Comparison of MRI features and surgical outcome among the subtypes of focal cortical dysplasia

Hierarchical particle optimization for cortical shape correspondence in temporal lobe resection

BACKGROUND

Anterior temporal lobe resection is an effective treatment for temporal lobe epilepsy. The post-surgical structural changes could influence the follow-up treatment. Capturing post-surgical changes necessitates a well-established cortical shape correspondence between pre- and post-surgical surfaces. Yet, most cortical surface registration methods are designed for normal neuroanatomy. Surgical changes can introduce wide ranging artifacts in correspondence, for which conventional surface registration methods may not work as intended.

METHODS

In this paper, we propose a novel particle method for one-to-one dense shape correspondence between pre- and post-surgical surfaces with temporal lobe resection. The proposed method can handle partial structural abnormality involving non-rigid changes. Unlike existing particle methods using implicit particle adjacency, we consider explicit particle adjacency to establish a smooth correspondence. Moreover, we propose hierarchical optimization of particles rather than full optimization of all particles at once to avoid trappings of locally optimal particle update.

RESULTS

We evaluate the proposed method on 25 pairs of T1-MRI with pre- and post-simulated resection on the anterior temporal lobe and 25 pairs of patients with actual resection. We show improved accuracy over several cortical regions in terms of ROI boundary Hausdorff distance with 4.29 mm and Dice similarity coefficients with average value 0.841, compared to existing surface registration methods on simulated data. In 25 patients with actual resection of the anterior temporal lobe, our method shows an improved shape correspondence in qualitative and quantitative evaluation on parcellation-off ratio with average value 0.061 and cortical thickness changes. We also show better smoothness of the correspondence without self-intersection, compared with point-wise matching methods which show various degrees of self-intersection.

CONCLUSION

The proposed method establishes a promising one-to-one dense shape correspondence for temporal lobe resection. The resulting correspondence is smooth without self-intersection. The proposed hierarchical optimization strategy could accelerate optimization and improve the optimization accuracy. According to the results on the paired surfaces with temporal lobe resection, the proposed method outperforms the compared methods and is more reliable to capture cortical thickness changes.

Prognostic analysis in children with focal cortical dysplasia II undergoing epilepsy surgery: Clinical and radiological factors

OBJECTIVE

The aim of this study was to investigate the value of clinical profiles and radiological findings in assessing postsurgical outcomes in children with focal cortical dysplasia (FCD) II while exploring prognostic predictors of this disease.

METHODS

We retrospectively reviewed 50 patients with postoperative pathologically confirmed FCD II from January 2016 to June 2021. The clinical profiles and preoperative radiological findings were measured and analyzed. The patients were classified into four classes based on the Engel Class Outcome System at the last follow-up. For the analysis, the patients were divided into two categories based on Engel I and Engel II-IV, namely, seizure-free and non-seizure-free groups. Qualitative and quantitative factors were subsequently compared by groups using comparative statistics. Receiver operating characteristic (ROC) curves were used to identify the predictors of prognosis in children with FCD II.

RESULTS

Thirty-seven patients (74%) had Engel class I outcomes. The minimum postsurgical follow-up was 1 year. At the epilepsy onset, patients who attained seizure freedom were older and less likely to have no apparent lesions on the preoperative MRI ("MRI-negative"). The non-seizure-free group exhibited a higher gray matter signal intensity ratio (GR) on 3D T1-MPRAGE images (p = 0.006), with a lower GR on T2WI images (p = 0.003) and FLAIR images (p = 0.032). The ROC curve indicated that the model that combined the GR value of all MRI sequences (AUC, 0.87; 95% CI, 0.77-0.97; p < 0.001; 86% sensitivity, 85% specificity) was able to predict prognosis accurately.

CONCLUSION

A lower age at the onset or the MRI-negative finding of FCD lesions suggests a poor prognosis for children with FCD II. The model consisting of GR values from three MRI sequences facilitates the prognostic assessment of FCD II patients with subtle MRI abnormalities to prevent worse outcomes.

Case report: The origin of transmantle-like features

The transmantle sign is considered to be a magnetic resonance imaging feature specific to patients with type II focal cortical dysplasia; however, this sign can be difficult to distinguish from other pathologies, such as a radial-oriented white matter band in tuberous sclerosis. Here, we report a case showing a high-intensity area on T2-weighted and fluid-attenuated inversion recovery images extending from the ventricle to the cortex associated with atypical histopathological findings containing corpora amylacea. This case demonstrates that some instances of transmantle signs may be due to corpora amylacea accumulation.

Neuroimaging gradient alterations and epileptogenic prediction in focal cortical dysplasia Ⅲa

INTRODUCTION

Focal cortical dysplasia Type Ⅲa (FCD Ⅲa) is a highly prevalent temporal lobe epilepsy but the seizure outcomes are not satisfactory after epilepsy surgery. Hence, quantitative neuroimaging, epileptogenic alterations, as well as their values in guiding surgery are worth exploring.

