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Left lateral view of scalp electrode montage according to the International 10-1 0 system over the temporal lobe area and according to the 10-20 system over the rest of the scalp. Montage on right side included corresponding electrodes with even nurnbers. Additionally, bilateral sphenoidal electrodes were placed in all patients (left, Sp,; right, S,,J.
Source publication
It remains controversial whether a specific pattern of interictal epileptiform activity exists that may help to differentiate temporal lobe epilepsy (TLE) due to hippocampal sclerosis (HS) from other forms of TLE. In this study, we characterized the distribution of interictal epileptiform discharges in TLE due to HS as compared with those in patien...
Contexts in source publication
Context 1
... EEG was digitally recorded by using 39 scalp electrodes and additional left and right sphenoidal elec- trodes (Spl and Sp2) in all patients. The scalp electrodes were placed according to the International 10-10 system over both temporal areas and according to the 10-20 system over the rest of the scalp (Fig. 1) (18). Electrode impedances were kept <5 kOhm. During acquisition, the bandpass was 0.5-70 Hz, and sensitivity was 15 kV/mm. The sampling rate was at 200 ...
Context 2
... could be either the left or the right side in each patient. In addition, electrodes S,,,,, F,,,, F,,,,, FT,,,, and FT,,,o were referred to as anterior temporal electrodes, elec- trodes T,,,, T9,,,, TP,,,, TP,,,,, and P,,, were referred to as lateral temporal electrodes, and the rest of scalp elec- trodes were defined as extratemporal electrodes (Fig. 1). The first author (H.M.H.), who reviewed all the pa- tients' EEGs, was blinded to the pathologic diagnosis during the EEG analyses. If >50 discharges were avail- able, the epileptiform activity was sampled evenly throughout the entire length of monitoring. A spike or sharp wave had duration of <200 ms and could be dis- tinguished by ...
Context 3
... other than unilateral HS on MRI or pathology; (c) seizure-free outcome after limited an- terior temporal resection with removal of the medial structures; (d) prolonged video-EEG monitoring with electrode montage according to the International 10-10 B 100 I-v--J--pv system over both temporal lobes and additional bilateral sphenoidal electrodes (Fig. 1); (e) interictal spikedsharp waves recorded; and (f) follow-up of 2 1 year after sur- gical resection (range, 1 4 . 5 ...
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Background:
Epilepsy, a well-known mostly idiopathic neurologic disorder, has to be correctly diagnosed and properly treated. Up to now, several diagnostic approaches have been processed to determine the epileptic focus.
Objectives:
The aim of this study was to discover whether proton-MR-spectroscopic imaging (MRSI) aids in the diagnosis of temp...
Citations
... The percentage of FL of IEDs has been described as 6.3-25.9%, higher than ictal discharges [18][19][20][21][22]. Our result of 10.3-10.5% in FL of IEDs seems consistent with previous reports. ...
... The characteristics of IED FL have been mentioned to include cerebral atrophy or damage on the side of seizure focus [13,21], hippocampal sclerosis rather than tumor in the case of the temporal lobe [20], and a left-sided focus [24]. From our study, the localization of the CM, particularly with a medial and deep location, appears to be another characteristic of IED FL. ...
Background
Cavernous malformation (CM) is a well-known cause of epilepsy. Although the location of the CM is usually consistent with the side of seizure onset, some reports have described discrepancies between results from scalp electroencephalography (EEG) and CM location. This study investigated the prevalence and features of patients showing false lateralization (FL). Particularly, we tested the hypothesis that patients showing FL were more likely to have CM in medial and deep areas of the brain than in other areas.
Methods
Patients diagnosed with CM-associated epilepsy in our institution between March 2009 and March 2023 were included in this retrospective analysis. We investigated the presence or absence of FL of interictal epileptiform discharges (IEDs) or ictal discharges against MRI findings or against the true focus as determined from surgical outcomes. We compared the FL group with the non-false-lateralization group (NFL group) to clarify features of CM-associated epilepsy patients showing FL.
