Scalp-EEG Recording via Methohexital Narcosis

This study sought to compare the localization of methohexital induced activation in the epileptogenic zone between scalp derived and subdural electrode ECoG recordings and to correlate with seizure outcome after epilepsy surgery. Electroencephalogram (EEG) and ECoG recordings of 15 patients (15–53 years of age, mean: 34 years) with a preoperative methohexital narcosis (low dose 40–50 mg and high dose 80–100 mg) were postoperatively analyzed. Six out of eight patients with both scalp recordings and ECoG recordings showed congruous epileptogenic zone activation (temporal/frontal) in noninvasive and invasive recordings. All improved postoperatively 1, 2. Five postoperatively improved patients (two with ECoG and three with EEG) had an additional temporal spike induction opposite the operated hemisphere 1, 3. One postoperatively seizure-free patient had no temporal activation in EEG but did in ECoG 1, 4. In none of the postoperatively improved patients was EEG falsely localizing [2]. Five of seven patients with scalp-EEG recording showed exclusive activation, one patient predominant activation of the temporal epileptogenic zone. All of these patients improved postoperatively [3]. Postoperatively, all but one patient were seizure-free or had > 75% improvement. One patient with an EEG activation incongruous with the side of operation had no postoperative improvement. Methohexital induced activation of epileptogenic foci is congruent in EEG and ECoG and is a reliable method for lateralization and localization of the epileptogenic zone.     

Clonidine- and Methohexital-Induced Epileptiform Discharges Detected by Magnetoencephalography (MEG) in Patients with Localization-Related Epilepsies

Summary: Purpose: During presurgical evaluation, 14 patients with medically intractable focal epilepsies underwent magnetoencephalographic (MEG) recordings to localize the epileptogenic focus. To increase the number of epileptiform discharges required for MEG analysis, methohexital a short-acting barbiturate that is known to activate epileptiform activity, was used. Additionally, we investigated the spike-provoking properties of clonidine in comparison to methohexital. Methods: After oral premedication with clonidine, short-lasting anesthesia was provided by intravenously administered methohexital. The number and location of epileptiform MEG discharges were assessed after clonidine premedication and during methohexital anesthesia. Results were compared with baseline MEG recordings. Results: Methohexital increased the frequency of focal epileptiform discharges in eight of 13 patients (one of the 14 patients did not receive methohexital after premedication with clonidine). Additionally, premedication with clonidine was found to increase focal epileptiform discharges in nine of 14 patients. When compared with baseline MEG recordings, recordings after treatment with both clonidine premedication and methohexital anesthesia showed a significant increase in the total number of epileptiform signals and the number of spikes contributing to MEG source localizations. Conclusions: This study confirms the selective proconvulsant effects of methohexital on the epileptogenic focus as suggested previously by EEG and electrocorticogram (ECoG) investigations. Additionally, our data establish for the first time that clonidine increases epileptiform activity in patients with seizure disorders. These results indicate that clonidine is suited as an activating agent for the localization of epileptogenic foci by means of MEG. This effect of clonidine on specific epileptic activity also indicates that clonidine should be used with caution as an antihypertensive drug in patients with seizure disorders.     

Localization of the Epileptic Focus During Methohexital-Induced Anesthesia

A short anesthesia was provided by methohexital for painless percutaneous removal of subdural electrodes in 27 patients with medically intractable, complex partial seizures who had undergone invasive preoperative evaluation. Electrocorticographic(ECoG) recordings performed before and during the narcosis were submitted to visual (n = 27) and computerized (n = 3) analysis to obtain additional information about the location of the epileptic focus (or foci). The following observations were made: focal epileptiform potentials were induced in 24 of 27 patients (89%); (b) in 20 of these 24, the induced spikes appeared amid or were followed by isoelectric or subdelta activity. These spikes were characterized by high amplitude as well as rhythmic and synchronized appearance over a circumscribed focal area (or areas) known to be spontaneously epileptogenic. This phenomenon, termed spike-burst-suppression (SBS) pattern, allowed identification of the primary epileptic focus in many patients with temporal lobe epilepsy. Furthermore, it indicated a good outcome of epilepsy surgery. Computerized analysis of the induced synchronized spikes (n = 3) allowed further delineation of the primary site of epileptogenicity and quantitative comparison of multiple epileptic generators. ECoG recording during deep methohexital-induced narcosis is a valuable tool for lateralization and delineation of the primary epileptogenic focus.     