METHODS

We examined 69 patients with pathologically verified FCD Ⅲa using multimodal neuroimaging and stereoelectroencephalography (SEEG). Among them, 18 received postoperative imaging which showed the extent of surgical resection and 9 underwent SEEG implantation. We also explored neuroimaging gradient alterations along with the distance to the temporal pole. Subsequently, the machine learning regression model was employed to predict whole-brain epileptogenicity. Lastly, the correlation between neuroimaging or epileptogenicity and surgical cavities was assessed.

RESULTS

FCD Ⅲa displayed neuroimaging gradient alterations on the temporal neocortex, morphology-signal intensity decoupling, low similarity of intra-morphological features and high similarity of intra-signal intensity features. The support vector regression model was successfully applied at the whole-brain level to calculate the continuous epileptogenic value at each vertex (mean-squared error = 13.8 ± 9.8).

CONCLUSION

Our study investigated the neuroimaging gradient alterations and epileptogenicity of FCD Ⅲa, along with their potential values in guiding suitable resection range and in predicting postoperative seizure outcomes. The conclusions from this study may facilitate an accurate presurgical examination of FCD Ⅲa. However, further investigation including a larger cohort is necessary to confirm the results.

A Rare Cause of Epilepsy: Ulegyria Revisited in a Series of 10 Patients

Introduction. Ulegyria results from perinatal hypoxic-ischemic brain injury in term infants. The specific mushroom-shaped configuration of ulegyria results from small atrophic circumvolutions at the bottom of a sulcus underlying an intact gyral apex. Clinically, ulegyria is generally associated with epilepsy. Here, we aimed to delineate the characteristics of patients with ulegyria and the epileptic seizures they experience. Material and methods. Medical records including radiology and pathology reports, video-electroencephalographic (EEG) analysis, operative notes, hospital progress and outpatient clinic notes were reviewed retrospectively in a total of 10 ulegyria patients. Results. Patients ages ranged between 24 and 58 years (mean, 32 ± 9.8 years). Past medical history was confirmed for neonatal asphyxia in 2 (20%). Neurological examination was remarkable for spastic hemiparesis in 1 (10%) patient with perisylvian ulegyria and for visual field deficits in 2 patients (20%) with occipital ulegyria. Ulegyria most commonly involved the temporoparietal region (n = 5, 50%) followed by the perisylvian area (n = 2, 20%). Except the one with bilateral perisylvian ulegyria, all patients had unilateral lesions (n = 9, 90%). Hippocampal sclerosis accompanied ulegyria in 2 patients (20%). All patients experienced epileptic seizures. Mean age at seizure onset was 8.8 ± 5.4 years (range, 2-20 years). Interictal scalp EEG and EEG-video monitoring records demonstrated temporoparietal and frontotemporal activities in 5 (50%) and 2 (20%) patients, respectively. The seizures were successfully controlled by antiepileptic medication in 8 patients (n = 8, 80%). The remaining 2 patients (%20) with concomitant hippocampal sclerosis required microsurgical resection of the seizure foci due to medically resistant seizures. Discussion. Ulegyria is easily recognized with its unique magnetic resonance imaging characteristics and clinical presentation in the majority of cases. It is highly associated with either medically resistant or medically controllable epileptic seizures. The treatment strategy depends on the age at onset and extends of the lesion that has a significant impact on the severity of the clinical picture.

Electroclinical and Multimodality Neuroimaging Characteristics and Predictors of Post-Surgical Outcome in Focal Cortical Dysplasia Type IIIa

Focal cortical dysplasia (FCD) type IIIa is an easily ignored cause of intractable temporal lobe epilepsy. This study aimed to analyze the clinical, electrophysiological, and imaging characteristics in FCD type IIIa and to search for predictors associated with postoperative outcome in order to identify potential candidates for epilepsy surgery. We performed a retrospective review including sixty-six patients with FCD type IIIa who underwent resection for drug-resistant epilepsy. We evaluated the clinical, electrophysiological, and neuroimaging features for potential association with seizure outcome. Univariate and multivariate analyses were conducted to explore their predictive role on the seizure outcome. We demonstrated that thirty-nine (59.1%) patients had seizure freedom outcomes (Engel class Ia) with a median postsurgical follow-up lasting 29.5 months. By univariate analysis, duration of epilepsy (less than 12 years) (p = 0.044), absence of contralateral insular lobe hypometabolism on PET/MRI (p_Log-rank = 0.025), and complete resection of epileptogenic area (p_Log-rank = 0.004) were associated with seizure outcome. The incomplete resection of the epileptogenic area (hazard ratio = 2.977, 95% CI 1.218–7.277, p = 0.017) was the only independent predictor for seizure recurrence after surgery by multivariate analysis. The results of past history, semiology, electrophysiological, and MRI were not associated with seizure outcomes. Carefully included patients with FCD type IIIa through a comprehensive evaluation of their clinical, electrophysiological, and neuroimaging characteristics can be good candidates for resection. Several preoperative factors appear to be predictive of the postoperative outcome and may help in optimizing the selection of ideal candidates to benefit from epilepsy surgery.

