Motor Evoked Potential Monitoring Research Articles

Motor evoked potential monitoring can evaluate ischemic tolerance to carotid artery occlusion during surgery.

Balloon test occlusion (BTO) is a useful examination for evaluating ischemic tolerance to internal carotid artery (ICA) occlusion. The aim of this study was to investigate the relationships between intraoperative motor evoked potential (MEP) monitoring and the results of preoperative BTO. Between 2013 and 2017, 32 patients undergoing surgery under general anesthesia with intraoperative MEP monitoring, in whom preoperative BTO was performed, were identified. A receiver operator characteristic (ROC) analysis was performed to determine the appropriate cutoff value of MEP amplitude for BTO-positive. Furthermore, the accuracy of MEP monitoring for BTO-positive was compared with electroencephalogram (EEG) and somatosensory evoked potential (SEP) monitoring. Four of 32 (12.5%) patients were BTO-positive. The cutoff value of MEP amplitude for BTO-positive was a > 80% reduction from the baseline level, which showed sensitivity of 100% and specificity of 100%. Thus, the sensitivity and specificity for BTO-positive were significantly higher for MEP than for EEG (100% and 72.0%, p = 0.02) in 28 patients, but they were not significantly different compared with SEP (33.3% and 100%, p = 0.48) in 21 patients. MEP monitoring might be one of the alternatives for evaluating ischemic tolerance to ICA occlusion during surgery. The cutoff value of MEP amplitude was a > 80% reduction.

Cautionary findings for motor evoked potential monitoring in intracranial aneurysm surgery after a single administration of rocuronium to facilitate tracheal intubation.

Administration of rocuronium to facilitate intubation has traditionally been regarded as acceptable for intraoperative motor evoked potential (MEP) monitoring because of sufficiently rapid spontaneous neuromuscular blockade recovery. We hypothesized that residual neuromuscular blockade, in an amount that could hinder optimal neuromonitoring in patients undergoing intracranial aneurysm clipping, was still present at dural opening. We sought to identify how often this was occurring and to identify factors which may contribute to prolonged blockade. Records of 97 patients were retrospectively analyzed. Rocuronium was administered to facilitate intubation with no additional neuromuscular blockade given. Prolonged spontaneous recovery time to a train-of-four (TOF) ratio of 0.75 after rocuronium administration was defined as 120min, which was approximately when dural opening and the setting of baseline MEPs were occurring. Logistic regression analysis was used to identify factors related to prolonged spontaneous recovery time. Prolonged spontaneous recovery time to a TOF ratio of 0.75 was observed in 44.3% of patients. Multivariable analysis showed that only the dosage of rocuronium based on ideal body weight had a positive correlation with prolonged spontaneous recovery time (P = 0.01). There was no significant association between dosage of rocuronium based on total body weight, age, sex, or body temperature and prolonged recovery time. This study demonstrates that the duration of relaxation for MEP monitoring purposes is well-beyond the routinely recognized clinical duration of rocuronium. Residual neuromuscular blockade could result in lower amplitude MEP signals and/or lead to higher required MEP stimulus intensities which can both compromise monitoring sensitivity.

"Quadripolar" Transcranial Electrical Stimulation for Motor Evoked Potentials.

To determine if transcranial electrical stimulation (TES)-induced motor evoked potentials (MEPs) are of higher amplitude when using two electrodes as anodes and two as cathodes, known as "quadripolar stimulation." Patients who underwent TES MEP monitoring in which control, bipolar stimulation and four variations of quadripolar stimulation were used were evaluated. The bipolar stimulation montage was C3-C4 (C3 was used as anode for stimulation first, then the polarity was switched to stimulate the contralateral side). Four quadripolar montages were used: C3/C1-C4/C2 (step 1), M3/M1-M4/M2 (step 2), C3/M1-C4/M2 (step 3), and M3/C1-M4/C2 (step 4). The area under the curve for the right foot TES MEP was compared for the various montages using descriptive statistics and Fisher exact test for proportions. Sixteen patients were retrospectively evaluated. The mean age as 51.6 years, range 4 to 80 years; 11 were female. The transcranial electrical stimulation MEP area under the curve for the right foot MEP was highest in the bipolar montage in 1 of 16 patients (6.3%). Meanwhile, it was highest in step 4 (M3/C1-M4/C2) in 9 of 16 patients (56.3%; P = 0.027). The highest right foot MEP area under the curve with one of the quadripolar montages was seen in 15 of 16 patients (93.8%; P = 0.0001). Quadripolar stimulation resulted in higher area under the curve for right foot MEP compared with conventional bipolar stimulation.

