Risk factors for intraoperative stimulation-related seizures during awake surgery: an analysis of 109 consecutive patients.

INTRODUCTION: During surgery for lesions in eloquent areas the goal is to achieve the widest resection possible, without loss of neurological function. Intraoperative seizures may lead to abandonment of the procedure or damages to the patient. Awareness regarding the predictors of IOS would help the surgeon. The aim of this retrospective study was to identify the factors associated with the occurrence of IOS in patients who underwent awake surgery for removal of gliomas in eloquent areas. METHODS: This was a retrospective analysis of prospectively collected data of 109 patients who underwent awake craniotomy between January 2010 and December 2017 for removal of gliomas. IOS were defined as tonic-clonic seizures or loss of consciousness resulting in communication difficulties with the patient occurring during cortical and subcortical mapping. RESULTS: A total of 109 patients were included in this study and IOS occurred in 9 (8.2%) patients. Demographic and clinical factors were comparable between patients with and without IOS. In the IOS group, 7 (77.8%) patients had seizures preoperatively and 4 (57.1%) were on more than one perioperative antiepileptic drugs (AED). CONCLUSIONS: The current series add some hints to the poorly studied IOS risk during awake surgery. The risk of IOS appears to be relatively higher in patients with anteriorly located tumors and in patients operated without intraoperative brain activity monitoring and different patterns of stimulation for language and sensory-motor mapping. Further studies are needed to clarify the role of intraoperative techniques.

Impact of intraoperative stimulation mapping on high-grade glioma surgery outcome: a meta-analysis.

BACKGROUND: Intraoperative stimulation mapping (ISM) using electrocortical mapping (awake craniotomy, AC) or evoked potentials has become a solid option for the resection of supratentorial low-grade gliomas in eloquent areas, but not as much for high-grade gliomas. This meta-analysis aims to determine whether the surgeon, when using ISM and AC, is able to achieve improved overall survival and decreased neurological morbidity in patients with high-grade glioma as compared to resection under general anesthesia (GA). METHODS: A systematic search was performed to identify relevant studies. Adult patients were included who had undergone craniotomy for high-grade glioma (WHO grade III or IV) using ISM (among which AC) or GA. Primary outcomes were rate of postoperative complications, overall postoperative survival, and percentage of gross total resections (GTR). Secondary outcomes were extent of resection and percentage of eloquent areas. RESULTS: Review of 2049 articles led to the inclusion of 53 studies in the analysis, including 9102 patients. The overall postoperative median survival in the AC group was significantly longer (16.87 versus 12.04 months; p < 0.001) and the postoperative complication rate was significantly lower (0.13 versus 0.21; p < 0.001). Mean percentage of GTR was significantly higher in the ISM group (79.1% versus 47.7%, p < 0.0001). Extent of resection and preoperative patient KPS were indicated as prognostic factors, whereas patient KPS and involvement of eloquent areas were identified as predictive factors. CONCLUSIONS: These findings suggest that surgeons using ISM and AC during their resections of high-grade glioma in eloquent areas experienced better surgical outcomes: a significantly longer overall postoperative survival, a lower rate of postoperative complications, and a higher percentage of GTR.

Hearing preservation after removal of small vestibular schwannomas by retrosigmoid approach: comparison of two different ABR neuromonitoring techniques.

BACKGROUND AND OBJECTIVE: Goals of small vestibular schwannoma (VS) microneurosurgery are as follows: radical resection, facial nerve (FN) preservation, and hearing preservation (HP). Microsurgical advances make HP possible in many patients with preoperative socially useful hearing (SUH). We evaluated postoperative HP in VS with maximum diameter < 2 cm monitored with two different auditory brainstem response (ABR) techniques. MATERIALS AND METHODS: Twenty-eight consecutive non-randomized patients with SUH suffering from small VS underwent keyhole microneurosurgery by retrosigmoid (RS) approach. Selection criteria are as follows: speech discrimination > 50%, pure tone audiogram < 50 dB loss (50/50 criterion; AAO-HNS classes A-B), maximum diameter < 2 cm. HP was attempted with intraoperative ABR, evoked by classical Click (16 cases, group 1) and LS-CE-Chirp® stimulus (12, group 2). RESULTS: Mean age was 47.5 years (16-75); average maximum diameter was 1.35 cm (0.5-1.9 mm). Total and nearly total resection (> 95%) was obtained in all, as confirmed by 24-48-h postoperative enhanced MRI. Mortality and major morbidity were 0. In all cases, FN was preserved; in 3, incomplete deficit recovered within few weeks. Socially useful HP (pre- and postoperatively) was 64.3% (18 of 28): 56.25% group 1 and 75% group 2 (p = NS). Postoperative ipsilateral deafness was observed in 5 cases of group 1 (p < 0.0001). Preoperative tinnitus had negative impact on HP (p < 0.05). CONCLUSIONS: Microsurgery can cure small growing VS with SUH. Our limited experience confirms that keyhole RS removal assisted by intraoperative ABR monitoring leads to valuable rates of SUH. LS-CE-Chirp-evoked ABRs allow a safe, effective, and clear neurophysiological feedback and are faster and, thus, more useful than the Click-ABR.

