One-Stage, Limited-Resection Epilepsy Surgery for Bottom-of-Sulcus Dysplasia

Identification and treatment of surgically-remediable causes of infantile epileptic spasms syndrome

INTRODUCTION

Infantile epileptic spasms syndrome (IESS) is a common developmental and epileptic encephalopathy with poor long-term outcomes. A substantial proportion of patients with IESS have a potentially surgically remediable etiology. Despite this, epilepsy surgery is underutilized in this patient group. Some surgically remediable etiologies, such as focal cortical dysplasia and malformation of cortical development with oligodendroglial hyperplasia in epilepsy (MOGHE), are under-diagnosed in infants and young children. Even when a surgically remediable etiology is recognised, for example, tuberous sclerosis or focal encephalomalacia, epilepsy surgery may be delayed or not considered due to diffuse EEG changes, unclear surgical boundaries, or concerns about operating in this age group.

AREAS COVERED

In this review, the authors discuss the common surgically remediable etiologies of IESS, their clinical and EEG features, and the imaging techniques that can aid in their diagnosis. They then describe the surgical approaches used in this patient group, and the beneficial impact that early epilepsy surgery can have on developing brain networks.

EXPERT OPINION

Epilepsy surgery remains underutilized even when a potentially surgically remediable cause is recognized. Overcoming the barriers that result in under-recognition of surgical candidates and underutilization of epilepsy surgery in IESS will improve long-term seizure and developmental outcomes.

Postoperative Neurologic Outcome in Patients Undergoing Resective Surgery for Parietal Lobe Epilepsy: A Systematic Review

BACKGROUND AND OBJECTIVES

Parietal lobe epilepsy (PLE) surgery can be an effective treatment for selected patients with intractable epilepsy but can be associated with the risk of serious neurologic deficits. We performed a systematic review of the literature to obtain a comprehensive summary of the frequency and types of new postoperative neurologic deficits in patients undergoing PLE resective surgery.

METHODS

We searched MEDLINE, Embase, and Cochrane Central Register of Controlled Trials for articles published between January 1, 1990, and April 28, 2022. We included studies that reported postoperative neurologic outcome following PLE resective surgery confined to the parietal lobe. We required that studies included ≥5 patients. The data collected included demographic information and specific details of postoperative neurologic deficits. When available, individual patient data were collected. We used the Risk of Bias in Nonrandomized Studies of Interventions tool to assess the risk of bias and Grading of Recommendations Assessment, Development, and Evaluation to assess the quality of the evidence.

RESULTS

Of the 3,461 articles screened, 33 studies met the inclusion criteria. A total of 370 patients were included. One hundred patients (27.0%) had a new deficit noted postoperatively. Approximately half of the patients with deficits experienced only transient deficits. Motor deficits were the most commonly identified deficit. The rates of motor deficits noted after PLE surgery were 5.7%, 3.2%, and 2.2% for transient, long-term, and duration not specified, respectively. Sensory and visual field deficits were also commonly reported. Gerstmann syndrome was noted postoperatively in 4.9% of patients and was almost always transient. Individual patient data added information on parietal lobe subregion postoperative neurologic outcome.

DISCUSSION

Our systematic review provides a comprehensive summary of the frequency and types of neurologic deficits associated with PLE surgery. A significant percentage of postoperative deficits are transient. In addition to the expected sensory and visual deficits, PLE surgery is associated with a notable risk of motor deficits. The available literature has important deficiencies. Our study highlights gaps in the literature and provides recommendations for future directions.

TRIAL REGISTRATION INFORMATION

This systematic review was registered on PROSPERO (CRD42022313108, May 26, 2022).

Why did my seizures start now? Influences of lesion connectivity and genetic etiology on age at seizure onset in focal epilepsy

OBJECTIVE

Patients with focal, lesional epilepsy present with seizures at variable ages. Larger lesion size and overlap with sensorimotor or default mode network (DMN) have been associated with younger age at seizure onset in cohorts with mixed types of focal cortical dysplasia (FCD). Here, we studied determinants of age at seizure onset in patients with bottom-of-sulcus dysplasia (BOSD), a discrete type of FCD with highly localized epileptogenicity.

