Focal cortical dysplasia: etiology, epileptogenesis, classification, clinical presentation, imaging, and management

The molecular genetics of PI3K/PTEN/AKT/mTOR pathway in the malformations of cortical development

Malformations of cortical development (MCD) are a group of developmental disorders characterized by abnormal cortical structures caused by genetic or harmful environmental factors. Many kinds of MCD are caused by genetic variation. MCD is the common cause of intellectual disability and intractable epilepsy. With rapid advances in imaging and sequencing technologies, the diagnostic rate of MCD has been increasing, and many potential genes causing MCD have been successively identified. However, the high genetic heterogeneity of MCD makes it challenging to understand the molecular pathogenesis of MCD and to identify effective targeted drugs. Thus, in this review, we outline important events of cortical development. Then we illustrate the progress of molecular genetic studies about MCD focusing on the PI3K/PTEN/AKT/mTOR pathway. Finally, we briefly discuss the diagnostic methods, disease models, and therapeutic strategies for MCD. The information will facilitate further research on MCD. Understanding the role of the PI3K/PTEN/AKT/mTOR pathway in MCD could lead to a novel strategy for treating MCD-related diseases.

Analysis of clinical characteristics and histopathological transcription in 40 patients afflicted by epilepsy stemming from focal cortical dysplasia

OBJECTIVE

This study aims to comprehensively analyze the clinical characteristics and identify the differentially expressed genes associated with drug-resistant epilepsy (DRE) in patients with focal cortical dysplasia (FCD).

METHODS

A retrospective investigation was conducted from July 2019 to June 2022, involving 40 pediatric cases of DRE linked to FCD. Subsequent follow-ups were done to assess post-surgical outcomes. Transcriptomic sequencing and quantitative reverse transcription polymerase chain reaction (qRT-PCR) were used to examine differential gene expression between the FCD and control groups.

RESULTS

Among the 40 patients included in the study, focal to bilateral tonic-clonic seizures (13/40, 32.50%) and epileptic spasms (9/40, 22.50%) were the predominant seizure types. Magnetic resonance imaging (MRI) showed frequent involvement of the frontal (22/40, 55%) and temporal lobes (12/40, 30%). In cases with negative MRI results (13/13, 100%), positron emission tomography/computed tomography (PET-CT) scans revealed hypometabolic lesions. Fused MRI/PET-CT images demonstrated lesion reduction in 40.74% (11/27) of cases compared with PET-CT alone, while 59.26% (16/27) yielded results consistent with PET-CT findings. FCD type II was identified in 26 cases, and FCD type I in 13 cases. At the last follow-up, 38 patients were prescribed an average of 1.27 ± 1.05 anti-seizure medications (ASMs), with two patients discontinuing treatment. After a postoperative follow-up period of 23.50 months, 75% (30/40) of patients achieved Engel class I outcome. Transcriptomic sequencing and qRT-PCR analysis identified several genes primarily associated with cilia, including CFAP47, CFAP126, JHY, RSPH4A, and SPAG1.

SIGNIFICANCE

This study highlights focal to bilateral tonic-clonic seizures as the most common seizure type in patients with DRE due to FCD. Surgical intervention primarily targeted lesions in the frontal and temporal lobes. Patients with FCD-related DRE showed a promising prognosis for seizure control post-surgery. The identified genes, including CFAP47, CFAP126, JHY, RSPH4A, and SPAG1, could serve as potential biomarkers for FCD.

PLAIN LANGUAGE SUMMARY

This study aimed to comprehensively evaluate the clinical data of individuals affected by focal cortical dysplasia and analyze transcriptomic data from brain tissues. We found that focal to bilateral tonic-clonic seizures were the most prevalent seizure type in patients with drug-resistant epilepsy. In cases treated surgically, the frontal and temporal lobes were the primary sites of the lesions. Moreover, patients with focal cortical dysplasia-induced drug-resistant epilepsy exhibited a favorable prognosis for seizure control after surgery. CFAP47, CFAP126, JHY, RSPH4A, and SPAG1 have emerged as potential pathogenic genes for the development of focal cortical dysplasia.

Experimental models of human cortical malformations: from mammals to 'acortical' zebrafish

Human neocortex controls and integrates cognition, emotions, perception and complex behaviors. Aberrant cortical development can be triggered by multiple genetic and environmental factors, causing cortical malformations. Animal models, especially rodents, are a valuable tool to probe molecular and physiological mechanisms of cortical malformations. Complementing rodent studies, the zebrafish (Danio rerio) is an important model organism in biomedicine. Although the zebrafish (like other fishes) lacks neocortex, here we argue that this species can still be used to model various aspects and brain phenomena related to human cortical malformations. We also discuss novel perspectives in this field, covering both advantages and limitations of using mammalian and zebrafish models in cortical malformation research. Summarizing mounting evidence, we also highlight the importance of translationally-relevant insights into the pathogenesis of cortical malformations from animal models, and discuss future strategies of research in the field.