Robot-guided neuromapping during nerve-sparing taTME for low rectal cancer.

PURPOSE: Intraoperative pelvic neuromapping with electrophysiological evaluation of autonomic nerve preservation during robotic total mesorectal excision (TME) for rectal cancer is conventionally performed by the bedside assistant with a hand-guided probe. Our goal was to return autonomy over the neuromonitoring process to the colorectal surgeon operating the robotic console. METHODS: A recently described prototype microfork electrostimulation probe was evaluated intraoperatively during abdominal robotic-assisted transanal TME (taTME) surgery for low rectal cancer in three consecutive male patients. RESULTS: An intraoperative video demonstrates the good control and maneuverability of the prototype probe with electrophysiological confirmation of bilateral pelvic autonomic nerve preservation. CONCLUSIONS: This study presents the first in situ application of a new microfork probe for fully robot-guided neuromapping in three patients undergoing TME surgery for low rectal cancer.

Does the Use of Intraoperative Microelectrode Recording Influence the Final Location of Lead Implants in the Ventral Intermediate Nucleus for Deep Brain Stimulation?

To determine if the use of intraoperative microelectrode recording (MER) influences the final location of lead implant in deep brain stimulation (DBS) of the ventral intermediate nucleus (VIM), and to evaluate the incidence of associated complications. The usefulness of intraoperative MER in DBS is debated, some centers suggesting it increases complications without additional benefit. We conducted a retrospective chart review of all patients who underwent VIM DBS with MER at the University of Texas Health Science Center in Houston from June 1, 2009 to October 1, 2013. Initial (MRI determined) and final (intraoperative MER determined) coordinates of implant were compared. To assess incidences of hemorrhagic and infectious complications, we reviewed postoperative CT scans and follow-up notes. Forty-five lead implants on 24 patients were reviewed. The mean age at implantation was 62.42 years (range 18-83). The average duration from diagnosis to surgery was 21.5 years (range 1-52). A statistically significant mean difference was observed in the superior-inferior plane (0.52 ± 0.80 mm inferiorly, p < 0.05) and the anterior-posterior plane (0.45 ± 0.86 mm posteriorly, p < 0.05). A non-statistically significant difference was also observed in the medial-lateral plane (0.02± 0.15 mm, p > 0.05). One patient developed an infectious complication (4.2 %) that required removal of leads; two patients had minimal asymptomatic intra-ventricular bleeding (8.3 %). In our DBS center, intraoperative MER in VIM DBS implant does not seem to have a higher rate of surgical complications compared to historical series not using MER, and might also be useful in determining the final lead location.

[Intraoperative monitoring of the facial nerve : Vestibular schwannoma surgery]. / Intraoperative Funktionsüberwachung des N. facialis : Operationen an Vestibularisschwannomen.

BACKGROUND: In vestibular schwannoma surgery, facial nerve injury with consecutive functional impairment is one of the most important complications. Intraoperative monitoring of facial nerve function has been developed in order to avoid this complication. OBJECTIVE: Which methods for intraoperative monitoring have been developed? Which methods are in use today and what can they achieve in modern vestibular schwannoma surgery? MATERIAL AND METHODS: This article provides an evaluation and summary of the literature, as well as a discussion of the methods and their ability to achieve the goals of intraoperative monitoring. RESULTS: Intraoperative functional monitoring aims to identify and map the facial nerve in the surgical field during surgery. It also aims to identify potentially damaging events and allow for intraoperative prognosis of functional outcome. Available methods are direct electrical stimulation, free-running electromyogram (EMG), facial nerve evoked potentials, and processed EMG. CONCLUSION: Identification and mapping of the facial nerve in the surgical field can be reliably achieved by direct electrical stimulation; potentially dangerous events can be identified in real time by the free-running EMG and the processed EMG, and almost in real time by facial nerve evoked potentials. Intraoperative prognostics are hampered by false-positive results with all available methods and have limited reliability.

