Is it worth pursuing surgery for epilepsy in patients with normal neuroimaging?

Non-lesional epilepsy does not necessarily convey poor outcomes after invasive monitoring followed by resection or thermal ablation

OBJECTIVE

We aimed to compare outcomes including seizure-free status at the last follow-up in adult patients with medically refractory focal epilepsy identified as lesional vs. non-lesional based on their magnetic resonance imaging (MRI) findings who underwent invasive evaluation followed by subsequent resection or thermal ablation (LiTT).

METHODS

We identified 88 adult patients who underwent intracranial monitoring between 2014 and 2021. Of those, 40 received resection or LiTT, and they were dichotomized based on MRI findings, as lesional (N = 28) and non-lesional (N = 12). Patient demographics, seizure characteristics, non-invasive interventions, intracranial monitoring, and surgical variables were compared between the groups. Postsurgical seizure outcome at the last follow-up was rated according to the Engel classification, and postoperative seizure freedom was determined by Kaplan-Meyer survival analysis. Statistical analyses employed Fisher's exact test to compare categorical variables, while a t-test was used for continuous variables.

RESULTS

There were no differences in baseline characteristics between groups except for more often noted PET abnormality in the lesional group (p = 0.0003). 64% of the lesional group and 57% of the non-lesional group received surgical resection or LiTT (p = 0.78). At the last follow-up, 78.5% of the patients with lesional MRI findings achieved Engel I outcomes compared to 66.7% of non-lesional patients (p = 0.45). Kaplan-Meier curves did not show a significant difference in seizure-free duration between both groups after surgical intervention (p = 0.49).

SIGNIFICANCE

In our sample, the absence of lesion on brain MRI was not associated with worse seizure outcomes in adult patients who underwent invasive intracranial monitoring followed by resection or thermal ablation.

Who are the Better Candidates for Epilepsy Surgery?

The resective epilepsy surgery can be the effective procedure to get seizure-free outcome in these drug resistant epilepsy (DRE) patients. Class I evidence firmly establishes the superiority of epilepsy surgery over medical treatments in both seizure control and quality of life for DRE patients. For the effective identification of optimal surgical candidates, it's essential to understand the prognostic factors of epilepsy surgery based on the surgical methods employed. Established positive prognostic indicators for temporal resection include the presence of hippocampal sclerosis on magnetic resonance imaging (MRI), focal lesions on MRI, unilateral temporal spikes, concordant ictal electroencephalography (EEG), and a history of prolonged febrile convulsion. Potential negative predictors encompass preoperative secondary generalized tonic-clonic seizures, a normal MRI, postoperative EEG spikes, and age at the time of surgery. For neocortical epilepsy, the prognostic factors identified through multivariate analysis were the presence of a discrete lesion, localized hypometabolism on Fluorodeoxyglucose positron emission tomography (FDG-PET), and localized ictal EEG. A significant correlation was found between achieving a seizure-free outcome in no visible lesion on MRI (MR-negative) epilepsy patients and having concordance in two or more presurgical evaluations, specifically in interictal EEG, ictal EEG, FDG-PET, and ictal single-photon emission computed tomography. There was a marked improvement in the seizure-free outcome in MR-negative temporal lobe epilepsy (TLE) by the application of this strategy. The better surgical candidates for epilepsy surgery are the followings: patients displaying a discrete lesion on MRI with concordant video-EEG monitoring (VEM) results, patients diagnosed with unilateral hippocampal sclerosis who have concordant VEM results, patients with unilateral hippocampal sclerosis but discordant VEM results, patients with focal cortical dysplasia and concordant VEM results, and patients diagnosed with MR-negative TLE who exhibit two or more consistent results from presurgical evaluations.

Resective epilepsy surgery in a limited-resource settings: A cohort from a multi-disciplinary epilepsy team in a developing country

BACKGROUND

Multidisciplinary pre-surgical evaluation is vital for epilepsy surgery decision and outcomes. Resective epilepsy surgery with assisted monitoring is currently a standard treatment for focal drug resistant epilepsy (DRE). In resource-limited countries, lack of epilepsy surgery center is a huge challenge. We presented and illustrated how to create a multidisciplinary protocol with resource-limited settings in a developing country and epilepsy surgery outcome using brain mapping and monitoring techniques for ensuring satisfactory resection.

METHODS

We created multicentric incomplete but complementary units covering all epilepsy-related sub-specialties and covering a wide geographical area in our country. Then, we conducted a prospective and multicentric study with low resource settings on patients with focal DRE, who underwent resective epilepsy surgery and were followed up for at least 12 months and were evaluated for postoperative seizure outcome and complications if present. Preoperative comprehensive clinical, neurophysiological, neuropsychological, and radiological evaluations were performed by multidisciplinary epilepsy team. Intraoperative brain mapping including awake craniotomy and direct stimulation techniques, neurophysiological monitoring, and electrocorticography was carried out during surgical resection.

RESULTS

The study included 47 patients (18 females and 29 males) with mean age 20.4 ± 10.02 years. Twenty-two (46.8%) patients were temporal epilepsy while 25 (53.2%) were extra-temporal epilepsy. The epilepsy surgery outcome at the last follow up was Engel Class I (seizure free) in 35 (74.5%), Class II (almost seizure free) in 8 (17%), Class III (worthwhile improvement) in 3 (6.4%), and Class IV (no worthwhile improvement) in 1 patient (2.1%).

CONCLUSION

With low resource settings and lack of single fully equipped epilepsy center, favorable outcomes after resective surgery in patients with focal DRE could be achieved using careful presurgical multidisciplinary selection, especially with using intraoperative brain mapping and electrocorticography techniques.

Is intracranial electroencephalography mandatory for MRI-negative neocortical epilepsy surgery?

OBJECTIVE

MRI-negative focal epilepsy is one of the most challenging cases in surgical epilepsy treatment. Many epilepsy centers recommend intracranial electroencephalography (EEG) for MRI-negative cases, especially neocortical epilepsy. This retrospective study aimed to explore whether intracranial monitoring is mandatory in MRI-negative neocortical epilepsy surgery and the factors that significantly influence the decision on whether to perform intracranial recording.

METHODS

In this study, consecutive surgical patients with focal MRI-negative neocortical epilepsy were recruited. All patients underwent routine preoperative evaluation according to the dedicated protocol of the authors' epilepsy center to determine the treatment strategy. Patients were divided into two groups according to the surgical strategy, i.e., a direct group and a stereo-EEG (SEEG)-guided group. History of epilepsy, seizure frequency, interictal and ictal EEG data, PET data, PET/MRI coregistration data, neuropathological findings, and surgical outcomes were compared between the two groups. Multivariate analysis was performed to identify factors influencing the decision to perform SEEG monitoring.

RESULTS

Sixty-four patients were included in this study, 19 and 45 of whom underwent direct and SEEG-guided cortical resection, respectively. At an average follow-up of 3.9 years postoperatively, 56 patients (87.5%) had Engel class I results without permanent neurological deficits. Surgical outcomes were not significantly different between the direct and SEEG-guided groups (94.7% vs 84.4%). PET hypometabolic abnormalities were detected in all patients. There were significant differences between the two groups in the extent of hypometabolism (focal vs nonfocal, p < 0.01) and pathological subtype (focal cortical dysplasia type II vs others, p = 0.03). Multivariate analysis revealed that the extent of hypometabolism (OR 0.01, 95% CI 0.00-0.15; p = 0.001) was the only independent factor affecting the treatment strategy.