METHODS

Eighty-four patients (77% operated) with BOSD were studied. Demographic, histopathologic, and genetic findings were recorded. BOSD volume and anatomical, primary versus association, rostral versus caudal, and functional network locations were determined. Normative functional connectivity analyses were performed using each BOSD as a region of interest in resting-state functional magnetic resonance imaging data of healthy children. Variables were correlated with age at seizure onset.

RESULTS

Median age at seizure onset was 5.4 (interquartile range = 2-7.9) years. Of 50 tested patients, 22 had somatic and nine had germline pathogenic mammalian target of rapamycin (mTOR) pathway variants. Younger age at seizure onset was associated with greater BOSD volume (p = .002), presence of a germline pathogenic variant (p = .04), DMN overlap (p = .04), and increased functional connectivity with the DMN (p < .05, false discovery rate corrected). Location within sensorimotor cortex and networks was not associated with younger age at seizure onset in our relatively small but homogenous cohort.

SIGNIFICANCE

Greater lesion size, pathogenic mTOR pathway germline variants, and DMN connectivity are associated with younger age at seizure onset in small FCD. Our findings strengthen the suggested role of DMN connectivity in the onset of FCD-related focal epilepsy and reveal novel contributions of genetic etiology.

The clinical, imaging, pathological and genetic landscape of bottom-of-sulcus dysplasia

Bottom-of-sulcus dysplasia (BOSD) is increasingly recognized as a cause of drug-resistant, surgically-remediable, focal epilepsy, often in seemingly MRI-negative patients. We describe the clinical manifestations, morphological features, localization patterns and genetics of BOSD, with the aims of improving management and understanding pathogenesis. We studied 85 patients with BOSD diagnosed between 2005-2022. Presenting seizure and EEG characteristics, clinical course, genetic findings and treatment response were obtained from medical records. MRI (3 T) and 18F-FDG-PET scans were reviewed systematically for BOSD morphology and metabolism. Histopathological analysis and tissue genetic testing were performed in 64 operated patients. BOSD locations were transposed to common imaging space to study anatomical location, functional network localization and relationship to normal MTOR gene expression. All patients presented with stereotyped focal seizures with rapidly escalating frequency, prompting hospitalization in 48%. Despite 42% patients having seizure remissions, usually with sodium channel blocking medications, most eventually became drug-resistant and underwent surgery (86% seizure-free). Prior developmental delay was uncommon but intellectual, language and executive dysfunction were present in 24%, 48% and 29% when assessed preoperatively, low intellect being associated with greater epilepsy duration. BOSDs were missed on initial MRI in 68%, being ultimately recognized following repeat MRI, 18F-FDG-PET or image postprocessing. MRI features were grey-white junction blurring (100%), cortical thickening (91%), transmantle band (62%), increased cortical T1 signal (46%) and increased subcortical FLAIR signal (26%). BOSD hypometabolism was present on 18F-FDG-PET in 99%. Additional areas of cortical malformation or grey matter heterotopia were present in eight patients. BOSDs predominated in frontal and pericentral cortex and related functional networks, mostly sparing temporal and occipital cortex, and limbic and visual networks. Genetic testing yielded pathogenic mTOR pathway variants in 63% patients, including somatic MTOR variants in 47% operated patients and germline DEPDC5 or NPRL3 variants in 73% patients with familial focal epilepsy. BOSDs tended to occur in regions where the healthy brain normally shows lower MTOR expression, suggesting these regions may be more vulnerable to upregulation of MTOR activity. Consistent with the existing literature, these results highlight (i) clinical features raising suspicion of BOSD; (ii) the role of somatic and germline mTOR pathway variants in patients with sporadic and familial focal epilepsy associated with BOSD; and (iii) the role of 18F-FDG-PET alongside high-field MRI in detecting subtle BOSD. The anatomical and functional distribution of BOSDs likely explain their seizure, EEG and cognitive manifestations and may relate to relative MTOR expression.

