Detection of epileptiform activity by human interpreters: blinded comparison between electroencephalography and magnetoencephalography

PURPOSE: Objectively to evaluate whether independent spike detection by human interpreters is clinically valid in magnetoencephalography (MEG) and to characterize detection differences between MEG and scalp electroencephalography (EEG). METHODS: We simultaneously recorded scalp EEG and MEG data from 43 patients with intractable focal epilepsy. Raw EEG and MEG waveforms were reviewed independently by two experienced epileptologists, one for EEG and one for MEG, blinded to the other modality and to the clinical information. The number and localization of spikes detected by EEG and/or MEG were compared in relation to clinical diagnosis based on postoperative seizure freedom. RESULTS: Interictal spikes were captured in both EEG and MEG in 31, in MEG alone in eight, in EEG alone in one, and in neither modality in three patients. The number of detections ranged widely with no statistical difference between modalities. A median of 25.7% of total spikes was detectable by both modalities. Spike localization was similarly consistent with the epilepsy diagnosis in 85.2% (EEG) and 78.1% (MEG) of the patients. Inaccurate localization occurred only in those cases with very few spikes detected, especially when the detections were in one modality alone. CONCLUSIONS: Interictal epileptiform discharges are easily perceived in MEG. Independent spike identification in MEG can provide clinical results comparable, but not superior, to EEG. Many spikes were seen in only one modality or the other; therefore the use of both EEG and MEG may provide additional information.     

Epileptic high‐frequency oscillations in intraoperative electrocorticography: The effect of propofol

Purpose: Epileptic high‐frequency oscillations (HFOs; 80–500 Hz) may be used to guide neurosurgeons during epilepsy surgery to identify epileptogenic tissue. We studied the effect of the anesthetic agent propofol on the occurrence of HFOs in intraoperative electrocorticography (ECoG). Methods: We selected patients who were undergoing surgery for temporal lobe epilepsy with a standardized electrode grid placement. Intraoperative ECoG was recorded at 2,048 Hz following cessation of propofol. The number and distribution of interictal spikes, ripples (R [80–250 Hz]), and fast ripples (FRs; 250–500 Hz) were analyzed. The amount of events on mesiotemporal channels and lateral neocortical channels were compared between patients with a suspected mesiotemporal and lateral epileptogenic area (Student’s t‐test), and HFOs were compared with the irritative zone, using correlation between amounts of events per channel, to provide evidence for the epileptic nature of the HFOs. Next, the amount of events within the first minute and the last minute were compared to each other and the change in events over the entire epochs was analyzed using correlation analyses of 10 epochs during the emergence periods (Spearman rank test). We studied whether the duration of HFOs changed over time. The change in events within presumed epileptogenic area was compared to the change outside this area (Student’s t‐test). Periods of burst suppression and continuous background activity were compared between and within patients (t‐test). Key Findings: Twelve patients were included: five with suspected mesiotemporal epileptogenic area and three with suspected lateral epileptogenic area (and four were “other”). Spikes, ripples, and FRs were related to the suspected epileptogenic areas, and HFO zones were related to the irritative zones. Ripples and FRs increased during emergence from propofol anesthesia (mean number of ripples from first minute–last minute: 61.5–73.0, R = 0.46, p < 0.01; FRs: 3.1–5.7, R = 0.30, p < 0.01) and spikes remained unchanged (80.1–79.9, R = ?0.05, p = 0.59). There was a decrease in number of channels with spikes (R = ?0.18, p = 0.05), but no change in ripples (R = ?0.13, p = 0.16) or FRs (R = 0.11, p = 0.45). There was no change in the durations of HFOs. The amount of HFOs in the presumed epileptogenic areas did not change more than the amount outside the presumed epileptogenic area, whereas spikes paradoxically decreased more within the suspected epileptogenic area. Six patients showing burst‐suppression had lower rates of ripples than six other patients with continuous background activity (p = 0.02). No significant difference was found between burst suppression and continuous background activity in four patients, but there was a trend toward showing more ripples during continuous background activity (p = 0.16). Significance: Propofol, known for its antiepileptic effects, reduces the number of epileptic HFOs, but has no effect on spikes. This enforces the hypothesis that, in epilepsy, HFOs mirror the disease activity and HFOs might be useful for monitoring antiepileptic drug treatment. It is feasible to record HFOs during surgery, but propofol infusion should be interrupted for some minutes to improve detection.     

