Interictal scalp electroencephalography and intraoperative electrocorticography in magnetic resonance imaging-negative temporal lobe epilepsy surgery

Excitatory neurons and oligodendrocyte precursor cells are vulnerable to focal cortical dysplasia type IIIa as suggested by single-nucleus multiomics

BACKGROUND

Focal cortical dysplasia (FCD) is a heterogeneous group of cortical developmental malformations that constitute a common cause of medically intractable epilepsy. FCD type IIIa (FCD IIIa) refers to temporal neocortex alterations in architectural organisation or cytoarchitectural composition in the immediate vicinity of hippocampal sclerosis. Slight alterations in the temporal neocortex of FCD IIIa patients pose a challenge for the preoperative diagnosis and definition of the resection range.

METHODS

We have performed multimodal integration of single-nucleus RNA sequencing and single-nucleus assay for transposase-accessible chromatin sequencing in the epileptogenic cortex of four patients with FCD IIIa, and three relatively normal temporal neocortex were chosen as controls.

RESULTS

Our study revealed that the most significant dysregulation occurred in excitatory neurons (ENs) and oligodendrocyte precursor cells (OPCs) in the epileptogenic cortex of FCD IIIa patients. In ENs, we constructed a transcription factor (TF)-hub gene regulatory network and found DAB1high ENs subpopulation mediates neuronal immunity characteristically in FCD IIIa. Western blotting and immunofluorescence were used to validate the changes in protein expression levels caused by some of the key genes. The OPCs were activated and exhibited aberrant phenotypes in FCD IIIa, and TFs regulating reconstructed pseudotime trajectory were identified. Finally, our results revealed aberrant intercellular communication between ENs and OPCs in FCD IIIa patients.

CONCLUSIONS

Our study revealed significant and intricate alterations in the transcriptomes and epigenomes in ENs and OPCs of FCD IIIa patients, shedding light on their cell type-specific regulation and potential pathogenic involvement in this disorder. This work will help evaluate the pathogenesis of cortical dysplasia and epilepsy and explore potential therapeutic targets.

KEY POINTS

Paired snRNA-seq and snATAC-seq data were intergrated and analysed to identify crucial subpopulations of ENs and OPCs in the epileptogenic cortex of FCD IIIa patients and explore their possible pathogenic role in the disease. A TF-hub gene regulatory network was constructed in ENs, and the DAB1high Ex-1 mediated neuronal immunity was characterstically in FCD IIIa patients. The OPCs were activated and exhibited aberrant phenotypes in FCD IIIa patients, and TFs regulating reconstructed pseudotime traectory were identified. Aberrant intercelluar communications between ENs and OPCs in FCD IIIa patients were identified.

Multimodal non-invasive evaluation in MRI-negative epilepsy patients

Presurgical evaluation is still challenging for MRI-negative epilepsy patients. As non-invasive modalities are the easiest acceptable and economic methods in determining the epileptogenic zone, we analyzed the localization value of common non-invasive methods in MRI-negative epilepsy patients. In this study, we included epilepsy patients undergoing presurgical evaluation with presurgical negative MRI. MRI post-processing was performed using a Morphometric Analysis Program (MAP) on T1-weighted volumetric MRI. The relationship between MAP, magnetoencephalography (MEG), scalp electroencephalogram (EEG), and seizure outcomes was analyzed to figure out the localization value of different non-invasive methods. Eighty-six patients were included in this study. Complete resection of the MAP-positive regions or the MEG-positive regions was positively associated with seizure freedom (p = 0.028 and 0.007, respectively). When an area is co-localized by MAP and MEG, the resection of the area was significantly associated with seizure freedom (p = 0.006). However, neither the EEG lateralization nor the EEG localization showed statistical association with the surgical outcome (p = 0.683 and 0.505, respectively). In conclusion, scalp EEG had a limited role in presurgical localization and predicting seizure outcome, combining MAP and MEG results can significantly improve the localization of epileptogenic lesions and have a positive association with seizure-free outcome. PLAIN LANGUAGE SUMMARY: Due to the lack of obvious structure abnormalities on neuroimaging examinations, the identification of epilepsy lesions in MRI-negative epilepsy patients can be difficult. In this study, we intended to use non-invasive examinations to explore the potential epileptic lesions in MRI-negative epilepsy patients and to determine the results accuracy by comparing the neuroimaging results with the epilepsy surgery outcomes. A total of 86 epilepsy patients without obvious structure lesions on MRI were included, and we found that the combinations of different non-invasive examinations and neuroimaging post-processing methods are significantly associated with the seizure freedom results of epilepsy surgery.

Yield of non-invasive imaging in MRI-negative focal epilepsy

OBJECTIVE

The absence of MRI-lesion reduces considerably the probability of having an excellent outcome (International League Against Epilepsies [ILAE] class I-II) after epilepsy surgery. Surgical success in magnetic-resonance imaging (MRI)-negative cases relies therefore mainly on non-invasive techniques such as positron-emission tomography (PET), subtraction ictal/inter-ictal single-photon-emission-computed-tomography co-registered to MRI (SISCOM), electric source imaging (ESI) and morphometric MRI analysis (MAP). We were interested in identifying the optimal imaging technique or combination to achieve post-operative class I-II in patients with MRI-negative focal epilepsy.

METHODS

We identified 168 epileptic patients without MRI lesion. Thirty-three (19.6%) were diagnosed with unifocal epilepsy, underwent surgical resection and follow-up ⩾ 2 years. Sensitivity, specificity, predictive values, and diagnostic odds ratio (OR) were calculated for each technique individually and in combination (after co-registration).

RESULTS

23/33 (70%) were free of disabling seizures (75.0% with temporal and 61.5% extratemporal lobe epilepsy). None of the individual modalities presented an OR > 1.5, except ESI if only patients with interictal epileptiform discharges (IEDs) were considered (OR 3.2). On a dual combination, SISCOM with ESI presented the highest outcome (OR = 6). MAP contributed to detecting indistinguishable focal cortical dysplasia in particular in extratemporal epilepsies with a sensitivity of 75%. Concordance of PET, ESI on interictal epileptic discharges, and SISCOM was associated with the highest chance for post-operative seizure control (OR = 11).