Hypometabolic patterns are related to post-surgical seizure outcomes in focal cortical dysplasia: A semi-quantitative study

OBJECTIVE

Fluorine-18-fluorodeoxyglucose-positron emission tomography (FDG-PET) is routinely used for presurgical evaluation in many epilepsy centers. Hypometabolic characteristics have been extensively examined in prior studies, but the metabolic patterns associated with specific pathological types of drug-resistant epilepsy remain to be fully defined. This study was developed to explore the relationship between metabolic patterns or characteristics and surgical outcomes in type I and II focal cortical dysplasia (FCD) patients based on results from a large cohort.

METHODS

Data from individuals who underwent epilepsy surgery from 2014 to 2019 with a follow-up duration of over 3 years and a pathological classification of type I or II FCD in our hospital were retrospectively analyzed. Hypometabolic patterns were quantitatively identified via statistical parametric mapping (SPM) and qualitatively analyzed via visual examination of PET-MRI co-registration images. Univariate analyses were used to explore the relationship between metabolic patterns and surgical outcomes.

RESULTS

In total, this study included data from 210 patients. Following SPM calculations, four hypometabolic patterns were defined including unilobar, multi-lobar, and remote patterns as well as cases where no pattern was evident. In type II FCD patients, the unilobar pattern was associated with the best surgical outcomes (p = 0.014). In visual analysis, single gyrus (p = 0.032) and Clear-cut hypometabolism edge (p = 0.040) patterns exhibited better surgery outcomes in the type II FCD group.

CONCLUSIONS

PET metabolic patterns are well-correlated with the prognosis of type II FCD patients. However, similar correlations were not observed in type I FCD, potentially owing to the complex distribution of the epileptogenic region.

PLAIN LANGUAGE SUMMARY

In this study, we demonstrated that FDG-PET was a crucial examination for patients with FCD, which was a common cause of epilepsy. We compared the surgical prognosis for patients with different hypometabolism distribution patterns and found that clear and focal abnormal region in PET was correlated with good surgical outcome in type II FCD patients.

Intraoperative ECoG in bottom-of-the-sulcus syndrome using a novel flexible strip electrode

The recording of epileptiform discharges from bottom-of-sulcus focal cortical dysplasia (BOSD) is often difficult during intraoperative electrocorticography (ECoG) due to the deep localization. We describe the use in this scenario of a new-generation electrode strip with high flexibility, easily adapted to cortical gyri and sulci. A right-handed 20-year-old male with drug-resistant focal epilepsy due to BOSD of the inferior frontal gyrus and daily focal aware seizures was evaluated for epilepsy surgery. Based on electroclinical and neuroimaging results, a focal cortectomy guided by ECoG was proposed. ECoG recordings were performed with new-generation cortical strips (Wise Cortical Strip; WCS®) and standard cortical strips. ECoG, performed on the convexity of the frontal cortical surface, recorded only sporadic spikes with both types of strips. Then, after microsurgical trans-sulcal dissection, WCS was molded along the sulcal surface of the suspected BOSD based on 3D-imaging reconstruction, showing continuous/subcontinuous 3-4-Hz rhythmic spike activity from the deepest electrode. Registration after resection of the BOSD did not show any epileptiform activity. Pathology showed dysmorphic neurons and gliosis. No surgical complications occurred. The patient is seizure-free after 12 months. This single case experience shows that highly flexible electrode strips with adaptability to cortical gyrations can identify IEDs originating from deep location and could therefore be useful in cases of bottom of the sulcus dysplasia.

Successful stereoelectroencephalography re-evaluation in epilepsy patients after failed initial subdural grid evaluation

OBJECTIVE

Epilepsy surgery success is dependent on accurate localization of the epileptogenic zone. Despite the use of invasive EEG using subdural grids and strips, surgical failures can occur. In this series, we explore the utility of a second evaluation with stereoelectroencephalography in patients whose initial invasive evaluation with subdural grid electrodes was unsuccessful in localizing seizure origin.

METHODS

We conducted a retrospective review of patients who underwent subdural grid evaluation (SDE) at our center and identified patients who underwent a re-evaluation with stereoelectroencephalography (SEEG).