脑磁图在神经外科中的应用

目的 探讨脑磁图（MEG）在癫痫外科中的定位价值。方法 本组26例癫痫患，男18例，女8例，术前均行脑电图（EEG）检查和影像学检查，同时做了脑磁图（MEG）检查。所有患手术均在MEG指导下进行，术中加用皮层脑电图（ECoG)监测。结果 26例患均能通过MEG进行术前致痫灶与功能定位，其阳性率明显高于EEG和影像学检查。术后复查EEG，22例患较好。短期随访1－3个月，25例患癫痫发作完全消失。结论 MEG是一项术前痫灶定位和功能保护的有效检查方法。     

Detection of temporal lobe spikes: Comparing nasopharyngeal, cheek and anterior temporal electrodes to simultaneous subdural recordings

OBJECTIVE: To compare nasopharyngeal (NP), cheek and anterior temporal (AT) electrodes for the detection yield and localization of interictal spikes in temporal lobe epilepsy. METHODS: In patients evaluated for epilepsy surgery with subdural electrocorticography electrodes, we simultaneously recorded NP, cheek and AT electrodes. Two observers identified spikes in EEG traces and marked in which channels they occurred. Interobserver agreement was calculated using Cohen's kappa. For localization, data-sets with high interobserver agreement (kappa-value 0.4) were evaluated. The subdural distribution of NP and AT spikes was mapped. RESULTS: Seven patients were included, six were analyzed for localization. Only 1.5% of spikes recorded by cheek electrodes were not seen on temporal leads, while 25% of NP spikes were not seen on either. Spikes only recorded by NP electrodes had mesiobasal, while AT spikes had lateral temporal distribution. CONCLUSIONS: NP electrodes can increase EEG spike detection rate in temporal lobe epilepsy and are more useful than cheek electrodes. Spikes that are seen only on NP electrodes tend to be mesiobasal temporal lobe spikes. SIGNIFICANCE: Adding NP electrodes to scalp EEG can aid interictal spike detection and source localization, especially in short recordings like MEG-EEG.     

脑磁图与神经导航结合在癫痫外科的应用

目的探讨脑磁图定位和神经导航方法二者结合在癫痫外科的应用价值。方法选择12例顽固性癫痫手术,术前脑磁图确定皮质癫痫灶及中央后回感觉皮质范围,然后与神经外科导航系统结合应用于手术当中。结果脑磁图癫痫灶定位与术中皮质脑电图定位符合率100％。按Engel分级作为癫痫疗效标准,术后癫痫发作完全停止9例(1级),发作减少90％以上2例(2或3级),发作减少不到90％1例(4级)。无一例出现手术后神经功能障碍。结论脑磁图是无创确定癫痫灶和功能区皮质空间位置关系的重要工具,脑磁图定位结合神经导航方法的应用可使癫痫外科手术更精确,侵袭更小。     

Sensitivity and specificity of seizure-onset zone estimation by ictal magnetoencephalography

Purpose: Ictal video–electroencephalography (EEG) is commonly used to establish ictal onset‐zone location. Recently software development has enabled systematic studies of ictal magnetoencephalography (MEG). In this article, we evaluate the ability of ictal MEG signals to localize the seizure‐onset zone. Methods: Twenty‐six patients underwent ictal MEG and epilepsy surgery. Prediction of seizure‐onset zone by ictal and interictal MEG was retrospectively compared with ictal‐onset area found by intracranial EEG in 12 patients. The specificity and sensitivity of the prediction were calculated at hemisphere‐lobe (HL) and at hemisphere‐lobe‐surface (HLS) levels. Key Findings: The sensitivity of ictal MEG source localization was 0.958 on HL and 0.706 on HLS levels, and its specificity was 0.900 on HL and 0.731 on HLS levels. The interictal MEG dipole cluster, defined as >10 dipoles on one lobar surface, had sensitivity of 0.400 and specificity of 0.769. Ictal MEG was equally sensitive and specific on dorsolateral and nondorsolateral neocortical surfaces up to a depth of 4 cm from the scalp. Significance: Sources of ictal‐onset MEG signals and interictal dipole clusters are essentially equally specific in estimation of the ictal‐onset zone on lobar surface resolution, but ictal MEG is more sensitive. On the lobe resolution, ictal MEG estimates ictal‐onset zone with high sensitivity and specificity.     