Improving surgical outcome with electric source imaging and high field magnetic resonance imaging

While most patients with focal epilepsy present with clear structural abnormalities on standard, 1.5 or 3 T MRI, some patients are MRI-negative. For those, quantitative MRI techniques, such as volumetry, voxel-based morphometry, and relaxation time measurements can aid in finding the epileptogenic focus. High-field MRI, just recently approved for clinical use by the FDA, increases the resolution and, in several publications, was shown to improve the detection of focal cortical dysplasias and mild cortical malformations. For those cases without any tissue abnormality in neuroimaging, even at 7 T, scalp EEG alone is insufficient to delimitate the epileptogenic zone. They may benefit from the use of high-density EEG, in which the increased number of electrodes helps improve spatial sampling. The spatial resolution of even low-density EEG can benefit from electric source imaging techniques, which map the source of the recorded abnormal activity, such as interictal epileptiform discharges, focal slowing, and ictal rhythm. These EEG techniques help localize the irritative, functional deficit, and seizure-onset zone, to better estimate the epileptogenic zone. Combining those technologies allows several drug-resistant cases to be submitted to surgery, increasing the odds of seizure freedom and providing a must needed hope for patients with epilepsy.

Predictors of surgical outcome in focal cortical dysplasia and its subtypes

OBJECTIVE

The authors analyzed predictors of surgical outcome in patients with focal cortical dysplasia (FCD) and its ILAE (International League Against Epilepsy) subtypes after noninvasive multimodal evaluation and calculated time to first seizure.

METHODS

Data of 355 patients with refractory epilepsy, confirmed FCD pathology, and 2-13 years of postsurgical follow-up were analyzed to determine the predictive roles of clinical, EEG, imaging, and surgical factors that influence seizure freedom.

RESULTS

The mean ± SD age at surgery was 20.26 ± 12.18 years. In total, 142 (40.0%) patients had daily seizures and 90 (25.3%) had multiple seizure types. MRI showed clear-cut FCD in 289 (81.4%) patients. Pathology suggested type I FCD in 27.3% of patients, type II in 28.4%, and type III in 42.8% of patients. At latest follow-up, 72.1% of patients were seizure free and 11.8% were seizure free and not receiving antiepileptic drugs. Among the subtypes, 88.8% of patients with type III, 69.3% with type II, and 50.5% with type I FCD were seizure free. Multiple seizure types, acute postoperative seizures (APOS), and type I FCD were predictors of persistent seizures, whereas type III FCD was the strongest predictor of seizure freedom. Type I FCD was associated with daily seizures, frontal and multilobar distribution, subtle findings on MRI, incomplete resection, and persistent seizures. Type II and III FCD were associated with clear-cut lesion on MRI, regional interictal and ictal EEG onset pattern, focal pattern on ictal SPECT, complete resection, and seizure freedom. Type III FCD was associated with temporal location, whereas type I and II FCD were associated with extratemporal location. Nearly 80% of patients with persistent seizures, mostly those with type I FCD, had their first seizure within 6 months postsurgery.

CONCLUSIONS

Long-term seizure freedom after surgery can be achieved in more than two-thirds of patients with FCD after noninvasive multimodal evaluation. Multiple seizure types, type I FCD, and APOS were predictors of persistent seizures. Seizures recurred in about 80% of patients within 6 months postsurgery.

Post-Surgical Outcome and Its Determining Factors in Patients Operated on With Focal Cortical Dysplasia Type II-A Retrospective Monocenter Study

Purpose: Focal cortical dysplasias (FCDs) are a frequent cause of drug-resistant focal epilepsies. These lesions are in many cases amenable to epilepsy surgery. We examined 12-month and long-term post-surgical outcomes and its predictors including positive family history of epilepsy.

Methods: Twelve-month and long-term outcomes regarding seizure control after epilepsy surgery in patients operated on with FCD type II between 2002 and 2019 in the Epilepsy Center of Bonn were evaluated based on patient records and telephone interviews.

Results: Overall, 102 patients fulfilled the inclusion criteria. Seventy-one percent of patients at 12 months of follow-up (FU) and 54% of patients at the last available FU (63 ± 5.00 months, median 46.5 months) achieved complete seizure freedom (Engel class IA), and 84 and 69% of patients, respectively, displayed Engel class I outcome. From the examined variables [histopathology: FCD IIA vs. IIB, lobar lesion location: frontal vs. non-frontal, family history for epilepsy, focal to bilateral tonic–clonic seizures (FTBTCS) in case history, completeness of resection, age at epilepsy onset, age at surgery, duration of epilepsy], outcomes at 12 months were determined by interactions of age at onset, duration of epilepsy, age at surgery, extent of resection, and lesion location. Long-term post-surgical outcome was primarily influenced by the extent of resection and history of FTBTCS. Positive family history for epilepsy had a marginal influence on long-term outcomes only.

Conclusion: Resective epilepsy surgery in patients with FCD II yields very good outcomes both at 12-month and long-term follow-ups. Complete lesion resection and the absence of FTBTCS prior to surgery are associated with a better outcome.