Clonidine and Methohexital-Induced Epileptic Magnetoencephalographic Discharges in Patients with Focal Epilepsies

Summary: Purpose : During presurgical evaluation, 14 patients with medically intractable focal epilepsies underwent magnetoencephalographic (MEG) recordings for focus localization. To increase the number of epileptic discharges required for MEG analysis, we administered methohexital (MHT), a short-acting barbiturate known to provoke epileptic activity. We also investigated the spike-provoking properties of clonidine in comparison with MHT.
Methods : Patients were briefly anesthetized with intravenously administered MHT after being premedicated orally with clonidine. Numbers and locations of epileptic MEG discharges were assessed after clonidine premedication as well as during MHT anesthesia. Results were compared with baseline MEG recordings.
Results : MHT increased the frequency of focal epileptic discharges in 8 of 13 patients (1 of the 14 patients did not receive MHT after premedication with clonidine). Premedication with clonidine also increased focal epileptic discharges in 9 of 14 patients. The numbers of epileptic signals and numbers of spikes contributing to MEG source localizations were significantly increased in MEG recordings under both treatment conditions (clonidine premedication and MHT anesthesia) as compared with baseline MEG recordings.
Conclusions : Our results confirmed the selective proconvulsive effects of MHT on the epileptic focus, as previously suggested by EEG and electrocorticographic (ECoG) investigations. However, our present data establish for the first time that clonidine increases epileptic activity in patients with seizure disorders and indicate that clonidine is suitable as an activating agent for localization of epileptogenic foci by MEG. This effect of clonidine on specific epileptic activity also indicates that specific care must be taken when clonidine is used as an antihypertensive drug in patients with seizure disorders.     

Specific response of the epileptic focus to anesthesia with propofol

Twenty patients suffering from medically intractable epilepsy were submitted to invasive presurgical evaluation using subdural strip electrodes for chronic electrocorticographic (ECoG) recordings. A short anesthesia of 12–15 min was induced to ensure painless percutaneous removal of the subdural electrode strips. Anesthesia was provided by two consecutive intravenous injections of propofol (50 and 70 mg or 70 and 140 mg) preceded by fentanyl (0.1–0.15 mg) in 12 patients. In order to test whether the epileptic focus showed a specific response following application of propofol, the first 12 min of ECoG recordings, prior to removal of the subdural strip electrodes, were visually analyzed. Specific patterns of response confined to the epileptic focus (foci) were observed in 18 of 20 patients following application of at least one of the two doses of propofol. Patterns observed in the epileptogenic area consisted of (a) a loss or marked reduction of activity induced by propofol (n = 16), (b) a maximum of suppression of brain activity (n = 12), (c) suppression of spontaneous interictal activity (n = 10), (d) induction of epileptiform activity (n = 5), and (e) induction of a habitual seizure (n = 1). In summary, ECoG recordings during anesthesia with propofol provide complementary information about the epileptic focus in the process of presurgical evaluation of epileptics.     

Intraoperative electrocorticography in temporal lobe epilepsy surgery

Although in clinical use for many years, the validity of intraoperative electrocorticography (ECoG) in guiding resective temporal lobe epilepsy (TLE) surgery is uncertain. Advances in neuroimaging and extraoperative intracranial recordings have contributed greatly to the identification of epileptogenic lesions and cortex, clarifying the limitations of a brief intraoperative interictal recording. Studies of undifferentiated ECoG findings (which classify all interictal cortical spike discharges as equal) tend to not support this method. This article reviews ECoG and presents data from 86 TLE surgeries at the University of British Columbia suggesting that differentiation of ECoG features may enhance the contribution of this time honored method. Specifically, independent foci may be more important for epileptogenesis than synchronous foci, and postexcision activation appears to be a benign phenomenon, while residual spikes unaltered by the resection correlate with a greater proportion of seizure recurrence.     

Electroencephalographic features of midline spikes in the cat penicillin focus and in human epilepsy

We used EEG and ECoG to analyze and compare surface fields of interictal spikes from penicillin foci located on the mesial cortex of cats and from patients with midline spikes. Findings from the experimental model predicted results of the human study. When the field of a mesial cortical focus extended over the convexity, cortical scalp-recorded epileptiform discharges could be vertex negative, positive over the lateral convexity or a combination of these two in a surface dipole. Associated clinical features were in agreement with previous reports. We point out pitfalls in interpreting EEG recordings from patients with midline epileptogenic foci.     

