The efficacy of motor-evoked potentials on cerebral aneurysm surgery and new-onset postoperative motor deficits.J Neurosurg Anesthesiol. 2010;22:247-251. [PMID: 20548170 DOI: 10.1097/ANA.0b013e3181de4eae]

Treatment Outcomes in Patients with Unruptured Anterior Choroidal Artery Aneurysms: A Single-Center Experience

Objective

Treatment of anterior choroidal artery (AChA) aneurysms is frequently associated with ischemic complications. This study aimed to report the outcomes of treatment of unruptured AChA aneurysms in our hospital.

Methods

Between January 2015 and March 2022, 40 patients were treated for an unruptured AChA aneurysm in our hospital. Age, sex, aneurysm size, AChA branching type, treatment, occlusion rate, complications, modified Rankin Scale (mRS) score before surgery and after 90 days, and recurrence were investigated. The branching type was classified as internal carotid artery (ICA), neck, or dome type based on the location of the AChA origin.

Results

The mean age was 61.1 ± 1.9 years; 15 patients were men and 25 were women. The mean aneurysm diameter was 4.4 ± 0.3 mm. The branching type was ICA in four patients, neck in 35, and dome in one. Treatment was surgical clipping in 22 patients and endovascular coil embolization in 18 (14 with stent assistance). Motor-evoked potential (MEP) monitoring was used in all patients of the clipping group and 9 cases of the coiling group. Treatment complications occurred in eight patients (20%). mRS score worsened by more than one point 90 days after treatment in four patients (10%); however, the proportion of patients who experienced this did not significantly differ between the clipping and coiling groups. Although the odds of a thrombotic complication were higher with coiling than clipping, the difference was not significant (odds ratio: 10.2; P = 0.08). The rate of complete occlusion was lower in the coiling group (72.2% vs. 95.3%), but the difference was not significant. The median follow-up was 696 days (range: 99-2053). No aneurysm recurrence or rupture occurred.

Conclusion

AChA branching type is important for treatment decision-making in patients with AChA aneurysms. Rates of complications and occlusion do not significantly differ between clipping and coiling of AChA aneurysms. MEP monitoring may be useful in preventing thrombotic complications during coil embolization.

Usefulness of Transcranial Motor Evoked Potential in Clipping Surgery for Cerebral Aneurysms-Introduction of a New Protocol for Stable Monitoring

The usefulness of transcranial motor evoked potentials (Tc-MEPs) in clipping surgery has been reported. However, numerous false positive and false negative cases were reported. We report the usefulness of a new protocol compared with direct cortical MEP (Dc-MEP).Materials were 351 patients who underwent aneurysmal clipping under simultaneous monitoring of Tc- and Dc-MEPs. A total of 337 patients without hemiparesis and 14 with hemiparesis were separately analyzed. Intraoperative changes of Tc-MEP thresholds were examined in the first 50 patients without hemiparesis. The stimulation strength of Tc-MEP was set at +20% of the stimulation threshold. As thresholds changed intraoperatively, thresholds were examined every 10 min and changed stimulation strength.Stimulation thresholds of Tc-MEP were significantly decreased after craniotomy and significantly increased after CSF aspiration. The recording ratios of Tc- and Dc-MEPs were 98.8% and 90.5%, respectively. Out of 304 patients without MEP change, 5 patients developed transient or mild hemiparesis with infarction of the territory of the perforating artery arising from the posterior communicating artery. Out of 31 patients whose MEP transiently disappeared, 3 patients developed transient or mild hemiparesis. The other two patients without MEP recovery manifested persistent hemiparesis. In 14 patients with preoperative hemiparesis, 3 patients whose healthy/affected ratio of Tc-MEP was large developed severe persistent hemiparesis.We clarified the intraoperative changes of Tc-MEP thresholds for the first time. A new protocol of Tc-MEP that followed thresholds and changed stimulation strength to +20% of thresholds is useful for stable monitoring. The usefulness of Tc-MEP is the same as that or better than that of Dc-MEP.

Cathodal Genesis of Ipsilateral Hand (Crossover) Motor Evoked Potentials: Evidence from a Patient with Previous Stroke

A case is described where baseline transcranial electrical motor evoked potentials (TcMEP) and somatosensory evoked potentials (SSEP) results were unilaterally absent in a patient with previous hemispheric stroke undergoing a right-sided carotid endarterectomy. SSEP data confirmed right cortical pathology and excluded a technical rationale for absent motor evoked responses. Attempts at generating left-hand (contralateral) TcMEP from right cortical anodal stimulation failed despite high stimulus intensities. However, TcMEP responses from anodal stimulation of the right cortex were recorded from the right-hand (ipsilateral) which were attributed to "crossover." Ipsilateral TcMEP onset latencies derived from the stimulus-response data supports the idea that crossover is a product of cathodal stimulation initially acting on pericortical motor pathways.

Infundibular Widening of Angiographically Invisible Duplicate Anterior Choroidal Artery Mimicking Typical Anterior Choroidal Artery Aneurysm

A diagnosis of an intracranial aneurysm depends on the angiographic configuration and should be cautiously differentiated from aneurysm mimics. In cases of duplicate anterior choroidal arteries (AChAs), infundibular widening of the distal minor AChA can be an aneurysm mimic. If the minor AChA with a smaller diameter is obscured angiographically due to poor contrast filling, an associated infundibular widening beside the proximal large AChA can misinterpreted as a typical AChA aneurysm in angiograms. The authors report on two such cases of duplicate AChAs with infundibular widening presenting like a typical AChA aneurysm in angiograms. Surgical exploration revealed a perforating artery emitting from the dome of the saccular lesion, confirming infundibular widening of a duplicate AChA. No reparative procedure was applied to the infundibular widening in a 48-year-old man, while two vascular outpouchings from the infundibular widening were clipped preserving the duplicate AChA in a 55-year-old woman.

Intraoperative motor and somatosensory evoked potential monitoring during surgical clipping of ruptured and unruptured intracranial aneurysms: a comparative study

OBJECTIVE

The current study investigated the correlation between intraoperative motor evoked potential (MEP) and somatosensory evoked potential (SSEP) monitoring and both short-term and long-term motor outcomes in aneurysm patients treated with surgical clipping. Moreover, the authors provide a relatively optimal neurophysiological predictor of postoperative motor deficits (PMDs) in patients with ruptured and unruptured aneurysms.

METHODS

A total of 1017 patients (216 with ruptured aneurysms and 801 with unruptured aneurysms) were included. Patient demographic characteristics, clinical features, intraoperative monitoring data, and follow-up data were retrospectively reviewed. The efficacy of using changes in MEP/SSEP to predict PMDs was assessed using binary logistic regression analysis. Subsequently, receiver operating characteristic curve analysis was performed to determine the optimal critical value for duration of MEP/SSEP deterioration.