CONCLUSION

If MRI is negative, the chances to benefit from epilepsy surgery are almost as high as in lesional epilepsy, provided that multiple established non-invasive imaging tools are rigorously applied and co-registered together.

[Analysis of Residual Post-Resection Electrocorticography Status and Related Risk Factors in Patients With Medically Intractable Epilepsytractable Epilepsy]

Objective

To analyze the residual post-resection electrocorticography (ECoG) status and the related risk factors in patients with medically intractable epilepsy (MIE).

Methods

A retrospective analysis was conducted to cover 146 MIE patients who underwent craniotomy for surgical resection in the department of Neurosurgery, Second Affiliated Hospital of Chengdu Medical College between January 2006 and January 2018. The patients were divided into a non-residual group ( n=54) and a residual group ( n=92) according to their ECoG results after the first resection surgery. Then, the 92 patients in the residual group underwent additional palliative surgery and they were further divided into an improvement subgroup ( n=50) and a non-improvement subgroup ( n=42), according to the reevaluation results of improvements in their postoperative ECoG. The differences in the mean annual seizure-free rate among the groups were compared. Univariate and multivariate logistic regression analysis was conducted to analyze the risk factors of residual post-resection ECoG.

Results

During the ten-year follow-up after the operation, the mean annual seizure-free rate was 86.7% in the non-residual group and 57.1% in the residual group, showing significant difference between the two groups ( P<0.001). In the subgroups, the mean annual seizure-free rate was 71% in the improvement subgroup and 46.5% in the non-improved subgroup, showing significant difference between the two subgroups ( P=0.003). Logistic regression showed that risk factors associated with residual post-resection ECoG included being female, patient age at the time of surgery being over 18, multi-lobe epilepsy, functional area involvement, and negative MRI findings ( P<0.05). Analysis of the subgroups showed that multi-lobe epilepsy and functional area involvement were risk factors related to not showing improvements in post-resection ECoG ( P<0.05).

Conclusions

Findings based on the status of residual post-resection ECoG have shown that patients without residual post-resection ECoG had the best treatment outcomes, and patients who had residual post-resection ECoG, but showed significant improvement after palliative surgery had the second best treatment outcomes. Patients who were female, who had their surgeries when they were older than 18, and who had multi-lobe epilepsy, functional area involvement, or negative MRI results were more likely to have residual post-resection ECoG. Among patients with residual post-resection ECoG, those with multi-lobe epilepsy and functional area involvement showed little improvement in residual post-resection ECoG even after undergoing additional palliative surgery.

Intraoperative electrocorticography during laser-interstitial thermal therapy predicts seizure outcome in mesial temporal lobe epilepsy

OBJECTIVE

Magnetic resonance-guided laser interstitial thermal therapy (MRLiTT) for treating temporal lobe epilepsy has recently gained popularity. We aimed to investigate the predictive value of pre-and post-MRLiTT epileptiform discharges (EDs) on intraoperative electrocorticography (iECoG) in seizure outcomes for patients with mesial temporal lobe epilepsy (mTLE).

METHODS

We conducted a pilot, prospective single-center cohort study on seven consecutive patients with mTLE that underwent MRLiTT. Pre- and post-MRLiTT iECoG was performed using a 1x8 contact depth electrode along the same trajectory used for the laser catheter.

RESULTS

The responders had a robust reduction in ED frequency compared to pre-MRLiTT iECoG (86% vs 13%, p < 0.01). Clinical characteristics, including risk factors for epilepsy, duration of epilepsy, presence of mesial temporal lobe sclerosis, prior intracranial monitoring, the absolute frequency of pre- or post-MRLiTT EDs, and ablation volume were not significantly associated with responder status.

CONCLUSIONS

This is the first demonstration that intraoperative reduction in EDs during mesial temporal lobe MRLiTT may potentially predict seizure outcomes and may serve as an intraoperative biomarker for satisfactory ablation. However, larger prospective studies are needed to confirm our findings and evaluate the utility of iECoG during MRLiTT.

SIGNIFICANCE

iECoG during mesial temporal lobe MRLiTT may help assess seizure outcomes.

'Hippocampal innate inflammatory gliosis only' in pharmacoresistant temporal lobe epilepsy

Drug-resistant mesial-temporal lobe epilepsy is a devastating disease with seizure onset in the hippocampal formation. A fraction of hippocampi samples from epilepsy-surgical procedures reveals a peculiar histological pattern referred to as 'gliosis only' with unresolved pathogenesis and enigmatic sequelae. Here, we hypothesize that 'gliosis only' represents a particular syndrome defined by distinct clinical and molecular characteristics. We curated an in-depth multiparameter integration of systematic clinical, neuropsychological as well as neuropathological analysis from a consecutive cohort of 627 patients, who underwent hippocampectomy for drug-resistant temporal lobe epilepsy. All patients underwent either classic anterior temporal lobectomy or selective amygdalohippocampectomy. On the basis of their neuropathological exam, patients with hippocampus sclerosis and 'gliosis only' were characterized and compared within the whole cohort and within a subset of matched pairs. Integrated transcriptional analysis was performed to address molecular differences between both groups. 'Gliosis only' revealed demographics, clinical and neuropsychological outcome fundamentally different from hippocampus sclerosis. 'Gliosis only' patients had a significantly later seizure onset (16.3 versus 12.2 years, P = 0.005) and worse neuropsychological outcome after surgery compared to patients with hippocampus sclerosis. Epilepsy was less amendable by surgery in 'gliosis only' patients, resulting in a significantly worse rate of seizure freedom after surgery in this subgroup (43% versus 68%, P = 0.0001, odds ratio = 2.8, confidence interval 1.7-4.7). This finding remained significant after multivariate and matched-pairs analysis. The 'gliosis only' group demonstrated pronounced astrogliosis and lack of significant neuronal degeneration in contrast to characteristic segmental neuron loss and fibrillary astrogliosis in hippocampus sclerosis. RNA-sequencing of gliosis only patients deciphered a distinct transcriptional programme that resembles an innate inflammatory response of reactive astrocytes. Our data indicate a new temporal lobe epilepsy syndrome for which we suggest the term 'Innate inflammatory gliosis only'. 'Innate inflammatory gliosis only' is characterized by a diffuse gliosis pattern lacking restricted hippocampal focality and is poorly controllable by surgery. Thus, 'innate inflammatory gliosis only' patients need to be clearly identified by presurgical examination paradigms of pharmacoresistant temporal lobe epilepsy patients; surgical treatment of this subgroup should be considered with great precaution. 'Innate inflammatory gliosis only' requires innovative pharmacotreatment strategies.