Results
Thirty-two epilepsy patients with CM were analyzed. The frequency of FL to MRI was 10.3% for IEDs and 7.7% for ictal discharges, while the frequency of FL to true focus after removal surgery was 10.5% for IEDs and 7.7% for ictal discharges. Regarding the FL of IEDs against MRI findings, the percentage of medial and deep lesions was significantly higher in the FL group (3/3, 100%) than in the NFL group (6/26, 23.1%; p = 0.023). No significant differences in age, sex, seizure type, or size of the CM were seen between groups.
Conclusions
CM-associated epilepsy can also present with FL, particularly if the location of the CM is medial and deep. Caution may be needed in determining the area for resection based solely on scalp EEG findings.
... As extratemporal lobe epilepsies were either LEATs, FCDs or cavernomas, this could have influenced the size of resection and the amount and morphology of IEDs. 45,46 However, the group size in our cohort was too small to study this in detail. Patients with non-lesional and lesional MRI had 86% (6/7) and 57% (8/14) sublobar concordance rates, respectively. ...
Objective
Presurgical high‐density electric source imaging (hdESI) of interictal epileptic discharges (IEDs) is only used by few epilepsy centers. One obstacle is the time‐consuming workflow both for recording as well as for visual review. Therefore, we analyzed the effect of (a) an automated IED detection and (b) the number of IEDs on the accuracy of hdESI and time‐effectiveness.
Methods
In 22 patients with pharmacoresistant focal epilepsy receiving epilepsy surgery (Engel 1) we retrospectively detected IEDs both visually and semi‐automatically using the EEG analysis software Persyst in 256‐channel EEGs. The amount of IEDs, the Euclidean distance between hdESI maximum and resection zone, and the operator time were compared. Additionally, we evaluated the intra‐individual effect of IED quantity on the distance between hdESI maximum of all IEDs and hdESI maximum when only a reduced amount of IEDs were included.
Results
There was no significant difference in the number of IEDs between visually versus semi‐automatically marked IEDs (74 ± 56 IEDs/patient vs 116 ± 115 IEDs/patient). The detection method of the IEDs had no significant effect on the mean distances between resection zone and hdESI maximum (visual: 26.07 ± 31.12 mm vs semi‐automated: 33.6 ± 34.75 mm). However, the mean time needed to review the full datasets semi‐automatically was shorter by 275 ± 46 min (305 ± 72 min vs 30 ± 26 min, P < 0.001).
The distance between hdESI of the full versus reduced amount of IEDs of the same patient was smaller than 1 cm when at least a mean of 33 IEDs were analyzed. There was a significantly shorter intraindividual distance between resection zone and hdESI maximum when 30 IEDs were analyzed as compared to the analysis of only 10 IEDs (P < 0.001).
Significance
Semi‐automatized processing and limiting the amount of IEDs analyzed (~30–40 IEDs per cluster) appear to be time‐saving clinical tools to increase the practicability of hdESI in the presurgical work‐up.
... Clinicians increasingly saw cases of spike-seizure discordance, including patients with bitemporal spikes rendered seizure-free with a unilateral temporal lobectomy. 8 This led to the belief that the "epileptogenic zone" (EZ), the cortex we must remove to stop seizures, is typically a subset of the "irritative zone," the cortex that generates spikes. 6 Epileptologists and surgeons lamented that there was no way to distinguish the spikes that needed to be resected from the innocent spikes that are better left alone. ...
Electroencephalography (EEG) has been the primary diagnostic tool in clinical epilepsy for nearly a century. Its review is performed using qualitative clinical methods that have changed little over time. However, the intersection of higher resolution digital EEG and analytical tools developed in the past decade invites a re‐exploration of relevant methodology. In addition to the established spatial and temporal markers of spikes and high‐frequency oscillations, novel markers involving advanced postprocessing and active probing of the interictal EEG are gaining ground. This review provides an overview of the EEG‐based passive and active markers of cortical excitability in epilepsy and of the techniques developed to facilitate their identification. Several different emerging tools are discussed in the context of specific EEG applications and the barriers we must overcome to translate these tools into clinical practice.
... 43 mTLE patients without dual pathology had a higher probability of interictal spikes localized in the anterior temporal lobe region than those with temporal lobe tumors (95.2% vs. 0%). 43 We built and validated a novel source localization method. The innovation lies in incorporating the length of white matter tracts allowing monosynaptic spike propagations. ...