RESULTS

Both intraoperative MEP and SSEP monitoring were significantly effective for predicting short-term (p < 0.001 for both) and long-term (p < 0.001 for both) PMDs in aneurysm patients. The critical values for predicting short-term PMDs were amplitude decrease rates of 57.30% for MEP (p < 0.001 and area under the curve [AUC] 0.732) and 64.10% for SSEP (p < 0.001 and AUC 0.653). In patients with an unruptured aneurysm, the optimal critical values for predicting short-term PMDs were durations of deterioration of 17 minutes for MEP (p < 0.001 and AUC 0.768) and 21 minutes for SSEP (p < 0.001 and AUC 0.843). In patients with a ruptured aneurysm, the optimal critical values for predicting short-term PMDs were durations of deterioration of 12.5 minutes for MEP (p = 0.028 and AUC 0.706) and 11 minutes for SSEP (p = 0.043 and AUC 0.813).

CONCLUSIONS

The authors found that both intraoperative MEP and SSEP monitoring are useful for predicting short-term and long-term PMDs in patients with unruptured and ruptured aneurysms. The optimal intraoperative neuromonitoring method for predicting PMDs varies depending on whether the aneurysm has ruptured or not.

Evaluation of multimodal intraoperative neurophysiologic monitoring during supratentorial aneurysm surgery: a comparative study

The objective of this study is to determine the role of multimodal intraoperative neurophysiologic monitoring (IONM) in the overall outcome of intracranial aneurysms surgery, and the risk factors associated with ischemic complications. We grouped 268 ruptured and unruptured intracranial aneurysms surgically treated at our institution into 2 cohorts, based on the use of IONM (180; 67.16%) or non-use of IONM (88; 32.84%). The IONM technique used was multimodal: electroencephalogram (EEG), somatosensory evoked potentials (SSEPs), transcranial (TES), and direct cortical (DCS) stimulation motor evoked potentials (MEPs). There was a significant difference, with a reduction in perioperative strokes (p = 0.011) and better motor surgery-related outcome in the IONM group (p = 0.016). Independent risk factors identified for surgery ischemic complications were temporary clipping time ≥ 6'05″ (odds ratio [OR]: 3.03; 95% CI: 1.068-8.601; p = 0.037), aneurysm size ≥ 7.5 mm (OR: 2.65; 95% CI: 1.127-6.235; p = 0.026), and non-use of IONM (OR: 2.79; 95% CI: 1.171-6.636; p = 0.021). Conversely, aneurysm rupture was not detected as an independent risk factor (OR: 2.5; 95% CI: 0.55-4.55; p = 0.4). Longer temporary clipping time, larger aneurysm size, and the non-use of IONM could be considered as risk factors for ischemic complications during microsurgical clipping. A standardized designed protocol including multimodal IONM with DCS provides continuous information about blood supply and allows reduction of treatment-related morbidity. Multimodal IONM is a valuable technique in intracranial aneurysm surgery.

Surgery and intraoperative neurophysiologic monitoring for aneurysm clipping

This chapter describes the feasibility, utilization, and value of intraoperative neurophysiologic monitoring (IONM) in cerebrovascular cases. Practical advice on the integration of these adjunct methods into the modern neurosurgical operating room is based on our own neurophysiologic and neurosurgical experience. Most IONM is done for anterior circulation aneurysms. Somatosensory and motor evoked potentials are the modalities of choice covering vascular territories of the internal, anterior, and middle cerebral arteries. While monitoring both hemispheres with the unoperated side as control, monitoring focus is laid upon those territories at risk and bearing the aneurysm. The specificity of IONM is close to 1, and sensitivity ranges from 0.2 to 1, depending on the categorization of transient changes. The overall likelihood of worsened neurologic outcome after any intraoperative signal deterioration (transient or permanent) is 0.4.

Sequential approach of internal maxillary-to-middle cerebral artery bypass and endovascular occlusion for giant middle cerebral artery aneurysm: a case report

Background

The combined approach to complex brain МСА aneurysm seems to be generally considered viable. Although it is fairly common, the combinations of modalities, which are suggested in different case reports, vary significantly. This case discusses a sequential approach of reconstructive microsurgery with internal maxillary-to-middle cerebral artery bypass followed by the balloon test occlusion and endovascular embolization of the aneurysm and the MCA. The combined approach together with use of maxillary artery helped minimize the intraoperative and postoperative complications.

Case presentation

A 62-year-old female with rare episodes of headache and depression revealed giant middle cerebral artery aneurysm. The patient underwent a combined operation in a hybrid operating room with no serious neurologic deficit after surgery.

Conclusions

Multimodality management in a hybrid operating room should be considered in case of complex fusiform aneurysm of MCA, which is associated with high risks of clipping. Thus, the sequential procedures will improve patient outcomes in treatment of complex МСА aneurysms.

Anesthetic technique for awake artery malformation clipping with motor evoked potential and somatosensory evoked potential: A case report

BACKGROUND

Awake craniotomy has been widely used for tumor resection, epilepsy surgery, deep brain stimulation, and carotid endarterectomy. The report on awake artery malformation clipping is rare, especially for anesthesia management.

CASE SUMMARY

A 62-year-old female diagnosed with malformation of anterior cerebral artery at the right side. We clipped the artery malformation with intraoperative neuromonitoring (IONM) in awake craniotomy. Spontaneous respiration was maintained throughout the procedure by nasopharyngeal airway during the surgery successfully.

CONCLUSION

The technique of monitoring anesthesia care can be performed successfully for the patient with IONM.

Motor Evoked Potential Warning Criteria in Supratentorial Surgery: A Scoping Review

During intraoperative monitoring of motor evoked potentials (MEP), heterogeneity across studies in terms of study populations, intraoperative settings, applied warning criteria, and outcome reporting exists. A scoping review of MEP warning criteria in supratentorial surgery was conducted in accordance with the Preferred Reporting Items for Systematic reviews and Meta-Analyses extension for Scoping Reviews (PRISMA-ScR). Sixty-eight studies fulfilled the eligibility criteria. The most commonly used alarm criteria were MEP signal loss, which was always a major warning sign, followed by amplitude reduction and threshold elevation. Irreversible MEP alterations were associated with a higher number of transient and persisting motor deficits compared with the reversible changes. In almost all studies, specificity and Negative Predictive Value (NPV) were high, while in most of them, sensitivity and Positive Predictive Value (PPV) were rather low or modest. Thus, the absence of an irreversible alteration may reassure the neurosurgeon that the patient will not suffer a motor deficit in the short-term and long-term follow-up. Further, MEPs perform well as surrogate markers, and reversible MEP deteriorations after successful intervention indicate motor function preservation postoperatively. However, in future studies, a consensus regarding the definitions of MEP alteration, critical duration of alterations, and outcome reporting should be determined.

A Hybrid Strategy for Patients With Complex Cerebral Aneurysm: STA-MCA Bypass in Combination With Endovascular Embolization

Objective: This work aims to present our experience of patients with complex cerebral aneurysm treated with a hybrid approach: superficial temporal artery–middle cerebral artery (STA–MCA) bypass in combination with endovascular exclusion of the aneurysm.

Method: Patients with aneurysms deemed unclippable and uncoilable were included. All patients were treated with a hybrid approach. After STA–MCA bypass, the parent artery was temporarily occluded. If the intraoperative motor evoked potential (MEP) and somatosensory evoked potential (SEP) waveforms remain normal and last for 30 min, the aneurysm and te parent artery will be embolized permanently with detachable balloons or coils.