The clinical application of neuro-robot in the resection of epileptic foci: a novel method assisting epilepsy surgery

During surgery for foci-related epilepsy, neurosurgeons face significant difficulties in identifying and resecting MRI-negative or deep-seated epileptic foci. Here, we present a neuro-robotic navigation system that is specifically designed for resection of MRI negative epileptic foci. We recruited 52 epileptic patients, and randomly assigned them to treatment group with either neuro-robotic navigation or conventional neuronavigation system. For each patient, in the neuro-robotic navigation group, we integrated multimodality imaging including MRI and PET-CT into the robotic workstation and marked the boundary of foci from the fused image. During surgery, this boundary was delineated by the robotic laser device with high accuracy, guiding resection for the surgeon. For deeply seated foci, we exploited the neuro-robotic navigation system to localize the deepest point with biopsy needle insertion and methylene dye application to locate the boundary of the foci. Our results show that, compared with the conventional neuronavigation, the neuro-robotic navigation system performs equally well in MRI positive epilepsy patients (ENGEL I ratio: 71.4% vs 100%, p = 0.255) systems and show better performance in patients with MRI-negative focal cortical dysplasia (ENGEL I ratio: 88.2% vs 50%, p = 0.0439). At present, there are no documented neurosurgery robots with similar function and application in the field of epilepsy. Our research highlights the added value of using neuro-robotic navigation systems in resection surgery for epilepsy, particularly in cases that involve MRI-negative or deep-seated epileptic foci.

Associated factors with stimulation induced seizures and the relevance with surgical outcomes

OBJECTIVE

To analyze the associated factors with stimulation-induced seizures (SIS) and the relevant factors in predicting surgical outcomes.

METHODS

We analyzed 80 consecutive epilepsy patients explored by stereo-electroencephalography with routine electrical stimulation mapping (ESM). If seizures induced by ESM, patients were classified as SIS-positive (SIS-P); otherwise, SIS-negative (SIS-N). Patients received radical surgery were further classified as favorable (Engel I) and unfavorable (Engel II-IV) groups.

RESULTS

Of the 80 patients included, we identified 44 (55.0%) and 36(45.0%) patients in the SIS-P and SIS-N groups, respectively. Multivariate analysis revealed that the seizure onset pattern (SOP) of preceding repetitive epileptiform discharges following LVFA (PRED→LVFA) (OR 3.319, 95% CI 1.200-9.183, P = 0.021) and pathology of focal cortical dysplasia (FCD) type II (OR 3.943, 95% CI 1.093-14.226, P = 0.036) were independent factors influencing whether the electrical stimulation can induce a seizure. Among the patients received radical surgery, there were 55 and 15 patients in the favorable and unfavorable groups separately. Multivariate analysis revealed that the SOP of PRED→LVFA induced seizures by stimulation (OR 11.409, 95% CI 1.182-110.161, P = 0.035) and bilateral implantation (OR 0.048, 95% CI 0.005-0.497, P = 0.011) were independent factors affecting surgical outcomes. The previous epilepsy surgery had a trend to be a negative factor with SIS (OR 0.156, 95% CI 0.028-0.880, P = 0.035) and surgical outcomes (OR 0.253, 95% CI 0.053-1.219, P = 0.087).

CONCLUSION

ESM is a highly valuable method for localizing the seizure onset zone. The SOP of PRED→LVFA and FCD type II were associated with elicitation of SIS by ESM, whereas a previous epilepsy surgery showed a negative association. Furthermore, the SOP of PRED→LVFA together with SIS in the same patient predicted favorable surgical outcomes, whereas bilateral electrode implantation predicted unfavorable outcomes.

An Assessment of the Pathological Classification and Postoperative Outcome of Focal Cortical Dysplasia by Simultaneous Hybrid PET/MRI