Objective
To determine the structural networks that constrain propagation of ictal oscillations during epileptic spasm events, and compare the observed propagation patterns across patients with successful or unsuccessful surgical outcomes.
Methods
Subdural electrode recordings of 18 young patients (age 1–11 years) were analyzed during epileptic spasm events to determine ictal networks and quantify the amplitude and onset time of ictal oscillations across the cortical surface. Corresponding structural networks were generated with diffusion magnetic resonance imaging (MRI) tractography by seeding the cortical region associated with the earliest average oscillation onset time, and white matter pathways connecting active electrode regions within the ictal network were isolated. Properties of this structural network were used to predict oscillation onset times and amplitudes, and this relationship was compared across patients who did and did not achieve seizure freedom following resective surgery.
Results
Onset propagation patterns were relatively consistent across each patient’s spasm events. An electrode's average ictal oscillation onset latency was most significantly associated with the length of direct corticocortical tracts connecting to the area with the earliest average oscillation onset (p < .001, model R² = .54). Moreover, patients demonstrating a faster propagation of ictal oscillation signals within the corticocortical network were more likely to have seizure recurrence following resective surgery (p = .039). In addition, ictal oscillation amplitude was associated with connecting tractography length and weighted fractional anisotropy (FA) measures along these pathways (p = .002/.030, model R² = .31/.25). Characteristics of analogous corticothalamic pathways did not show significant associations with ictal oscillation onset latency or amplitude.
Significance
Spatiotemporal propagation patterns of high‐frequency activity in epileptic spasms align with length and FA measures from onset‐originating corticocortical pathways. Considering the data in this individualized framework may help inform surgical decision‐making and expectations of surgical outcomes.
... 43 mTLE patients without dual pathology had a higher probability of interictal spikes localized in the anterior temporal lobe region than those with temporal lobe tumors (95.2% vs. 0%). 43 We built and validated a novel source localization method. The innovation lies in incorporating the length of white matter tracts allowing monosynaptic spike propagations. ...
Objective
This study was undertaken to build and validate a novel dynamic tractography‐based model for localizing interictal spike sources and visualizing monosynaptic spike propagations through the white matter.
Methods
This cross‐sectional study investigated 1900 spike events recorded in 19 patients with drug‐resistant temporal lobe epilepsy (TLE) who underwent extraoperative intracranial electroencephalography (iEEG) and resective surgery. Twelve patients had mesial TLE (mTLE) without a magnetic resonance imaging‐visible mass lesion. The remaining seven had a mass lesion in the temporal lobe neocortex. We identified the leading and lagging sites, defined as those initially and subsequently (but within ≤50 ms) showing spike‐related augmentation of broadband iEEG activity. In each patient, we estimated the sources of 100 spike discharges using the latencies at given electrode sites and diffusion‐weighted imaging‐based streamline length measures. We determined whether the spatial relationship between the estimated spike sources and resection was associated with postoperative seizure outcomes. We generated videos presenting the spatiotemporal change of spike‐related fiber activation sites by estimating the propagation velocity using the streamline length and spike latency measures.
Results
The spike propagation velocity from the source was 1.03 mm/ms on average (95% confidence interval = .91–1.15) across 133 tracts noted in the 19 patients. The estimated spike sources in mTLE patients with International League Against Epilepsy Class 1 outcome were more likely to be in the resected area (83.9% vs. 72.3%, φ = .137, p < .001) and in the medial temporal lobe region (80.5% vs. 72.5%, φ = .090, p = .002) than those associated with the Class ≥2 outcomes. The resulting video successfully animated spike propagations, which were confined within the temporal lobe in mTLE but involved extratemporal lobe areas in lesional TLE.
Significance
We have, for the first time, provided dynamic tractography visualizing the spatiotemporal profiles of rapid propagations of interictal spikes through the white matter. Dynamic tractography has the potential to serve as a unique epilepsy biomarker.
... Focal epileptic discharges with a maximum potential at F7 or F8 were considered to be temporal focal epileptic discharges. Other focal epileptic discharges were considered to be nontemporal focal epileptic discharges [6][7][8]. ...