Results: A total of 20 patients with 22 aneurysms were included in this study. There were 13 women and 7 men, with an average age of 42.5 years. Intraoperative angiography showed the good patency of all the STA grafts, and neither SEP nor MEP abnormalities were detected. After the parent artery and the aneurysm were occluded, the intraoperative angiography showed an immediately successful exclusion of the aneurysm in 20 aneurysms and immediate contrast stasis in two. All patients recovered uneventfully without ischemic or hemorrhagic complication. Angiography at 6-month follow-up showed the total obliteration in 20 aneurysms. Two aneurysms showed residuals and were recoiled. All STA grafts showed a good patency, and the mean graft flow was 124.2 ml/min.

Conclusion: STA–MCA bypass in combination with endovascular exclusion is an appropriate option for patients with complex cerebral aneurysms that are not amenable to direct surgical clipping or endovascular embolization.

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 120 min, 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.

Introduction of intraoperative neuromonitoring does not necessarily improve overall long-term outcome in elective aneurysm clipping

OBJECTIVE

Intraoperative neuromonitoring (IOM), particularly of somatosensory-evoked potentials (SSEPs) and motor-evoked potentials (MEPs), evolved as standard of care in a variety of neurosurgical procedures. Case series report a positive impact of IOM for elective microsurgical clipping of unruptured intracranial aneurysms (ECUIA), whereas systematic evaluation of its predictive value is lacking. Therefore, the authors analyzed the neurological outcome of patients undergoing ECUIA before and after IOM introduction to this procedure.

METHODS

The dates of inclusion in the study were 2007-2014. In this period, ECUIA procedures before (n = 136, NIOM-group; 2007-2010) and after introduction of IOM (n = 138, IOM-group; 2011-2014) were included. The cutoff value for SSEP/MEP abnormality was chosen as an amplitude reduction ≥ 50%. SSEP/MEP changes were correlated with neurological outcome. IOM-undetectable deficits (bulbar, vision, ataxia) were not included in risk stratification.

RESULTS

There was no significant difference in sex distribution, follow-up period, subarachnoid hemorrhage risk factors, aneurysm diameter, complexity, and location. Age was higher in the IOM-group (57 vs 54 years, p = 0.012). In the IOM group, there were 18 new postoperative deficits (13.0%, 5.8% permanent), 9 hemisyndromes, 2 comas, 4 bulbar symptoms, and 3 visual deficits. In the NIOM group there were 18 new deficits (13.2%; 7.3% permanent, including 7 hemisyndromes). The groups did not significantly differ in the number or nature of postoperative deficits, nor in their recovery rate. In the IOM group, SSEPs and MEPs were available in 99% of cases. Significant changes were noted in 18 cases, 4 of which exhibited postoperative hemisyndrome, and 1 suffered from prolonged comatose state (5 true-positive cases). Twelve patients showed no new detectable deficits (false positives), however 2 of these cases showed asymptomatic infarction. Five patients with new hemisyndrome and 1 comatose patient did not show significant SSEP/MEP alterations (false negatives). Overall sensitivity of SSEP/MEP monitoring was 45.5%, specificity 89.8%, positive predictive value 27.8%, and negative predictive value 95.0%.

CONCLUSIONS

The assumed positive impact of introducing SSEP/MEP monitoring on overall neurological outcome in ECUIA did not reach significance. This study suggests that from a medicolegal point of view, IOM is not stringently required in all neurovascular procedures. However, future studies should carefully address high-risk patients with complex procedures who might benefit more clearly from IOM than others.

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.

A Retrospective Study in Microsurgical Procedures of Large and Giant Intracranial Aneurysms: An Outcome Analysis

OBJECTIVE

Intracranial aneurysms are considered large if >10 mm and giant if >25 mm. The risk of aneurysmal rupture compounds with increase in size of the aneurysm, thus, warranting appropriate intervention. In this study, we have analyzed the outcome and effectiveness of microsurgical procedures in large and giant aneurysms.

METHODS

A retrospective analysis of all the patients who underwent microsurgical procedures for large and giant cerebral aneurysms from 2014-2018 in our institute was conducted. There were a total of 52 patients, in which direct clipping was performed in 42 (80.7%) patients, proximal trapping in 3 (5.7%) patients, trapping with bypass in 3 (5.7%) patients, suction decompression in 3 (5.7%) patients, and 1 (1.9%) patient underwent surgical reconstruction.

RESULTS

Among the 52 patients, in the postoperative period, 1 (1.9%) patient became comatose, 1 (1.9%) patient developed hemiplegia, 1 (1.9%) patient had a transient hemiparesis, and 1 (1.9%) patient had transient lower cranial nerve palsy. Two (3.8%) patients had chronic subdural hematoma during the 3-month follow-up. There was no mortality in our series.

CONCLUSIONS

There are several treatment strategies available to manage large and giant cerebral aneurysms. In this study, we had minimal morbidity (3.8%), favorable outcome (96.1%), and no mortality. Therefore, we would like to conclude that appropriate microsurgical procedures, in experienced hands, can be considered as first line in the management for large and giant intracranial aneurysms, especially those with complex anatomy, wide neck, mass effect, partial thrombosis, and the presence of critical perforating vessels from the aneurysm wall.

Prediction of postoperative motor deficits using motor evoked potential deterioration duration in intracranial aneurysm surgery

OBJECTIVE

The study aimed to investigate the predictive value of motor evoked potential (MEP) deterioration duration for postoperative motor deficits in patients undergoing intracranial aneurysm surgery.

METHODS

Data from 587 patients were reviewed and 92 patients with MEP deterioration were enrolled. MEP deterioration duration was compared between patients with and without postoperative motor deficits. Receiver operating characteristic (ROC) curve analysis was performed to define the threshold value for predicting postoperative motor deficit risk. Additionally, the association between MEP deterioration duration and postoperative CT findings was explored.

RESULTS

Patients with postoperative motor deficits had a significantly longer MEP deterioration duration (p < 0.01). An MEP deterioration duration greater than or equal to 13 min was identified as an independent predictor of immediate (p < 0.01), short-term (p < 0.01), and long-term postoperative motor deficits (p < 0.05). There was no significant association between MEP deterioration duration and new CT abnormalities.

CONCLUSION

MEP deterioration duration could be used for predicting intracranial aneurysm surgical outcome.

SIGNIFICANCE

The study first proposed a threshold value of MEP deterioration duration (13 min) for predicting the risk of postoperative motor deficits in patients undergoing intracranial aneurysm surgery.

Intraoperative use of transcranial motor/sensory evoked potential monitoring in the clipping of intracranial aneurysms: evaluation of false-positive and false-negative cases

OBJECTIVE

Somatosensory and motor evoked potentials (SEPs and MEPs) are often used to prevent ischemic complications during aneurysm surgeries. However, surgeons often encounter cases with suspicious false-positive and false-negative results from intraoperative evoked potential (EP) monitoring, but the incidence and possible causes for these results are not well established. The aim of this study was to investigate the efficacy and reliability of EP monitoring in the microsurgical treatment of intracranial aneurysms by evaluating false-positive and false-negative cases.