Neuroimaging Phenotyping and Assessment of Structural-Metabolic-Electrophysiological Alterations in the Temporal Neocortex of Focal Cortical Dysplasia IIIa

BACKGROUND

Focal cortical dysplasia IIIa (FCD IIIa) is a common histopathological finding in temporal lobe epilepsy. However, subtle alterations in the temporal neocortex of FCD IIIa renders presurgical diagnosis and definition of the resective range challenging.

PURPOSE

To explore neuroimaging phenotyping and structural-metabolic-electrophysiological alterations in FCD IIIa.

STUDY TYPE

Retrospective.

SUBJECTS

One hundred and sixty-seven subjects aged 4-39 years, including 64 FCD IIIa patients, 89 healthy controls and 14 FCD I patients as disease controls.

FIELD STRENGTH/SEQUENCE

3 T, fast-spin-echo T₂ -weighted fluid-attenuated inversion recovery (FLAIR), synthetic T₁ -weighted magnetization prepared rapid acquisition gradient echo (MPRAGE).

ASSESSMENT

Surface-based linear model was applied to reveal neuroimaging phenotyping in FCD IIIa and assess its relationship with clinical variables. Logistic regression was implemented to identify FCD IIIa patients. Epileptogenicity mapping (EM) was conducted to explore the structural-metabolic-electrophysiological alterations in temporal neocortex of FCD IIIa.

STATISTICAL TESTS

Student's t-test was applied to determine the significance of paired differences. Calibration curves were plotted to assess the goodness-of-fit (GOF) of the models, combined with the Hosmer-Lemeshow test.

RESULTS

FCD IIIa exhibited widespread hyperintensities in temporal neocortex, and these alterations correlated with disease duration (P_uncorrected  < 0.01). Machine learning model accurately identified 84.4% of FCD IIIa patients, 92.1% of healthy controls and 92.9% of FCD I patients. Cross-modality analysis showed a significant negative correlation between FLAIR hyperintensity and positron emission tomography hypometabolism P < 0.01). Furthermore, epileptogenic cortices were located predominantly in brain regions with FLAIR hyperintensity and hypometabolism.

DATA CONCLUSION

FCD IIIa exhibited widespread temporal neocortex FLAIR hyperintensity. Automated machine learning of neuroimaging patterns is conducive for accurate identification of FCD IIIa. The degree and distribution of morphological alterations related to the extent of metabolic and epileptogenic abnormalities, lending support to its potential value for reduction of the radiative and invasive approaches during presurgical workup.

LEVEL OF EVIDENCE

3 TECHNICAL EFFICACY STAGE: 2.

Neuroimaging and genetic characteristics of malformation of cortical development due to mTOR pathway dysregulation: clues for the epileptogenic lesions and indications for epilepsy surgery

Introduction: Malformation of cortical development (MCD) is strongly associated with drug-resistant epilepsies for which surgery to remove epileptogenic lesions is common. Two notable technological advances in this field are identification of the underlying genetic cause and techniques in neuroimaging. These now question how presurgical evaluation ought to be approached for 'mTORpathies.'Area covered: From review of published primary and secondary articles, the authors summarize evidence to consider focal cortical dysplasia (FCD), tuber sclerosis complex (TSC), and hemimegalencephaly (HME) collectively as MCD mTORpathies. The authors also consider the unique features of these related conditions with particular focus on the practicalities of using neuroimaging techniques currently available to define surgical targets and predict post-surgical outcome. Ultimately, the authors consider the surgical dilemmas faced for each condition.Expert opinion: Considering FCD, TSC, and HME collectively as mTORpathies has some merit; however, a unified approach to presurgical evaluation would seem unachievable. Nevertheless, the authors believe combining genetic-centered classification and morphologic findings using advanced imaging techniques will eventually form the basis of a paradigm when considering candidacy for early surgery.

Brain MRI post-processing with MAP07 in the preoperative evaluation of patients with pharmacoresistant epilepsy - Croatian single centre experience

OBJECTIVE

This study aimed to determine the role of brain MRI post-processing method MAP07 (Morphometric Analysis Program) in detecting epileptogenic brain lesions in patients with pharmacoresistant epilepsy (PE). MAP07 is a sophisticated diagnostic program that offers several morphometric maps and facilitates the detection and localization of hippocampal sclerosis (HS), focal cortical dysplasias (FCD), and other types of cortical malformations, which could be undetected by conventional visual MRI analysis (CVA).

METHODS

120 patients aged > 16 years with PE have been recruited. 3 T MRI was performed according to epilepsy imaging protocol followed by image postprocessing with a fully automated MATLAB script, MAP07, by applying SPM5 algorithms. Statistical analysis was performed in IBM SPSS Statistics, version 25.0.

RESULTS

Analysis in our patients showed a high sensitivity of MAP07 with low specificity and with a high proportion of false-positive patients. After MRI analysis, out of 120 patients, 32 were found to have no structural abnormalities by conventional visual analysis in whom after MAP07 in 5 patients structural lesions were found (in one HS, in one FCD, in two perinatal vascular lesions, and in one hippocampal hyperintensity). There was a quite high overall coincidence of the findings of MAP07 and MRI for the detection of FCD, HS, perinatal ischemia/chronic vascular lesions, heterotopias, and polymicrogyria (kappa coefficient above 0.700).