... Regarding EEG abnormalities, the results of the present study indicate that patients with focal epileptic discharge at anterior temporal regions are more likely to experience irritability due to LEV, while patients with focal epileptic discharge in other regions are more likely to experience irritability due to PER. Epileptic discharge in the anterior temporal regions is a characteristic finding in patients with mesial temporal lobe epilepsy, especially that associated with hippocampal sclerosis [7,8]. Therefore, our results indi-cate that irritability owing to LEV may be associated with mesial temporal lobe epilepsy due to hippocampal sclerosis, while irritability due to PER may be associated with other types of focal epilepsy. ...
Purpose
The present study evaluated whether patients with epilepsy who received both levetiracetam (LEV) and perampanel (PER) therapy showed side effects of irritability. The study also examined the relationship between patient characteristics and irritability when it occurred as a side effect.
Methods
We retrospectively examined medical records of 98 patients with epilepsy who were treated with both LEV and PER at the Department of Psychiatry in the Epilepsy Center of Nishiniigata Chuo National Hospital in Japan. We performed multiple regression analyses with the presence/absence of irritability due to LEV or PER as the dependent variables and clinical characteristics of the patients as independent variables.
Results
LEV and PER caused irritability in 7 and 17 of 98 patients, respectively. LEV- and PER-related irritability did not occur in the same patients. A logistic multiple regression analysis revealed that EEG findings of temporal focal epileptic discharge were significantly associated with increased incidence of irritability due to LEV. LEV-related irritability decreased significantly with higher dosages of LEV. Another logistic multiple regression analysis revealed that a psychiatric comorbidity of irritability and EEG findings of nontemporal focal epileptic discharge were significantly associated with increased incidence of irritability due to PER.
Conclusions
LEV and PER cause irritability in different patient groups. Additionally, irritability as a side effect was present only at low dosages of LEV, but PER tended to cause irritability even at high dosages.
... Overall, despite the widely available ictal EEG recordings in most patients, neuroimaging during presurgical evaluation (except for ictal SPECT) relies on interictal epileptic activity. However, epilepsy surgery aims at eliminating the origin of seizures and not of IEDs, and SOZ and IZ are not necessarily concordant (Hamer et al., 1999;Bartolomei et al., 2016). Therefore, it is of high clinical value to localize the sources of seizures complementary to those of interictal epileptic activity. ...
Electroencephalographic (EEG) source imaging localizes the generators of neural activity in the brain. During presurgical epilepsy evaluation, EEG source imaging of interictal epileptiform discharges is an established tool to estimate the irritative zone. However, the origin of interictal activity can be partly or fully discordant with the origin of seizures. Therefore, source imaging based on ictal EEG data to determine the seizure onset zone can provide precious clinical information. In this descriptive review, we address the importance of localizing the seizure onset zone based on noninvasive EEG recordings as a complementary analysis that might reduce the burden of the presurgical evaluation. We identify three major challenges (low signal-to-noise ratio of the ictal EEG data, spread of ictal activity in the brain, and validation of the developed methods) and discuss practical solutions for these issues. We provide an extensive overview of the existing clinical studies to illustrate the potential clinical utility of EEG-based localization of the seizure onset zone. Finally, we conclude with future perspectives and the needs for translating ictal EEG source imaging into clinical practice.
... These results extend the findings of previous scalp EEG-based studies which showed that the irritative zone in tumor-related epilepsy tends to be extensive and can even be located on the contralateral side. 16 Interictal spike patterns of patients with tumor-related epilepsy appear to differ from those of non-tumor-related epilepsy patients. Our previous study had analyzed 32 temporal lobe epilepsy patients who underwent both extraoperative ECoG monitoring and epilepsy surgery in Seoul National University Hospital from 2006 to 2010. ...
Background and purpose:
Although some surgeons utilize interictal spikes recorded via electrocorticography (ECoG) when planning extensive peritumoral resection in patients with tumor-related epilepsy, the association between interictal spikes and epileptogenesis has not been fully described. We investigated whether the resection of interictal spikes recorded by ECoG is associated with more favorable surgical outcomes in tumor-related epilepsy.