Dorsal Rhizotomy in the Pediatric Patient.

SUMMARY: The majority of cases of dorsal rhizotomy surgeries in children are done to improve the spasticity associated with cerebral palsy, and more recent techniques are selective in nature and referred to as selective dorsal rhizotomy (SDR). The techniques applied to selective dorsal rhizotomy surgery has changed since it was first described and continues to undergo modifications. Approaches to surgery and monitoring vary slightly among centers. This article provides a review of the rationale, variety of surgical approaches, and intraoperative neurophysiologic monitoring methods used along with discussion of the risks, complications and outcomes in these surgeries.

Multi-sensor esophageal temperature probe used during radiofrequency ablation for atrial fibrillation is associated with increased intraluminal temperature detection and increased risk of esophageal injury compared to single-sensor probe.

BACKGROUND: Radiofrequency (RF) ablation in the posterior left atrium has risk of thermal injury to the adjacent esophagus. Increased intraluminal esophageal temperature has been correlated with risk of esophageal injury. The objective of this study was to compare esophageal temperature monitoring (ETM) using a multi-sensor temperature probe with 12 sensors to a single-sensor probe during catheter ablation for atrial fibrillation (AF). METHODS AND RESULTS: We compared the detection of intraluminal esophageal temperature rises in 543 patients undergoing RF ablation for AF with ETM. Esophageal endoscopy (EGD) was performed on all patients with maximum esophageal temperature ≥ 39°C. Esophageal lesions were classified by severity as mild or severe ulcerations. Four hundred fifty-five patients underwent RF ablation with single-sensor ETM and 88 patients with multi-sensor ETM. Thirty-nine percent of patients with single-sensor versus 75% with multi-sensor ETM reached a maximum detected esophageal temperature ≥ 39°C (P < 0.0001). Esophageal injury was detected by EGD in 29% of patients with maximum temperature ≥ 39°C by single-sensor versus 46% of patients with multi-sensor ETM (P = 0.021). Thirty-nine percent of patients with lesions in the single-sensor probe group had severe ulcerations compared to 33% of patients in the multi-sensor probe group (P = 0.641). CONCLUSIONS: Intraluminal esophageal temperature ≥ 39°C is detected more frequently by the multi-sensor temperature probe versus the single-sensor probe, with more frequent esophageal injury and with comparable severity of injury. Despite detecting esophageal temperature rises in more patients, the multi-sensor probe may not have any measurable benefit compared to a single-sensor probe.

Neurophysiological Intraoperative Monitoring in Patients with Cochlear Implant Undergoing Posterior Spinal Fusion: A Case Report.

CASE: Transcranial electric stimulation motor-evoked potentials (tcMEPs) are the most sensitive technique in multimodality intraoperative neuromonitoring (IONM) for posterior spinal fusion (PSF). The presence of a cochlear implant (CI) is considered a contraindication to IONM because of theoretical risk of implant device and local tissue damage from voltages induced by tcMEPs. We present the case of a 10-year-old girl with CI who underwent successful PSF with tcMEP and monopolar electrocautery (MoEC) without perioperative complications or CI damage. CONCLUSION: With proper precautions, such as MoEC usage at a minimal voltage, motor-evoked potential monitoring can be safely performed in pediatric patients with CI undergoing PSF.

Intraoperative neurophysiologic monitoring in thoracoabdominal aortic aneurysm surgery can provide real-time feedback for strategic decision making.