Using electrocorticography for presurgical language mapping in epilepsy patients

Of five epilepsy patients with implanted subdural electrodes, electrical cortical stimulation (ECS) on left posterior inferior frontal gyri (LPIFG) of dominant language hemisphere, did not elicit language production related symptoms. These patients were then subjected to six language production tasks with simultaneously electrocorticographic (ECoG) recording. Dada analysis revealed several cortical sites showed event-related cortical high gamma activities. These sites were linked to certain functions, e.g., auditory, visual, and sensorimotor, according to their different activation patterns among tasks. Sites labeled as sensorimotor-related by ECoG showed high accordance with those identified via ECS. Yet ECoG identified few extra crucial sites in LPIFG either. These results demonstrated consistency between ECS and ECoG and reaffirmed the utility of ECoG in preoperative functional cortical mapping.     

High frequency oscillations in intra-operative electrocorticography before and after epilepsy surgery

ObjectiveRemoval of brain tissue showing high frequency oscillations (HFOs; ripples: 80–250 Hz and fast ripples: 250–500 Hz) in preresection electrocorticography (preECoG) in epilepsy patients seems a predictor of good surgical outcome. We analyzed occurrence and localization of HFOs in intra-operative preECoG and postresection electrocorticography (postECoG).MethodsHFOs were automatically detected in one-minute epochs of intra-operative ECoG sampled at 2048 Hz of fourteen patients. Ripple, fast ripple, spike, ripples on a spike (RoS) and not on a spike (RnoS) rates were analyzed in pre- and postECoG for resected and nonresected electrodes.ResultsRipple, spike and fast ripple rates decreased after resection. RnoS decreased less than RoS (74% vs. 83%; p = 0.01). Most fast ripples in preECoG were located in resected tissue. PostECoG fast ripples occurred in one patient with poor outcome. Patients with good outcome had relatively high postECoG RnoS rates, specifically in the sensorimotor cortex.ConclusionsOur observations show that fast ripples in intra-operative ECoG, compared to ripples, may be a better biomarker for epileptogenicity. Further studies have to determine the relation between resection of epileptogenic tissue and physiological ripples generated by the sensorimotor cortex.SignificanceFast ripples in intra-operative ECoG can help identify the epileptogenic zone, while ripples might also be physiological.     

Cortical resection with electrocorticography for intractable porencephaly-related partial epilepsy

PURPOSE: We evaluated the results of cortical resection of epileptogenic tissue for treatment of intractable porencephaly-related epilepsy. METHODS: We examined clinical features, electrophysiological data, surgical findings, and seizure outcomes after cortical resection in eight patients with intractable epilepsy related to porencephalic cysts. RESULTS: All eight patients had hemiparesis. Five retained motor function in the hemiparetic extremities; six retained visual fields. All had partial seizures, six with secondary generalization. Seven patients had simple and three had complex partial seizures (CPSs); two also had drop attacks. Four patients had multiple seizure types. Long-term scalp video-EEG (LVEEG) localized interictal epileptic abnormalities that anatomically corresponded to the cyst location in three patients. LVEEG recorded ictal-onset zones in five; these anatomically corresponded to the cyst location in three of the five. EEG recorded generalized seizures in two patients, hemispheric in one, and multifocal in two. Intraoperative electrocorticography (ECoG) revealed interictal epileptic areas extending beyond the margins of the cyst in seven patients. We resected ECoG-localized interictal epileptic areas completely in five patients and partially in two. Cortical resection was based on seizure semiology and LVEEG in one patient whose ECoG showed no epileptiform discharges. After a minimum follow-up of 1 year, six patients had excellent seizure outcome (Engel class I), and two had a >90% seizure reduction (Engel class III) without complications. CONCLUSIONS: Cortical resection guided by ECoG allows preservation of motor function and visual field and provides an effective surgical procedure for treatment of intractable epilepsy secondary to porencephaly.     

脑磁图对有颅内肿瘤的癫痫病人局部致痫灶的定位价值

目的研究脑磁图（magnetoencephlography,MEG）在颅内肿瘤的癫痫病人中致痫灶的定位价值.方法选择经手术、病理证实的颅内肿瘤25例,术前通过148信道MEG系统记录和分析自发脑磁活动.结果本组25例患者中有21例术前致癫灶MEG定位结果与术中ECoG证明的一致,两者符合率达84%.术后随访3～37个月,平均17个月.手术总有效率达96%.25例患者中19例肿瘤的位置和癫痫灶的位置一致,致癫灶位于肿瘤边缘者10例;距肿瘤约2cm者9例;远隔部位异常者4例;MEG检查没有阳性发现者2例.结论MEG对于预测颅内肿瘤的致痫灶是一种有用的方法,它有助于制定切除病变并同时处理癫痫外科的手术计划.     