Can intraoperative electrocorticography be used to minimize the extent of resection in patients with temporal lobe epilepsy associated with hippocampal sclerosis?

OBJECTIVE

Tailored surgery to extensively resect epileptogenic lesions using intraoperative electrocorticography (ioECoG) may improve seizure outcomes. However, resection of large areas is associated with decreased memory function postoperatively. The authors assessed whether ioECoG could provide useful information on how to minimize the focus resection and obtain better seizure outcomes without memory deterioration. They examined the postoperative seizure-free period and memory alteration in a retrospective cohort of patients with mesial temporal lobe epilepsy (TLE) due to hippocampal sclerosis (HS) in whom the extent of removal was determined using ioECoG findings.

METHODS

The authors enrolled 82 patients with TLE associated with HS who were treated surgically. Transsylvian amygdalohippocampectomy was indicated as the first step. When visual inspection identified interictal epileptic discharges from the lateral temporal lobe on ioECoG, anterior temporal lobectomy (ATL) was eventually performed. The patients were divided into the selective amygdalohippocampectomy (SA, n = 40) and ATL (n = 42) groups. Postoperative seizure outcomes were assessed at 1, 2, 3, 5, and 7 years postoperatively using the International League Against Epilepsy classification. The Kaplan-Meier survival analysis was applied to evaluate the period of seizure recurrence between the SA and ATL groups. Factors attributed to seizure recurrence were analyzed using the Cox proportional hazards model, and they were as follows: epileptic focal laterality; age at seizure onset (< 10 or ≥ 10 years old); seizure frequency (more than weekly or less than weekly seizures); history of focal to bilateral tonic-clonic seizure; infectious etiology; and surgical procedure. The Wechsler Memory Scale-Revised was used to evaluate memory function pre- and postoperatively.

RESULTS

Seizure outcomes were significantly worse in the SA group than in the ATL group at 2 years postoperatively (p = 0.045). The International League Against Epilepsy class 1 outcomes at 7 years postoperatively in the SA and ATL groups were 63% and 81%, respectively. Kaplan-Meier analysis showed that seizure recurred significantly earlier in the SA group than in the ATL group (p = 0.031). The 2-way ANOVA analysis was used to compare the SA and ATL groups in each memory category, and revealed that there was no significant difference regardless of the side of surgery.

CONCLUSIONS

Visual assessment of ioECoG cannot be used as an indicator to minimize epileptic focus resection in patients with TLE associated with HS. ATL is more effective in obtaining seizure-free outcomes; however, both ATL and SA can preserve memory function.

Postsurgical seizure outcome in temporal lobe epilepsy patients with normal or subtle, nonspecific MRI findings

OBJECTIVE

The authors' objective was to report postsurgical seizure outcome of temporal lobe epilepsy (TLE) patients with normal or subtle, nonspecific MRI findings and to identify prognostic factors related to seizure control after surgery.

METHODS

This was a retrospective study of patients who underwent surgery from 1999 to 2014 at two comprehensive epilepsy centers. Patients with a clear MRI lesion according to team discussion and consensus were excluded. Presurgical information, surgery details, pathological data, and postsurgical outcomes were retrospectively collected from medical charts. Multiple logistic regression analysis was used to assess the effect of clinical, surgical, and neuroimaging factors on the probability of Engel class I (favorable) versus class II-IV (unfavorable) outcome at last follow-up.

RESULTS

The authors included 73 patients (59% were female; median age at surgery 35.9 years) who underwent operations after a median duration of epilepsy of 13 years. The median follow-up after surgery was 30.6 months. At latest follow-up, 44% of patients had Engel class I outcome. Favorable prognostic factors were focal nonmotor aware seizures and unilateral or no spikes on interictal scalp EEG.

CONCLUSIONS

Favorable outcome can be achieved in a good proportion of TLE patients with normal or subtle, nonspecific MRI findings, particularly when presurgical investigation suggests a rather circumscribed generator. Presurgical factors such as the presence of focal nonmotor aware seizures and unilateral or no spikes on interictal EEG may indicate a higher probability of seizure freedom.

Quantitative Analysis of Visually Reviewed Normal Scalp EEG Predicts Seizure Freedom Following Anterior Temporal Lobectomy

Objective

Anterior temporal lobectomy (ATL) is a widely performed and successful intervention for drug‐resistant temporal lobe epilepsy (TLE). However, up to one third of patients experience seizure recurrence within 1 year after ATL. Despite the extensive literature on presurgical electroencephalography (EEG) and magnetic resonance imaging (MRI) abnormalities to prognosticate seizure freedom following ATL, the value of quantitative analysis of visually reviewed normal interictal EEG in such prognostication remains unclear. In this retrospective multicenter study, we investigate whether machine learning analysis of normal interictal scalp EEG studies can inform the prediction of postoperative seizure freedom outcomes in patients who have undergone ATL.

Methods

We analyzed normal presurgical scalp EEG recordings from 41 Mayo Clinic (MC) and 23 Cleveland Clinic (CC) patients. We used an unbiased automated algorithm to extract eyes closed awake epochs from scalp EEG studies that were free of any epileptiform activity and then extracted spectral EEG features representing (a) spectral power and (b) interhemispheric spectral coherence in frequencies between 1 and 25 Hz across several brain regions. We analyzed the differences between the seizure‐free and non–seizure‐free patients and employed a Naïve Bayes classifier using multiple spectral features to predict surgery outcomes. We trained the classifier using a leave‐one‐patient‐out cross‐validation scheme within the MC data set and then tested using the out‐of‐sample CC data set. Finally, we compared the predictive performance of normal scalp EEG‐derived features against MRI abnormalities.