Methods:
Of 132 patients who underwent epilepsy surgery for tumor-related epilepsy from 2006 to 2013, seven patients who underwent extraoperative ECoG were included in this study. In each patient, ECoG interictal spike sources were localized using standardized low-resolution brain electromagnetic tomography and were co-registered into a reconstructed brain model. Correspondence to the resection volume was estimated by calculating the percentage of interictal spike sources in the resection volume.
Results:
All patients achieved gross total resection without oncological recurrence. Five patients achieved favorable surgical outcomes, whereas the surgical outcomes of two patients were unfavorable. Correspondence rates to the resection volume in the favorable and unfavorable surgical outcome groups were 44.6%±27.8% and 43.5%±22.8%, respectively (p=0.96). All patients had interictal spike source clusters outside the resection volume regardless of seizure outcome.
Conclusions:
In these cases of tumor-related epilepsy, the extent of the resection of ECoG interictal spikes was not associated with postoperative seizure outcomes. Furthermore, the presence of interictal spike sources outside of the resection area was not related to seizure outcomes. Instead, concentrating more on the complete removal of the brain tumor appears to be a rational approach.
... Complementarily, patients with low spike rates have classically less severe epilepsy (later age at seizure onset, as well as less frequent and less severe seizures) (Rosati et al., 2003). Finally, patients with hippocampal sclerosis tend to have more restricted IEDs than patients with mesial temporal tumours (Hamer et al., 1999). ...
Electroencephalographic (EEG) investigations are crucial in the diagnosis and management of patients with focal epilepsies. EEG may reveal different interictal epileptiform discharges (IEDs: abnormal spikes, sharp waves). The EEG visibility of a spike depends on the surface area of cortex involved (> 10 cm2) and the brain localization of cortical generators. Regions generating IEDs (defining the “irritative zone”) are not necessarily equivalent to the seizure onset zone. Focal seizures are dynamic processes originating from one or several brain regions (that generate fast oscillations and are called the epileptogenic zone) before spreading to other structures (that generate lower frequency oscillations and are called the propagation zone). Several factors limit the expression of seizures on scalp EEG, such as the area involved, degree of synchronization, and depth of the cortical generators. Different scalp EEG seizure onset patterns may be observed: fast discharge, background flattening, rhythmic spikes, sinusoidal discharge, or sharp activity. However, to a large extent EEG changes are linked to seizure propagation.
Finally, in the context of presurgical evaluation, the combination of interictal and ictal EEG features is crucial to provide an optimal hypothesis concerning the epileptogenic zone.
... It is well established that resection of the SOZ alone is not always sufficient to achieve seizure freedom and inclusion of the irritative zone, an area that generates interictal epileptiform discharges (IEDs), is necessary. The spatial distribution of the irritative zone is highly variable between patients: in some, it co-localizes with the SOZ (3,4), while in others, the irritative zone can be extensive, with IEDs distributed over multiple brain areas of one or both hemispheres (5,6). The resection of the entire irritative zone increases the probability of a favorable outcome after epilepsy surgery (7). ...
Between seizures, irritative network generates frequent brief synchronous activity, which manifests on the EEG as interictal epileptiform discharges (IEDs). Recent insights into the mechanism of IEDs at the microscopic level have demonstrated a high variance in the recruitment of neuronal populations generating IEDs and a high variability in the trajectories through which IEDs propagate across the brain. These phenomena represent one of the major constraints for precise characterization of network organization and for the utilization of IEDs during presurgical evaluations. We have developed a new approach to dissect human neocortical irritative networks and quantify their properties. We have demonstrated that irritative network has modular nature and it is composed of multiple independent sub-regions, each with specific IED propagation trajectories and differing in the extent of IED activity generated. The global activity of the irritative network is determined by long-term and circadian fluctuations in sub-region spatiotemporal properties. Also, the most active sub-region co-localizes with the seizure onset zone in 12/14 cases. This study demonstrates that principles of recruitment variability and propagation are conserved at the macroscopic level and that they determine irritative network properties in humans. Functional stratification of the irritative network increases the diagnostic yield of intracranial investigations with the potential to improve the outcomes of surgical treatment of neocortical epilepsy.