Patients with Epileptic Seizures and Cerebral Lesions Who Underwent Lesionectomy Restricted to or Associated with the Adjacent Irritative Area

PURPOSE: To analyze the best surgical procedure for patients with epileptic seizures and cerebral lesions-i.e., resection restricted to the lesion or resection associated with the adjacent irritative area-based on the clinical evolution of patients' seizure outcome and electroencephalographic (EEG) and electrocorticographic (ECoG) findings. METHODS: This study comprised 37 patients with epileptic seizures and cerebral lesions, ranging in age from 9 to 66 years. Patients were divided into two groups: Group 1 consisted of 21 patients with medically intractable epilepsy, Group 2 of 16 patients with medically controlled epilepsy. Eleven of the 21 patients in Group 1 (Subgroup A) underwent surgical resection of the cerebral lesion and adjacent irritative area as shown by ECoG. For the remaining 10 patients in Group 1 (Subgroup B), the resection was restricted to the lesion. The 16 patients in Group 2 all underwent lesionectomies. RESULTS: Of the 11 patients in group 1 who underwent resection of the cerebral lesion and adjacent irritative area, 91% became seizure free. Sixty percent of the remaining patients in group I whose resections were restricted to the lesion also became seizure free, as did all the patients in group 2. An overall analysis of the EEGs for all patients showed a statistically significant decrease in paroxysmal activity. CONCLUSIONS: In patients with uncontrolled seizures, resection of the cerebral lesion associated with the irritative area shows a tendency to obtain better seizure-outcome results than restricted lesionectomy.     

脑磁图对颅内电极脑电图电极埋置的指导价值

目的 通过研究脑磁图(MEG)对侵入性颅内电极脑电图(icEEG)中电极埋置策略的影响,评价MEG在癫痫外科术前评估中的应用价值.方法 收集83例经临床发作症状学、电生理及影像学诊断为难治性部分性癫痫患者,根据MEG是否参与评估电极埋置策略分为两组,比较两组手术疗效的差异.手术疗效按照Engel疗效评价标准分级,Engel Ⅰ、Ⅱ、Ⅲ级为手术有效,Engel Ⅳ级为手术无效.结果 两组中,MEG未参与电极埋置策略评估的共43例,术后有效23例,占54％;而MEG参与评估电极埋置策略的共40例,术后有效31例,占78％,两组手术疗效差异有统计学意义(x2=5.256,P=0.022).结论 MEG能够指导电极埋置位置,增加发作起始区被电极覆盖的几率,提高颅内电极脑电监测的定位准确率,从而提高手术疗效.     

Benign epilepsy with centrotemporal spikes

Benign epilepsy with centrotemporal spikes (BECTS) is a common disorder in childhood. After a brief overview of BECTS, a review of the data in favor of treatment with anticonvulsant medications is followed by the data indicating that treatment is not indicated. Some children appear to have cognitive consequences from BECTS. The parents and children with BECTS require a full discussion of the pros and cons of treatment, but based on data available at this time, it is concluded that treatment is generally not indicated for most patients. Future research may lead to changes in the recommendations.     

脑磁图对非病灶性新皮质癫痫术前评估的价值

目的 研究非病灶性新皮质癫痫发作间期脑磁图(MEG)与手术切除范围一致性与预后的关系.方法 25例非病灶性新皮质癫痫,术前行发作间期MEG检测以及颅内视频脑电监测(i-VEEG),术后随访1年以上并运用Engel法评价预后.结果 术后总体无发作率(Engel IA) 36％ (9/25)、有效率(Engel Ⅰ级、Ⅱ级)68％(17/25).14例MEG与手术切除范围一致组术后8例无发作,无发作率57％(8/14),有效率71％ (10/14);11例不一致组,术后无发作率9％(1/11),有效率64％(7/11),一致组术后无发作率优于不一致组(P＜0.05).结论 非病灶性新皮质癫痫发作间期MEG与手术切除范围一致与术后无发作率有明确相关性.     