Diagnostic impact of monitoring transcranial motor-evoked potentials to prevent ischemic complications during endovascular treatment for intracranial aneurysms.

The present study aimed to determine the incidence of intraprocedural motor-evoked potential (MEP) changes and to correlate them with intraprocedural ischemic complications and postprocedural neurological deficits in patients after endovascular intracranial aneurysm treatment. This study analyzed data from 164 consecutive patients who underwent endovascular coil embolization to treat intracranial aneurysms under transcranial MEP monitoring. We analyzed associations between significant changes in MEP defined as > 50% decrease in amplitude, and intraprocedural complications as well as postoperative neurological deficits. Factors associated with postprocedural neurological deficits were also assessed. The treated aneurysms were predominantly located in the anterior circulation (71%). Fourteen (9%) were located at perforators or branches that supplied the pyramidal tract. Intraprocedural complications developed in eight (5%) patients, and four of eight (50%) patients occurred postprocedural neurological deficits. Significant intraprocedural MEP changes occurred during seven of eight endovascular procedures associated with intraprocedural complications and salvage procedures were performed immediately. Among these changes, four transient MEP changes, recovered within 10min, were not associated with postprocedural neurological deficits, whereas three permanent MEP changes were associated with postprocedural neurological deficits and mRS ≥ 1 at discharge. Aneurysms located at perforators/branches supplying the pyramidal tract, and permanent intraprocedural MEP changes were associated with postprocedural neurological deficits. We conclude that intraprocedural transcranial MEP monitoring can reliably identify ischemic changes and can initiate prompt salvage procedures during endovascular aneurysm treatment.

Motor evoked potentials during revascularization in ischemic stroke predict motor pathway ischemia and clinical outcome

ObjectiveThe relevance of motor evoked potential (MEP) recovery during mechanical endovascular thrombectomy (MT) in patients with ischemic stroke is unclear. We correlated MEP recovery during MT to symptom improvement and to ischemia in eloquent motor areas on magnetic resonance imaging (MRI) and compared the predictive value of MEPs to visual angiographic reperfusion status, classified by modified Thrombolysis in Cerebral Infarction grading (mTICI). MethodsPatients with hemisyndrome and large-vessel occlusion undergoing MT were included (n35, 49% females; 73.9 ± 14.5 years; n31 anterior circulation). MEPs were elicited transcranially and recorded at the abductor pollicis brevis muscle bilaterally throughout the procedure. An MRI was acquired within 7 days after MT. ResultsThe median door-to-needle time was 3.5 hours. Median National Institutes of Health Stroke Scale at presentation was 16 (7 – 37). Median Modified Rankin Scale score was 4 at day 7 and 3 months. After MT, MEP-recovery occurred in 21 cases after a median time span of 4.5 min [range 2 – 11 min]. Symptom improvement at day 7 (3 months) was noted in 22 (21) cases. Absence of ischemia on postinterventional MRI was noted in 21 cases, 19 of whom showed MEP-recovery. Stratified for symptom improvement at day 7, sensitivity (specificity) of MEP-recovery was 86% (85%) and of mTICI ≥ 2b was 95% (23%). Stratified for absence of ischemia on postinterventional MRI, sensitivity (specificity) of MEP-recovery was 90% (86%) and of mTICI ≥ 2b was of 95% (21%). ConclusionsMEP recovery occurs early after successful endovascular mechanical revascularization and is superior to mTICI grading in predicting postoperative neurological outcome and postoperative motor-pathway ischemia. SignificanceThis is a new, significant and clinically important study since it emphasizes the additional value of MEP monitoring in a field, which has been traditionally unaffiliated with neurophysiological monitoring.

Application of intraoperative electrophysiological monitoring in vertebral canal decompression surgery for acute spinal cord injury.

ObjectiveThis study aimed to evaluate the joint monitoring of somatosensory evoked potentials (SEPs) and motor evoked potentials (MEPs) in vertebral canal decompression surgery for acute spinal cord injury.MethodsTwenty-four patients, who were admitted to the hospital for the surgical treatment of spinal cord injury with SEP and MEP monitoring, were assigned to the intraoperative monitoring group (group I). In addition, 24 patients who were admitted to the hospital for the surgical treatment of spinal cord injury without SEP or MEP monitoring were assigned to the control group (group C).ResultsIn group I, there were significant changes before and after decompression surgery in the P40 latency and amplitude, and in the latency of MEP in the abductor hallucis brevis (AHB), in patients with improved spinal nerve function following surgery. In contrast, there were no significant differences in the P40 latency or amplitude, or the latency of MEP in the AHB, in patients who showed no improvement after surgery.ConclusionIn vertebral canal decompression surgery for acute spinal cord injury, the application of joint MEP and SEP monitoring can timely reflect changes in spinal cord function.