CONCLUSIONS

Careful selection of patients with MRI-negative neocortical epilepsy may yield favorable outcomes after direct cortical resection without intracranial monitoring. PET/MRI coregistration plays an essential role in the preoperative evaluation and subsequent resection of these patients. Intracranial monitoring is not a mandatory requirement for surgery if the focal hypometabolic areas are consistent with the findings of semiology and scalp EEG.

Value of ultra-high field MRI in patients with suspected focal epilepsy and negative 3 T MRI (EpiUltraStudy): protocol for a prospective, longitudinal therapeutic study

PURPOSE

Resective epilepsy surgery is a well-established, evidence-based treatment option in patients with drug-resistant focal epilepsy. A major predictive factor of good surgical outcome is visualization and delineation of a potential epileptogenic lesion by MRI. However, frequently, these lesions are subtle and may escape detection by conventional MRI (≤ 3 T).

METHODS

We present the EpiUltraStudy protocol to address the hypothesis that application of ultra-high field (UHF) MRI increases the rate of detection of structural lesions and functional brain aberrances in patients with drug-resistant focal epilepsy who are candidates for resective epilepsy surgery. Additionally, therapeutic gain will be addressed, testing whether increased lesion detection and tailored resections result in higher rates of seizure freedom 1 year after epilepsy surgery. Sixty patients enroll the study according to the following inclusion criteria: aged ≥ 12 years, diagnosed with drug-resistant focal epilepsy with a suspected epileptogenic focus, negative conventional 3 T MRI during pre-surgical work-up.

RESULTS

All patients will be evaluated by 7 T MRI; ten patients will undergo an additional 9.4 T MRI exam. Images will be evaluated independently by two neuroradiologists and a neurologist or neurosurgeon. Clinical and UHF MRI will be discussed in the multidisciplinary epilepsy surgery conference. Demographic and epilepsy characteristics, along with postoperative seizure outcome and histopathological evaluation, will be recorded.

CONCLUSION

This protocol was reviewed and approved by the local Institutional Review Board and complies with the Declaration of Helsinki and principles of Good Clinical Practice. Results will be submitted to international peer-reviewed journals and presented at international conferences.

TRIAL REGISTRATION NUMBER

www.trialregister.nl : NTR7536.

The role of hybrid FDG-PET/MRI on decision-making in presurgical evaluation of drug-resistant epilepsy

Background

When MRI fails to detect a potentially epileptogenic lesion, the chance of a favorable outcome after epilepsy surgery becomes significantly lower (from 60 to 90% to 20–65%). Hybrid FDG-PET/MRI may provide additional information for identifying the epileptogenic zone. We aimed to investigate the possible effect of the introduction of hybrid FDG-PET/MRI into the algorithm of the decision-making in both lesional and non-lesional drug-resistant epileptic patients.

Methods

In a prospective study of patients suffering from drug-resistant focal epilepsy, 30 nonlesional and 30 lesional cases with discordant presurgical results were evaluated using hybrid FDG-PET/MRI.

Results

The hybrid imaging revealed morphological lesion in 18 patients and glucose hypometabolism in 29 patients within the nonlesional group. In the MRI positive group, 4 patients were found to be nonlesional, and in 9 patients at least one more epileptogenic lesion was discovered, while in another 17 cases the original lesion was confirmed by means of hybrid FDG-PET/MRI. As to the therapeutic decision-making, these results helped to indicate resective surgery instead of intracranial EEG (iEEG) monitoring in 2 cases, to avoid any further invasive diagnostic procedures in 7 patients, and to refer 21 patients for iEEG in the nonlesional group. Hybrid FDG-PET/MRI has also significantly changed the original therapeutic plans in the lesional group. Prior to the hybrid imaging, a resective surgery was considered in 3 patients, and iEEG was planned in 27 patients. However, 3 patients became eligible for resective surgery, 6 patients proved to be inoperable instead of iEEG, and 18 cases remained candidates for iEEG due to the hybrid FDG-PET/MRI. Two patients remained candidates for resective surgery and one patient became not eligible for any further invasive intervention.

Conclusions

The results of hybrid FDG-PET/MRI significantly altered the original plans in 19 of 60 cases. The introduction of hybrid FDG-PET/MRI into the presurgical evaluation process had a potential modifying effect on clinical decision-making.

Trial registration

Trial registry: Scientific Research Ethics Committee of the Medical Research Council of Hungary. Trial registration number: 008899/2016/OTIG. Date of registration: 08 February 2016.

Cost-effectiveness analysis of invasive EEG monitoring in drug-resistant epilepsy

PURPOSE

Our aim was to determine the cost-effectiveness of two intracranial electroencephalography (iEEG) interventions: 1) stereoelectroencephalography (SEEG) and 2) placement of subdural grid electrodes (SDGs) both followed by resective surgery in patients with drug-resistant, partial-onset epilepsy, compared with medical management (MM) in Hungary from payer's perspective.

METHODS

The incremental health gains and costs of iEEG interventions have been determined with a combination of a decision tree and prevalence Markov process model over a 30-year time horizon in a cost-utility analysis (CUA). To address the effect of parameter uncertainty on the incremental cost-effectiveness ratio (ICER), deterministic and probabilistic sensitivity analyses were performed.

RESULTS

Our results showed that both SEEG and SDG interventions represent a more expensive but more effective strategy than MM representing the current standard of care. The total discounted cost of SEEG and SDG were € 32,760 and € 25,028 representing € 18,108 and € 10,375 additional cost compared with MM, respectively. However, they provide an additional 3.931 (in SEEG group) and 3.444 quality-adjusted life years (QALYs; in SDG group), correspondingly. Thus, the ICER of SEEG is € 4607 per QALY gain, while the ICER for SDG is € 3013 per QALY gain, compared with MM. At a cost-effectiveness threshold of € 41,058 per QALY in Hungary, both subtypes of iEEG interventions are cost-effective and provide good value for money.

SIGNIFICANCE

Because of the high cost of implanting electrodes and monitoring, the invasive EEG for patients with refractory epilepsy is currently not available in the Hungarian national healthcare system. Our study demonstrated that these procedures in Hungary are cost-effective compared with the MM. As a result, the introduction of iEEG interventions to the reimbursement list of the National Health Insurance Fund Administration was initiated.

The Brain is Not Flat: Conformal Electrode Arrays Diminish Complications of Subdural Electrode Implantation, A Series of 117 Cases

BACKGROUND

Intracranial recordings are integral to evaluating patients with pharmacoresistant epilepsy whom noninvasive testing fails to localize seizure focus. Although stereo-electroencephalography is the preferred method of intracranial recordings in most centers, subdural electrode (SDE) implantation is necessary in selected cases.

OBJECTIVE

To identify imaging correlates that predict SDE complications (extra-axial fluid collections [EFCs]), and determine if modifications that diminish stiffness of electrode sheets reduce complications.

METHODS

A prospective epilepsy surgery database was used to identify adults undergoing craniotomy for SDE implantation over a 14-year period. EFCs and midline shift were measured via magnetic resonance imaging and computed tomography imaging. Correlation analyses and multivariable logistic regression explored associations between use of conformal arrays, serial order of patients, previous ipsilateral intracranial surgery, midline shift, number of SDEs, and neurologic complications.