Results

We found that several spectral power and coherence features showed significant differences correlated with surgical outcomes and that they were most pronounced in the 10–25 Hz range. The Naïve Bayes classification based on those features predicted 1‐year seizure freedom following ATL with area under the curve (AUC) values of 0.78 and 0.76 for the MC and CC data sets, respectively. Subsequent analyses revealed that (a) interhemispheric spectral coherence features in the 10–25 Hz range provided better predictability than other combinations and (b) normal scalp EEG‐derived features provided superior and potentially distinct predictive value when compared with MRI abnormalities (>10% higher F1 score).

Significance

These results support that quantitative analysis of even a normal presurgical scalp EEG may help prognosticate seizure freedom following ATL in patients with drug‐resistant TLE. Although the mechanism for this result is not known, the scalp EEG spectral and coherence properties predicting seizure freedom may represent activity arising from the neocortex or the networks responsible for temporal lobe seizure generation within vs outside the margins of an ATL.

Surgical Outcomes and EEG Prognostic Factors After Stereotactic Laser Amygdalohippocampectomy for Mesial Temporal Lobe Epilepsy

Objective: To assess the seizure outcomes of stereotactic laser amygdalohippocampectomy (SLAH) in consecutive patients with mesial temporal lobe epilepsy (mTLE) in a single center and identify scalp EEG and imaging factors in the presurgical evaluation that correlate with post-surgical seizure recurrence.

Methods: We retrospectively reviewed the medical and EEG records of 30 patients with drug-resistant mTLE who underwent SLAH and had at least 1 year of follow-up. Surgical outcomes were classified using the Engel scale. Univariate hazard ratios were used to evaluate the risk factors associated with seizure recurrence after SLAH.

Results: The overall Engel class I outcome after SLAH was 13/30 (43%), with a mean postoperative follow-up of 48.9 ± 17.6 months. Scalp EEG findings of interictal regional slow activity (IRSA) on the side of surgery (HR = 4.05, p = 0.005) and non-lateralizing or contra-lateralizing seizure onset (HR = 4.31, p = 0.006) were negatively correlated with postsurgical seizure freedom. Scalp EEG with either one of the above features strongly predicted seizure recurrence after surgery (HR = 7.13, p < 0.001) with 100% sensitivity and 71% specificity.

Significance: Understanding the factors associated with good or poor surgical outcomes can help choose the best candidates for SLAH. Of the variables assessed, scalp EEG findings were the most clearly associated with seizure outcomes after SLAH.

Advances in the Surgical Management of Epilepsy: Drug-Resistant Focal Epilepsy in the Adult Patient

Pharmacoresistant seizures occur in nearly one-third of people with epilepsy. Medial temporal lobe and lesional epilepsy are the most favorable surgically remediable epileptic syndromes. Successful surgery may render the patient seizure-free, reduce antiseizure drug(s) adverse effects, improve quality of life, and decrease mortality. Surgical management should not be considered a procedure of "last resort." Despite the results of randomized controlled trials, surgery remains an underutilized treatment modality for patients with drug-resistant epilepsy (DRE). Important disparities affect patient referral and selection for surgical treatment. This article discusses the advances in surgical treatment of DRE in adults with focal seizures.

The clinical utility of intraoperative electrocorticography in pediatric epilepsy surgical strategy and planning

OBJECTIVE

In this study, the authors aimed to determine 1) whether the use of intraoperative electrocorticography (ECoG) affects outcomes and complication rates of children undergoing resective epilepsy surgery; 2) which patient- and epilepsy-related variables might influence ECoG-based surgical strategy; and 3) what the predictors of epilepsy surgery outcomes are.

METHODS

Over a period of 12 years, data were collected on pediatric patients who underwent tailored brain resections in the Motol Epilepsy Center. In patients in whom an abnormal ECoG pattern (e.g., spiking, suppression burst, or recruiting rhythm) was not observed beyond presurgically planned resection margins, the authors did not modify the surgical plan (group A). In those with significant abnormal ECoG findings beyond resection margins, the authors either did (group B) or did not (group C) modify the surgical plan, depending on the proximity of the eloquent cortex or potential extent of resection. Using Fisher's exact test and the chi-square test, the 3 groups were compared in relation to epilepsy surgery outcomes and complication rate. Next, multivariate models were constructed to identify variables associated with each of the groups and with epilepsy surgery outcomes.

RESULTS

Patients in group C achieved significantly lower rates of seizure freedom compared to groups A (OR 30.3, p < 0.001) and B (OR 35.2, p < 0.001); groups A and B did not significantly differ (p = 0.78). Patients in whom the surgical plan was modified suffered from more frequent complications (B vs A+C, OR 3.8, p = 0.01), but these were mostly minor (duration < 3 months; B vs A+C, p = 0.008). In all cases, tissue samples from extended resections were positive for the presence of the original pathology. Patients with intended modification of the surgical plan (groups B+C) suffered more often from daily seizures, had a higher age at first seizure, had intellectual disability, and were regarded as MR-negative (p < 0.001). Unfavorable surgical outcome (Engel class II-IV) was associated with focal cortical dysplasia, incomplete resection based on MRI and/or ECoG findings, negative MRI finding, and inability to modify the surgical plan when indicated.

CONCLUSIONS

Intraoperative ECoG serves as a reliable tool to guide resection and may inform the prognosis for seizure freedom in pediatric patients undergoing epilepsy surgery. ECoG-based modification of the surgical plan is associated with a higher rate of minor complications. Children in whom ECoG-based modification of the surgical plan is indicated but not feasible achieve significantly worse surgical outcomes.

Reassessing the impact of intraoperative electrocorticography on postoperative outcome of patients undergoing standard temporal lobectomy for MRI-negative temporal lobe epilepsy

OBJECTIVE

Almost 30% of the patients with suspected temporal lobe epilepsy (TLE) have normal results on MRI. Success rates for resection of MRI-negative TLE are less favorable, ranging from 36% to 76%. Herein the authors describe the impact of intraoperative electrocorticography (ECoG) augmented by opioid activation and its effect on postoperative seizure outcome.