RESULTS

We identified three patients who had both subdural and SEEG electrodes in the region of the identified epileptogenic zone in whom the initial SDE evaluation failed to make the patients seizure-free. Two of these patients underwent a second resection and became seizure-free.

SIGNIFICANCE

Stereoelectroencephalography can be useful in the re-evaluation and re-operation of patients who previously had surgical failure using SDE.

Epilepsy surgery outcomes in patients with GATOR1 gene complex variants: Report of new cases and review of literature

AIM

To report seizure outcomes in children with GATOR1 gene complex disorders who underwent epilepsy surgery and perform a systematic literature search to study the available evidence.

METHODS

The records of children with pathogenic/likely pathogenic variants in GATOR1 gene complex who underwent epilepsy surgery were reviewed. Clinical, radiological, neurophysiological, and histological data were extracted/summarized. The systematic review included all case series/reports and observational studies reporting on children or adults with genetic (germline or somatic) variants in the GATOR1 complex genes (DEPDC5, NPRL2, NPRL3) with focal epilepsy with/without focal cortical dysplasia who underwent epilepsy surgery; seizure outcomes were analyzed.

RESULTS

Eight children with pathogenic/likely pathogenic variants in GATOR1 complex genes were included. All had drug-resistant epilepsy. Six children had significant neurodevelopmental delay. Epilepsy surgery was performed in all; clinical seizure freedom was noted in 4 children (50%). Systematic literature search identified 17 eligible articles; additional 30 cases with patient-level data were studied. Lesional MRI brain was seen in 80% cases. The pooled rate of seizure freedom following surgery was 60%; FCD IIa was the most encountered pathology.

INTERPRETATION

Epilepsy surgery may be effective in some children with GATOR1 complex gene variants. Seizure outcomes may be compromised by extensive epileptogenic zones.

Frontoparietal 18F-FDG-PET hypo-metabolism in Lennox-Gastaut syndrome: further evidence highlighting the key network

INTRODUCTION

Lennox Gastaut syndrome (LGS) can be conceptualised as a "secondary network epilepsy", in which the shared electroclinical manifestations reflect epileptic recruitment of a common brain network, despite a range of underlying aetiologies. We aimed to identify the key networks recruited by the epileptic process of LGS using interictal 2-deoxy-2-(¹⁸F)fluoro-D-glucose positron emission tomography (¹⁸F-FDG-PET).

METHODS

Group analysis of cerebral ¹⁸F-FDG-PET, comparing 21 patients with LGS (mean age = 15 years) and 18 pseudo-controls (mean age = 19 years), studied at Austin Health Melbourne, between 2004 and 2015. To minimise the influence of individual patient lesions in the LGS group, we only studied brain hemispheres without structural MRI abnormalities. The pseudo-control group consisted of age- and sex-matched patients with unilateral temporal lobe epilepsy, using only the hemispheres contralateral to the side of epilepsy. Voxel-wise permutation testing compared ¹⁸F-FDG-PET uptake between groups. Associations were explored between areas of altered metabolism and clinical variables (age of seizure onset, proportion of life with epilepsy, and verbal/nonverbal ability). Penetrance maps were calculated to explore spatial consistency of altered metabolic patterns across individual patients with LGS.

RESULTS

Although not always readily apparent on visual inspection of individual patient scans, group analysis revealed hypometabolism in a network of regions including prefrontal and premotor cortex, anterior and posterior cingulate, inferior parietal lobule, and precuneus (p < 0.05, corrected for family-wise error). These brain regions tended to show a greater reduction in metabolism in non-verbal compared to verbal LGS patients, although this difference was not statistically significant. No areas of hypermetabolism were detected on group analysis, although ∼25 % of individual patients showed increased metabolism (relative to pseudo-controls) in the brainstem, putamen, thalamus, cerebellum, and pericentral cortex.

DISCUSSION

Interictal hypometabolism in frontoparietal cortex in LGS is compatible with our previous EEG-fMRI and SPECT studies showing that interictal bursts of generalised paroxysmal fast activity and tonic seizures recruit similar cortical regions. This study provides further evidence that these regions are central to the electroclinical expression of LGS.