RESULTS

A total of 111 consecutive patients (59 female) underwent 117 craniotomies (mean, 115 electrode contacts) for SDE implantation. There were 8 surgical complications, 3 in the first 17 (17.7%). and 5 (after electrode modifications) in a subsequent 100 craniotomies (5.0%). We noted an increase in electrode numbers implanted over time (P < 0.001) and decreased midline shift with conformal grids (ρ = - 0.32; P < 0.001). A multivariable regression showed that midline shift correlated with complications (odds ratio, 2.32; 95% confidence interval, 1.12-4.78; P = 0.023).

CONCLUSIONS

Hemorrhagic complications after SDE implantation are difficult to detect because of artifact from electrodes, but predictable by prominent midline shift (>4 mm). Risks inherent to SDE implantation may be minimized using conformal grids. With symptomatic EFCs, a single electrode cable exit site allows hematoma evacuation without terminating intracranial recordings.

Prediction of seizure freedom after epilepsy surgery - Critical reappraisal of significance of intracranial EEG parameters

OBJECTIVE

To analyze the significance of intracranial electroencephalography (iEEG) parameters such as seizure onset patterns (SOP) and size of seizure onset zone (SOZ) with respect to prediction of seizure freedom after resective epilepsy surgery.

METHODS

All patients who underwent iEEG with subdural electrodes between January 2006 and December 2015 in our epilepsy-center were included. Various iEEG parameters were retrospectively analyzed regarding their predictive value to post-operative seizure freedom. Furthermore, associations of specific SOPs with underlying histopathology and brain regions of the SOZ were examined.

RESULTS

Eighty-one patients (34 female) with 324 seizures were assessed. Low-voltage fast activity (37%) and sharp activity <13 Hz (30%) were the most frequent SOPs. Focal SOZ (≤2 cm) was the only iEEG parameter independently associated with 1-year post-operative seizure freedom (OR 4.1, 95% CI 1.433-11.679). While no SOP was linked to specific histopathologies, some associations between SOPs and anatomical regions of SOZ were found.

CONCLUSIONS

A circumscribed SOZ, but no specific SOP was predictive for seizure freedom after epilepsy surgery.

SIGNIFICANCE

Intracranial EEG may be helpful to predict post-operative seizure freedom. Multicenter studies with larger numbers of patients are required to reliably assess the significance of specific SOPs for successful resective epilepsy surgery.

Regularized siamese neural network for unsupervised outlier detection on brain multiparametric magnetic resonance imaging: Application to epilepsy lesion screening

In this study, we propose a novel anomaly detection model targeting subtle brain lesions in multiparametric MRI. To compensate for the lack of annotated data adequately sampling the heterogeneity of such pathologies, we cast this problem as an outlier detection problem and introduce a novel configuration of unsupervised deep siamese networks to learn normal brain representations using a series of non-pathological brain scans. The proposed siamese network, composed of stacked convolutional autoencoders as subnetworks is designed to map patches extracted from healthy control scans only and centered at the same spatial localization to 'close' representations with respect to the chosen metric in a latent space. It is based on a novel loss function combining a similarity term and a regularization term compensating for the lack of dissimilar pairs. These latent representations are then fed into oc-SVM models at voxel-level to produce anomaly score maps. We evaluate the performance of our brain anomaly detection model to detect subtle epilepsy lesions in multiparametric (T1-weighted, FLAIR) MRI exams considered as normal (MRI-negative). Our detection model trained on 75 healthy subjects and validated on 21 epilepsy patients (with 18 MRI-negatives) achieves a maximum sensitivity of 61% on the MRI-negative lesions, identified among the 5 most suspicious detections on average. It is shown to outperform detection models based on the same architecture but with stacked convolutional or Wasserstein autoencoders as unsupervised feature extraction mechanisms.

Predictive Factors of Surgical Outcome in Frontal Lobe Epilepsy Explored with Stereoelectroencephalography

BACKGROUND

Resective surgery established treatment for pharmacoresistant frontal lobe epilepsy (FLE), but seizure outcome and prognostic indicators are poorly characterized and vary between studies.

OBJECTIVE

To study long-term seizure outcome and identify prognostic factors.

METHODS

We retrospectively analyzed 42 FLE patients having undergone surgical resection, mostly preceded by invasive recordings with stereoelectroencephalography (SEEG). Postsurgical outcome up to 10-yr follow-up and prognostic indicators were analyzed using Kaplan-Meier analysis and multivariate and conditional inference procedures.

RESULTS

At the time of last follow-up, 57.1% of patients were seizure-free. The estimated chance of seizure freedom was 67% (95% confidence interval [CI]: 54-83) at 6 mo, 59% (95% CI: 46-76) at 1 yr, 53% (95% CI: 40-71) at 2 yr, and 46% (95% CI: 32-66) at 5 yr. Most relapses (83%) occurred within the first 12 mo. Multivariate analysis showed that completeness of resection of the epileptogenic zone (EZ) as defined by SEEG was the main predictor of seizure outcome. According to conditional inference trees, in patients with complete resection of the EZ, focal cortical dysplasia as etiology and focal EZ were positive prognostic indicators. No difference in outcome was found in patients with positive vs negative magnetic resonance imaging.

CONCLUSION

Surgical resection in drug-resistant FLE can be a successful therapeutic approach, even in the absence of neuroradiologically visible lesions. SEEG may be highly useful in both nonlesional and lesional FLE cases, because complete resection of the EZ as defined by SEEG is associated with better prognosis.

7T MRI in epilepsy patients with previously normal clinical MRI exams compared against healthy controls

Objective

To compare by 7 Tesla (7T) magnetic resonance imaging (MRI) in patients with focal epilepsy who have non-lesional clinical MRI scans with healthy controls.

Methods

37 patients with focal epilepsy, based on clinical and electroencephalogram (EEG) data, with non-lesional MRIs at clinical field strengths and 21 healthy controls were recruited for the 7T imaging study. The MRI protocol consisted of high resolution T₁-weighted, T₂-weighted and susceptibility weighted imaging sequences of the entire cortex. The images were read by two neuroradiologists, who were initially blind to clinical data, and then reviewed a second time with knowledge of the seizure onset zone.

Results

A total of 25 patients had findings with epileptogenic potential. In five patients these were definitely related to their epilepsy, confirmed through surgical intervention, in three they co-localized to the suspected seizure onset zone and likely caused the seizures. In seven patients the imaging findings co-localized to the suspected seizure onset zone but were not the definitive cause, and ten had cortical lesions with epileptogenic potential that did not localize to the suspected seizure onset zone. There were multiple other findings of uncertain significance found in both epilepsy patients and healthy controls. The susceptibility weighted imaging sequence was instrumental in guiding more targeted inspection of the other structural images and aiding in the identification of cortical lesions.

Significance

Information revealed by the improved resolution and enhanced contrast provided by 7T imaging is valuable in noninvasive identification of lesions in epilepsy patients who are non-lesional at clinical field strengths.

The Single Word Auditory Comprehension (SWAC) test: A simple method to identify receptive language areas with electrical stimulation

OBJECTIVES

Resective surgery for medically refractory epilepsy in proximity to speech receptive areas requires balancing adequate resection of the epileptogenic zone for optimal seizure control with preservation of function. We develop a simple test (Single Word Auditory Comprehension or SWAC) to localize speech receptive areas by evaluating patients' ability to comprehend a single word.