伴有癫癇发作的脑内病灶的手术治疗

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颅骨修补围手术期癫痫灶的脑电研究

目的:研究颅骨缺损与外伤性癫痫(PTE)的关系。方法:随机对33例重型颅脑外伤后颅骨修补术病人围手术期多形式脑电图(EEG)进行了前瞻性研究。结果:33例中术前28例EEG局灶性异常,术中皮层脑电图(ECoG)31例有痫样放电。29例癫痫灶全切除,2例因癫痫灶位于功能区仅行部分切除。术后31例无癫痫发作,2例仍有癫痫发作,但较术前减轻,近期效果良好。结论:本研究结果提示,颅骨修补围手术期应常规作多形式EEG及术中ECoG监测,发现癫痫灶时尽可能切除,可望降低颅骨修补术后PTE的发生率。     

磁源影像导航辅助显微手术治疗顽固性癫(癎)

目的探讨磁源影像引导的神经导航技术在显微手术治疗顽固性癫癎的作用。方法顽固性癫癎病人14例,术前行视频脑电图、磁共振、脑磁图等检查,综合评估确定致癎灶的位置。术中运用磁源影像引导的stealstation神经导航系统及皮层脑电图,进行显微手术。结果术中皮层脑电图与术前定位符合率100%,术后癎样放电消失9例明显好转5例。患者神经功能保持良好。10例随访疗效满意。结论致癎灶的定位需要综合分析,磁源影像是一重要的定位方法,神经导航的应用有助于癫癎的微侵袭手术。     

难治性癫痫的致痫灶定位及手术治疗研究

目的评价难治性癫痫的致痫灶定位方法和皮层电极监测下致痫灶切除,加行多处软脑膜下横纤维切断术(MST)治疗癫痫的疗效。方法对47例难治性癫痫病人的致痫灶,采用CT MRI EEG 单光子发射计算机体层摄影(SPECT) 皮层脑电脑(ECoG)联合检测定位。对检出的阳性病灶在皮层电极监测显微镜下行致痫灶切除,切除后监测仍有癫痫波者加行MST;致痫灶位于重要功能区者单行MST。结果致痫灶阳性检出率86%。皮层电极检测显微镜下致痫灶切除加MST,术后91%的病人癫痫发作停止,半年后约15%的病人复发,但症状较术前减轻,持续时间较术前短。结论CT MRI EEG SPECT ECoG联合检测,对手术定位具有较高价值。皮层电极监测下致痫灶切除术及MST创伤轻微、效果比较可靠、治愈率高、并发症少、复发率低。病灶及致痫灶的不完全切除和形成皮层软化及疤痕,可能是导致癫痫复发的重要原因。     

功能性磁共振和皮质脑电图在伴继发性癫(癎)脑肿瘤手术中的应用(附13例分析)

目的探讨术前功能磁共振成像（fMRI）和术中皮质脑电图（ECoG）在伴继发性癫疒间脑肿瘤手术中的应用价值。方法回顾性分析13例脑运动皮质区附近肿瘤病人的临床资料。术前通过fMRI了解相应脑功能区皮质和白质纤维束的形态和分布;术中在切除肿瘤前后行ECoG检测,确定致疒间灶的位置,指导肿瘤及致疒间灶的切除。结果手运动功能区受肿瘤推挤而出现功能转移或重组9例,行肿瘤全切除;功能区局部重叠2例,行肿瘤次全切除;大部分重叠2例,行肿瘤部分切除。ECoG确定的致疒间灶距肿瘤2 cm以内9例,3～5 cm 2例,与肿瘤重叠2例。术后出现短暂性失语1例,一过性偏瘫2例。结论fMRI能准确显示运动皮质中枢位置,对脑肿瘤术前手术方案制定和手术时减少重要功能区损伤具有重要意义。ECoG确定致疒间灶大多距肿瘤2 cm以内。     

Remifentanil-induced spike activity as a diagnostic tool in epilepsy surgery

Objectives –  To assess the value of remifentanil in intraoperative evaluation of spike activity in patients undergoing surgery for mesial temporal lobe epilepsy (MTLE).
Materials and methods –  Twenty-five patients undergoing temporal lobectomy for medically intractable MTLE were enrolled in the study. Electrocorticography (ECoG) recordings were performed on the intraventricular hippocampus and from the anterior inferior temporal and lateral neocortex before and after a 300 μg intravenous bolus of remifentanil. Spike activity was quantified as spike-count per minute.
Results –  A significant increase ( P  <   0.005) in spike activity was observed after administration of remifentanil in 23 of 25 patients (92%). Furthermore, two patients who did not have any spike activity on the baseline ECoG developed spikes after administration of remifentanil.
Conclusions –  The results suggest that remifentanil can enhance spike activity in the epileptogenic zone and reveal otherwise concealed epileptogenic tissue in patients with MTLE. Thus, remifentanil may prove to be an important diagnostic tool during surgical treatment for intractable focal epilepsy.     