CONCLUSIONS

MAP07 analysis is a useful, additional, and automated method that may guide re-evaluation of MRI by highlighting suspicious cortical regions, as a complementary method to CVA, by enhancing the visualization of cortical malformations and lesions.

Radiologic and Pathologic Features of the Transmantle Sign in Focal Cortical Dysplasia: The T1 Signal Is Useful for Differentiating Subtypes

BACKGROUND AND PURPOSE

The transmantle sign is a characteristic MR imaging finding often seen in focal cortical dysplasia type IIb. The transmantle sign is typically hyperintense on T2WI and FLAIR and hypointense on T1WI. However, in some cases, it shows T1 high signal. We evaluated the imaging and pathologic findings to identify the causes of the T1 high signal in the transmantle sign.

MATERIALS AND METHODS

We retrospectively reviewed the preoperative imaging data of 141 consecutive patients with histologically proved focal cortical dysplasia. We selected 25 patients with focal cortical dysplasia with the transmantle sign and divided them into groups based on the pathologic focal cortical dysplasia subtype and T1 signal of the transmantle sign. We evaluated the clinical, radiologic, and pathologic findings, including the number of balloon cells and dysmorphic neurons and the severity of gliosis or calcifications and compared them among the groups.

RESULTS

Nine of the 25 patients had a T1-high-signal transmantle sign; the other 16 patients did not. All 9 patients with a T1-high-signal transmantle sign were diagnosed as type IIb (group A). Of the 16 patients with no T1-high-signal transmantle sign, 13 were diagnosed as having type IIb (group B), and the other 3 patients, as type IIa (group C). The number of balloon cells was significantly higher in group A than in the other groups, but there were no differences regarding dysmorphic neurons, the severity of gliosis, or calcifications.

CONCLUSIONS

Approximately 6% (9/141) of this patient series had a T1-high-signal transmantle sign, and all were type IIb. The signal may reflect a rich density of balloon cells. This finding could support the differentiation of subtypes, especially type IIb.

Evaluation of different ulegyria patterns with magnetic resonance imaging

Ulegyria is a parenchymal sequel of hypoxic ischemic encephalopathy causing mushroom-like appearance in gyri. Aim of the present study was to evaluate clinico-radiological findings of patients who applied with different clinical features, predominantly epilepsy, and who were found to have ulegyria formations in MRI examinations. The study included a total of 30 patients (12 female and 18 male) who applied with different types of seizures in February 2011-August 2016 period and had brain MRI examinations using 1.5T MRI scanner. Mushroom-shaped gyri accompanied by gliosis and atrophy in subcortical white matter were considered ulegyria. Locations, MRI features and accompanying pathologies of ulegyria formations were studied. Age of the patients ranged from 4 to 62 (mean 26.0 ± 13.8). Both cerebral lobes were involved in 18 patients. In terms of involved area, symmetrical or asymmetrical involvements were observed in occipital lobes in 26 patients, parietal lobes in 19, frontal lobes in 12 and temporal lobes in 4. The most common involvement type was bilateral occipital and bilateral parieto-occipital lobe involvements with five patients each. Lesions were symmetrical in 11 patients. Six patients had cingulate gyrus atrophy. Nineteen patients had different levels of symmetrical or asymmetrical ventricular dilatation. Cranial asymmetry was observed in six patients with unilateral involvement and in one patient with generalized involvement. Although ulegyria predominantly involves parasagittal watershed areas in MRI examinations of patients applying with epilepsy, clinical manifestations and appearance of lesions could vary depending upon the size of involved area and level of injury.

Impact of focal cortical dysplasia Type IIIa on seizure outcome following anterior mesial temporal lobe resection for the treatment of epilepsy

OBJECTIVE

Temporal lobe epilepsy (TLE) is the most common type of pharmacoresistant focal epilepsy, for which anterior mesial temporal lobe resection (AMTLR) is a treatment option. Focal cortical dysplasia Type IIIa (FCD IIIa), a developmental lesion resulting from defects in neuronal formation and migration into the temporal pole (FCD I) combined with hippocampal sclerosis (HS), can be a neuropathological finding. In this study, the authors investigate the impact of FCD IIIa on seizure outcome in patients with TLE who underwent AMTLR.

METHODS

The authors performed a retrospective analysis of all patients with TLE who underwent AMTLR at their institution between June 2011 and April 2014. Histopathological analysis was used to determine whether patients had HS together with FCD I (FCD IIIa) or HS alone. The groups were compared with regard to age, sex, years of epilepsy, and seizure outcome using the Engel classification.

RESULTS

A total of 51 patients with TLE underwent AMTLR at the authors’ institution. FCD IIIa was diagnosed in 13 cases. The patients experienced seizures for a mean duration of 31.1 years. The mean length of follow-up after the procedure was 18 months. All patients with FCD IIIa had a favorable seizure outcome (Engel Class I or II) compared with 71% of the patients with no pathological findings in the temporal pole (p < 0.01).