METHODS

Patients were studied during presurgical or intraoperative assessment for epilepsy with intracranial electrodes. They were asked to listen to a common word (target word) and to describe what it meant without saying the target word. Electrical stimulation (trains of biphasic 2-ms pulses, 50 Hz for 3 s) was delivered while the patient listened to the target word, not while the patient explained the meaning of the word. In six patients, SWAC test was carried out during extraoperative chronic recordings, and in one patient in the operating theater under local anesthesia.

RESULTS

Among the 7 patients where the test identified deficits, 6 underwent resection (4 temporal, 1 supramarginal, and 1 occipital). Two patients showed temporary minor speech deficits after resection. No patient showed permanent speech deficits after resection.

CONCLUSION/SIGNIFICANCE

The SWAC test is reliable, simple and fast to implement, and suitable for intraoperating mapping. It could be used as a simple initial test to identify receptive language areas where more complex additional tests can be performed.

Multilobar Resections for 3T MRI-Negative Epilepsy: Worth the Trouble?

OBJECTIVE

Multilobar resection in magnetic resonance imaging (MRI)-negative drug-resistant epilepsy warrants attention because they account for up to one third of MRI-negative epilepsy surgery. Despite their high prevalence, data are sparse, and the risk/benefit ratio continues to be debated. The present study investigated the postoperative seizure outcomes in this especially challenging subgroup.

METHODS

We retrospectively analyzed the data of 4 consecutive patients with 3T MRI-negative findings and drug-resistant focal epilepsy who had undergone multilobar epilepsy surgery at our institution.

RESULTS

The mean age at first surgery was 28.5 years (range, 14-48); 1 patient required 2 consecutive reoperations. The final resection was in the frontotemporal and temporo-parieto-occipital regions in 2 patients each. Histopathological examination revealed mild malformations of cortical development in 2 patients and focal cortical dysplasia type Ia and type IIa in 1 patient each. At the last follow-up examination (median, 3.3 years; range, 1-11), 2 patients were completely seizure free (Engel class Ia), 1 patient had experienced some disabling seizures after surgery but had been free of disabling seizures for 2 years at the last follow-up examination (Engel class Ic), and 1 patient had experienced worthwhile improvement (Engel class IIb) and had been seizure free for 1 year at the last follow-up examination. No surgical complications developed.

CONCLUSIONS

Our results have demonstrated that multilobar epilepsy surgery is effective for lasting seizure control for selected 3T MRI-negative candidates, leading to favorable outcomes for all 4 of our patients. Comprehensive multimodal preoperative evaluation is a prerequisite for postoperative success. Reevaluation should be considered for patients with seizure recurrence, because reoperation could be especially beneficial for selected patients who have not responded to an initially limited resection.

The oxymoron of image-guided resection in 3 T MRI-negative extratemporal epilepsy: Technique and postoperative results

OBJECTIVE

We share our experience with extratemporal MRI-negative epilepsies that received "image-guided" resection with the use of neuronavigation after invasive presurgical video-EEG monitoring. We describe and discuss our technique of image generation, navigation system registration, and surgical resection. In addition, we evaluate seizure outcome with respect to the preoperatively planned versus achieved resection.

PATIENTS AND METHODS

Seven patients with 3 T MRI-negative extratemporal epilepsy received navigation-guided resective surgery. The resection plan was based on electrophysiological data from intracranial EEG recordings. For each case a resection segment was created in the neuronavigation device in a systematic manner. We compared the preoperatively planned segment to the achieved resection and looked for correlation with postoperative seizure outcome according to Engel classification, at last follow-up (mean 2.4 years, range 1-4 years).

RESULTS

Mean volume of planned resections was 23.8 ± 15.3 cm³ and of achieved resections 17 ± 10.4 cm³. There was complete overlap with planned resection in 4 patients and partial overlap in 3. Postoperative seizure outcome was class I in 4 patients (57%), IIIA in 1 patient and IVB in 2 patients. Three patients reached seizure-freedom (Engel IA). Volume of planned resection, volume difference of planned versus achieved resection and level of overlap (complete versus partial) did not significantly correlate to seizure outcome.

CONCLUSION

The use of neuronavigation for planning and executing a tailored resection in MRI-negative extratemporal epilepsy is elaborate but can be an effective procedure.

3 Tesla MRI-negative focal epilepsies: Presurgical evaluation, postoperative outcome and predictive factors

OBJECTIVE

To investigate presurgical diagnostic modalities, clinical and seizure outcome as well as predictive factors after resective epilepsy surgery in 3 Tesla MRI-negative focal epilepsies.

PATIENTS AND METHODS

This retrospective study comprises 26 patients (11 males/15 females, mean age 34±12years, range 13-50 years) with 3 Tesla MRI-negative focal epilepsies who underwent resective epilepsy surgery. Non-invasive and invasive presurgical diagnostic modalities, type and localization of resection, clinical and epileptological outcome with a minimum follow-up of 1year (range 1-11 years, mean 2.5±2.3years) after surgery as well as outcome predictors were evaluated.

RESULTS

All patients underwent invasive video-EEG monitoring after implantation of intracerebral depth and/or subdural electrodes. Ten patients received temporal and 16 extratemporal or multilobar (n=4) resections. There was no perioperative death or permanent morbidity. Overall, 12 of 26 patients (46%) were completely seizure-free (Engel IA) and 65% had a favorable outcome (Engel I-II). In particular, seizure-free ratio was 40% in the temporal and 50% in the extratemporal group. In the temporal group, long duration of epilepsy correlated with poor seizure outcome, whereas congruent unilateral FDG-PET hypometabolism correlated with a favorable outcome.

CONCLUSIONS

In almost two thirds of temporal and extratemporal epilepsies defined as "non-lesional" by 3 Tesla MRI criteria, a favorable postoperative seizure outcome (Engel I-II) can be achieved with accurate multimodal presurgical evaluation including intracranial EEG recordings. In the temporal group, most favorable results were obtained when FDG-PET displayed congruent unilateral hypometabolism.

Seizure Outcome of Patients with Magnetic Resonance Imaging-Negative Epilepsies: Still An Ongoing Debate

BACKGROUND

Surgical results regarding MRI-negative epilepsy were presented and related clinical and histopathological parameters were discussed.

METHODS

Thirty-six MRI-negative epilepsy patients were retrospectively analyzed. Histopathological specimens were re-reviewed by 2 blind neuropathologists and re-classified based on the current classifications.

RESULTS

The mean age at surgery and seizure onset was 24.5 years and 9.3 years, respectively. Eight patients were younger than 18 years. Mean duration of seizures was 15.3 years. All but 2 underwent invasive monitorization. Eighteen patients had hypometabolism on FDG-PET with temporal lobe involvement in majority (66.7%). Hypometabolism was found in all patients with hippocampal sclerosis (HS), which was present in 50% and 66.7% of focal cortical dysplasia (FCD) type I and II patients, respectively. The frontal lobe resection was the most frequent type of operation followed by resections in temporal, parietal and occipital lobes. In 7 patients, multilobar resection was performed. Histopathological diagnosis was FCD type I, II, III, HS, and gliosis in 14, 12, 2, 3 and 2 patients, respectively. The mean follow-up was 5.8 years. Seventeen patients were seizure free and favorable outcome (Engel's I and II) was found in 69.7%. FCD type I tend to have more favorable seizure outcome. Duration of epilepsy and hypometabolism on FDG-PET was significantly related to outcome, whereas involved lobe was not.

CONCLUSIONS

Our results suggest it is worth pursuing resective surgery in adults as well as in children with drug-resistant epilepsy with normal MRI.