OBJECTIVES: Despite the introduction of several adjuncts to improve spinal perfusion, spinal cord ischemia (SCI) remains a devastating complication of thoracoabdominal aortic aneurysm (TAAA) repair. Our aim was to assess the effects on clinical outcome of interventions triggered by motor evoked potentials (MEP) alerts. Furthermore, we want to assess whether a multimodal intraoperative neurophysiologic monitoring (IONM) protocol is helpful for stratifying patients according to the risk of SCI at the end of the vascular phase of surgery. METHODS: We prospectively studied one-hundred consecutive patients who underwent TAAA repair. We applied a multimodal IONM including MEP, somatosensory evoked potentials (SEP) and peripheral nerve monitoring techniques. Signal deteriorations were classified as reversible/irreversible according to whether they recovered or not at the end of monitoring (EOM), set at the end of the vascular phase of surgery. Significant MEP changes drove a series of corrective measures aimed to improve spinal perfusion. RESULTS: The rate of immediate postoperative motor deficits consistent with SCI was significantly higher with irreversible MEP deteriorations compared to reversible ones. The interpretation of MEP findings at the EOM led to the development of risk categories for SCI, based on the association between MEP results and motor outcome. CONCLUSIONS: Our data seem to justify interventions made to reverse MEP deterioration in order to improve the clinical outcome. A multimodal IONM protocol could improve MEP interpretation at the end of the vascular phase of surgery, supporting the surgeon in their decision-making, before concluding vascular maneuvers.

Predicting transient ischemic attack after carotid endarterectomy: The role of intraoperative neurophysiological monitoring.

OBJECTIVE: Transient ischemic attacks (TIA) after carotid endarterectomy (CEA) are not well-studied. We aimed to investigate the characteristics and the predictive role of intraoperative neurophysiological monitoring (IONM) in TIA post-CEA. METHODS: Patients who underwent CEA utilizing IONM from 2009-2020 were included. Analyses included TIA incidence, sensitivity, specificity, and predictive values of IONM, risk factor regression analyses, and mortality Kaplan Meier plots. RESULTS: Out of 2232 patients, 46 experienced TIA, 14 of which were within 24 hours of CEA (p < 0.01). Nine of these patients displayed significant IONM changes during CEA. The odds of TIA increased with somatosensory evoked potential (SSEP) changes (Odds Ratio (OR): 2.48 95% Confidence Interval (CI): 1.14-5.4), electroencephalogram (EEG) changes (OR: 2.65 95% CI: 1.22-5.77), and combined SSEP/EEG changes (OR: 2.98 95% CI: 1.17-7.55). Patients with TIA were less likely to be alive after an average of 4.3 years (OR: 0.5 95% CI: 0.26-0.96). CONCLUSIONS: The odds a patient will have TIA post-CEA are greater in patients with IONM changes. This risk is inversely related to the time post-CEA. SIGNIFICANCE: Changes in IONM during CEA predict postoperative TIA. Post-CEA TIA may increase long-term mortality, thus further research is needed to better elucidate clinical implications of postoperative TIA.

Influence of Intraoperative Microelectrode Recording in Deep Brain Stimulation.

BACKGROUND: There is considerable debate regarding the use of intraoperative microelectrode recording (MER) in deep brain stimulation (DBS). OBJECTIVE: To determine if the use of intraoperative MER impacts the final position of the lead implant in DBS of the subthalamic nucleus (STN) and globus pallidus (GPi) and to evaluate the incidence of complications. METHODS: The authors conducted a retrospective chart review of all patients who underwent STN and GPi DBS with MER, at the University of Texas Health Science Center in Houston from June 1, 2009 to October 1, 2013 to compare initial and final coordinates. Hemorrhagic and infectious complications were reviewed. RESULTS: A total of 90 lead implants on 46 patients implanted at the center during this time period were reviewed and included in the study. A statistically significant difference between the initial and final coordinates was observed in the superior-inferior direction with a mean difference of 0.40 mm inferiorly (±0.96 mm, P<0.05) and 0.96 mm inferiorly (±1.32 mm, P<0.05) in the STN and GPi locations, respectively. A nonstatistically significant difference was also observed in the anterior-posterior direction in both locations. There were no intraparenchymal hemorrhages on postoperative computed tomography. Two patients developed postoperative seizures (7.4%). One STN electrode (1.1%) required revision because of a suboptimal response. CONCLUSIONS: Intraoperative MER in STN and GPi DBS implant does not seem to have a higher rate of surgical complications compared with historical series not using MER and might also be useful in determining the final lead location.

A Review of Techniques, Time Demand, Radiation Exposure, and Outcomes of Skin-anchored Intraoperative 3D Navigation in Minimally Invasive Lumbar Spinal Surgery.