Objectives: The purpose of this research was to investigate whether MRI and Simultaneous Hybrid PET/MRI images were consistent in the histological classification of patients with focal cortical dysplasia. Additionally, this research aimed to evaluate the postoperative outcomes with the MRI and Simultaneous Hybrid PET/MRI images of focal cortical dysplasia. Methods: A total of 69 cases in this research were evaluated preoperatively for drug-resistant seizures, and then surgical resection procedures of the epileptogenic foci were performed. The postoperative result was histopathologically confirmed as focal cortical dysplasia, and patients then underwent PET and MRI imaging within one month of the seizure. In this study, head MRI was performed using a 3.0 T magnetic resonance scanner (Philips) to obtain 3D T1WI images. The Siemens Biograph 16 scanner was used for a routine scanning of the head to obtain PET images. BrainLAB’s iPlan software was used to fuse 3D T1 images with PET images to obtain PET/MRI images. Results: Focal cortical dysplasia was divided into three types according to ILAE: three patients were classified as type I, twenty-five patients as type II, and forty-one patients as type III. Patients age of onset under 18 and age of operation over 18 had a longer duration (p = 0.036, p = 0.021). MRI had a high lesion detection sensitivity of type III focal cortical dysplasia (p = 0.003). Simultaneous Hybrid PET/MRI showed high sensitivity in detecting type II and III focal cortical dysplasia lesions (p = 0.037). The lesions in Simultaneous Hybrid PET/MRI-positive focal cortical dysplasia patients were mostly located in the temporal and multilobar (p = 0.005, 0.040). Conclusion: Simultaneous Hybrid PET/MRI has a high accuracy in detecting the classification of focal cortical dysplasia. The results of this study indicate that patients with focal cortical dysplasia with positive Simultaneous Hybrid PET/MRI have better postoperative prognoses.

Glucocorticoid receptors participate in epilepsy in FCDII patients and MP model rats: A potential therapeutic target for epilepsy in patients with focal cortical dysplasia II (FCDII)

BACKGROUND

Glucocorticoid receptors (GRs) and mineralocorticoid receptors (MRs) are involved in neuronal excitability, neurogenesis, and neuroinflammation. However, the roles of GRs and MRs in epilepsy in focal cortical dysplasia II (FCDII) have not been reported.

RESEARCH DESIGN AND METHODS

We evaluated GRs and MRs expression and distribution in FCDII patients and methylazoxymethanol-pilocarpine-induced epilepsy model rats (MP rats), and the effects of a GR agonist on neurons in human FCDII and investigated the electrophysiological properties of cultured neurons and neurons of MP rats after lentivirus-mediated GR knockdown or overexpression and GR agonist or antagonist administration.

RESULTS

GR expression (not MR) was decreased in specimens from FCDII patients and model rats. GR agonist dexamethasone reduced neuronal excitatory transmission and increased neuronal inhibitory transmission in FCDII. GR knockdown increased the excitability of cultured neurons, and GR overexpression rescued the hyperexcitability of MP-treated neurons. Moreover, dexamethasone decreased neuronal excitability and excitatory transmission in MP rats, while GR antagonist exerted the opposite effects. Dexamethasone reduced the seizure number and duration by approximately 85% and 60% in MP rats within one to two hours.

CONCLUSIONS

These results suggested that GRs play an important role in epilepsy in FCDII and GR activation may have protective and antiepileptic effects in FCDII.

Focal Cortical Dysplasia Type Ⅲ Related Medically Refractory Epilepsy: MRI Findings and Potential Predictors of Surgery Outcome

This study aims to explore the relationship between neuropathologic and the post-surgical prognosis of focal cortical dysplasia (FCD) typed-Ⅲ-related medically refractory epilepsy. A total of 266 patients with FCD typed-Ⅲ-related medically refractory epilepsy were retrospectively studied. Presurgical clinical data, type of surgery, and postsurgical seizure outcome were analyzed. The minimum post-surgical follow-up was 1 year. A total of 266 patients of FCD type Ⅲ were included in this study and the median follow-up time was 30 months (range, 12~48 months). Age at onset ranged from 1.0 years to 58.0 years, with a median age of 12.5 years. The number of patients under 12 years old was 133 (50%) in patients with FCD type Ⅲ. A history of febrile seizures was present in 42 (15.8%) cases. In the entire postoperative period, 179 (67.3%) patients were seizure-free. Factors with p < 0.15 in univariate analysis, such as age of onset of epilepsy (p = 0.145), duration of epilepsy (p = 0.004), febrile seizures (p = 0.150), being MRI-negative (p = 0.056), seizure type (p = 0.145) and incomplete resection, were included in multivariate analysis. Multivariate analyses revealed that MRI-negative findings of FCD (OR 0.34, 95% CI 0.45-0.81, p = 0.015) and incomplete resection (OR 0.12, 95% CI 0.05-0.29, p < 0.001) are independent predictors of unfavorable seizure outcomes. MRI-negative finding of FCD lesions and incomplete resection were the most important predictive factors for poor seizure outcome in patients with FCD type Ⅲ.