Microscopic mild focal cortical dysplasia in temporal lobe dual pathology: An electrocorticography study

BackgroundAssociations between electrophysiological and histological findings might provide an insight into the epileptogenicity of mild focal cortical dysplasia (FCD) in patients with temporal lobe epilepsy (TLE) and a dual pathology.Subjects and methodsA total of 22 patients with pharmacoresistant TLE were included in the study, 16 of them with histologically confirmed hippocampal sclerosis (HS) associated with neocortical temporal mild Palmini Type-I FCD subtypes and 6 with HS. Intraoperative electrocorticography (ECoG) recordings were analysed for epileptiform discharge frequency and morphology. Associations between histological, and electrocorticography pattern findings in these patients were analysed. Electroclinical outcomes in these patients were also evaluated.ResultsNeocortical areas with mild Palmini Type-I FCD showed a significantly higher spike frequency (SF) recorded in the inferior temporal gyrus than those neocortical areas in patients with HS. There was a tendency to higher spike frequency and lower amplitude in neocortical areas with histopathologic subtype IB FCD in relation with IA during intraoperative ECoG. Post-SF excision and amplitude were significantly lower during neocortical post-excision intraoperative ECoG than during neocortical pre-excision recording. There was no difference found in the clinical outcome between patients with and without FCD.ConclusionsIntraoperative electrocorticographic interictal spike frequency recorded in the neocortical inferior temporal gyrus may help to characterize the histopathologic subtypes of mild Palmini Type-I FCD in patients with temporal lobe epilepsy (TLE) and a dual pathology. Our data support the epileptogenicity of neocortical mild FCD in TLE and assessments of ECoG patterns are relevant to determine the extent of the resection in these patients which can influence the electroclinical outcome.     

Magnetoencephalography to confirm epileptiform discharges mimicking small sharp spikes in temporal lobe epilepsy

ObjectiveTo determine whether magnetoencephalography (MEG) can identify epileptiform discharges mimicking small sharp spikes (SSSs) on scalp electroencephalography (EEG) in patients with temporal lobe epilepsy (TLE).MethodsWe retrospectively reviewed simultaneous scalp EEG and MEG recordings of 83 consecutive patients with TLE and 49 with extra-TLE (ETLE).ResultsSSSs in scalp EEG were detected in 15 (18.1%) of 83 TLE patients compared to only two (4.1%) of 49 ETLE patients (p = 0.029). Five of the 15 TLE patients had MEG spikes with concurrent SSSs in EEG, but neither of the 2 ETLE patients. Three of these 5 TLE patients had additional interictal epileptiform discharges (IEDs) in EEG and MEG. Equivalent current dipoles (ECDs) of MEG spikes with concurrent SSSs and IEDs showed no difference in temporal lobe localization and horizontal orientation, whereas ECD moments were smaller in MEG spikes with concurrent SSSs than those with IEDs.ConclusionsSSSs were more common in TLE than in ETLE. At least some morphologically diagnosed SSSs are true but low-amplitude epileptiform discharges in TLE which can be identified with simultaneous MEG.SignificanceSimultaneous MEG is useful to identify epileptiform discharges mimicking SSSs in patients with TLE.     

Utility of magnetoencephalography in the evaluation of recurrent seizures after epilepsy surgery

PURPOSE: To study the role of magnetoencephalography (MEG) in the surgical evaluation of children with recurrent seizures after epilepsy surgery. METHODS: We studied 17 children with recurrent seizures after epilepsy surgery using interictal and ictal scalp EEG, intracranial video EEG (IVEEG), MRI, and MEG. We analyzed the location and distribution of MEG spike sources (MEGSSs) and the relationship of MEGSSs to the margins of previous resections and surgical outcome. RESULTS: Clustered MEGSSs occurred at the margins of previous resections within two contiguous gyri in 10 patients (group A), extended spatially from a margin by < or =3 cm in three patients (group B), and were remote from a resection margin by >3 cm in six patients (group C). Two patients had concomitant group A and C clusters. Thirteen patients underwent second surgeries. IVEEG was used in four patients. Six of seven patients with group A MEGSS clusters did not require IVEEG for second surgeries. Follow-up periods ranged from 0.6 to 4.3 years (mean: 2.6 years). Eleven children, including eight who became seizure-free, achieved Engel class I or II. CONCLUSION: Our data demonstrate the utility of MEG for evaluating patients with recurrent seizures after epilepsy surgery. Specific MEGSS cluster patterns delineate epileptogenic zones. Removing cluster regions adjacent to the margins of previous resections, in addition to removing recurrent lesions, achieves favorable surgical outcome. Cluster location and extent identify which patients require IVEEG, potentially eliminating IVEEG for some. Patients with remotely located clusters require IVEEG for accurate assessment and localization of the entire epileptogenic zone.