Graph analysis of epileptogenic networks in human partial epilepsy

Purpose: The current gold standard for the localization of the cortical regions responsible for the initiation and propagation of the ictal activity is through the use of invasive electrocorticography (ECoG). This method is utilized to guide surgical intervention in cases of medically intractable epilepsy by identifying the location and extent of the epileptogenic focus. Recent studies have proposed mechanisms in which the activity of epileptogenic cortical networks, rather than discrete focal sources, contributes to the generation of the ictal state. If true, selective modulation of key network components could be employed for the prevention and termination of the ictal state. Methods: Here, we have applied graph theory methods as a means to identify critical network nodes in cortical networks during both ictal and interictal states. ECoG recordings were obtained from a cohort of 25 patients undergoing presurgical monitoring for the treatment of intractable epilepsy at the Mayo Clinic (Rochester, MN, U.S.A.). Key Findings: One graph measure, the betweenness centrality, was found to correlate with the location of the resected cortical regions in patients who were seizure‐free following surgical intervention. Furthermore, these network interactions were also observed during random nonictal periods as well as during interictal spike activity. These network characteristics were found to be frequency dependent, with high frequency gamma band activity most closely correlated with improved postsurgical outcome as has been reported in previous literature. Significance: These findings could lead to improved understanding of epileptogenesis. In addition, this theoretically allows for more targeted therapeutic interventions through the selected modulation or disruption of these epileptogenic networks.     

Comparison of scalp to subdural recordings for localizing epileptogenic foci

We reviewed a group of 124 patients who were seizure-free after epilepsy surgery to determine the relative accuracy for identifying epileptogenic foci with (a) interictal scalp recordings, (b) ictal scalp recordings, and (c) ictal subdural electrode recordings. If considering only patients undergoing temporal lobe surgery, ictal subdural strip recordings were accurate in 100% of cases. Ictal scalp recordings were accurate in 44% of cases, whereas interictal scalp recordings were accurate in only 31% of cases. The data also indicate that noninvasive recordings have a false lateralization or localization error rate of 10% when used for identifying unilateral epileptogenic foci in preparation for epilepsy surgery.     

局灶性皮质发育不良所致难治性癫痫的微创神经外科治疗

目的应用神经导航结合术中皮质电极描记,微创治疗局灶性皮质发育不良(focal cortical dysplasia,FCD)所致的难治性癫痫。方法 26例局灶性皮质发育不良所致的难治性癫痫患者,术前常规使用CT、磁共振成像(magnetic resonanceimaging,MRI)、长程视频脑电图(digital video signal and electroencephalogram,VEEG)、磁共振波谱分析(MR Spectroscopy,MRS)等检查,如病灶位于功能区则行功能性磁共振成像(functional magnetic resonance imaging,fMRI)。术中通过神经导航确定的病灶与ECoG确定的致痫灶位置及范围进行对比,了解两者的吻合程度及差异,综合分析后精确并标记出癫痫波的起源位置和范围,将局灶性皮质发育不良病灶和周边的致痫皮质切除;如致痫灶位于功能区或附近,在保留功能区皮质的基础上,给予低功率皮质热灼。结果术后病理结果:26例患者病理标本符合FCD。术后患者无明显并发症出现。根据Engel术后效果分级进行评估,Ⅰ级23例,Ⅱ级2例,Ⅲ级1例。结论神经导航结合术中皮质电极描记在局灶性皮质发育不良所致的难治性癫痫手术中,具有定位准确、损伤少的优点,在切除致痫灶的同时能最大程度保护脑功能。     

Two magneto-encephalographic epileptic foci did not coincide with the electrocorticographic ictal onset zone in a patient with temporal lobe epilepsy.

To evaluate the usefulness and limitations of magneto-encephalography (MEG) for epilepsy surgery, we compared 'interictal' epileptic spike fields on MEG with ictal electrocorticography (ECoG) using invasive chronic subdural electrodes in a patient with intractable medial temporal lobe epilepsy (MTLE) associated with vitamin K deficiency intracerebral hemorrhage. A 19-year-old male with an 8-year history of refractory complex partial seizures, secondarily generalized, and right hemispheric atrophy and porencephaly in the right frontal lobe on MRI, was studied with MEG to define the interictal paroxysmal sources based on the single-dipole model. This was followed by invasive ECoG monitoring to delineate the epileptogenic zone. MEG demonstrated two paroxysmal foci, one each on the right lateral temporal and frontal lobes. Ictal ECoG recordings revealed an ictal onset zone on the right medial temporal lobe, which was different from that defined by MEG. Anterior temporal lobectomy with hippocampectomy was performed and the patient has been seizure free for two years. Our results indicate that interictal MEG does not always define the epileptogenic zone in patients with MTLE.     