Feasibility of Full Neuromuscular Blockade During Transcranial Motor-evoked Potential Monitoring of Neurosurgical Procedures.

Feasibility of Full Neuromuscular Blockade During Transcranial Motor-evoked Potential Monitoring of Neurosurgical Procedures.

A novel effective paradigm of intraoperative electrical stimulation mapping in children.

Resective epilepsy surgery is an established treatment method for children with focal intractable epilepsy, but the use of this method introduces the risk of postsurgical motor deficits. Electrical stimulation mapping (ESM), used to define motor areas and pathways, frequently fails in children. The authors developed and tested a novel ESM protocol in children of all age categories. The ESM protocol utilizes high-frequency electric cortical stimulation combined with continuous intraoperative motor-evoked potential (MEP) monitoring. The relationships between stimulation current intensity and selected presurgical and surgery-associated variables were analyzed in 66 children (aged 7 months to 18 years) undergoing 70 resective epilepsy surgeries in proximity to the motor cortex or corticospinal tracts. ESM elicited MEP responses in all children. Stimulation current intensity was associated with patient age at surgery and date of surgery (F value = 6.81, p < 0.001). Increase in stimulation current intensity predicted postsurgical motor deficits (F value = 44.5, p < 0.001) without effects on patient postsurgical seizure freedom (p > 0.05). The proposed ESM paradigm developed in our center represents a reliable method for preventing and predicting postsurgical motor deficits in all age groups of children. This novel ESM protocol may increase the safety and possibly also the completeness of epilepsy surgery. It could be adopted in pediatric epilepsy surgery centers.

Gross Total Resection of a Grade IV Astrocytoma Adjacent to the Precentral Gyrus With Nonawake Motor Mapping and Motor-Evoked Potential Monitoring: 3-Dimensional Operative Video.

Surgical treatment of the gliomas located in or adjacent to the eloquent areas poses significant challenge to neurosurgeons. The main goal of the surgery is to achieve maximal safe resection while preserving the neurological function. This might be possible with utilizing pre- and intraoperative adjuncts such as functional magnetic resonance imaging (MRI), image guidance, mapping of the function of interest, intraoperative MRI, and neurophysiological monitoring. In this video, we demonstrate the utilization of nonawake mapping and motor-evoked potential (MEP) monitoring for the resection of a right-sided posterior superior frontal gyrus grade IV astrocytoma adjacent to the primary motor cortex. The patient is a 69-yr-old woman presented with multiple episodes of simple partial seizures involving her left leg and spreading to the left arm. MRI and functional MRI examinations showed a heterogeneously enhancing mass with peritumoral edema adjacent to the primary motor cortex. Because the patient did not want to undergo an awake craniotomy, a decision was made to perform the resection of the tumor with nonawake motor mapping and continuous MEP monitoring. Nonawake motor mapping and MEP monitoring enabled us to perform gross total resection. Because it has been shown that supratotal resection may provide improved survival outcome,1,2 we extended the white matter resection beyond the contrast enhancing area in noneloquent parts of the tumor. Surgical steps in dealing with vascular anatomy as well as utilizing intraoperative adjuncts such as motor mapping and MEP monitoring to enhance the extent of resection while preserving the function are demonstrated in this 3-dimensional surgical video. The patient consented to publication of her operative video.

Commentary: Gross Total Resection of a Grade IV Astrocytoma Adjacent to the Precentral Gyrus With Nonawake Motor Mapping and Motor-Evoked Potential Monitoring: 3-Dimensional Operative Video.

Commentary: Gross Total Resection of a Grade IV Astrocytoma Adjacent to the Precentral Gyrus With Nonawake Motor Mapping and Motor-Evoked Potential Monitoring: 3-Dimensional Operative Video.