METHODS

From January 2012 to April 2016, 1514 patients underwent surgery for unruptured intracranial aneurysms (UIAs) with EP monitoring at the authors' institution. An EP amplitude decrease of 50% or greater compared with the baseline amplitude was defined as a significant EP change. Correlations between immediate postoperative motor weakness and EP monitoring results were retrospectively reviewed. The authors calculated the sensitivity, specificity, and positive and negative predictive values of intraoperative MEP monitoring, as well as the incidence of false-positive and false-negative results.

RESULTS

Eighteen (1.19%) of the 1514 patients had a symptomatic infarction, and 4 (0.26%) had a symptomatic hemorrhage. A total of 15 patients showed motor weakness, with the weakness detected on the immediate postoperative motor function test in 10 of these cases. Fifteen false-positive cases (0.99%) and 8 false-negative cases (0.53%) were reported. Therefore, MEP during UIA surgery resulted in a sensitivity of 0.10, specificity of 0.94, positive predictive value of 0.01, and negative predictive value of 0.99.

CONCLUSIONS

Intraoperative EP monitoring has high specificity and negative predictive value. Both false-positive and false-negative findings were present. However, it is likely that a more meticulously designed protocol will make EP monitoring a better surrogate indicator of possible ischemic neurological deficits.

Intraoperative evoked potential monitoring for detecting cerebral injury during adult aneurysm clipping surgery: a systematic review and meta-analysis of diagnostic test accuracy

OBJECTIVES

We aim to evaluate the diagnostic test accuracy (DTA) of intraoperative evoked potential (EP) monitoring to detect cerebral injury during clipping of cerebral aneurysms.

DESIGN

Systematic review.

DATA SOURCES

Major electronic databases including MEDLINE, EMBASE, LILACS.

ELIGIBILITY CRITERIA

We included studies that reported the DTA of intraoperative EP monitoring during intracranial aneurysm clipping procedures in adult patients.

DATA EXTRACTION AND SYNTHESIS

After quality assessment, we performed a meta-analysis using the bivariate random effects model, and calculated the possible range of DTA point estimates using a new best-case/worst-case scenario approach to quantify the impact of rescue intervention on DTA.

RESULTS

A total of 35 studies involving 4011 patients were included. The quality of the primary studies was modest and the heterogeneity across studies was high. The pooled sensitivity and specificity for predicting postoperative neurological deficits for the somatosensory evoked potential (SSEP) monitoring was 59% (95% CI: 39% to 76%; I²: 76%) and 86% (95% CI: 77% to 92%; I²: 94%), for motor evoked potential (MEP) monitoring was 81% (95% CI: 58% to 93%; I²: 54%) and 90% (95% CI: 86% to 93%; I²: 81%), and for combined SSEP and MEP monitoring was 92% (95% CI: 62% to 100%) and 88% (95% CI: 83% to 93%). The best-case/worst-case range for the pooled point estimates for sensitivity and specificity for SSEP was 50%-63% and 81%-100%, and for MEP was 59%-74% and 93%-100%, and for combined SSEP and MEP was 89%-94% and 83%-100%.

CONCLUSIONS

Due to the modest quality and high heterogeneity of the existing primary studies, it is not possible to confidently support or refute the diagnostic value of EP monitoring in cerebral aneurysm clipping surgery. However, combined SSEP and MEP appears to provide the best DTA for predicting postoperative stroke. Contrary to popular assertion, the modest sensitivity of SSEP monitoring is not explained by the use of rescue intervention.

PROSPERO REGISTRATION NUMBER

CRD42015016884.

Predictive value of neurophysiologic monitoring during neurovascular intervention for postoperative new neurologic deficits

PURPOSE

Forms of intraoperative neurophysiologic monitoring (IONM), including somatosensory evoked potentials (SSEPs) and motor evoked potentials (MEPs), have been widely used in the field of neurosurgery. This study aimed to evaluate the diagnostic efficacy of IONM in identifying intraoperative events and predicting postoperative neurologic deficits in neurovascular intervention.

METHODS

From January 2013 to December 2016, we retrospectively reviewed patients who underwent neurovascular intervention under general anesthesia with the use of IONM. Associations between significant changes in MEPs or SSEPs which were defined as a decrease more than 50% in amplitude and/or an increase more than 10% in latency and any identifiable intraoperative events and/or postoperative neurologic deficits were determined. The sensitivity and specificity values for both MEPs and SSEPs were calculated.

RESULTS

In total, 578 patients (175 men and 403 women) were included. Their mean age was 59.5 years. SSEP changes occurred in 1% (n = 6), and MEP changes occurred in 1.2% (n = 7). Four patients suffered postoperative neurologic deficits, and identifiable intraoperative events were observed in seven patients. Both SSEP and MEP changes were significantly associated with identifiable intraoperative events and/or postoperative neurologic deficits (p < 0.001, Fisher's exact test). The calculated sensitivity and specificity of MEP monitoring were 50 and 99.5%, respectively. The sensitivity and specificity of SSEP monitoring were both 100%.

CONCLUSION

Intraoperative SSEP monitoring might be a reliable and sensitive method to surveil neurologic complications during neurovascular intervention. Intraoperative MEP monitoring appears to be feasible. However, it is unclear whether MEP monitoring has any additive benefit over SSEP monitoring.

Intraoperative Measurement of Arterial Blood Flow in Aneurysm Surgery

Intraoperative flowmetry (IF) has been recently introduced during cerebral aneurysm surgery in order to obtain a safer surgical exclusion of the aneurysm. This study evaluates the usefulness of IF during surgery for cerebral aneurysms and compares the results obtained in the joined surgical series of Verona and Padua to the more recent results obtained at the neurosurgical department of Verona.In the first surgical series, between 2001 and 2010, a total of 312 patients were submitted to IF during surgery for cerebral aneurysm at the neurosurgical departments of Verona and Padua: 162 patients presented with subarachnoid hemorrhage (SAH) whereas 150 patients harbored unruptured aneurysms. In the second series, between 2011 and 2016, 112 patients were submitted to IF during surgery for cerebral aneurysm at the neurosurgical department of Verona; 24 patients were admitted for SAH, whereas 88 patients were operated on for unruptured aneurysms.Comparison of the baseline values in the two surgical series and the baseline values between unruptured and ruptured aneurysms showed no statistical differences between the two clinical series. Analysis of flowmetry measurements showed three types of loco-regional flow derangements: hyperemia after temporary arterial occlusion, redistribution of flow in efferent vessels after clipping, and low flow in patients with SAH-related vasospasm.IF provides real-time data about flow derangements caused by surgical clipping of cerebral aneurysm, thus enabling the surgeon to obtain a safer exclusion; furthermore, it permits the evaluation of other effects of clipping on the loco-regional blood flow. It is suggested that-in contribution with intraoperative neurophysiological monitoring-IF may now constitute the most reliable tool for increasing safety in aneurysm surgery.

Effectiveness and Limitations of Intraoperative Monitoring with Combined Motor and Somatosensory Evoked Potentials During Surgical Clipping of Unruptured Intracranial Aneurysms

OBJECTIVE

Postoperative neurologic deficits are one of the devastating complications that can result from surgical clipping of unruptured intracranial aneurysms. Intraoperative monitoring (IOM) of motor and somatosensory evoked potentials (EPs) has been used to reduce neurologic sequelae. We evaluated the effectiveness and limitations of IOM in prevention of surgical complications during aneurysm clipping.