Interictal HFO and FDG-PET correlation predicts surgical outcome following SEEG

OBJECTIVE

This study aimed to investigate the quantitative relationship between interictal ¹⁸ F-fluorodeoxyglucose-positron emission tomography (FDG-PET) and interictal high-frequency oscillations (HFOs) from stereo-electroencephalography (SEEG) recordings in patients with refractory epilepsy.

METHODS

We retrospectively included 32 patients. FDG-PET data were quantified through statistical parametric mapping (SPM) t test modeling with normal controls. Interictal SEEG segments with four, 10-min segments were selected randomly. HFO detection and classification procedures were automatically performed. Channel-based HFOs separating ripple (80-250 Hz) and fast ripple (FR; 250-500 Hz) counts were correlated with the surrounding metabolism T score at the individual and group level, respectively. The association was further validated across anatomic seizure origins and sleep vs wake states. We built a joint feature FR × T reflecting the FR and hypometabolism concordance to predict surgical outcomes in 28 patients who underwent surgery.

RESULTS

We found a negative correlation between interictal FDG-PET and HFOs through the linear mixed-effects model (R²  = .346 and .457 for ripples and FRs, respectively, p < .001); these correlations were generalizable to different epileptogenic-zone lobar localizations and vigilance states. The FR × T inside the resection volume could be used as a predictor for surgical outcomes with an area under the curve of 0.81.

SIGNIFICANCE

The degree of hypometabolism is associated with HFO generation rate, especially for FRs. This relationship would be meaningful for selection of SEEG candidates and for optimizing SEEG scheme planning. The concordance between FRs and hypometabolism inside the resection volume could provide prognostic information regarding surgical outcome.

Clinical utility of intraoperative electrocorticography for epilepsy surgery: A systematic review and meta-analysis

Despite the widespread use of intraoperative electrocorticography (iECoG) during resective epilepsy surgery, there are conflicting data on its overall efficacy and inability to predict benefit per pathology. Given the heterogeneity of iECoG use in resective epilepsy surgery, it is important to assess the utility of interictal-based iECoG. This individual patient data (IPD) meta-analysis seeks to identify the benefit of iECoG during resective epilepsy surgery in achieving seizure freedom for various pathologies. Embase, Scopus, and PubMed were searched from inception to January 31, 2021 using the following terms: "ecog", "electrocorticography", and "epilepsy". Articles were included if they reported seizure freedom at ≥12-month follow-up in cohorts with and without iECoG for epilepsy surgery. Non-English articles, noncomparative iECoG cohorts, and studies with <10% iECoG use were excluded. This meta-analysis followed the PRISMA 2020 guidelines. The primary outcome was seizure freedom at last follow-up and time to seizure recurrence, if applicable. Forest plots with random effects modeling assessed the relationship between iECoG use and seizure freedom. Cox regression of IPD was performed to identify predictors of longer duration of seizure freedom. Kaplan-Meier curves with log-rank test were created to visualize differences in time to seizure recurrence. Of 7504 articles identified, 18 were included for study-level analysis. iECoG was not associated with higher seizure freedom at the study level (relative risk = 1.09, 95% confidence interval [CI] = 0.96-1.23, p = .19, I²  = 64%), but on IPD (n = 7 studies, 231 patients) iECoG use was independently associated with more favorable seizure outcomes (hazard ratio = 0.47, 95% CI = .23-.95, p = .037). In Kaplan-Meier analysis of specific pathologies, iECoG use was significantly associated with longer seizure freedom only for focal cortical dysplasia (FCD; p < .001) etiology. Number needed to treat for iECoG was 8.8, and for iECoG in FCD it was 4.7. We show iECoG seizure freedom is not achieved uniformly across centers. iECoG is particularly beneficial for FCD etiology in improving seizure freedom.

Intrinsic and secondary epileptogenicity in focal cortical dysplasia type II

OBJECTIVE

Favorable seizure outcome is reported following resection of bottom-of-sulcus dysplasia (BOSD). We assessed the distribution of epileptogenicity and dysplasia in and around BOSD to better understand this clinical outcome and the optimal surgical approach.