Precise MEP monitoring with a reduced interval is safe and useful for detecting permissive duration for temporary clipping

Although temporary clipping of the parent artery is an indispensable technique in clipping surgery for intracranial aneurysms, the permissive duration of temporary clipping is still not well known. The aim of this study is to confirm the safety of precise motor evoked potential (MEP) monitoring and to estimate the permissive duration of temporary clipping for middle cerebral artery (MCA) aneurysm based on precise MEP monitoring results. Under precise MEP monitoring via direct cortical stimulation every 30 seconds to 1 minute, surgeons released a temporary clip and waited for MEP amplitude to recover following severe (>50%) reduction of MEP amplitude during temporary clipping. Precise MEP monitoring was safely performed. Twenty-eight instances of temporary clipping were performed in 42 MCA aneurysm clipping surgeries. Because precise MEP monitoring could be used to determine when to release a temporary clip even with a severe reduction in MEP amplitude due to lengthy temporary clipping, no patients experienced permanent postoperative hemiparesis. Based on logistic regression analysis, if a temporary clip is applied for 312 seconds or more, there is a higher probability of a severe reduction in MEP amplitude. We should therefore release temporary clips after 5 minutes in order to avoid permanent postoperative hemiparesis.

Neuroanesthesia Guidelines for Optimizing Transcranial Motor Evoked Potential Neuromonitoring During Deformity and Complex Spinal Surgery: A Delphi Consensus Study.

Expert opinion-modified Delphi study. We used a modified Delphi approach to obtain consensus among leading spinal deformity surgeons and their neuroanesthesiology teams regarding optimal practices for obtaining reliable motor evoked potential (MEP) signals. Intraoperative neurophysiological monitoring of transcranial MEPs provides the best method for assessing spinal cord integrity during complex spinal surgeries. MEPs are affected by pharmacological and physiological parameters. It is the responsibility of the spine surgeon and neuroanesthesia team to understand how they can best maintain high-quality MEP signals throughout surgery. Nevertheless, varying approaches to neuroanesthesia are seen in clinical practice. We identified 19 international expert spinal deformity treatment teams. A modified Delphi process with two rounds of surveying was performed. Greater than 50% agreement on the final statements was considered "agreement"; >75% agreement was considered "consensus." Anesthesia regimens and protocols were obtained from the expert centers. There was a large amount of variability among centers. Two rounds of consensus surveying were performed, and all centers participated in both rounds of surveying. Consensus was obtained for 12 of 15 statements, and majority agreement was obtained for two of the remaining statements. Total intravenous anesthesia was identified as the preferred method of maintenance, with few centers allowing for low mean alveolar concentration of inhaled anesthetic. Most centers advocated for <150 μg/kg/min of propofol with titration to the lowest dose that maintains appropriate anesthesia depth based on awareness monitoring. Use of adjuvant intravenous anesthetics, including ketamine, low-dose dexmedetomidine, and lidocaine, may help to reduce propofol requirements without negatively effecting MEP signals. Spine surgeons and neuroanesthesia teams should be familiar with methods for optimizing MEPs during deformity and complex spinal cases. Although variability in practices exists, there is consensus among international spinal deformity treatment centers regarding best practices. 5.

Neurophysiological and paraspinal oximetry monitoring to detect spinal cord ischemia in patients during and after descending aortic repair: An international multicenter explorative study

BackgroundDuring descending aortic repair, critically decreased blood flow to the myelum can result in ischemic spinal cord injury and transient or permanent paraplegia. Assessment of motor evoked potentials (MEPs) has been shown to be a valuable tool which allows to detect spinal cord ischemia (SCI) intraoperatively within a therapeutic window suitable to prevent progression to paraparesis or paraplegia. MEP monitoring is not feasible during postoperative care in the awakening patient. Therefore, ancillary techniques to monitor integrity of spinal cord function are needed to detect delayed spinal cord ischemia. ObjectiveThe purpose of this study is to evaluate whether assessment of long loop reflexes (LLR; F-waves) and paraspinal muscle oximetry using Near-Infrared Spectroscopy (NIRS) are feasible and valid in detecting delayed SCI. MethodsWe aim to include patients from three tertiary referral centers undergoing aortic repair with MEP monitoring in this study.F-wave measurements and paraspinal NIRS oximetry will be operated intra- and postoperatively. Measurement characteristics and feasibility will be assessed in the first 25 patients. Subsequently, a second cohort of 75 patients will be investigated to determine the sensitivity and specificity of F-waves and NIRS in detecting perioperative SCI. In this context for the MEP group SCI is defined intraoperatively as significant MEP changes and postoperatively as newly developed paraplegia. ConclusionsA clinical study design and protocol is proposed to assess if F-waves and/or NIRS-based paraspinal oximetry are feasible and valid in detecting and monitoring for occurrences of delayed SCI.