Mesial Extratemporal Lobe Epilepsy: Clinical Features and Surgical Strategies

BACKGROUND: Extratemporal lobe epilepsy surgery remains a diagnostic and therapeutic challenge. Scalp electroencephalography (EEG) correlates, clinical semiology, and imaging findings are often ambiguous or difficult to interpret, necessitating the need for invasive recordings. This is particularly true for those extratemporal lobe epilepsy cases in which seizures develop from the midline.

OBJECTIVE: The aim of this study was to examine the clinical features and surgical strategies in mesial extratemporal lobe epilepsy.

METHODS: A retrospective study reviewing clinical and surgical characteristics was conducted in 30 patients who underwent epilepsy surgery in mesial extratemporal areas at our institution between 1991 and 2011.

RESULTS: Although the location of the epileptogenic zone was associated with specific seizure types, semiology proved to be heterogeneous. Although scalp EEG was of good lateralizing value, it was poor for localizing the epileptogenic zone, necessitating a frequent need for invasive electroencephalographic recordings.

CONCLUSION: Surgical resections in mesial extratemporal regions were found to be safe and resulted in satisfactory seizure outcomes.

Cost-utility analysis of magnetoencephalography used to inform intracranial electrode placement in patients with drug resistant epilepsy: a model based analysis

OBJECTIVES

We estimated the cost-effectiveness of adding magnetoencephalography to a standard assessment for epilepsy surgery consisting of neuropsychology, magnetic resonance imagining, scalp electroencephalography, video electroencephalography and intracranial electroencephalography, in the capacity of informing intracranial electroencephalography electrode placement.

METHODS

We used Microsoft Excel (2007) to construct a decision model. Discounted costs and quality adjusted life years are aggregated to calculate incremental cost-effectiveness ratios. Sensitivity analyses are conducted to assess robustness of findings.

RESULTS

Our base case analysis yielded a result of $14 300 per quality adjusted life year gained. A total of 82.7% of probabilistic sensitivity analysis iterations resulted in incremental cost-effectiveness ratios below $100 000 in 2014 Canadian dollars.

CONCLUSIONS

Our findings demonstrate that the inclusion of Magnetoencephalography in the assessment for epilepsy surgery in the capacity of informing intracranial electroencephalography electrode placement is likely not cost saving but does represent a reasonable allocation of resources from a value for money perspective.

Epilepsy surgery in the posterior part of the brain

Posterior cortex epilepsy surgery is rarely performed and is associated with a high number of surgical failures, partly because accurate localization of the epileptogenic zone in the posterior part of the brain is extremely difficult. We present the characteristics as well as the surgical outcome and its determinants of a cohort of 208 consecutive patients (adults/children: 125/83) operated on for drug-resistant posterior cortex epilepsy at the "Claudio Munari" Epilepsy Surgery Centre, Milan between May 1996 and May 2013 (mean postsurgical follow-up: 9.6years). In addition, we highlight the differences in anatomoelectroclinical features and outcome between (i) patients who necessitated an invasive preoperative evaluation and those who proceeded directly to surgery and (ii) adults and children. Mean age at epilepsy onset was 6.8years (91.4% with onset before 14years of age). A high seizure frequency was reported by 51% of subjects, interictal and ictal EEG features were localizing in 16% and 28% of cases, and 86% of patients had a positive, judged as more or less informative, MRI. Invasive presurgical evaluation by stereoelectroencephalography was performed in 54% of patients; explorations may schematically be grouped in three main implantation patterns. Globally, 70% of subjects achieved seizure freedom, and further, 10% achieved Engel class II, with the patients operated on in childhood achieving significantly better postsurgical results in terms of seizure freedom and drug discontinuation. Duration of epilepsy represented the most consistent predictor of surgical outcome, with early surgery being correlated with higher chances of surgical success. Therefore, we recommend an early surgical referral in cases of pharmacoresistant posterior cortex seizures. Furthermore, we suggest that surgical failure might be predicted very early, namely within the first 6 postoperative months. We conclude that surgical management of posterior cortex epilepsy may attain excellent results.

Prognostic factors for seizure outcome in patients with MRI-negative temporal lobe epilepsy: A meta-analysis and systematic review

PURPOSE

To perform a systematic review and meta-analysis to identify predictors of postoperative seizure freedom in patients with magnetic resonance imaging (MRI)-negative temporal lobe epilepsy.

METHOD

Publications were screened from electronic databases (MEDLINE, EMBASE), epilepsy archives, and bibliographies of relevant articles that were written in English. We recorded all possible risk factors that might predict seizure outcome after surgery. We calculated odds ratio (OR) with corresponding 95% confidence intervals (95% CI) of predictors for postoperative seizure freedom. Heterogeneity was assessed with I(2). All meta-analyses were performed using Review Manager.

RESULTS

Epilepsy duration (OR=2.57, 95% CI=1.21-5.47, p<0.05, I(2)=1%) and ictal or interictal electroencephalographic anomalies precisely localized in the ipsilateral temporal lobe (OR=3.89, 95% CI=1.66-9.08, p<0.01, I(2)=0 and OR=3.38, 95% CI=1.57-7.25, p<0.05, I(2)=0, respectively) were significantly associated with a higher rate of seizure freedom after surgery. However, the positron emission tomography (PET) results were not predictive of postoperative seizure freedom (OR=2.11, 95% CI=0.95-4.65, p=0.06, I(2)=0). No significant difference in seizure freedom was observed between the positive and negative pathology groups (OR=1.36, 95% CI=0.70-2.63, p=0.36, I(2)=0).

CONCLUSIONS

A shorter epilepsy duration and scalp electroencephalogram (EEG) signals localized precisely in the temporal lobe predicted a better seizure outcome in patients with MRI-negative temporal lobe epilepsy.

7T MRI in focal epilepsy with unrevealing conventional field strength imaging

OBJECTIVE

To assess the diagnostic yield of 7T magnetic resonance imaging (MRI) in detecting and characterizing structural lesions in patients with intractable focal epilepsy and unrevealing conventional (1.5 or 3T) MRI.

METHODS

We conducted an observational clinical imaging study on 21 patients (17 adults and 4 children) with intractable focal epilepsy, exhibiting clinical and electroencephalographic features consistent with a single seizure-onset zone (SOZ) and unrevealing conventional MRI. Patients were enrolled at two tertiary epilepsy surgery centers and imaged at 7T, including whole brain (three-dimensional [3D] T1 -weighted [T1W] fast-spoiled gradient echo (FSPGR), 3D susceptibility-weighted angiography [SWAN], 3D fluid-attenuated inversion recovery [FLAIR]) and targeted imaging (2D T2*-weighted dual-echo gradient-recalled echo [GRE] and 2D gray-white matter tissue border enhancement [TBE] fast spin echo inversion recovery [FSE-IR]). MRI studies at 1.5 or 3T deemed unrevealing at the referral center were reviewed by three experts in epilepsy imaging. Reviewers were provided information regarding the suspected localization of the SOZ. The same team subsequently reviewed 7T images. Agreement in imaging interpretation was reached through consensus-based discussions based on visual identification of structural abnormalities and their likely correlation with clinical and electrographic data.

RESULTS

7T MRI revealed structural lesions in 6 (29%) of 21 patients. The diagnostic gain in detection was obtained using GRE and FLAIR images. Four of the six patients with abnormal 7T underwent epilepsy surgery. Histopathology revealed focal cortical dysplasia (FCD) in all. In the remaining 15 patients (71%), 7T MRI remained unrevealing; 4 of the patients underwent epilepsy surgery and histopathologic evaluation revealed gliosis.