METHODS

A retrospective analysis was performed, involving 386 operations for 429 unruptured intracranial aneurysms in 386 patients with consecutively collected IOM data.

RESULTS

Significant EP changes were detected during clipping of 23 aneurysms in 23 patients (5.4% of aneurysms). Among them, 8 patients (accounting for 2.1% of operations and 1.9% of aneurysms) experienced postoperative motor deficits, including 3 permanent and 5 temporary motor deficits with corresponding radiologic lesions. In detecting postoperative motor deficits, the sensitivity and specificity of motor EP monitoring were 0.38 and 0.99, respectively, and those of somatosensory EP monitoring were 0.25 and 0.96, respectively. Seven patients (1.8% of operations) with unchanged EPs had other kinds of postoperative neurologic complications, including altered mentality in 5 cases, motor aphasia in 1, and gaze limitation in 1, with corresponding radiologic abnormalities. However, all 7 patients with other neurologic symptoms recovered within 6 months after surgery.

CONCLUSIONS

IOM of motor and somatosensory EPs was useful and reliable in predicting and preventing postoperative motor deficits. However, it also showed some limitations in the significance of positive EP changes and detection of neurologic deficits other than motor function.

Electrophysiological influence of temporal occlusion of the parent artery during aneurysm surgery

Intraoperative monitoring of the motor evoked potential (MEP) during cerebral aneurysm surgery has been widely used to confirm surgical safety. In this study, we retrospectively analyzed the influence of the MEP amplitude resulting from temporal occlusion of the parent artery, and appropriate judgement in the surgery was discussed. Ten patients underwent temporal occlusion of the parent artery during aneurysm surgery, and five of these patients showed a decrease in the MEP amplitude following temporal arterial occlusion. Clinical factors in patients with and without MEP decrease were compared. The time gap between the surgical procedure and the MEP change and recovery was then investigated. A decrease in the MEP amplitude caused by temporal occlusion had a significantly higher occurrence compared with permanent clip failure. The time from the release procedure to MEP amplitude recovery was relatively longer than the time from the occlusion procedure to the decrease in MEP amplitude. The time from release procedure to MEP amplitude recovery showed a weak correlation with the parent artery occlusion time. There is a time gap between releasing the temporal arterial occlusion and MEP recovery that is similar to temporal parent arterial occlusion and the MEP decrease. The cause of MEP amplitude should be judged carefully, and influence of parent artery temporal occlusion should be taken into consideration during aneurysm clipping.

The Diagnostic Accuracy of Evoked Potential Monitoring Techniques During Intracranial Aneurysm Surgery for Predicting Postoperative Ischemic Damage: A Systematic Review and Meta-Analysis

OBJECTIVE

To investigate the diagnostic accuracy of various evoked potential monitoring techniques in predicting postoperative neurologic deficit in intracranial aneurysm surgery.

METHODS

A literature search of the MEDLINE, Embase, and Cochrane databases was conducted for English language articles published between March 31, 1983 and March 31, 2016. Original studies that reported the use of evoked potential monitoring during intracranial aneurysm surgery in predicting postoperative neurologic damage were selected, and their relevant reference lists were hand searched. Test performance characteristics were summarized using hierarchic summary receiver operating characteristic (ROC) curves and bivariable random-effects models.

RESULTS

Thirteen qualifying studies (1597 patients; 1689 aneurysms) from 6 countries were identified. Eight studies investigated the use of the somatosensory evoked potential (SSEP) monitoring technique, 5 investigated transcranial motor evoked potential (TcMEP) and another 5 investigated direct cortical motor evoked potential (DMEP). Bivariable pooled sensitivity and specificity were 48% (95% confidence interval [CI], 30.7-65.0) and 92% (CI, 88%-94.4%), respectively, for SSEP; 73% (CI, 21.0%-96.7%) and 94% (CI, 87.1%-97.5%) for TcMEP; and 97% (CI, 74.43%-99.99%) and 89% (CI, 84.0%-94.5%) for DMEP. ROC curve analysis showed that TcMEP had the highest accuracy (area under ROC curve 0.95; 95% CI, 0.93-0.97), followed by DMEP (0.91, 0.89-0.94) and SSEP (0.88, 0.85-0.91).

CONCLUSIONS

TcMEP and DMEP have higher diagnostic accuracy than SSEP in predicting postoperative neurologic deficit. The type of anesthetic agent, the use of neuromuscular blocking drugs, and the choice of diagnostic criteria for significant change in cerebral blood flow during aneurysm surgery affect the diagnostic accuracy of evoked potential techniques in predicting postoperative neurologic deficit.

Predictive Value of Motor Evoked Potential Monitoring during Surgery of Unruptured Anterior Circulation Cerebral Aneurysms

Objective and Background:

Surgery of unruptured aneurysms is always a great challenge to neurovascular surgeons because no postoperative neurological deficits should be expected postoperatively as the patients are fully asymptomatic before the surgery. Here, we present our experience with selective motor evoked potential (MEP) monitoring of our patients in a 2-year time window.

Patients and Methods:

From 2012 to 2014, 27 patients with unruptured intracranial aneurysms were operated in our institute with the help of MEP monitoring. All patients underwent endoscope-assisted microsurgery with pre- and post-clipping indocyanine green angiography.

Results:

In this period, no mortality was observed, but 18.5% of the patients developed postoperative deficits which showed good recovery in all cases. Overall, MEP showed about 90% accuracy in predicting postoperative deficits.

Conclusions:

MEP as a part of multimodality monitoring of aneurysm surgeries is a valuable tool to improve the outcome. However, we should know its limitations as its results are not always consistent with the outcome.

Bypass surgery for complex middle cerebral artery aneurysms: an algorithmic approach to revascularization

OBJECT Management of complex aneurysms of the middle cerebral artery (MCA) can be challenging. Lesions not amenable to endovascular techniques or direct clipping might require a bypass procedure with aneurysm obliteration. Various bypass techniques are available, but an algorithmic approach to classifying these lesions and determining the optimal bypass strategy has not been developed. The objective of this study was to propose a comprehensive and flexible algorithm based on MCA aneurysm location for selecting the best of multiple bypass options. METHODS Aneurysms of the MCA that required bypass as part of treatment were identified from a large prospectively maintained database of vascular neurosurgeries. According to its location relative to the bifurcation, each aneurysm was classified as a prebifurcation, bifurcation, or postbifurcation aneurysm. RESULTS Between 1998 and 2015, 30 patients were treated for 30 complex MCA aneurysms in 8 (27%) prebifurcation, 5 (17%) bifurcation, and 17 (56%) postbifurcation locations. Bypasses included 8 superficial temporal artery-MCA bypasses, 4 high-flow extracranial-to-intracranial (EC-IC) bypasses, 13 IC-IC bypasses (6 reanastomoses, 3 reimplantations, 3 interpositional grafts, and 1 in situ bypass), and 5 combination bypasses. The bypass strategy for prebifurcation aneurysms was determined by the involvement of lenticulostriate arteries, whereas the bypass strategy for bifurcation aneurysms was determined by rupture status. The location of the MCA aneurysm in the candelabra (Sylvian, insular, or opercular) determined the bypass strategy for postbifurcation aneurysms. No deaths that resulted from surgery were found, bypass patency was 90%, and the condition of 90% of the patients was improved or unchanged at the most recent follow-up. CONCLUSIONS The bypass strategy used for an MCA aneurysm depends on the aneurysm location, lenticulostriate anatomy, and rupture status. A uniform bypass strategy for all MCA aneurysms does not exist, but the algorithm proposed here might guide selection of the optimal EC-IC or IC-IC bypass technique.