STUDY DESIGN: Retrospective cohort. OBJECTIVE: To describe our technique for and evaluate the time demand, radiation exposure and outcomes of skin-anchored intraoperative three-dimensional navigation (ION) in minimally invasive (MIS) lumbar surgery, and to compare these parameters to 2D fluoroscopy for MI-TLIF. SUMMARY OF BACKGROUND DATA: Limited visualization of anatomic landmarks and narrow access corridor in MIS procedures result in greater reliance on image guidance. Although two-dimensional fluoroscopy has historically been used, ION is gaining traction. METHODS: Patients who underwent MIS lumbar microdiscectomy, laminectomy, or MI-TLIF using skin-anchored ION and MI-TLIF by the same surgeon using 2D fluoroscopy were selected. Operative variables, radiation exposure, and short-term outcomes of all procedures were summarized. Time-demand and radiation exposure of fluoroscopy and ION for MI-TLIF were compared. RESULTS: Of the 326 patients included, 232 were in the ION cohort (92 microdiscectomies, 65 laminectomies, and 75 MI-TLIFs) and 94 in the MI-TLIF using 2D fluoroscopy cohort. Time for ION setup and image acquisition was a median of 22 to 24 minutes. Total fluoroscopy time was a median of 10 seconds for microdiscectomy, 9 for laminectomy, and 26 for MI-TLIF. Radiation dose was a median of 15.2 mGy for microdiscectomy, 16.6 for laminectomy, and 44.6 for MI-TLIF, of this, 93%, 95%, and 37% for microdiscectomy, laminectomy, and MI-TLIF, respectively were for ION image acquisition, with the rest attributable to the procedure. There were no wrong-level surgeries. Compared with fluoroscopy, ION for MI-TLIF resulted in lower operative times (92 vs. 108 min, P < 0.0001), fluoroscopy time (26 vs. 144 s, P < 0.0001), and radiation dose (44.6 vs. 63.1 mGy, P = 0.002), with equivalent time-demand and length of stay. ION lowered the radiation dose by 29% for patients and 55% for operating room personnel. CONCLUSION: Skin-anchored ION does not increase time-demand compared with fluoroscopy, is feasible, safe and accurate, and results in low radiation exposure. LEVEL OF EVIDENCE: 3.

Bradycardic Arrest During Somatosensory-Evoked Potential Monitoring: A Case Report.

Intraoperative neurophysiological monitoring involves electrical stimulation of nerve pathways and is used to assess the integrity of both motor and sensory pathways. Whereas motor pathway monitoring involves transcranial stimulation and peripheral nerve monitoring, somatosensory monitoring involves peripheral nerve stimulation and cranial monitoring. Arrhythmias are a known complication of motor-evoked potential monitoring but have not been reported with somatosensory monitoring. We describe a case of bradycardic arrest with somatosensory-evoked potential monitoring using median nerve electrodes in a patient with no previous rhythm abnormality. Clinicians caring for patients receiving somatosensory monitoring should be aware of the potential for severe arrhythmias.

Crossover Phenomena in Motor Evoked Potentials During Intraoperative Neurophysiological Monitoring of Cranial Surgeries.

PURPOSE: Transcranial motor evoked potentials (TcMEPs) are used to assess the corticospinal tract during surgery. Transcranial motor evoked potentials are elicited by preferentially activating the anode over the target cortex. Crossover occurs when stimulation also induces activation of ipsilateral motor evoked responses. These responses are believed to be generated by activation of corticospinal tract on more caudal neural structures. The presence of cross activation poses a problem in craniotomy surgeries because activation of neural structures occurs distal to the area of interest leading to false negatives. Eliminating crossover may lead to activation of the motor pathway proximal to the surgical site, thus potentially reducing false-negative responses. There are no data on how often crossover signals occur or the conditions in which they take place. This study examines the frequency of crossover, the surgical procedures in which they occur, and their stimulation parameters. METHODS: We reviewed all the TcMEP data files for intracranial procedures performed in 2016 at Keck Hospital of USC. We recorded demographic information about the surgical side, lobe, diagnosis, age, and sex. Only baseline TcMEPs were analyzed. Crossover responses were deemed present if recorded amplitudes were greater than 25µv on the ipsilateral side. We evaluated the rate of crossover presence, the lowest voltage associated with crossover, the highest voltage without crossover, if crossover resolved, and the last muscles to remain present when crossover is eliminated. Transcranial motor evoked potentials were divided into four groups. Group A: crossover present and was not resolved, group B1: crossover present but resolved with desired signals, group B2: no crossover seen with desired signals in both limbs, and group C: crossover resolved with loss of signals in either limb. The Difference between lowest amplitude with crossover and highest amplitude without crossover was obtained for each patient, and the mean of this difference was calculated using paired t-test. RESULTS: We analyzed 186 TcMEPs. Forty-four TcMEPs were in group A, 52 in B1, 68 in B2, and 22 TcMEPs were in group C. Of total crossovers (118), 63% resolved at baseline, whereas 37% did not resolve. The mean difference between minimum value with crossover and maximum value without crossover was 50 V (P < 0.0001). In five TcMEPs, this difference was 0 and the median was 250 V. There was no significant difference between surgical site, stimulation side, pathology, or sex between crossover (A) and noncrossover (B + C) groups. There was a significant association found between age group ≤50 years versus >50 years and being in crossover versus noncrossover groups (P = 0.01). For 95% of the cases in group C, the last muscles to stay were hand muscles. CONCLUSIONS: Transcranial motor evoked potential crossover may pose a problem during surgeries leading to false-negative results. Crossover is a frequent phenomenon that should not be overlooked. Stimulation intensity is the main factor contributing to the reduction of crossover. Crossover can be reduced in most TcMEPs performed (63%) leading to adequate monitoring in 76% of TcMEPs. Despite best efforts, there are still one quarter (24%) of TcMEPs where crossover cannot be eliminated. Newer strategies should be sought to reduce crossover. Teams should focus their efforts on reducing crossover of TcMEPs to make monitoring of intracranial surgeries more reliable.