SIGNIFICANCE

7T MRI improves detection of epileptogenic FCD that is not visible at conventional field strengths. A dedicated protocol including whole brain FLAIR and GRE images at 7T targeted at the suspected SOZ increases the diagnostic yield.

Surgery for amygdala enlargement with mesial temporal lobe epilepsy: pathological findings and seizure outcome

OBJECTIVE

Amygdala enlargement (AE) has been suggested to be a subtype of mesial temporal lobe epilepsy (MTLE). However, most reports related to AE have referred to imaging studies, and there have been few reports regarding surgical and pathological findings. The present study was performed to clarify the surgical outcomes and pathology of AE.

METHODS

Eighty patients with drug-resistant MTLE were treated surgically at the Tokyo Metropolitan Neurological Hospital between April 2010 and July 2013. Of these patients, 11 were diagnosed as AE based on presurgical MRI. Nine patients with AE underwent selective amygdalohippocampectomy, while the remaining two patients underwent selective amygdalotomy with hippocampal transection. Intraoperative EEG was routinely performed. The histopathology of the resected amygdala tissue was evaluated and compared with the amygdala tissue of patients with hippocampal sclerosis.

RESULTS

Pathological findings indicated that 10 of 11 specimens had closely clustering hypertrophic neurons with vacuolisation of the background matrix. Slight gliosis was seen in nine specimens, while the remaining two showed no gliotic changes. Intraoperative EEG showed abnormal sharp waves that seemed to originate not from the amygdala but from the hippocampus in all cases. Ten patients became seizure-free during the postoperative follow-up period.

CONCLUSIONS

Histopathologically, clustering hypertrophic neurons and vacuolation with slight gliosis or without gliosis were considered to be pathological characteristics of AE. Amygdalohippocampectomy or hippocampal transection with amygdalotomy is effective for seizure control in patients with AE.

Prognostic value of the second ictal intracranial pattern for the outcome of epilepsy surgery

OBJECTIVE

To investigate the prognostic value of the second ictal pattern (SIP) that follows the first ictal pattern (FIP) seen at seizure onset in order to predict seizure control after epilepsy surgery.

METHODS

SIPs were analysed in 344 electro-clinical and subclinical seizures recorded with intracranial electrodes in 63 patients. SIPs were classified as (a) electrodecremental event (EDE); (b) fast activity (FA); (c) runs of spikes; (d) spike-wave activity; (e) sharp waves; (f) alpha activity; (g) delta activity and (h) theta activity. Engel surgical outcome scale was used.

RESULTS

The mean follow-up period was 42.1 months (SD=30.1). EDE was the most common SIP seen (41%), followed by FA (19%), spike-wave activity (18%), alpha activity (8%), sharp-wave activity (8%), delta activity (3%), runs of spikes (2%) and theta activity (2%). EDE as SIP was associated with favourable outcome when compared with FA (p=0.0044) whereas FA was associated with poor outcome when compared with any other pattern (p=0.0389). FA as SIP tends to occur after EDE (75%) whereas EDE tends to evolve from a FIP containing FA (77%). SIP extent was focal in 46% of patients, lobar in 24%, multilobar in 14% and bilateral in 16%. There is a gradual decrease in the proportion of Engel grade I with the extent of SIP. Focal and delayed (in temporal lobe epilepsy) SIPs appear to be associated with better outcome.

CONCLUSIONS

As SIP, EDE was associated with favourable surgical outcome whereas FA was associated with poor outcome, probably because outcome is dominated by FIP.

SIGNIFICANCE

EDE as SIP should not discourage surgery. However, FA as SIP should be contemplated with caution. SIP focality and latency can have prognostic value in epilepsy surgery.

Cortical feature analysis and machine learning improves detection of "MRI-negative" focal cortical dysplasia

Focal cortical dysplasia (FCD) is the most common cause of pediatric epilepsy and the third most common lesion in adults with treatment-resistant epilepsy. Advances in MRI have revolutionized the diagnosis of FCD, resulting in higher success rates for resective epilepsy surgery. However, many patients with histologically confirmed FCD have normal presurgical MRI studies ('MRI-negative'), making presurgical diagnosis difficult. The purpose of this study was to test whether a novel MRI postprocessing method successfully detects histopathologically verified FCD in a sample of patients without visually appreciable lesions. We applied an automated quantitative morphometry approach which computed five surface-based MRI features and combined them in a machine learning model to classify lesional and nonlesional vertices. Accuracy was defined by classifying contiguous vertices as "lesional" when they fell within the surgical resection region. Our multivariate method correctly detected the lesion in 6 of 7 MRI-positive patients, which is comparable with the detection rates that have been reported in univariate vertex-based morphometry studies. More significantly, in patients that were MRI-negative, machine learning correctly identified 14 out of 24 FCD lesions (58%). This was achieved after separating abnormal thickness and thinness into distinct classifiers, as well as separating sulcal and gyral regions. Results demonstrate that MRI-negative images contain sufficient information to aid in the in vivo detection of visually elusive FCD lesions.

Surgical outcome in patients with MRI-negative, PET-positive temporal lobe epilepsy

PURPOSE

The purpose of this study was to determine the long-term surgical outcomes of magnetic resonance imaging (MRI)-negative, fluorodeoxyglucose positron emission tomography (FDG-PET)-positive patients with temporal lobe epilepsy (TLE) and compare them with those of patients with mesial temporal sclerosis (MTS).

METHODS

One hundred forty-one patients with TLE who underwent anterior temporal lobectomy were included in the study. The surgical outcomes of 24 patients with unilateral temporal hypometabolism on FDG-PET without an epileptogenic lesion on MRI were compared with that of patients with unilateral temporal hypometabolism on FDG-PET with MTS on MRI (n=117). The outcomes were compared using Engel's classification at 2 years after surgery. Clinical characteristics, unilateral interictal epileptiform discharges (IEDs), histopathological data and operation side were considered as probable prognostic factors.

RESULTS

Class I surgical outcomes were similar in MRI-negative patients and the patients with MTS on MRI (seizure-free rate at postoperative 2 years was 79.2% and 82% in the MRI-negative and MTS groups, respectively). In univariate analysis, history of febrile convulsions, presence of unilateral IEDs and left temporal localization were found to be significantly associated with seizure free outcome. Multivariate analysis revealed that independent predictors of a good outcome were history of febrile convulsions and presence of unilateral IEDs.

CONCLUSION

Our results suggest that epilepsy surgery outcomes of MRI-negative, PET positive patients are similar to those of patients with MTS. This finding may aid in the selection of best candidates for epilepsy surgery.

Incidence of functional bi-temporal connections in the human brain in vivo and their relevance to epilepsy surgery

The incidence of functional connections between human temporal lobes and their latencies were investigated using intracranial EEG responses to electrical stimulation with 1 msec single pulses in 91 patients assessed for surgery for treatment of epilepsy. The areas studied were amygdala, hippocampus, parahippocampal gyrus, fusiform gyrus, inferior and mid temporal gyrus. Furthermore, we assessed whether the presence of such connections are related to seizure onset extent and postsurgical seizure control. Responses were seen in any region of the contralateral temporal lobe when stimulating temporal regions in 30 patients out of the 91 (32.96%). Bi-hippocampal or bi-amygdalar projections were seen in only 5% of temporal lobes (N = 60) and between both fusiform gyri in 7.1% (N = 126). All other bilateral connections occurred in less than 5% of hemispheres. Depending on the structures, latencies ranged between 20 and 90 msec, with an average value of 60.2 msec. There were no statistical difference in the proportion of patients showing Engel Class I between patients with and without contralateral temporal connections. No difference was found in the proportion of patients showing bilateral or unilateral seizure onset among patients with and without contralateral temporal projections. The present findings corroborate that the functionality of bilateral temporal connections in humans is limited and does not affect the surgical outcome.