METHODS

Adult and pediatric patients with medically resistant MRI-negative TLE who underwent standardized ECoG at the time of their elective anterior temporal lobectomy (ATL) with amygdalohippocampectomy between 1990 and 2016 were included in this study. Seizure recurrence comprised the primary outcome of interest and was assessed using Kaplan-Meier and multivariable Cox regression analysis plots based on distribution of interictal epileptiform discharges (IEDs) recorded on scalp electroencephalography, baseline and opioid-induced IEDs on ECoG, and extent of resection.

RESULTS

Of the 1144 ATLs performed at the authors' institution between 1990 and 2016, 127 (11.1%) patients (81 females) with MRI-negative TLE were eligible for this study. Patients with complete resection of tissue generating IED recorded on intraoperative ECoG were less likely to have seizure recurrence compared to those with incomplete resection on univariate analysis (p < 0.05). No difference was found in seizure recurrence between patients with bilateral independent IEDs and unilateral IEDs (p = 0.15), presence or absence of opioid-induced epileptiform activation (p = 0.61), or completeness of resection of tissue with opioid-induced IEDs on intraoperative ECoG (p = 0.41).

CONCLUSIONS

The authors found that incomplete resection of IED-generating tissue on intraoperative ECoG was associated with an increased chance of seizure recurrence. However, they found that induction of epileptiform activity with intraoperative opioid activation did not provide useful intraoperative data predictive of improving operative results for temporal lobectomy in MRI-negative epilepsy.

Prognostic factors of postoperative seizure outcome in patients with temporal lobe epilepsy and normal magnetic resonance imaging

PURPOSE

To retrospectively analyse a single-centre consecutive surgical series of patients with temporal lobe epilepsy (TLE) and negative MRI. To identify factors associated with postoperative seizure outcome among several presurgical, surgical and postsurgical variables.

METHODS

Clinical records of 866 patients who received temporal lobe resections and with a minimum follow-up of 12 months were retrospectively searched for MRI-negative cases. Anamnestic, clinical, neurophysiological, surgical, histopathological and postsurgical data were collected. Seizure outcome was categorised as favourable (Engel's class I) and unfavourable (Engel's classes II-IV). Uni- and multivariate statistical analysis was performed to identify variables having a significant association with seizure outcome.

RESULTS

Forty-eight patients matched the inclusion criteria. 26 (54.1%) patients required invasive EEG evaluation with Stereo-electro-encephalography (SEEG) before surgery. Histological evaluation was unremarkable in 34 cases (70.8%), revealed focal cortical dysplasias in 13 cases and hippocampal sclerosis in 2. 28 (58.3%) patients were in Engel's class I after a mean follow-up of 82 months (SD ± 74; range 12-252). Multivariate analysis indicated auditory aura, contralateral diffusion of the discharge at Video-EEG monitoring and use of ¹⁸F-FDG PET as variables independently associated with seizure outcome.

CONCLUSION

Carefully selected patients with MRI-negative TLE can be good candidates for surgery. Surgery should be considered with caution in patients with clinical features of neocortical seizure onset and contralateral propagation of the discharge. Use of ¹⁸F-FDG PET may be helpful to improve SEEG and surgical strategies. The presented data help in optimising the selection of patients with MRI-negative TLE with good chances to benefit from surgery.

Current value of intraoperative electrocorticography (iopECoG)

OBJECTIVE

Intraoperative electrocorticography (iopECoG) can contribute to delineate the resection borders of the anticipated epileptogenic zone in epilepsy surgery. However, it has several caveats that should be considered to avoid incorrect interpretation during intraoperative monitoring.

METHODS

The literature on iopECoG application was reviewed, and pros and cons as well as obstacles to this technique were analyzed.

RESULTS

The literature of the first half of the nineties was very enthusiastic in using iopECoG for tailoring the resection in temporal as well as extratemporal epilepsy surgery. Mostly, this resulted in a good correlation of postresection ECoG and excellent seizure outcome. In the second half of the nineties, many authors demonstrated lack of correlation between iopECoG and postoperative seizure outcome, especially in surgery for temporal lobe epilepsy with hippocampal sclerosis. In the noughties, investigators found that ECoG was significantly useful in neocortical lesional temporal lobe epilepsy as well as in extratemporal lesional epilepsies. Extratemporal epilepsy without lesions proved to be more a domain of chronic extraoperative ECoG, especially using depth electrode recordings. In recent years, iopECoG detecting high-frequency oscillations (ripples, 80-250 Hz, fast ripples, 250-500 Hz) for tailored resection was found to allow intraoperative prediction of postoperative seizure outcome.

CONCLUSION

After a period of scepticism, iopECoG seems back in the focus of interest for intraoperative guidance of resecting epileptogenic tissue to raise postoperative favorable seizure outcome. In temporal and extratemporal lesional epilepsies, especially in cases of focal cortical dysplasia, tuberous sclerosis, or cavernous malformations, an excellent correlation between iopECoG-guided resection and postoperative seizure relief was found.

Integrating artificial intelligence with real-time intracranial EEG monitoring to automate interictal identification of seizure onset zones in focal epilepsy

OBJECTIVE

An ability to map seizure-generating brain tissue, i.e. the seizure onset zone (SOZ), without recording actual seizures could reduce the duration of invasive EEG monitoring for patients with drug-resistant epilepsy. A widely-adopted practice in the literature is to compare the incidence (events/time) of putative pathological electrophysiological biomarkers associated with epileptic brain tissue with the SOZ determined from spontaneous seizures recorded with intracranial EEG, primarily using a single biomarker. Clinical translation of the previous efforts suffers from their inability to generalize across multiple patients because of (a) the inter-patient variability and (b) the temporal variability in the epileptogenic activity.