CONCLUSIONS

Patients with histopathologically proven FCD IIIa had a significantly better seizure outcome after AMTLR than patients with HS alone. Further effort should be made during presurgical evaluation to detect FCD IIIa so that the most suitable resection technique can be chosen and postoperative seizure outcome can be predicted for patient counseling.

Focal Cortical Dysplasia: Gene Mutations, Cell Signaling, and Therapeutic Implications

Focal cortical dysplasias (FCDs) are malformations of cortical development (MCDs) that are highly associated with medication-resistant epilepsy and are the most common cause of neocortical epilepsy in children. FCDs are a heterogeneous group of developmental disorders caused by germline or somatic mutations that occur in genes regulating the PI3K/Akt/mTOR pathway-a key pathway in neuronal growth and migration. Accordingly, FCDs are characterized by abnormal cortical lamination, cell morphology (e.g., cytomegaly), and cellular polarity. In some FCD subtypes, balloon cells express proteins typically seen in neuroglial progenitor cells. Because recurrent intractable seizures are a common feature of FCDs, epileptogenic electrophysiological properties are also observed in addition to local inflammation. Here, we will summarize the current literature regarding FCDs, addressing the current classification system, histopathology, molecular genetics, electrophysiology, and transcriptome and cell signaling changes.

Towards in vivo focal cortical dysplasia phenotyping using quantitative MRI

Focal cortical dysplasias (FCDs) are a range of malformations of cortical development each with specific histopathological features. Conventional radiological assessment of standard structural MRI is useful for the localization of lesions but is unable to accurately predict the histopathological features. Quantitative MRI offers the possibility to probe tissue biophysical properties in vivo and may bridge the gap between radiological assessment and ex-vivo histology. This review will cover histological, genetic and radiological features of FCD following the ILAE classification and will explain how quantitative voxel- and surface-based techniques can characterise these features. We will provide an overview of the quantitative MRI measures available, their link with biophysical properties and finally the potential application of quantitative MRI to the problem of FCD subtyping. Future research linking quantitative MRI to FCD histological properties should improve clinical protocols, allow better characterisation of lesions in vivo and tailored surgical planning to the individual.

Epilepsy prevalence and severity predictors in MRI-identified focal cortical dysplasia

OBJECTIVES

To determine the prevalence of epilepsy and drug-resistant epilepsy in pediatric patients with focal cortical dysplasia (FCD) identified by magnetic resonance imaging (MRI). To determine clinical and imaging differences between those with drug-resistant epilepsy, drug-responsive epilepsy, and no epilepsy among children with MRI-identified FCD.

METHODS

A keyword search of a hospital radiology database identified 97 study participants for inclusion in this retrospective study. Participants were included if they were under 18 years of age at time of database query and had an MRI between 2004 and 2013 showing FCD. Exclusion was based on imaging and clinical characteristics. Data was gathered using a chart review and supplemental questionnaire.

RESULTS

In this cohort of patients with imaging findings compatible with FCD, 29% had not developed epilepsy. The prevalence of epilepsy and drug-resistant epilepsy was 71.13% (95% C.I.=61.05-79.89%) and 32.99% (95% C.I.=23.78-43.27%), respectively. Patients with epilepsy were more likely to have temporal (p=0.029) or frontal (p=0.044) lobe lesions and a family history of seizures (p=0.003) than those without epilepsy. Age of seizure onset was later in those with drug-responsive epilepsy than those with drug-resistant epilepsy (p=0.0002). A later age of seizure onset (OR=1.22, p=0.0441, 95% C.I.=1.00-1.486) and absence of developmental delay (OR=3.624, p=0.0497, 95% C.I.=1.002-13.110) predicted a less severe epilepsy phenotype.

CONCLUSIONS

Previous studies have only assessed patient cohorts with FCD and epilepsy, limiting the data on "asymptomatic" or "atypically presenting" FCD. Identifying a surprisingly large, novel cohort of children with FCD that had not developed epilepsy helps define prognosis and inform clinical management of children with FCD on imaging.

Seven tesla MRI improves detection of focal cortical dysplasia in patients with refractory focal epilepsy

Objective

The aim of this study is to determine whether the use of 7 tesla (T) MRI in clinical practice leads to higher detection rates of focal cortical dysplasias in possible candidates for epilepsy surgery.

Methods

In our center patients are referred for 7 T MRI if lesional focal epilepsy is suspected, but no abnormalities are detected at one or more previous, sufficient‐quality lower‐field MRI scans, acquired with a dedicated epilepsy protocol, or when concealed pathology is suspected in combination with MR‐visible mesiotemporal sclerosis—dual pathology. We assessed 40 epilepsy patients who underwent 7 T MRI for presurgical evaluation and whose scans (both 7 T and lower field) were discussed during multidisciplinary epilepsy surgery meetings that included a dedicated epilepsy neuroradiologist. We compared the conclusions of the multidisciplinary visual assessments of 7 T and lower‐field MRI scans.

Results

In our series of 40 patients, multidisciplinary evaluation of 7 T MRI identified additional lesions not seen on lower‐field MRI in 9 patients (23%). These findings were guiding in surgical planning. So far, 6 patients underwent surgery, with histological confirmation of focal cortical dysplasia or mild malformation of cortical development.