Long-term epilepsy surgery outcomes in patients with PET-positive, MRI-negative temporal lobe epilepsy

This study compared the long-term efficacy of anterior temporal lobectomy (ATL) for the treatment of medically refractory temporal lobe epilepsy (TLE) in patients who presented with ipsilateral temporal PET hypometabolism and nonlesional magnetic resonance imaging (PET+/MRI-) with that in patients who had mesial temporal sclerosis (MTS) on MRI. We described the electroclinical, MRI, PET, and pathological characteristics and seizure outcome of 28 PET+/MRI--patients without discordant ictal and interictal electroencephalography (EEG) who underwent ATL (2004-2007) for medically refractory partial epilepsy while avoiding intracranial monitoring. The primary outcome was the percentages of Engel Class I outcomes at 2 and 5 years of PET+/MRI--patients compared with those of patients with MTS on MRI; neuropsychological testing was used as the secondary outcome. At 2-year follow-up, 21 (75%) patients in the PET+/MRI--group were in Engel Class I compared with 66 (75.9%) patients with MTS, and at 5-year follow-up, 20 (71.4%) patients in the PET+/MRI--group were in Engel Class I compared with 64 (73.6%) patients in the group with MTS. There were no significant differences between the groups at either time period. We concluded that normal MRI results should not preclude presurgical evaluations in patients with medically refractory TLE, as favorable long-term postoperative seizure outcomes are possible, especially in patients with unilateral anterior interictal epileptiform discharges and ipsilateral temporal PET hypometabolism.

Interhemispheric subdural electrodes: technique, utility, and safety

BACKGROUND

Invasive monitoring using subdural electrodes is often valuable for characterizing the anatomic source of seizures in intractable epilepsy. Covering the interhemispheric surface with subdural electrodes represents a particular challenge, with a potentially higher risk of complications than covering the dorsolateral cortex.

OBJECTIVE

To better understand the safety and utility of interhemispheric subdural electrodes (IHSE).

METHODS

We retrospectively reviewed the charts of 24 patients who underwent implantation of IHSE by a single neurosurgeon from 2003 to 2010. Generous midline exposure, meticulous preservation of veins, and sharp microdissection were used to facilitate safe interhemispheric grid placement under direct visualization.

RESULTS

The number of IHSE contacts implanted ranged from 10 to 106 (mean = 39.8) per patient. Monitoring lasted for 5.5 days on average (range, 2-24 days), with an adequate sample of seizures captured in all patients before explantation, and with a low complication rate similar to that reported for grid implantation of the dorsolateral cortex. One patient (of 24) experienced symptomatic mass effect. No other complications clearly related to grid implantation and monitoring, such as clinically evident neurological deficits, infection, hematoma, or infarction, were noted. Among patients implanted with IHSE, monitoring led to a paramedian cortical resection in 67%, a resection in a region not covered by IHSE in 17%, and explantation without resection in 17%.

CONCLUSION

When clinical factors suggest the possibility of an epileptic focus at or near the midline, invasive monitoring of the paramedian cortex with interhemispheric grids can be safely used to define the epileptogenic zone and map local cortical function.

Prognostic value of intracranial seizure onset patterns for surgical outcome of the treatment of epilepsy

OBJECTIVE

To investigate if intracranial EEG patterns at seizure onset can predict surgical outcome.

METHODS

Ictal onset patterns from intracranial EEG were analysed in 373 electro-clinical seizures and subclinical seizures from 69 patients. Seizure onset patterns were classified as: (a) Diffuse electrodecremental (DEE); (b) Focal fast activity (FA); (c) Simultaneous onset of fast activity and diffuse electrodecremental event (FA-DEE); (d) Spikes; (e) Spike-wave activity; (f) Sharp waves; (g) Alpha activity; (h) Delta activity. Presence of preceding epileptiform discharge (PED) was also studied. Engel and ILAE surgical outcome scales were used.

RESULTS

The mean follow-up period was 42.1 months (SD=30.1). Fast activity was the most common seizure onset pattern seen (33%), followed by (FA-DEE) (20%), DEE (19%), spike-wave activity (12%), sharp-waves (6%), alpha activity (6%), delta activity (3%) and spikes (1%). Preceding epileptiform discharges were present in 75% of patients. FA was associated with favourable outcome (p=0.0083) whereas DEE was associated with poor outcome (p=0.0025). A widespread PED was not associated with poor outcome (p=0.9559). There was no clear association between seizure onset pattern and specific pathology, except possibly between sharp/spike waves and mesial temporal sclerosis.

CONCLUSIONS

FA activity is associated with favourable outcome. DEE at onset was associated with poor surgical outcome. Widespread/bilateral PEDs were not associated with poor or good outcome.

SIGNIFICANCE

FA appears to be the best marker for the epileptogenic zone. Surgery should be contemplated with caution if DEE is the first ictal change. However, a widespread/bilateral PED at onset is common and should not discourage surgery.

Can we develop pathology-specific MRI contrast for "MR-negative" epilepsy?

Recent improvements in magnetic resonance imaging (MRI) hardware, software, and analysis routines are helping to put cases of "MR-negative" epilepsy on the decline. However, most standard-of-care MRI relies on careful manipulation and presentation of T1, T2, and diffusion-weighted contrast, which characterize the behavior of water in "bulk" tissue rather than providing pathology-specific contrast. Research efforts in MR physics continue to identify and develop novel theory, and methods such as diffusional kurtosis imaging (DKI) and temporal diffusion spectroscopy that can better characterize tissue substructure, and chemical exchange saturation transfer (CEST) that can target underlying biochemical processes. The potential role of each technique in targeting pathologies implicated in "MR-negative" epilepsy is outlined herein.

Prevalence of nonlesional focal epilepsy in an adult epilepsy clinic

PURPOSE

To evaluate the prevalence of nonlesional focal epilepsy in an adult epilepsy clinic and its refractoriness to antiepileptic drug therapy.

BACKGROUND

Focal epilepsy is frequently, but not always, associated with structural epileptogenic lesions identifiable on magnetic resonance imaging (MRI).

METHODS

We analyzed the data from all patients evaluated at an adult epilepsy clinic from January 2002 to December 2011. Clinical and paraclinical findings were used to diagnose focal epilepsy. Magnetic resonance imaging were reviewed and classified as normal, with an epileptogenic lesion, or with a lesion of unclear epileptogenicity. Epileptogenic lesions were further categorized as tumours, vascular malformations, gliosis (including hippocampal atrophy/sclerosis), and malformations of cortical development. Our study group included patients with no lesions on MRI. Pharmacoresistance of patients with nonlesional focal epilepsy was assessed using the ILAE and Perucca's criterias.

