (P = 0.012). CONCLUSIONS: In open-heart surgery for valvular heart disease, low preoperative baseline INVOS values were associated with cerebral ischemic stroke after surgery. The combination of appropriate preoperative screening for large vessel steno-occlusive disease and measurement of INVOS could be used as a simple and useful method in screening for the risk of ischemic stroke after open-heart surgery.

Comparison of Thresholds between Bipolar and Monopolar Electrical Cortical Stimulation.

Electrical cortical stimulation is widely performed and is the gold standard for functional mapping in intractable epilepsy patients; however, a standard protocol has not yet been established. With respect to stimulation methods, two techniques can be applied: monopolar and bipolar stimulation. We compared the threshold to induce clinical symptoms between these two stimulation techniques. Twenty patients with intractable epilepsy who underwent electrical cortical stimulation for functional mapping were retrospectively investigated. We evaluated the stimulation intensity thresholds required to induce motor, sensory, and language symptoms. A total of 114 electrodes in 20 patients were used to investigate motor, sensory, and language symptoms. The thresholds required to induce motor (median value, bipolar: 4 mA, monopolar: 5 mA, p < 0.05) and language symptoms (bipolar: 8 mA, monopolar: 10 mA, p < 0.0005) were significantly higher for monopolar stimulation than those for bipolar stimulation. However, for sensory symptoms, no significant differences were found in the required thresholds between monopolar and bipolar stimulation (bipolar: 4 mA, monopolar: 4 mA, p = 0.474). Bipolar cortical stimulation required lower intensities to produce clinical motor and language symptoms and thus would be safe and suitable for screening of the eloquent area in functional mapping.