Low-dose droperidol suppresses transcranial electrical motor-evoked potential amplitude: a retrospective study.

Low-dose droperidol has been widely used as an antiemetic during and after surgery. Although high-dose droperidol affects motor-evoked potential, the effects of low-dose droperidol on motor-evoked potential amplitude are unclear. The aim of this study was to investigate whether low-dose droperidol affects motor-evoked potential amplitude. We retrospectively reviewed the data of patients who underwent spine surgery under general anesthesia with motor-evoked potential monitoring from February 2016 to 2017. The outcome was the motor-evoked potential amplitude of the bilateral abductor pollicis brevis muscle, tibialis anterior muscle, and abductor hallucis muscle within 1 and 1-2 h after droperidol administration, compared with the baseline motor-evoked potential value. Thirty-four patients were analyzed. The median dose of droperidol was 21 µg/kg. The motor-evoked potential amplitudes of all muscles were significantly reduced after droperidol administration and recovered to baseline values within 2 h. The reduction of all motor-evoked potential amplitudes after droperidol administration was 37-45% of baseline values. There were no significant differences in other drugs administered. There were no serious adverse effects of droperidol administration. Motor-evoked potential amplitude was suppressed by low-dose droperidol. During intraoperative motor-evoked potential monitoring in spine surgery, anesthesiologists should pay careful attention to the timing of administration of droperidol, even at low doses. Based on the results of this study, we are conducting a randomized controlled trial.

Clinical feasibility and safety of transoesophageal motor-evoked potential monitoring.

Canine experiments have shown that transoesophageal motor-evoked potential monitoring is feasible, safe and stable, with a quicker response to ischaemia and a better prognostic value than transcranial motor-evoked potentials. We aimed to elucidate whether or not these findings were clinically reproducible. A bipolar oesophageal electrode mounted on a large-diameter silicon tube and a train of 5 biphasic wave stimuli were used for transoesophageal stimulation. Results of 18 patients (median age 74.5 years, 13 males) were analysed. There were no mortalities, spinal cord injuries or complications related with transoesophageal stimulation. Transcranial motor-evoked potential could not be monitored up to the end of surgery in 3 patients for unknown reasons, 2 of whom from the beginning. Transoesophageal motor-evoked potential became non-evocable after manipulation of a transoesophageal echo probe in 2 patients. Strenuous movement of the upper limbs during transoesophageal stimulation was observed in 3 patients. In 14 patients who successfully completed both monitoring methods up to the end of surgery (11 thoraco-abdominal and 3 descending aortic repair), the final results were judged as false positives in 6 by transcranial stimulation and in 1 by transoesophageal stimulation. The stimulation intensity was significantly lower and the upper limb amplitude was significantly higher by transoesophageal stimulation, while the lower limb amplitude was comparable. Transoesophageal motor-evoked potential monitoring is clinically feasible and safe with a low false positive rate. A better electrode design is required to avoid its migration by transoesophageal echo manipulation. Further studies may be warranted. UMIN000022320.

Prediction of postoperative motor deficits using intraoperative motor-evoked potentials in middle cerebral artery aneurysm.

To explore the relationship between postoperative motor deficits and the duration of reduced motor-evoked potentials (MEPs) in patients with middle cerebral artery (MCA) aneurysm. This study included 285 cases of MCA aneurysm treated with clipping surgery with MEP monitoring. The effects of MEP changes on postoperative motor function were assessed, and the key time point for minimizing the incidence of postoperative motor dysfunction was found through receiver operating characteristic (ROC) curve analysis. Motor dysfunction was significantly associated with the occurrence of MEP changes, and patients with irreversible changes were more likely to suffer motor dysfunction than were those with reversible changes. The critical duration of MEP changes that minimized the risk of postoperative motor dysfunction was 8.5min. This study revealed that MEP monitoring is an effective method for preventing ischemic brain injury during surgical treatment of MCA aneurysm and proposes a critical cutoff for the duration of MEP deterioration of 8.5min for predicting postoperative motor dysfunction.

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English

Assesment of Functional Results for the Lesions Located in Eloquent Areas with Using Intraoperative Cortical-Subcortical Stimulation and Cortical Mapping.