Comparison of false-negative/positive results of intraoperative evoked potential monitoring between no and partial neuromuscular blockade in patients receiving propofol/remifentanil-based anesthesia during cerebral aneurysm clipping surgery: A retrospective analysis of 685 patients

Although the elicited responses of motor evoked potential (MEP) monitoring are very sensitive to suppression by anesthetic agents and muscle relaxants, the use of neuromuscular blockade (NMB) during MEP monitoring is still controversial because of serious safety concerns and diagnostic accuracy. Here, we evaluated the incidence of unacceptable movement and compared false-negative MEP results between no and partial NMB during cerebral aneurysm clipping surgery. We reviewed patient medical records for demographic data, anesthesia regimen, neurophysiology event logs, MEP results, and clinical outcomes. Patients were divided into 2 groups according to the intraoperative use of NMB: no NMB group (n = 276) and partial NMB group (n = 409). We compared the diagnostic accuracy of MEP results to predict postoperative outcomes between both groups. Additionally, we evaluated unwanted patient movement during MEP monitoring in both groups. Of the 685 patients, 622 (90.8%) manifested no intraoperative changes in MEP and no postoperative motor deficits. Twenty patients showed postoperative neurologic deficits despite preserved intraoperative MEP. False-positive MEP results were 3.6% in the no NMB group and 3.9% in the partial NMB group (P = 1.00). False-negative MEP results were 1.1% in the no NMB group and 4.2% in the partial NMB group (P = 0.02). No spontaneous movement or spontaneous respiration was observed in either group. Propofol/remifentanil-based anesthesia without NMB decreases the stimulation intensity of MEPs, which may reduce the false-negative ratio of MEP monitoring during cerebral aneurysm surgery. Our anesthetic protocol enabled reliable intraoperative MEP recording and patient immobilization during cerebral aneurysm clipping surgery.

Intraoperative Transcranial Motor-Evoked Potentials Predict Motor Function Outcome in Intracerebral Hemorrhage Surgery

OBJECTIVE

Prediction of motor function after intracerebral hemorrhage (ICH) often poses a diagnostic challenge. This study was performed to investigate whether intraoperative monitoring of motor-evoked potentials (MEPs) could predict postoperative motor function recovery.

METHODS

We reviewed 16 consecutive patients undergoing evacuation of supratentorial ICH with hemiplegia between June 2011 and October 2014. Patients were categorized according to the results of MEPs before and after evacuation of hematoma. The correlation between detection of MEPs and prognosis of motor function was analyzed.

RESULTS

In 10 of 16 cases (62%), stable MEPs were detected before and after evacuation of hematoma, and postoperative motor function was improved in all cases, including 3 cases with severe preoperative motor impairment on manual muscle test (1-2). In 3 cases (19%) in which MEPs were not detected throughout the procedure, motor function was not improved. In the other 3 cases (19%), MEPs were not measured before evacuation of ICH but were detected after evacuation despite poor prognosis of motor function. The results of postevacuation MEPs were considered false-negative results. Predictions using pre-evacuation MEP results were completely consistent with prognosis for recovery, whereas MEPs obtained during and after evaluation were useful for monitoring.

CONCLUSIONS

Intraoperative MEPs may indicate preservation of pyramidal tracts, and pre-evacuation MEPs can predict motor function outcome after ICH surgery.

Strategies and Pitfalls of Motor-Evoked Potential Monitoring during Supratentorial Aneurysm Surgery

BACKGROUND

The aims of this study were to reveal the strategies and pitfalls of motor-evoked potential (MEP) monitoring methods during supratentorial aneurysm surgery, and to discuss the drawbacks and advantages of each method by reviewing our experiences.

METHODS

Intraoperative MEP monitoring was performed in 250 patients. Results from 4 monitoring techniques using combinations of 2 stimulation sites and 2 recording sites were analyzed retrospectively.

RESULTS

MEP was recorded successfully in 243 patients (97.2%). Direct cortical stimulation (DCS)-spinal recorded MEP (sMEP) was used in 134 patients, DCS-muscle recorded MEP (mMEP) in 97, transcranial electrical stimulation (TES)-mMEP in 11 and TES-sMEP in 1. TES-mMEP during closure of the skull was used in 21 patients. DCS-mMEP was able to detect waveforms from upper and/or lower limb muscles. Alternatively, DCS-sMEP (direct [D]-wave) could accurately estimate amplitude changes. A novel "early warning sign" indicating ischemia was found in 21 patients, which started with a transiently increased amplitude of D-wave and then decreased after proximal interruption of major arteries. False-negative findings in MEP monitoring in 2 patients were caused by a blood insufficiency in the lenticulostriate artery and by a TES-sMEP recording, respectively.

CONCLUSIONS

The results of this study suggest that to perform accurate MEP monitoring, DCS-mMEP or DCS-sMEP recording should be used as the situation demands, with combined use of TES-mMEP recording during closure of the skull. DCS-sMEP is recommended for accurate analysis of waveforms. We also propose a novel "early warning sign" of blood insufficiency in the D-wave.

Intraoperative monitoring for intracranial aneurysms: the Michigan experience

Intraoperative neurophysiological monitoring is routinely used during the repair (endovascular or microsurgical) of intracranial aneurysms at major centers. There is a continued need of data sets from institutions with dedicated intraoperative neurophysiological monitoring services to further define the predictive factors of postoperative neurological deficits. We retrospectively reviewed and analyzed our database of all patients who underwent repair of intracranial aneurysms (endovascular or microsurgical). A total of 406 patients underwent 470 procedures. The changes were noted during monitoring in 3.83% of the cases. Most of the changes were first detected in somatosensory evoked potential (88.89%) followed by brainstem auditory evoked potential (16.67%). Changes were completely reversible in 44.44%, only partly reversible in 22.22%, and irreversible in 33.33% of cases. Intraoperative neurophysiological monitoring changes demonstrated high sensitivity, specificity, and negative predictive value for postoperative neurological deficits. The association between intraoperative neurophysiological monitoring changes and Glasgow outcome scale was significant for reversible changes compared against irreversible and partly reversible changes. Presence of any intraoperative neurophysiological monitoring modality change during repair of intracranial aneurysm may suggest a higher risk for postoperative neurological deficits. Reversibility of the changes is a favorable marker, whereas irreversible changes are predictive of postoperative neurological deficits with deterioration of Glasgow outcome scale on a longer follow-up.