Categorizing cortical dysplasia lesions for surgical outcome using network functional connectivity

OBJECTIVE

Focal cortical dysplasia (FCD) is often associated with drug-resistant epilepsy, leading to a recommendation to surgically remove the seizure focus. Predicting outcome for resection of FCD is challenging, requiring a new approach. Lesion-symptom mapping is a powerful and broadly applicable method for linking neurological symptoms or outcomes to damage to particular brain regions. In this work, the authors applied lesion network mapping, an expansion of the traditional approach, to search for the association of lesion network connectivity with surgical outcomes. They hypothesized that connectivity of lesion volumes, preoperatively identified by MRI, would associate with seizure outcomes after surgery in a pediatric cohort with FCD.

METHODS

This retrospective study included 21 patients spanning the ages of 3 months to 17.7 years with FCD lesions who underwent surgery for drug-resistant epilepsy. The mean brain-wide functional connectivity map of each lesion volume was assessed across a database of resting-state functional MRI data from healthy children (spanning approximately 2.9 to 18.9 years old) compiled at the authors' institution. Lesion connectivity maps were averaged across age and sex groupings from the database and matched to each patient. The authors sought to associate voxel-wise differences in these maps with subject-specific surgical outcome (seizure free vs persistent seizures).

RESULTS

Lesion volumes with persistent seizures after surgery tended to have stronger connectivity to attention and motor networks and weaker connectivity to the default mode network compared with lesion volumes with seizure-free surgical outcome.

CONCLUSIONS

Network connectivity-based lesion-outcome mapping may offer new insight for determining the impact of lesion volumes discerned according to both size and specific location. The results of this pilot study could be validated with a larger set of data, with the ultimate goal of allowing examination of lesions in patients with FCD and predicting their surgical outcomes.

Alterations of structural connectivity and structural co-variance network in focal cortical dysplasia

Background

The aim of this study was to investigate alterations in structural connectivity and structural co-variance network in patients with focal cortical dysplasia (FCD).

Methods

We enrolled 37 patients with FCD and 35 healthy controls. All subjects underwent brain MRI with the same scanner and with the same protocol, which included diffusion tensor imaging (DTI) and T1-weighted imaging. We analyzed the structural connectivity based on DTI, and structural co-variance network based on the structural volume with T1-weighted imaging. We created a connectivity matrix and obtained network measures from the matrix using the graph theory. We tested the difference in network measure between patients with FCD and healthy controls.

Results

In the structural connectivity analysis, we found that the local efficiency in patients with FCD was significantly lower than in healthy controls (2.390 vs. 2.578, p = 0.031). Structural co-variance network analysis revealed that the mean clustering coefficient, global efficiency, local efficiency, and transitivity were significantly decreased in patients with FCD compared to those in healthy controls (0.527 vs. 0.635, p = 0.036; 0.545 vs. 0.648, p = 0.026; 2.699 vs. 3.801, p = 0.019; 0.791 vs. 0.954, p = 0.026, respectively).

Conclusions

We demonstrate that there are significant alterations in structural connectivity, based on DTI, and structural co-variance network, based on the structural volume, in patients with FCD compared to healthy controls. These findings suggest that focal lesions with FCD could affect the whole-brain network and that FCD is a network disease.

Intraoperative Ultrasound Shear-Wave Elastography in Focal Cortical Dysplasia Surgery

Previous studies reported interest in intraoperative shear-wave elastography (SWE) guidance for brain-tumor and epilepsy surgeries. Focal cortical dysplasia (FCD) surgery is one of the most appropriate indications for using SWE guidance. The aim of this study was to evaluate the efficacy of ultrasound SWE techniques for the intraoperative detection of FCDs. We retrospectively analyzed data from 18 adult patients with drug-resistant epilepsy associated with FCD who had undergone SWE-guided surgery. Conventional B-mode images detected FCD in 2 patients (11.1%), while SWE detected FCD in 14 patients (77.8%). The stiffness ratios between MRI-positive and -negative cases were significantly different (3.6 ± 0.4 vs. 2.2 ± 0.6, respectively; p < 0.001). FCDs were significantly more frequently detected by interoperative SWE in women (OR 4.7, 95% CI (1.7–12.7); p = 0.004) and in patients in whom FCD was visible on magnetic resonance imaging (MRI; OR 2.3, 95% CI (1.3–4.3); p = 0.04). At 1 year after surgery and at last follow-up (mean = 21 months), seizure outcome was good (International League Against Epilepsy (ILAE) Class 1 or 2) in 72.2% and 55.6% of patients, respectively. Despite some limitations, our study highlighted the potential of SWE as an intraoperative tool to detect FCD. Future technical developments should allow for optimizing intraoperative surgical-cavity evaluation from the perspective of complete FCD resection. Interobserver reliability of SWE measurements should also be assessed by further studies.