皮层脑电图辅助立体定向下手术治疗颅内钙化灶引起的难治性癫痫

目的研究立体定向下开放式手术联合术中皮层脑电图(ECoG)监测治疗颅内钙化灶性癫痫的手术方法、注意事项及效果。方法 21例颅内单发钙化灶引起的癫痫患者(其中主要功能区钙化灶9例),在立体定向仪导向下,开放直视手术,ECoG监测钙化灶周围皮层脑电活动情况,切除钙化灶后再次ECoG监测,确定致痫灶的范围及处理方式。结果所有钙化灶均被顺利切除。钙化灶区域ECoG监测无明显异常5例,表现为阵发性与动脉搏动相一致的单发性棘慢复合波发放9例,表现为明显癫痫样放电7例。单纯钙化灶切除术14例,钙化灶+周边增生组织+致痫皮层切除术4例,钙化灶切除+功能区致痫皮层低功率电凝热灼术3例。术后ECoG监测发现异常放电消失11例,仍残存轻中度痫样放电5例。无严重并发症。随访6个月～8年,EngelⅠ级16例,EngelⅡ级5例,总有效率100%。结论 ECoG监测是立体定向下手术治疗颅内钙化灶性癫痫的重要辅助手段,能够指导术中采取相应的手术方式切除钙化灶,妥善处理致痫灶,避免过多损伤脑皮层。     

Time-frequency characterization of electrocorticographic recordings of epileptic patients using frequency-entropy similarity: a comparison to other bi-variate measures

Expert evaluation of electrocorticographic (ECoG) recordings forms the linchpin of seizure onset zone localization in the evaluation of epileptic patients for surgical resection. Numerous methods have been developed to analyze these complex recordings, including uni-variate (characterizing single channels), bi-variate (comparing channel pairs) and multivariate measures. Developing reliable algorithms may be helpful in clinical tasks such as localization of epileptogenic zones and seizure anticipation, as well as enabling better understanding of neuronal function and dynamics. Recently we have developed the frequency-entropy (F-E) similarity measure, and have tested its capability in mapping the epileptogenic zones. The F-E similarity measure compares time-frequency characterizations of two recordings. In this study, we examine the method's principles and utility and compare it to previously described bi-variate correspondence measures such as correlation, coherence, mean phase coherence and spectral comparison methods. Specially designed synthetic signals were used for illuminating theoretical differences between the measures. Intracranial recordings of four epileptic patients were then used for the measures' comparative analysis by creating a mean inter-electrode matrix for each of the correspondence measures and comparing the structure of these matrices during the inter-ictal and ictal periods. We found that the F-E similarity measure is able to discover spectral and temporal features in data which are hidden for the other measures and are important for foci localization.     

功能区皮层下小病灶相关性癫痫的手术治疗

目的评价综合应用多种定位技术治疗功能区皮层下小病灶相关性癫痫的手术方法及效果。方法 58例功能区皮层下小病灶引起的癫痫患者,在立体定向仪导向下,开放直视手术切除病灶,术中皮层脑电图(ECoG)监测定位致痫灶,术中神经电生理监测(IOM)判断致痫区的功能以及二者的重叠程度,辅助以麻醉唤醒定位语言区、实时超声检查病变切除程度,根据监测结果分别采取致痫灶切除术、多处软膜下横切术(MST)或皮层低功率电凝热灼术妥善处理致痫灶。结果病灶全部切除52例,少量残留6例。病灶区域ECoG监测除波幅略有降低外无明显异常13例,行占位病灶切除术;ECoG明显异常,在非主要功能区8例,行占位病灶+周边致痫皮层切除术;ECoG明显异常而又在主要功能区37例,行占位病灶+功能区致痫皮层多处软膜下横切术(MST)或低功率电凝热灼术。ECoG监测发现痫样放电消失、基本节律大致恢复正常29例,仍残留少量棘波13例,残存较多棘波且基本节律轻到中度异常16例。随访1～5年,EngelⅠ级46例,EngelⅡ级8例,EngelⅢ级4例,总有效率100%。出现暂时性轻偏瘫17例,暂时性失语8例,无严重永久性并发症。结论综合应用立体定向引导、术中IOM、ECoG、麻醉唤醒及实时超声定位治疗功能区小病灶相关性癫痫,能够精准定位并切除病灶及处理致痫灶,避免损伤功能区,是一种微创、安全、有效的手术方法。