Aneurysmal Subarachnoid Hemorrhage

Aneurysmal subarachnoid hemorrhage (SAH) is a worldwide health burden with high fatality and permanent disability rates. The overall prognosis depends on the volume of the initial bleed, rebleeding, and degree of delayed cerebral ischemia (DCI). Cardiac manifestations and neurogenic pulmonary edema indicate the severity of SAH. The International Subarachnoid Aneurysm Trial (ISAT) reported a favorable neurological outcome with the endovascular coiling procedure compared with surgical clipping at the end of 1 year. The ISAT trial recruits were primarily neurologically good grade patients with smaller anterior circulation aneurysms, and therefore the results cannot be reliably extrapolated to larger aneurysms, posterior circulation aneurysms, patients presenting with complex aneurysm morphology, and poor neurological grades. The role of hypothermia is not proven to be neuroprotective according to a large randomized controlled trial, Intraoperative Hypothermia for Aneurysms Surgery Trial (IHAST II), which recruited patients with good neurological grades. Patients in this trial were subjected to slow cooling and inadequate cooling time and were rewarmed rapidly. This methodology would have reduced the beneficial effects of hypothermia. Adenosine is found to be beneficial for transient induced hypotension in 2 retrospective analyses, without increasing the risk for cardiac and neurological morbidity. The neurological benefit of pharmacological neuroprotection and neuromonitoring is not proven in patients undergoing clipping of aneurysms. DCI is an important cause of morbidity and mortality following SAH, and the pathophysiology is likely multifactorial and not yet understood. At present, oral nimodipine has an established role in the management of DCI, along with maintenance of euvolemia and induced hypertension. Following SAH, hypernatremia, although less common than hyponatremia, is a predictor of poor neurological outcome.

Results of re-exploration because of compromised distal blood flow after clipping unruptured intracranial aneurysms

BACKGROUND

One of the major causes for performing unplanned re-exploration of a craniotomy after microsurgery for unruptured intracranial aneurysms (UIAs) is compromised distal blood flow after clipping. Therefore, it is important to identify the causes of compromised distal blood flow after clipping and the factors that influence the prognosis for re-exploration in order to decrease ischemic complications related to clipping UIAs.

METHOD

Between January 2007 and December 2013, 1954 patients underwent microsurgery for UIAs. In this cohort, 20 patients (1.0%) required unplanned re-exploration of the craniotomy for several reasons, and 11 patients (0.6%) underwent unplanned re-exploration with clip repositioning or changing of the previous clip because of compromised distal blood flow after clipping. Patient characteristics, aneurysm properties, intraoperative findings, annual incidence and prognosis were analyzed in these 11 patients.

RESULTS

The annual incidence of re-exploration has gradually decreased since the introduction of several intraoperative monitoring techniques. In total, 3.0% of UIAs in the M1 trunk, 0.8% of UIAs at the origin of the anterior choroidal artery (AchA) and 0.5% of UIAs at the bifurcation of the middle cerebral artery (MCA) required re-exploration. Here, all 11 UIAs had broad necks, and atherosclerosis was identified around 10 UIAs. Six patients with compromised MCA flow demonstrated relatively better outcomes following re-exploration than five patients with a compromised lenticulostriate artery (LSA) or AchA flow. Four patients with delayed ischemic symptoms demonstrated relatively better outcomes than the seven patients who developed ischemic symptoms immediately postoperatively.

CONCLUSION

Clinicians need to be more careful not to compromise distal blood flow when clipping UIAs at the MCA and AchA origin. Various intraoperative monitoring techniques can help reduce the incidence of compromised distal blood flow after clipping.

Blood blister-like aneurysm with rupture point close to origin of anterior choroidal artery

If a ruptured blood blister-like aneurysm (BBA) arises from the lateral or superolateral wall of the internal carotid artery (ICA) at the level of the anterior choroidal artery (AChA), its proximity to the origin of the AChA presents a serious surgical challenge to preserve the patency of the AChA. Two such rare cases are presented, along with successful surgical techniques, including the application of a C-shaped aneurysm clip parallel to the ICA and a microsuture technique to repair the arterial defect. The patency of the AChA and ICA was successfully preserved without recurrence or rebleeding of the BBA during a 1-year follow-up after the operation.

Motor evoked potential monitoring during surgery of middle cerebral artery aneurysms: a cohort study

BACKGROUND

Motor evoked potential (MEP) monitoring has been widely used in brain or spine surgery to recognize potential damage of the pyramidal motor system. However, its ability to detect ischemic injury during middle cerebral artery (MCA) aneurysm surgery remains unclear. A prospective cohort study was designed to evaluate MEP changes during MCA aneurysm surgery.

METHODS

From January 2009 to August 2011, 89 patients underwent MCA aneurysm surgery and were prospectively divided into 2 groups: MEP monitoring group and control group. Based on an amplitude decrement of >50% or loss, a 2-stage warning criterion of MEP changes was established. Concomitant somatosensory evoked potential changes were also recorded. MEP changes occurred in 15 patients, and various methods were used to avoid continued brain ischemia. Indocyanine green angiography and Doppler ultrasonography were performed if needed. A head computed tomography scan was performed immediately and the day after the operation.

RESULTS

At discharge, neither motor status nor Glasgow Coma Scale score was significantly different between the 2 groups. However, at the latest follow-up (mean, 31.9 months), motor status of the patients in the monitoring group was better (P = 0.037). MEP monitoring was identified as an independent prognostic factor for motor outcome in long-term results by multivariate analysis (P = 0.042). Both wave loss and >50% amplitude decrement of MEP monitoring showed good predictive value when used as part of a 2-stage warning criterion.

CONCLUSIONS

MEP monitoring is reliable for evaluation of the ischemic status of the pyramidal motor system during MCA aneurysm surgery and can improve surgical outcomes when used appropriately.

The significance of intraoperative monitoring of muscle motor evoked potentials during unruptured large and giant cerebral aneurysm surgery

The goal of this study was to characterize the utility of muscle motor evoked potentials (MMEPs) elicited by direct cortical stimulation as a means of monitoring during unruptured large and giant cerebral aneurysm surgery. This analysis focused on intraoperative changes in MMEPs and their relationship to postoperative motor function. The study population consisted of 50 patients who underwent surgery for large (n = 31) or giant (n = 19) cerebral aneurysms. Intraoperative MMEPs were continuously and successfully obtained in muscles belonging to the vascular territory of interest. There was no postoperative motor paresis in 31 (62%) patients in whom intraoperative MMEPs remained unchanged. Transient MMEP change occurred in 15 (30%) of the 50 patients, but 9 of those patients had no postoperative motor deficits, 5 had transient motor deficits, and 1 suffered permanent motor deficits resulting from postoperative delayed blood flow insufficiency due to arteriosclerosis of the parent artery. Permanent MMEP loss occurred in 4 (8%) of 50 patients, all of whom developed severe and permanent postoperative motor deficits. MMEP is a useful monitoring modality in patients undergoing surgery for large or giant cerebral aneurysms. This strategy can help predict functional prognosis or guide the neurosurgeon intraoperatively in an effort to promote better outcomes.