Adverse Events Related to Transcranial Electric Stimulation for Motor-evoked Potential Monitoring in High-risk Spinal Surgery.

STUDY DESIGN: Prospective multicenter study. OBJECTIVE: The aim of this study was to study the incidence of nonneurologic adverse events related to transcranial electric stimulation (TES) for intraoperative spinal cord monitoring (IOM) with motor-evoked potentials (MEPs) (Tc(E)- MEPs) and determine the need for safety precautions. SUMMARY OF BACKGROUND DATA: Tc(E)-MEPs monitoring requires high-voltage multipulse TES that causes widespread muscle contraction and movement. Improved awareness of TES-induced movement-related adverse events is needed. METHODS: We analyzed data from 2643 patients who underwent high-risk spinal surgery with intraoperative Tc(E)-MEPs at 11 spinal centers from 2010 to 2016. Information about neurologic and non-neurologic postoperative complications was collected, including type of surgical procedure, operative time, estimated blood loss, and treatment for postoperative adverse events. RESULTS: A 70% drop in Tc(E)-MEPs amplitude, which was the alarm criterion to interrupt surgery, predicted postoperative motor deficits with 93.5% sensitivity, 91.0% specificity, a false-positive rate of 8.2%, and a false-negative rate of 0.3%. Non-neurologic adverse events developed in 17 (0.64%) patients and were most commonly because of bite injuries (0.57%), including 11 cases of tongue laceration, two cases of lip laceration, and two cases of tooth breakage. Four (0.15%) tongue lacerations required surgical repair with sutures and two tooth breakages required dental treatment. One patient had hair loss corresponding to the TES site. One patient, who underwent additional IOM with transpharyngeal stimulation, had severe nasal hemorrhage following electrode placement by nasal route, which resolved spontaneously. Non-neurologic adverse events did not significantly affect the accuracy of IOM assessment. Neither operative times nor blood loss significantly influenced the occurrence of adverse events. CONCLUSION: During TES-IOM, both the surgeon and monitoring team must consider the possibility-although rare-of non-neurologic adverse events, particularly bite injuries. Such complications can be minimized by using a soft bite-block and frequently evaluating the intraoral integrity of the anesthetized patient. LEVEL OF EVIDENCE: 4.

Superselective methohexital challenge prior to intracranial endovascular embolization.