METHODS

We studied 27 children and adolescents with magnetic resonance imaging (MRI)-positive BOSD who underwent epilepsy surgery; 85% became seizure-free postresection (median = 5.0 years follow-up). All patients had resection of the dysplastic sulcus, and 11 had additional resection of the gyral crown (GC) or adjacent gyri (AG). Markers of epileptogenicity were relative cortical hypometabolism on preoperative 18 F-fluorodeoxyglucose (FDG) positron emission tomography (PET), and spiking, ripples, fast ripples, spike-high-frequency oscillation cross-rate, and phase amplitude coupling (PAC) on preresection and postresection electrocorticography (ECoG), all analyzed at the bottom-of-sulcus (BOS), top-of-sulcus (TOS), GC, and AG. Markers of dysplasia were increased cortical thickness on preoperative MRI, and dysmorphic neuron density and variant allele frequency of somatic MTOR mutations in resected tissue, analyzed at similar locations.

RESULTS

Relative cortical metabolism was significantly reduced and ECoG markers were significantly increased at the BOS compared to other regions. Apart from spiking and PAC, which were greater at the TOS compared to the GC, there were no significant differences in PET and other ECoG markers between the TOS, GC, and AG, suggesting a cutoff of epileptogenicity at the TOS rather than a tapering gradient on the cortical surface. MRI and tissue markers of dysplasia were all maximal in the BOS, reduced in the TOS, and mostly absent in the GC. Spiking and PAC reduced significantly over the GC after resection of the dysplastic sulcus.

SIGNIFICANCE

These findings support the concept that dysplasia and intrinsic epileptogenicity are mostly limited to the dysplastic sulcus in BOSD and support resection or ablation confined to the MRI-visible lesion as a first-line surgical approach. 18 F-FDG PET and ECoG abnormalities in surrounding cortex seem to be secondary phenomena.

[Neuroradiological and pathohistological markers of the main epileptogenic substrates in children.Cortical malformations]

High-resolution MRI is an important tool in the diagnosis of structural epilepsy in determining the seizure initiation zones, identification of the mechanisms of epileptogenesis in predicting outcomes and preventing postoperative complications in patients. In this article we demonstrate the neuroradiological and pathohistological characteristics of the main epileptogenic substrates in children using modern classification. The first part of the article is devoted to cortical malformations as the most common epileptogenic cerebral disorders.

Karawun: a software package for assisting evaluation of advances in multimodal imaging for neurosurgical planning and intraoperative neuronavigation

PURPOSE

The neuroimaging research community-which includes a broad range of scientific, medical, statistical, and engineering disciplines-has developed many tools to advance our knowledge of brain structure, function, development, aging, and disease. Past research efforts have clearly shaped clinical practice. However, translation of new methodologies into clinical practice is challenging. Anything that can reduce these barriers has the potential to improve the rate at which research outcomes can contribute to clinical practice. In this article, we introduce Karawun, a file format conversion tool, that has become a key part of our work in translating advances in diffusion imaging acquisition and analysis into neurosurgical practice at our institution.

METHODS

Karawun links analysis workflows created using open-source neuroimaging software, to Brainlab (Brainlab AG, Munich, Germany), a commercially available surgical planning and navigation suite. Karawun achieves this using DICOM standards supporting representation of 3D structures, including tractography streamlines, and thus offers far more than traditional screenshot or color overlay approaches.

RESULTS

We show that neurosurgical planning data, created from multimodal imaging data using analysis methods implemented in open-source research software, can be imported into Brainlab. The datasets can be manipulated as if they were created by Brainlab, including 3D visualizations of white matter tracts and other objects.

CONCLUSION

Clinicians can explore and interact with the results of research neuroimaging pipelines using familiar tools within their standard clinical workflow, understand the impact of the new methods on their practice and provide feedback to methods developers. This capability has been important to the translation of advanced analysis techniques into practice at our institution.