Discrepancy between voluntary movement and motor-evoked potentials in evaluation of motor function during clipping of anterior circulation aneurysms

BACKGROUND

Various modalities have been used to confirm the blood flow through parent arteries or surrounding perforating arteries during surgical aneurysm clipping, including motor-evoked potentials (MEPs), Doppler ultrasound, and indocyanine green videoangiography. Nonetheless, contralateral hemiparesis due to arterial blood flow insufficiency may arise because of false-positive or false-negative errors. By performing controlled intraoperative awakening during aneurysm clipping, we compared patients' voluntary movements with simultaneous MEP.

METHODS

Four patients with anterior choroidal artery aneurysms and one patient with a dorsal internal carotid artery aneurysm were included in this study. MEP and intraoperative voluntary movements under awake craniotomy were assessed simultaneously during and after the clipping procedure.

RESULTS

Aneurysms were safely and successfully clipped in all patients, with no evidence of postoperative neurological deficits. Voluntary movements and MEP findings did not differ from the control state in three patients. In the other two patients, we observed a discrepancy between MEP amplitudes and voluntary movements. In one patient, deterioration and subsequent improvement in voluntary movements were preceded by MEP amplitude reduction during clipping. In the other patient, MEP amplitude did not change although voluntary movement deteriorated during temporary occlusion of the internal carotid artery.

CONCLUSIONS

Intraoperative neurological assessment during aneurysmal clipping under awake craniotomy is feasible and safe, and should be valuable for the assessment of ischemia, especially in the anterior choroidal artery. From a neurophysiologic viewpoint, MEP may be insufficiently sensitive for evaluating voluntary movement under ischemia.

Anterior choroidal artery aneurysm surgery: ischemic complications and clinical outcomes revisited

Objective

Surgical results for anterior choroidal artery (AChA) aneurysms have previously been reported as unsatisfactory due to inadvertent occlusion of the AChA, while the low incidence of AChA aneurysms hampers the accumulation of surgical experience. The authors reviewed their related surgical experience to document the ischemic complications and surgical outcomes.

Methods

Identification of the AChA at its origin by rigorous visual scrutiny, careful microdissection, and meticulous clip placement to avoid the AChA origin are all crucial surgical maneuvers. A retrospective review of a surgical series of 62 consecutive cases of an AChA aneurysm between 2004 and 2012 was performed.

Results

All patients, except for five (8.1%) with a small residual neck, showed complete aneurysm obliteration in postoperative angiographic evaluations. There was no incidence of procedure-related permanent AChA syndrome or oculomotor nerve palsy, while three (4.8%) patients suffered from transient AChA syndrome. The clinical outcomes [the 3-month modified Rankin Scale (mRS)] of the patients were related to their preoperative World Federation of Neurologic Surgeons (WFNS) grade. As regards the 3-month mRS, significant differences were found between patients with an unruptured aneurysm (WFNS grade 0; n=20), good-grade subarachnoid hemorrhage (WFNS grade 1-3; n=30), and poor-grade subarachnoid hemorrhage (WFNS grade 4-5; n=4).

Conclusion

In surgical treatment of AChA aneurysms, a risk of AChA insufficiency can be minimized by taking every precaution to preserve the AChA patency and intraoperative monitoring. In addition, the surgical outcome is primarily determined by the preoperative clinical state.

Motor evoked potential monitoring of the vagus nerve with transcranial electrical stimulation during skull base surgeries

Object

Dysphasia is one of the most serious complications of skull base surgeries and results from damage to the brainstem and/or cranial nerves involved in swallowing. Here, the authors propose a method to monitor the function of the vagus nerve using endotracheal tube surface electrodes and transcranial electrical stimulation during skull base surgeries.

Methods

Fifteen patients with skull base or brainstem tumors were enrolled. The authors used surface electrodes of an endotracheal tube to record compound electromyographic responses from the vocalis muscle. Motor neurons were stimulated using corkscrew electrodes placed subdermally on the scalp at C3 and C4. During surgery, the operator received a warning when the amplitude of the vagal motor evoked potential (MEP) decreased to less than 50% of the control level. After surgery, swallowing function was assessed clinically using grading criteria.

Results

In 5 patients, vagal MEP amplitude permanently deteriorated to less than 50% of the control level on the right side when meningiomas were dissected from the pons or basilar artery, or when a schwannoma was dissected from the vagal rootlets. These 5 patients had postoperative dysphagia. At 4 weeks after surgery, 2 patients still had dysphagia. In 2 patients, vagal MEPs of one side transiently disappeared when the tumors were dissected from the brainstem or the vagal rootlets. After surgery, both patients had dysphagia, which recovered in 4 weeks. In 7 patients, MEP amplitude was consistent, maintaining more than 50% of the control level throughout the operative procedures. After surgery all 7 patients were neurologically intact with normal swallowing function.

Conclusions

Vagal MEP monitoring with transcranial electrical stimulation and endotracheal tube electrode recording was a safe and effective method to provide continuous real-time information on the integrity of both the supranuclear and infranuclear vagal pathway. This method is useful to prevent intraoperative injury of the brainstem corticobulbar tract or the vagal rootlets and to avoid the postoperative dysphagia that is often associated with brainstem or skull base surgeries.

Monitoring techniques for prevention of procedure-related ischemic damage in aneurysm surgery

OBJECTIVE

To describe the application of intraoperative monitoring techniques during aneurysm surgery and to discuss the advantages and limitations of these techniques in prevention of postoperative neurologic deficits.

METHODS

Articles found in the literature through PubMed for the time frame 1980-2011 and the authors' personal files were reviewed.

RESULTS

Various techniques for detection of vascular insufficiency are available, including direct methods to measure cerebral blood flow and indirect methods to evaluate the integrity of neurologic pathways.

CONCLUSIONS

The choice of monitoring modality should be governed by the vessel and by the vascular territory most at risk during the planned procedure with proper awareness of the potential limits related to each technique. Aneurysm surgery monitoring should help to address issues of continuity and provide a morphologic and functional assessment. Although the use of monitoring devices is still not routine in aneurysm surgery and no standards have been established, combining different monitoring techniques is crucial to optimize aneurysm surgery and avoid or minimize complications.

The use of motor evoked potential monitoring during cerebral aneurysm surgery to predict pure motor deficits due to subcortical ischemia

Subcortical infarcts are most commonly the consequence of perforating artery occlusion and pure motor deficit is the most frequent syndrome resulting from an interruption of the corticospinal tract at the level of the corona radiate, the internal capsule or the brainstem. Motor evoked potential (MEP) monitoring is used as an adjunct to surgery as somatosensory evoked potentials (SEP) have been found to be insensitive to these lesions. Two different techniques have been used for monitoring MEPs during aneurysm surgery: transcranial electrical stimulation (TES) and direct cortical stimulation (DCS). TES may result in patient movement, interfering with microdissection. There is also concern that TES MEP may not detect subcortical motor pathway ischemia by stimulating deeper subcortical structures and may thereby bypass the ischemic area. DCS produces focal muscle activation, less movement and more superficial stimulation that should detect cortical and superficial subcortical ischemia, hence avoiding false-negatives. However, this technique also has disadvantages including subdural bleeding and injury to the brain. Using close-to-motor-threshold stimulation and focal stimulating electrode montages, TES and DCS MEPs do not vary significantly in their capacity to detect lesions of the motor cortex or its efferent pathways. Both techniques are prone to interference by anesthetic agents.