Pharmacologic provocative testing (PT) and intraoperative neurophysiologic monitoring (IONM) both mitigate and predict risks associated with endovascular embolization procedures. We present a series of patients undergoing endovascular intracranial embolization predominantly for AVMs both under general anesthesia and awake with the use of IONM. We reviewed our database to identify all patients undergoing endovascular procedures between January 1, 2014 and January 1, 2016. Awake patients were tested with SSEP, EEG and real time neurologic examination while TcMEPs were performed in all anesthetized patients. BAEPs were performed in anesthetized patients if indicated. Methohexital was administered as an injection at a dose of 5 mg or 10 mg and repeat testing was performed if needed.Sixty-three endovascular procedures that met criteria were performed in 32 patients. 54 procedures in 28 patients were performed under general anesthesia, 9 procedures in 4 patients were performed in wakefulness. PT was negative in 61 procedures and subsequently completed embolizations without neurological sequelae. In two cases, the testing was positive and the procedure was terminated without embolization in one patient. The other patient underwent embolization at an alternative site without repeat PT. There were no new postoperative neurologic deficits after any of these procedures. Specificity of PT was 100% as none of the patients with a negative provocative test developed a new postoperative neurologic deficit after embolization. To our knowledge, this is the first review of PT with the use of neurophysiologic IONM techniques under general anesthesia. These data suggest a high specificity comparable to awake testing.

Modeling of Brain Tissue Heating Caused by Direct Cortical Stimulation for Assessing the Risk of Thermal Damage.

This paper aims to employ the numerical simulations to assess the risk of cellular damage during the application of a novel paradigm of electrical stimulation mapping (ESM) used in neurosurgery. The core principle of the paradigm is the use of short, high-intensity and high-frequency stimulation pulses. We developed a complex numerical model and performed coupled electro-thermal transient simulations. The model was optimized by incorporating ESM electrodes' resistance obtained during multiple intraoperative measurements and validated by comparing them with the results of temperature distribution measurement acquired by thermal imaging. The risk of heat-induced cellular damage was assessed by applying the Arrhenius equation integral on the computed time-dependent spatial distribution of temperature in the brain tissue. Our results suggest that the impact of the temperature increase during our novel ESM paradigm is thermally non-destructive. The presented simulation results match the previously published thermographic measurement and histopathological examination of the stimulated brain tissue and confirm the safety of the novel ESM.

Characterizing the Intraoperative Microelectrode Recording-Induced Microlesion Effect on Motor Symptoms in Patients with Parkinson's Disease Undergoing Deep Brain Stimulation of the Subthalamic Nucleus.

AIM: To investigate microelectrode recording (MER)-induced microlesion effect (MLE) on the motor symptoms of 30 patients with Parkinson’s disease (PD) who underwent deep brain stimulation of the subthalamic nucleus. MATERIAL AND METHODS: MER-induced MLE was evaluated based on the difference between tremor, rigidity, and bradykinesia scores in the preoperative off-state and intraoperative state following MER and before test stimulation. RESULTS: MLE scores improved by 21.7% [left (L) side] and by 13.6% [right (R) side] from baseline (p < 0.05). Tremor scores improved by 31.5% (L) and by 14.2% (R) (p < 0.05), rigidity scores improved by 17.3% (L) and by 14.2% (R) (p < 0.05) and bradykinesia scores improved by 20.6% (L) and by 11.5% (R) (p < 0.05) from baseline. There was no significant difference between MLE and the number of microelectrodes used (p > 0.05). CONCLUSION: MER-induced MLE improved motor symptoms and was not correlated with the number of microelectrodes used during the procedure.

Factors that modify the risk of intraoperative seizures triggered by electrical stimulation during supratentorial functional mapping.

OBJECTIVE: Intraoperative mapping via electrical stimulation is the gold standard technique for surgeries close to the eloquent cortex. However, it can trigger seizures which immediately impact patient's safety. We studied whether administration of antiepileptic drugs (AED) prior to and/or at the beginning of the surgery decreases the probability of triggering seizures, while adjusting for other risk factors. METHODS: 544 consecutive intraoperative mapping cases performed at a tertiary care center for epilepsy and brain tumor surgery were included in the study. Using a multivariate logistic regression analysis, we analyzed the independent impacts of AED loading at time of surgery, preoperative AED maintenance, history of seizures, type of stimulation paradigm, lobar location of stimulation, age, opioid administration and pathology on the probability of triggering seizures. RESULTS: Seizures were identified in 135 patients. Intravenous loading with AED decreased the odds of triggering seizures by 45% (OR = 0.55, p = 0.01), Penfield (versus multipulse train) stimulation and diffuse (versus well circumscribed) pathology increased it twice (OR = 1.97, p = 0.01) and 2.4 times (OR = 2.42, p = 0.003) respectively. No other factors had a significant impact. CONCLUSIONS: Seizures triggered during mapping occur frequently and are multifactorial. SIGNIFICANCE: Loading with AED independently reduces the risk of their occurrence.