The ILAE consensus classification of focal cortical dysplasia: An update proposed by an ad hoc task force of the ILAE diagnostic methods commission

Ongoing challenges in diagnosing focal cortical dysplasia (FCD) mandate continuous research and consensus agreement to improve disease definition and classification. An International League Against Epilepsy (ILAE) Task Force (TF) reviewed the FCD classification of 2011 to identify existing gaps and provide a timely update. The following methodology was applied to achieve this goal: a survey of published literature indexed with ((Focal Cortical Dysplasia) AND (epilepsy)) between 01/01/2012 and 06/30/2021 (n = 1349) in PubMed identified the knowledge gained since 2012 and new developments in the field. An online survey consulted the ILAE community about the current use of the FCD classification scheme with 367 people answering. The TF performed an iterative clinico-pathological and genetic agreement study to objectively measure the diagnostic gap in blood/brain samples from 22 patients suspicious for FCD and submitted to epilepsy surgery. The literature confirmed new molecular-genetic characterizations involving the mechanistic Target Of Rapamycin (mTOR) pathway in FCD type II (FCDII), and SLC35A2 in mild malformations of cortical development (mMCDs) with oligodendroglial hyperplasia (MOGHE). The electro-clinical-imaging phenotypes and surgical outcomes were better defined and validated for FCDII. Little new information was acquired on clinical, histopathological, or genetic characteristics of FCD type I (FCDI) and FCD type III (FCDIII). The survey identified mMCDs, FCDI, and genetic characterization as fields for improvement in an updated classification. Our iterative clinico-pathological and genetic agreement study confirmed the importance of immunohistochemical staining, neuroimaging, and genetic tests to improve the diagnostic yield. The TF proposes to include mMCDs, MOGHE, and "no definite FCD on histopathology" as new categories in the updated FCD classification. The histopathological classification can be further augmented by advanced neuroimaging and genetic studies to comprehensively diagnose FCD subtypes; these different levels should then be integrated into a multi-layered diagnostic scheme. This update may help to foster multidisciplinary efforts toward a better understanding of FCD and the development of novel targeted treatment options.

Seizure Outcome After Surgery for MRI-Diagnosed Focal Cortical Dysplasia: A Systematic Review and Meta-analysis

OBJECTIVE

Focal cortical dysplasia (FCD) has been associated with poorer post-surgical seizure outcomes compared to other pathologies. FCD surgical series have been assembled on the basis of a histological diagnosis, including patients with abnormal as well as normal pre-operative MRI. However, in clinical workflow, patient selection for surgery is based on pre-operative findings, including MRI. We performed a systematic review and meta-analysis of the literature to determine the rate and predictors of favorable seizure outcome after surgery for MRI-detected FCD.

METHODS

We devised our study protocol in accordance with PRISMA guidelines and registered the protocol with PROSPERO. We searched MEDLINE, EMBASE, and Web of Science for studies of patients followed for ≥12 months after resective surgery for drug-resistant epilepsy with MRI-detected FCD. Random-effects meta-analysis was used to calculate the proportion of patients attaining a favorable outcome, defined as Engel Class I, ILAE Classes 1-2, or "seizure-free" status. Meta-regression was performed to investigate sources of heterogeneity.

RESULTS

Our search identified 3,745 references. Of these, 35 studies (total of 1,353 patients) were included. Most studies (89%) followed patients for ≥24 months post-surgery. The overall post-surgical favorable outcome rate was 70% (95% CI: 64-75). There was high inter-study heterogeneity. Favorable outcome was associated with complete resection of the FCD lesion [risk ratio, RR=2.42 (95% CI: 1.55-3.76), p<0.001] and location of the FCD lesion in the temporal lobe [RR=1.38 (95% CI: 1.07-1.79), p=0013], but not lesion extent, intracranial EEG use, or FCD histological type. The number of FCD histological types included in the same study accounted for 7.6% of the observed heterogeneity.

CONCLUSIONS

70% of patients with drug-resistant epilepsy and MRI features of FCD attain a favorable seizure outcome following resective surgery. Our findings can be incorporated in routine pre-operative counselling and reinforce the importance of resecting completely the MRI-detected FCD where this is safe and feasible.