RESULTS

Out of 1521 patients evaluated (mean age 44 years; range 14-93 years), 843 had focal epilepsy. Magnetic resonance imaging data, available for 806 (96%) subjects, showed epileptogenic lesions in 65%, no obvious epileptogenic lesions in 31% and lesions of unclear epileptogenicity in 4%. Magnetic resonance imaging-identified lesions included gliosis due to an acquired insult (52% including 17% of hippocampal atrophy or sclerosis), tumours (29%), vascular malformations (16%) and malformations of cortical development (10%). Fifty-two percent of nonlesional focal epileptic patients were drug-refractory.

CONCLUSION

In a tertiary epilepsy clinic, close to a third of patients with focal epilepsy were found to be nonlesional, half of which were drug-resistant.

Local epileptic activity, histological and neuroimaging findings in symptomatic epilepsy

OBJECTIVE

This study is aimed at revealing the relationship between local interictal epileptic activity, cytoarchitectural disturbances and magnetic resonance imaging (MRI) findings.

MATERIAL AND METHODS

We prospectively investigated a series of 25 patients with symptomatic epilepsy due to isolated forms of focal cortical dysplasia (FCD) or hippocampal sclerosis and low-grade tumours associated with FCD, all of whom underwent tailored surgical procedures under intraoperative electrocorticography; we conducted neuropathological examinations of 92 biopsies taken from different places. We examined the relationship between dysplastic changes in the cortex and the absence or presence of seizure patterns (SPs), including regular spikes/sharp waves, recruiting discharges, paroxysmal fast activity and rhythmic delta-theta activity. Comparisons with MRI findings were also performed.

RESULTS

Complete removal of the SPs zone was associated with better results of surgical treatment. Areas with isolated architectural abnormalities were associated with SPs significantly more often than those where the cortex contains immature or giant neurons; these areas were associated with SPs more than areas containing dysmorphic neurons. The extent of MRI signs appearance in the neocortex correlated neither with the presence of SPs nor with the types of histological changes.

CONCLUSIONS

We suppose an inverse relationship between the morphological changes in neurons and their ability to generate epileptic activity. Electrocorticography may be used for the identification of the MRI-negative epileptogenic lesions.

Interictal magnetoencephalography used in magnetic resonance imaging-negative patients with epilepsy

PURPOSE

This study aims to investigate the contributions of magnetoencephalography (MEG) in magnetic resonance imaging (MRI)-negative patients.

METHODS

A total of 18 MRI-negative patients diagnosed with refractory epilepsy, subjected to MEG investigation, and subsequently underwent surgery were selected for retrospective analysis. A 1.5-tesla Magnetom Sonata with an eight-channel head array coil was used. MEG data were obtained using a 74/248-channel system.

RESULTS

A total of 16 patients (16/18) had positive MEG results, comprising 12 patients with monofocal localizations, five with multifocal localizations, and one with unremarkable results in MEG. In addition, 12 patients had indicative single photon-emission computed tomography (SPECT), five had indicative fluorodeoxyglucose positron emission tomography (FDG-PET), and all the patients had intracranial electroencephalography (EEG) (14 with subdural electrodes and four with electrocorticography). The intracranial EEG recordings of nine patients were guided by MEG informative results. Among these 18 patients, 10 exhibited good postoperative outcomes (Engel I and II), four of which were completely seizure-free. All these ten patients had clear monofocal localization in MEG, including nine with accordant indicative metabolic changes in either SPECT or FDG-PET, or both. None of the five patients with multifocal localizations achieved good postoperative outcomes.

CONCLUSION

For cases with negative MRI findings, epilepsy surgery may be an alternative option for pharmaco-resistant patients if epileptogenic focus localizations by MEG are present in multimodal evaluation.

Do neuroimaging results impact prognosis of epilepsy surgery? A meta-analysis

The neuroimaging results of drug-resistant epilepsy patients play an important role in the surgery decision and prognosis. The aim of this study was to evaluate the impact of these results on the efficacy of epilepay surgery, and then to explore surgical benefit for epilepsy patients with negative magnetic resonance (MR) images. Twenty-four subgroups describing the outcomes of 1475 epilepsy patients with positive-neuroimaging results and 696 patients with negative-neuroimaging results were involved in the meta-analysis. Overall, the odds of postoperational seizure-free rate were 2.03 times higher in magnetic resonance imaging-positive (MRI-positive) patients than in MRI-negative patients [odds ratio (OR)=2.03, 95% CI (1.67, 2.47), P<0.00001]. For patients with temporal lobe epilepsy (TLE), the odds were 1.76 times higher in those with MRI-positive results than in those with MRI-negative results [OR=1.76, 95% CI (1.34, 2.32), P<0.0001]. For patients with extra-temporal lobe epilepsy (extra-TLE), the odds were 2.88 times higher in MRI-positive patients than in MRI-negative patients [OR=2.88, 95% CI (1.53, 5.43), P=0.001]. It was concluded that the seizure-free rate of MRI-positive patients after surgery was higher than that of MRI-negative patients. For patients with negative results, an appropriate surgery should be concerned for TLE.

Localization value of magnetoencephalography interictal spikes in adult nonlesional neocortical epilepsy

Few studies have included magnetoencephalography (MEG) when assessing the diagnostic value of presurgical modalities in a nonlesional epilepsy population. Here, we compare single photon emission computed tomography (SPECT), positron emission tomography (PET), video-EEG (VEEG), and MEG, with intracranial EEG (iEEG) to determine the value of individual modalities to surgical decisions. We analyzed 23 adult epilepsy patients with no abnormal MRI findings who had undergone surgical resection. Localization of individual presurgical tests was determined for hemispheric and lobar locations based on visual analysis. Each localization result was compared with the ictal onset zone (IOZ) defined by using iEEG. The highest to the lowest hemispheric concordance rates were MEG (83%) > ictal VEEG (78%) > PET (70%) > ictal SPECT (57%). The highest to lowest lobar concordance rates were ictal VEEG = MEG (65%) > PET (57%) > ictal SPECT (52%). Statistical analysis showed MEG to have a higher hemispheric concordance than that of ictal SPECT (P = 0.031). We analyzed the effects of MEG clustered-area resection on surgical outcome. Patients who had resection of MEG clusters showed a better surgical outcome than those without such resection (P = 0.038). It is suggested that MEG-based localization had the highest concordance with the iEEG-defined IOZ. Furthermore, MEG cluster resection has prognostic significance in predicting surgical outcome.

Individually tailored extratemporal epilepsy surgery in children: anatomo-electro-clinical features and outcome predictors in a population of 53 cases

Surgery for refractory extratemporal lobe epilepsy (ETLE) in the pediatric age group has been reported to be associated with a high percentage of failure and relapse. We performed a retrospective study of 53 consecutive patients with epilepsy onset before 12 years of age, who underwent, mostly at a pediatric age, an individually tailored ETLE surgery (32 in frontal and 21 in posterior cerebral areas) for pharmacoresistant seizures; these patients were selected and followed by a single national tertiary care pediatric center. Mean age at seizure onset was 3.14 years, and mean age at surgery was 11.23 years. Complete seizure freedom was achieved in 75% of the subjects. Short duration of illness before surgery, MRI features, no invasive pre-surgical evaluation, a localized interictal and ictal pattern as well as the presence of ictal fast activity on scalp EEG, localized interictal fast rhythms and absence of a diffuse initial ictal modification during SEEG, a complete resection of the epileptogenic zone, a type II FCD, and the absence of acute postoperative seizures correlated in a statistically significant way with a seizure-free outcome. We conclude that the seizure outcome of ETLE surgery in a carefully selected pediatric population can be excellent.