To assess the classical and functional imaging features of patients with pathology located in the eloquent areas of the brain who were admitted to our centre between October 2012 and February 2018. We also studied intraoperative somatosensory evoked potential (SEP), motor evoked potentials (MEP), phase reversal, cortical mapping, the extent of resection and the calculation of postoperative morbidity. We compared our results with previous studies in which this technique was not used. The patient records of 163 patients were reviewed retrospectively after approval by the institutional ethics committee and comparisons were made with reports in the literature. The lesion was localised in the visual cortex in eight of the 163 patients. We did not encounter any abnormality in the VEP recordings, so the surgeries were continued. The remaining 155 cases were followed by intraoperative SEP and MEP monitoring. We observed a greater than 50% decrease in the amplitude and an increase in latencies that was greater than 10% in intraoperative MEP and SEP monitoring in 24 patients of 155. Although 8 of 24 patients with abnormal SEP and MEP values were corrected with manuveurs, 6 patients developed increased neurological deficits postoperatively. In conclusion, all of these methods should not be seen as competitive with each other; they could be considered as complementary. All of these methods are helpful for a surgical team regarding loss of neurological function. The rate of loss might be up to 100% and irreversible despite corrective maneveurs.

Neuroprotective effects of Ghrelin on traumatic brain injury in mice

Objective To investigate the neuroprotective effect of Ghrelin on traumatic brain injury (TBI) in mice. Methods TBI model of C57BL / 6 mice was established by electronic cortical impact instrument (eCCI). According to the random figure table method, twenty-four mice were randomly divided into sham group(Sham group), TBI group and Ghrelin intervention group(Ghrelin group) with 8 mice in each group. The model of TBI was established in TBI group and Ghrelin group.The mice in Ghrelin group was injected intraperitoneally 0.5 g/kg before and 1 h after injury respectively. And the mice Sham group and TBI group were injected with the same amount of normal saline. The changes of cerebral blood perfusion (CBP) were monitored in real time by laser speckle contrast analysis(LSCI), the changes of neuroelectrophysiology were observed by monitoring motor evoked potential (MEP), and the status of neurological deficit was evaluated by modified neurological deficit score (mNSS). Results Compared with Sham group, the mice in TBI group had significantly lower cerebral blood perfusion(CBP) (t=-12.36, P<0.01), longer latency and lower amplitude of motor evoked potential (MEP) (t=5.03, -11.55, all P<0.01), and significantly higher mNSS scores (t=9.34, P<0.01). However, compared with the TBI group, the cerebral blood perfusion(CBP) of Ghrelin group increased significantly at 12 h after TBI((196.87±17.36) PU/mm2vs (123.62±8.04)PU/mm2, t=10.45, P<0.01), while the latency of MEP decreased((5.30±0.33)ms vs (6.80±0.97)ms, t=-5.01, P<0.01), the amplitude of MEP increased((2.21±0.16)mV vs (1.27±0.27)mV, t=9.65, P<0.01). And compared with the TBI group, the neurological deficit score of Ghrelin group decreased significantly at 24 h after TBI((4.9±1.2) vs (8.4±2.6), t=-3.87, P<0.01). Conclusion Ghrelin exhibits a significant neuroprotective role by increasing cerebral blood flow perfusion, reducing the degree of neurological deficit and promoting motor function recovery in TBI mice. Key words: Traumatic brain injury; Ghrelin; Cerebral blood perfusion; Motor evoked potential; Neuroprotection; Mice

Direct cortical stimulation with cylindrical depth electrodes in the interhemispheric fissure for leg motor evoked potential monitoring

ObjectiveTo evaluate cylindrical depth electrodes in the interhemispheric fissure as an alternative to subdural strip electrodes for direct cortical stimulation (DCS) leg motor evoked potential (MEP) monitoring. MethodsA cylindrical depth electrode was positioned in the interhemispheric fissure of 37 patients who underwent supratentorial brain surgery. Leg sensory and motor cortices were localized by highest tibial nerve somatosensory evoked potential amplitude and lowest DCS leg MEP threshold; the lowest-threshold electrode was then used for DCS leg MEP monitoring. ResultsIntraoperative leg MEPs were obtained from all the patients in the series. The mean intensity applied for leg MEP monitoring with the cylindrical depth electrode was 15.2 ± 4.0 mA. No complications secondary to neurophysiological monitoring were detected. ConclusionsLower extremity MEPs were consistently recorded using a multi-contact cylindrical depth electrode in the interhemispheric fissure by DCS. SignificanceCylindrical depth electrodes may be a safe and effective alternative for DCS in the interhemispheric fissure, where subdural strips are difficult to place.