Significance

Seven T MRI improves detection of subtle focal cortical dysplasia and mild malformations of cortical development in patients with intractable epilepsy and may therefore contribute to identification of surgical candidates and complete resection of the epileptogenic lesion, and thus to postoperative seizure freedom.

Activation of extracellular regulated kinase and mechanistic target of rapamycin pathway in focal cortical dysplasia

Neuropathology of resected brain tissue has revealed an association of focal cortical dysplasia (FCD) with drug-resistant epilepsy (DRE). Recent studies have shown that the mechanistic target of rapamycin (mTOR) pathway is hyperactivated in FCD as evidenced by increased phosphorylation of the ribosomal protein S6 (S6) at serine 240/244 (S(240/244) ), a downstream target of mTOR. Moreover, extracellular regulated kinase (ERK) has been shown to phosphorylate S6 at serine 235/236 (S(235/236) ) and tuberous sclerosis complex 2 (TSC2) at serine 664 (S(664) ) leading to hyperactive mTOR signaling. We evaluated ERK phosphorylation of S6 and TSC2 in two types of FCD (FCD I and FCD II) as a candidate mechanism contributing to mTOR pathway dysregulation. Tissue samples from patients with tuberous sclerosis (TS) served as a positive control. Immunostaining for phospho-S6 (pS6(240/244) and pS6(235/236) ), phospho-ERK (pERK), and phospho-TSC2 (pTSC2) was performed on resected brain tissue with FCD and TS. We found increased pS6(240/244) and pS6(235/236) staining in FCD I, FCD II and TS compared to normal-appearing tissue, while pERK and pTSC2 staining was increased only in FCD IIb and TS tissue. Our results suggest that both the ERK and mTOR pathways are dysregulated in FCD and TS; however, the signaling alterations are different for FCD I as compared to FCD II and TS.

Post-surgical outcome for epilepsy associated with type I focal cortical dysplasia subtypes

Focal cortical dysplasias are a well-recognized cause of medically intractable seizures. The clinical relevance of certain subgroups of the International League Against Epilepsy (ILAE) classification scheme remains to be determined. The aim of the present work is to assess the effect of the focal cortical dysplasia type Ib and Ic histologic subtypes on surgical outcome with respect to seizure frequency. This study also provides an opportunity to compare the predictive value of the ILAE and Palmini et al classification schemes with regard to the type I focal cortical dysplasias. We retrospectively reviewed 91 focal cortical dysplasia patients (55% female; median age: 19 years (interquartile range 8-34); median seizure duration: 108 months (interquartile range 36-204)) with chronic epilepsy who underwent surgery. We compared the pathological subtypes, evaluating the patients' post-surgical outcome with respect to seizure frequency according to the Engel's classification and the ILAE outcome classification. Both the ILAE classification scheme and Palmini et al classification scheme were utilized to classify the histologic subtype. Using χ(2) and Fisher's exact tests, we compared the post-surgical outcomes among these groups. Of the 91 patients, there were 50 patients with ILAE focal cortical dysplasia type Ib, 41 with ILAE focal cortical dysplasia type Ic, 63 with Palmini et al focal cortical dysplasia type IA, and 28 with Palmini et al focal cortical dysplasia type IB. After surgery, 44 patients (48%) were seizure-free. Crude analysis revealed no significant difference between patients with subtypes of ILAE focal cortical dysplasia type I or Palmini et al focal cortical dysplasia type I concerning postoperative outcome according to the Engel and ILAE scoring systems on seizure frequency. Our findings revealed no significant difference concerning surgical outcome with respect to seizure frequency for the histologic subtypes of ILAE focal cortical dysplasia type I (Ib vs Ic) or Palmini et al focal cortical dysplasia type I (IA vs IB). In isolation, the histologic subtype of focal cortical dysplasia type I does not appear predictive of postoperative outcome.

Focal cortical dysplasia and epilepsy surgery

Focal cortical dysplasia (FCD) is the most commonly encountered developmental malformation that causes refractory epilepsy. With advances in neuroimaging techniques, in particular MRI, recent studies have revealed a higher prevalence of FCD than previously estimated and have improved the preoperative identification and classification of these abnormalities. However, MRI frequently does not show any abnormalities in patients with pathologically proven FCD. In this situation, functional neuroimaing such as FDG-PET and ictal SPECT can be helpful. FCD is thought to be intrinsically epileptogenic, because the dysplastic tissues contain aberrant neural networks that are highly susceptible to abnormal excitation. The response to the medical treatment of epilepsy has been documented as consistently poor. Therefore, surgical resection has been an important alternative treatment for patients with intractable epilepsy related to FCD. Incomplete resection of FCD has been consistently known to be a poor prognostic factor. However, the complete removal of FCD is often difficult because the demarcation of the lesion is frequently poor, and dysplastic tissues tend to be more extensive than is apparent on MRI. Evidence indicates that even patients with MRI abnormalities who have resective epilepsy surgery for FCD have worse surgical outcomes than those of patients who have surgery for other focal lesional epilepsy syndromes. Careful planning of evelauation using intracranial electrodes is necessary for successful epilepsy surgery.