APPROACH

Here, we report an artificial intelligence-based approach for combining multiple interictal electrophysiological biomarkers and their temporal characteristics as a way of accounting for the above barriers and show that it can reliably identify seizure onset zones in a study cohort of 82 patients who underwent evaluation for drug-resistant epilepsy.

MAIN RESULTS

Our investigation provides evidence that utilizing the complementary information provided by multiple electrophysiological biomarkers and their temporal characteristics can significantly improve the localization potential compared to previously published single-biomarker incidence-based approaches, resulting in an average area under ROC curve (AUC) value of 0.73 in a cohort of 82 patients. Our results also suggest that recording durations between 90 min and 2 h are sufficient to localize SOZs with accuracies that may prove clinically relevant.

SIGNIFICANCE

The successful validation of our approach on a large cohort of 82 patients warrants future investigation on the feasibility of utilizing intra-operative EEG monitoring and artificial intelligence to localize epileptogenic brain tissue. Broadly, our study demonstrates the use of artificial intelligence coupled with careful feature engineering in augmenting clinical decision making.

Visually validated semi-automatic high-frequency oscillation detection aides the delineation of epileptogenic regions during intra-operative electrocorticography

OBJECTIVE

To test the utility of a novel semi-automated method for detecting, validating, and quantifying high-frequency oscillations (HFOs): ripples (80-200 Hz) and fast ripples (200-600 Hz) in intra-operative electrocorticography (ECoG) recordings.

METHODS

Sixteen adult patients with temporal lobe epilepsy (TLE) had intra-operative ECoG recordings at the time of resection. The computer-annotated ECoG recordings were visually inspected and false positive detections were removed. We retrospectively determined the sensitivity, specificity, positive and negative predictive value (PPV/NPV) of HFO detections in unresected regions for determining post-operative seizure outcome.

RESULTS

Visual validation revealed that 2.81% of ripple and 43.68% of fast ripple detections were false positive. Inter-reader agreement for false positive fast ripple on spike classification was good (ICC = 0.713, 95% CI: 0.632-0.779). After removing false positive detections, the PPV of a single fast ripple on spike in an unresected electrode site for post-operative non-seizure free outcome was 85.7 [50-100%]. Including false positive detections reduced the PPV to 64.2 [57.8-69.83%].

CONCLUSIONS

Applying automated HFO methods to intraoperative electrocorticography recordings results in false positive fast ripple detections. True fast ripples on spikes are rare, but predict non-seizure free post-operative outcome if found in an unresected site.

SIGNIFICANCE

Semi-automated HFO detection methods are required to accurately identify fast ripple events in intra-operative ECoG recordings.

Intraoperative hippocampal electrocorticography frequently captures electrographic seizures and correlates with hippocampal pathology

OBJECTIVE

Relationship between electrographic seizures on hippocampal electrocorticography (IH-ECoG) and presence/type of hippocampal pathology remains unclear.

METHODS

IH-ECoG was recorded for 10-20 min from the ventricular surface of the hippocampus following removal of the temporal neocortex in 40 consecutive patients. Correlation between intraoperative hippocampal seizures and preoperative MRI, hippocampal histopathology, and EEG from invasive monitoring was determined.

RESULTS

IH-ECoG captured electrographic seizures in 15/40 patients (in 8/23 with abnormal hippocampal signal on MRI and 7/17 patients without MRI abnormality). Hippocampal neuronal loss was observed in 22/40 (Group 1), while 18/40 had no significant neuronal loss (Group 2). In Group 1, 4/22 had seizures on IH-ECoG, while 11/18 had electrographic seizures in Group 2. In 24/40 patients who underwent prolonged extraoperative intracranial EEG (IC-EEG) recording, hippocampal seizures were captured in 14. Of these, 7 also had seizures during IH-ECoG. In 10/24 IC-EEG patients without seizures, 3 had seizures on IH-ECoG.

CONCLUSIONS

IH-ECoG frequently captures spontaneous electrographic seizures. These are more likely to occur in patients with pathologic processes that do not disrupt/infiltrate hippocampus compared to patients with intractable epilepsy associated with disrupted hippocampal architecture.

SIGNIFICANCE

Intraoperative hippocampal seizures may result from deafferentation from the temporal neocortex and disinhibition of the perforant pathway.

Histopathology of 3 Tesla MRI-negative temporal lobe epilepsies

INTRODUCTION

Histopathology of MRI-negative temporal lobe epilepsies (TLE) shows heterogeneous findings. The use of either 1.5 or 3 Tesla MRI for the selection of MRI-negative cases and use of older classification systems instead of the current ILAE classification system may account for this heterogeneity. We focus on histopathology of 3 Tesla MRI-negative TLE according to ILAE criteria and investigate potential correlation to seizure outcome 1 year postoperatively.

MATERIALS AND METHODS

Twenty specimens (9 neocortical, 11 hippocampal) from eleven 3 Tesla MRI-negative patients with TLE were examined in two steps. Standard stains and immunohistochemical reactions as well as Palmini and Wyler criteria were used prospectively during the initial examination. Retrospectively, all specimens were re-examined and re-evaluated. Phospho-6 and calretinin stains and the ILAE criteria were used during the review examination.

RESULTS

Initial examination revealed 7 focal cortical dysplasias (FCDs) Palmini type 1, two cases of cortical gliosis, 4 cases of hippocampal sclerosis (HS) Wyler grade 1 and seven cases of hippocampal gliosis. The review examination according to ILAE criteria revealed 4 FCDs type I and 5 mild malformations of cortical development. All hippocampal specimens showed "no HS/gliosis only" after the review examination. Histopathology showed no correlation to seizure outcome.

DISCUSSION

This is the first histopathological study to include only 3 Tesla MRI-negative cases. The use of ILAE criteria lead to the diagnosis of "no HS/gliosis only" of all hippocampal specimens, a finding not in line with previously reported series. The spectrum of diagnoses within neocortical specimens showed accordingly more mild findings.