3T MRI improves the detection of transmantle sign in type 2 focal cortical dysplasia

PURPOSE

Type 2 focal cortical dysplasia (FCD2) is one of the main causes of refractory partial epilepsy, but often remains overlooked by MRI. This study aimed to elucidate whether 3T MRI offers better detection and characterization of FCD2 than 1.5T, using similar coils and acquisition time.

METHODS

Two independent readers reviewed the 1.5T and 3T MR images of 25 patients with histologically proven FCD2. For both magnetic fields, the ability to detect a lesion was analyzed. We compared the identification of each of the five criteria typical of FCD2 (cortical thickening, blurring, cortical signal changes, subcortical signal changes, and "transmantle" sign) and artifacts, using a four-point scale (0-3). Interobserver reliability for lesion detection was calculated.

KEY FINDINGS

Seventeen lesions (68%) were detected at 3T, two of which were overlooked at 1.5T. Interobserver reliability was better at 3T (κ = 1) than at 1.5T (κ = 0.83). The transmantle sign was more clearly identified at 3T than 1.5T (mean visualization score: 1.72 vs. 0.56; p = 0.002).

SIGNIFICANCE

The use of 3T MRI in patients suspected of type 2 FCD improves the detection rate and the lesion characterization owing to the transmantle sign being more clearly seen at 3T. This point is of interest, since this feature is considered as an MR signature of FCD2.

Stereoelectroencephalography following subdural grid placement for difficult to localize epilepsy

BACKGROUND

Despite the use of invasive subdural recording, failure to localize or resect the epileptogenic zone (EZ) occurs. Potential causes for this include EZ originating outside of the subdural grid coverage area, involvement of eloquent cortex, or complications requiring removal of electrodes without seizure localization. No study has examined the safety and efficacy of stereoelectroencephalography (SEEG) after subdural grid placement.

OBJECTIVE

To determine the efficacy of SEEG in patients who have previously undergone subdural grid placement.

METHODS

A prospective analysis was performed on 14 patients who had subdural grid evaluation and underwent subsequent SEEG monitoring. The follow-up period after the SEEG-guided resections ranged from 11 months to 34 months with an average follow-up of 20.1 months. Magnetic resonance imaging findings, EZ localization, outcomes, type of surgery, and perioperative complications were evaluated.

RESULTS

Ten patients (71%) underwent a resection after SEEG reimplantation. Of the 4 patients (29%) not undergoing resection, 2 had seizures arising from eloquent cortex, 1 had bitemporal epilepsy, and 1 had a previous temporal lobectomy contralateral to the EZ. An estimate of the EZ was achieved in all patients based on interictal and ictal recordings. In patients undergoing resection, 60% were seizure-free at 11 months. Perioperative complications were minimal and included 1 abscess, which required burr-hole drainage and antibiotics.

CONCLUSION

SEEG is a safe and effective method after subdural grid placement is inconclusive, providing an additional opportunity for seizure freedom in this highly challenging group of patients.

Surgical pathology of epilepsy-associated non-neoplastic cerebral lesions: a brief introduction with special reference to hippocampal sclerosis and focal cortical dysplasia

Among epilepsy-associated non-neoplastic lesions, mesial temporal lobe epilepsy with hippocampal sclerosis (mTLE-HS) and malformation of cortical development (MCD), including focal cortical dysplasia (FCD), are the two most frequent causes of drug-resistant focal epilepsies, constituting about 50% of all surgical pathology of epilepsy. Several distinct histological patterns have been historically recognized in both HS and FCD, and several studies have tried to perform clinicopathological correlations. However, results have been controversial, particularly in terms of post-surgical seizure outcome. Recently, the International League Against Epilepsy constituted a Task Forces of Neuropathology and FCD within the Commission on Diagnostic Methods, to establish an international consensus of histological classification of HS and FCD, respectively, based on agreement with the recognition of the importance of defining a histopathological classification system that reliably has some clinicopathological correlation. Such consensus classifications are likely to facilitate future clinicopathological studies. Meanwhile, we reviewed the neuropathology of 41 surgical cases of mTLE, and confirmed three type/patterns of HS along with no HS, based on the qualitative evaluation of the distribution and severity of neuronal loss and gliosis within hippocampal formation, that is, HS type 1 (61%) equivalent to "classical" Ammon's horn sclerosis, HS type 2 (2%) representing CA1 sclerosis, HS type 3 (17%) equivalent to end folium sclerosis, and no HS (19%). Furthermore, we performed a neuropathological comparative study on mTLE-HS and dementia-associated HS (d-HS) in the elderly, and confirmed that neuropathological features differ between mTLE-HS and d-HS in the distribution of hippocampal neuronal loss and gliosis, morphology of reactive astrocytes and their protein expression, and presence of concomitant neurodegenerative changes, particularly Alzheimer type and TDP-43 pathologies. These differences may account, at least in part, for the difference in pathogenesis and epileptogenicity of HS in mTLE and senile dementia. However, the etiology and pathogenesis of most epileptogenic lesions are yet to be elucidated.