Interictal high-frequency oscillations in focal human epilepsy

PURPOSE OF REVIEW

Localization of focal epileptic brain is critical for successful epilepsy surgery and focal brain stimulation. Despite significant progress, roughly half of all patients undergoing focal surgical resection, and most patients receiving focal electrical stimulation, are not seizure free. There is intense interest in high-frequency oscillations (HFOs) recorded with intracranial electroencephalography as potential biomarkers to improve epileptogenic brain localization, resective surgery, and focal electrical stimulation. The present review examines the evidence that HFOs are clinically useful biomarkers.

RECENT FINDINGS

Performing the PubMed search 'High-Frequency Oscillations and Epilepsy' for 2013-2015 identifies 308 articles exploring HFO characteristics, physiological significance, and potential clinical applications.

SUMMARY

There is strong evidence that HFOs are spatially associated with epileptic brain. There remain, however, significant challenges for clinical translation of HFOs as epileptogenic brain biomarkers: Differentiating true HFO from the high-frequency power changes associated with increased neuronal firing and bandpass filtering sharp transients. Distinguishing pathological HFO from normal physiological HFO. Classifying tissue under individual electrodes as normal or pathological. Sharing data and algorithms so research results can be reproduced across laboratories. Multicenter prospective trials to provide definitive evidence of clinical utility.

Preoperative prediction of temporal lobe epilepsy surgery outcome

PURPOSE

There is controversy about relative contributions of ictal scalp video EEG recording (vEEG), routine scalp outpatient interictal EEG (rEEG), intracranial EEG (iEEG) and MRI for predicting seizure-free outcomes after temporal lobectomy. We reviewed NIH experience to determine contributions at specific time points as well as long-term predictive value of standard pre-surgical investigations.

METHODS

Raw data was obtained via retrospective chart review of 151 patients. After exclusions, 118 remained (median 5 years follow-up). MRI-proven mesial temporal sclerosis (MTSr) was considered a separate category for analysis. Logistic regression estimated odds ratios at 6-months, 1-year, and 2 years; proportional hazard models estimated long-term comparisons. Subset analysis of the proportional hazard model was performed including only patients with commonly encountered situations in each of the modalities, to maximize statistical inference.

RESULTS

Any MRI finding, MRI proven MTS, rEEG, vEEG and iEEG did not predict two-year seizure-free outcome. MTSr was predictive at six months (OR=2.894, p=0. 0466), as were MRI and MTSr at one year (OR=10.4231, p=0. 0144 and OR=3.576, p=0. 0091). Correcting for rEEG and MRI, vEEG failed to predict outcome at 6 months, 1year and 2 years. Proportional hazard analysis including all available follow-up failed to achieve significance for any modality. In the subset analysis of 83 patients with commonly encountered results, vEEG modestly predicted long-term seizure-free outcomes with a proportional hazard ratio of 1.936 (p=0.0304).

CONCLUSIONS

In this study, presurgical tools did not provide unambiguous long-term outcome predictions. Multicenter prospective studies are needed to determine optimal presurgical epilepsy evaluation.

Post-resection electrocorticography has no added value in epilepsy surgery

Intra-operative electrocorticography (ECoG) has been traditionally used in the surgical management of medically refractory partial epilepsies to identify the limits of the epileptogenic zone. This retrospective study had as goal to evaluate whether tailored surgery based on the presurgical evaluation completed by intra-operative post-resection ECoG improves outcome. We reviewed 94 cases of epilepsy surgery with intra-operative ECoG and determined how many had an ECoG-guided surgical procedure in addition to the initial planned surgery. We also reviewed the presence of specific recurrent ECoG patterns of interictal epileptiform discharges (IED) in the exposed cortical surface, such as: electrographic seizures, bursts, intermittent spike waves, polyspikes or fast rhythms and continuous or quasi-continuous spiking. When performing a post-resection ECoG-tailored surgery, outcome did not improve in lesional or non-lesional epilepsy. Postoperative residual IED did not correlate with a poorer outcome. In our study, the persistence of post-resection IED on ECoG is not correlated with outcome in patients with lesional or non-lesional epilepsy.

Surgical Resection for Epilepsy Following Cerebral Gunshot Wounds

OBJECTIVE

The surgical management of epilepsy after penetrating gunshot wounds (GSWs) to the head has not been described in the modern era. Given the extensive damage to the cranium and cortex from such injuries, the safety and efficacy of surgical intervention are unclear. We report surgical strategy and outcomes after resection for medically refractory epilepsy following GSWs in 4 patients.

METHODS

A prospectively compiled database of 325 patients with epilepsy was used to identify patients undergoing surgery for medically refractory epilepsy after a GSW to the brain. Seizure frequency, scalp and intracranial electroencephalography evaluation, type of resection, and seizure outcomes were compiled.

RESULTS

All 4 patients underwent direct electrocorticography recordings either with implanted electrodes or intraoperatively that were used to drive surgical decision making. All patients had intracranial shrapnel fragments and large areas of encephalomalacia on imaging. Intracranial electrodes were placed in 2 patients to localize seizure onsets. Two patients underwent frontal lobe resections, and the other 2 patients underwent multilobar resections. Latency between injury and epilepsy surgery was 12 years, and mean age at surgery was 28 years. In all cases, epilepsy surgery led to a significant improvement in seizure control (Engel class I, 2 patients; II, 1 patient; and III, 1 patient).

CONCLUSIONS

Epilepsy is common after penetrating head injury, and the incidence is likely to increase given the growing numbers of armed conflicts in urban centers worldwide. In selected cases, intracranial monitoring and surgical resections may be safely performed and can lead to favorable seizure outcomes.

Differences between mesial and neocortical magnetic-resonance-imaging-negative temporal lobe epilepsy

OBJECTIVE

The aim of this study was to assess clinical and electrophysiological differences within a group of patients with magnetic-resonance-imaging-negative temporal lobe epilepsy (MRI-negative TLE) according to seizure onset zone (SOZ) localization in invasive EEG (IEEG).

METHODS

According to SOZ localization in IEEG, 20 patients with MRI-negative TLE were divided into either having mesial SOZ-mesial MRI-negative TLE or neocortical SOZ-neocortical MRI-negative TLE. We evaluated for differences between these groups in demographic data, localization of interictal epileptiform discharges (IEDs), and the ictal onset pattern in semiinvasive EEG and in ictal semiology.

RESULTS

Thirteen of the 20 patients (65%) had mesial MRI-negative TLE and 7 of the 20 patients (35%) had neocortical MRI-negative TLE. The differences between mesial MRI-negative TLE and neocortical MRI-negative TLE were identified in the distribution of IEDs and in the ictal onset pattern in semiinvasive EEG. The patients with neocortical MRI-negative TLE tended to have more IEDs localized outside the anterotemporal region (p=0.031) and more seizures without clear lateralization of ictal activity (p=0.044). No other differences regarding demographic data, seizure semiology, surgical outcome, or histopathological findings were found.

CONCLUSIONS

According to the localization of the SOZ, MRI-negative TLE had two subgroups: mesial MRI-negative TLE and neocortical MRI-negative TLE. The groups could be partially distinguished by an analysis of their noninvasive data (distribution of IEDs and lateralization of ictal activity). This differentiation might have an impact on the surgical approach.

Detection of Epileptic Seizures Using Phase-Amplitude Coupling in Intracranial Electroencephalography

Seizure detection using intracranial electroencephalography (iEEG) contributes to improved treatment of patients with refractory epilepsy. For that purpose, a feature of iEEG to characterize the ictal state with high specificity and sensitivity is necessary. We evaluated the use of phase–amplitude coupling (PAC) of iEEG signals over a period of 24 h to detect the ictal and interictal states. PAC was estimated by using a synchronisation index (SI) for iEEG signals from seven patients with refractory temporal lobe epilepsy. iEEG signals of the ictal state was characterised by a strong PAC between the phase of β and the amplitude of high γ. Furthermore, using SI values, the ictal state was successfully detected with significantly higher accuracy than by using the amplitude of high γ alone. In conclusion, PAC accurately distinguished the ictal state from the interictal state.

Surgical strategies for pediatric epilepsy

Pediatric epilepsy is a debilitating condition that impacts millions of patients throughout the world. Approximately 20-30% of children with recurrent seizures have drug-resistant epilepsy (DRE). For these patients, surgery offers the possibility of not just seizure freedom but significantly improved neurocognitive and behavioral outcomes. The spectrum of surgical options is vast, ranging from outpatient procedures such as vagus nerve stimulation to radical interventions including hemispherectomy. The thread connecting all of these interventions is a common goal-seizure freedom, an outcome that can be achieved safely and durably in a large proportion of patients. In this review, we discuss many of the most commonly performed surgical interventions and describe the indications, complications, and outcomes specific to each.

Surgical outcomes in patients with intraoperative Electrocorticography (EcoG) guided epilepsy surgery-experiences of a tertiary care centre in India

INTRODUCTION

The Comprehensive Epilepsy Surgery Program was started in 2001 at K.E.M. Hospital, Mumbai with the aim of performing epilepsy surgeries at highly concessional rates. We have started using intraoperative Electrocorticography (EcoG) since 2009 in patients with tumors, Mesial Temporal Sclerosis (MTS) plus and focal cortical dysplasia (FCD). This study highlights our experience with EcoG and it's utility in epilepsy surgery.introduction METHODS: 51 patients with drug resistant epilepsy due to temporal and extra-temporal tumors, MTS plus and FCD underwent pre-surgical evaluation and ECoG guided epilepsy surgery through our program. The surgical procedures employed included intraoperative EcoG guided lesionectomy or a lesionectomy with Anterior Temporal Lobectomy (ATL). Postoperative MRI and EEG were done. Seizure freedom was categorized as per Engel's classification.

RESULTS

At a mean follow up of 33 months (range: 14-69 months), 43 out of 51(84.31%) patients were completely seizure free post-surgery (Engel's Class I). Among the patients who were not seizure free, 3 patients were in Engel's Class II and 5 patients were in Engel's Class III. Presence of a residual lesion on postoperative MRI (p < 0.001), abnormal postoperative EEG (p < 0.001) and persistent spikes on post-resection EcoG (p < 0.05) had a significant statistical association with poor seizure freedom post-surgery.

CONCLUSION

The success of epilepsy surgery depends upon accurate localization and complete resection of the epileptogenic tissue, both of which are aided by intraoperative EcoG.Thus, intraoperative EcoG is a useful adjunct in epilepsy surgery to achieve optimal seizure freedom in cases of MTS plus, focal cortical dysplasia and tumors. Even the patients who are not seizure free can achieve worthwhile improvement post surgery.

Perspectives of epilepsy surgery in resource-poor countries: a study in Georgia

BACKGROUND

To identify patients with concordant seizure semiology, interictal epileptiform discharges on standard EEG and brain MRI changes to define the patients with pharmacoresistant epilepsy (PRE) who would be suitable for epilepsy surgery according to non-invasive protocol.

METHODS

The medical records of the patients with epilepsy seen in Epilepsy Center of Institute of Neurology and Neuropsychology (ECINN) (Tbilisi, Georgia) were reviewed retrospectively. The diagnostic work-up included neurological examination, standard EEG, and MRI. The degree of concordance of the seizure semiology, EEG, and neuroimaging was used to determine the potential candidates for surgery. The probability of seizure freedom rate was estimated based on known predictive values of anatomical, electrophysiological, and semiological characteristics.

RESULTS

A total of 83 (25 %) patients met the criteria of PRE. Fourteen (17 %) patients had complete concordance of seizure semiology, MRI, and EEG. Out of these patients, 11 had mesial temporal sclerosis on MRI and three had focal cortical dysplasia (FCD). Estimated seizure-free surgical success rate in this group was 75-95 % without the need for further investigations. Out of 25 (30 %) non-lesional MRI cases, the concordance of seizure semiology and EEG was in nine patients with probable success rate up to 60 %. Thirteen patients (16 %) had discordant EEG and MRI data and were not suitable for surgery without further testing.

CONCLUSIONS

A significant portion of PRE patients with concordant anatomical, electrophysiological, and semiological characteristics can be treated surgically in resource-limited countries. Nevertheless, most patients will still require further investigation for proper localization of epileptogenic focus.