Frontal lobe epilepsy and MOGHE: Further observations on electroclinical & imaging phenotypes and surgical perspectives

OBJECTIVE

Mild Malformation with Oligodendroglial Hyperplasia (MOGHE) is a recently described clinicopathologic entity, associated with drug-resistant epilepsy and extensive epileptogenic networks. Knowledge is accumulating about particular electroclinical phenotypes, correlations with imaging and potential prognostic significance for surgical outcome. The study adds relevant information by documenting the presence of a Hyperkinetic Frontal Lobe seizure phenotype in adolescents and an Epileptic Encephalopathy phenotype in young children.

METHODS

Five cases subjected to a structured presurgical evaluation protocol, including EEG-FMRI, chronic and acute invasive EEG, subjected to frontal lobe surgery with post-operative follow-up between 15 months and 7 years.

RESULTS

In the two adult cases, surface EEG demonstrated lateralized widespread Frontal Lobe epileptogenicity and hyperkinetic semiological features. MRI demonstrated cortical-white mater blurring and deeper white matter abnormalities. EEG-FMRI suggested concordant Frontal Lobe involvement. iEEG demonstrated a widespread frontal lobe epilepsy network. The three young children demonstrated a diffuse epileptic encephalopathy phenotype, with non-localizing, non-lateralizing surface EEG and "spasms" as the main seizure type. MRI demonstrated extensive frontal lobe subcortical gray and white matter abnormalities, consistent with MOGHE literature for this age, while EEG-FMRI, in 2/3, demonstrated concordant Frontal Lobe involvement. They did not undergo chronic iEEG and the resection was assisted by acute intraoperative ECoG. All cases were subjected to extensive frontal lobectomies with Engel class IA (2/5), IB (1/5) and IIB (2/5) outcomes.

SIGNIFICANCE

The study confirms the presence of Frontal Lobe Epilepsyand Epileptic Encephalopathy Phenotypes, in accordance to epilepsy phenotypes already described in MOGHE literature. Presurgical Evaluation Studies, including EEG-FMRI, can provide strong lateralizing and localizing evidence of the Epileptogenic Networks involved. All responded favorably to extensive Frontal Lobe Resections, despite widespread epileptic activity recorder by surface and intracranial EEG pre- and prostoperatively; an Epileptic Encephalopathy Phenotype, in the first years of life, should not discourage such a resection.

Validation of automatic MRI hippocampal subfield segmentation by histopathological evaluation in patients with temporal lobe epilepsy

OBJECTIVE

The present study validates the results of automated hippocampal subfield segmentation with histopathology in epilepsy patients undergoing epilepsy surgery.

METHODS

We performed an automated hippocampal subfield segmentation on presurgical three-dimensional, T1-weighted magnetization Prepared Rapid Acquisition of Gradient Echoes Magnetic Resonance Imaging (MRI) data of 25 patients with unilateral mesial temporal lobe epilepsy due to hippocampal sclerosis (HS), using Freesurfer Version 6.0. The resulting volumes of cornu ammonis (CA) subfields CA1, CA2/3, CA4 and the dentate gyrus (DG) were compared to the histopathological cell count.

RESULTS

We found a significant correlation between histopathology in subregion CA2 and automated segmentation of subregion CA1 (p = 0.0062), CA2/3 (p = 0.004), CA4 (p = 0.0062) and the DG (p = 0.0054), between histopathology in CA3 and automated segmentation of CA1 (p = 0.0132), CA2/3 (p = 0.0004), CA4 (p = 0.0032) and the DG (p = 0.0037), as well as between histopathology in the DG and automated segmentation of CA1 (p = 0.0115), CA2/3 (p < 0.0001), CA4 (p < 0.0001) and the DG (p = 0.0001). The histopathological finding of HS type 1 could correctly be classified in all cases on MRI.

SIGNIFICANCE

The present study shows significant correlations between histopathological evaluation and results of the automated segmentation of the hippocampus, thereby validating the automated segmentation method. As the differential involvement of different hippocampal subfields may be associated with clinical parameters and the outcome after epilepsy surgery, the automated segmentation is also promising for prognostic purposes.

Electro-clinical-pathological correlations in focal cortical dysplasia (FCD) at young ages

The prevalence of focal cortical dysplasia (FCD) in pediatric patients with focal epilepsy is not exactly known because authors of publications in which the etiologies of epilepsies are listed, but which are not dealing specifically with epilepsy surgery issues, tend to lump together the many kinds of malformations of cortical development (MCD), of which FCDs, because of their relative frequency, are the most relevant subtypes. Out of 561 patients with MCD (children and adults) operated at centers in Europe who do feed data into the "European Epilepsy Brain Bank," 426 (76 %) had FCD.

Frameless stereotactic functional neuronavigation combined with intraoperative magnetic resonance imaging as a strategy in highly eloquent located tumors causing epilepsy

BACKGROUND

Intractable epilepsy due to tumors located in highly eloquent brain regions is often considered surgically inaccessible because of a high risk of postoperative neurological deterioration. Intraoperative MRI and functional navigation contribute to overcome this problem.

OBJECTIVES

To retrospectively investigate the long-term results and impact of functional neuronavigation and 1.5-tesla intraoperative MRI on patients who underwent surgery of tumors associated with epilepsy located close to or within eloquent brain areas.

METHODS

Nineteen patients (9 female, 10 male, mean age 41.4 ± 13.4 years, 11 low-grade and 8 high-grade glial tumors) were evaluated preoperatively using BOLD imaging, diffusion-tensor imaging tractography and magnetoencephalography. Functional data were implemented into neuronavigation in this multimodal approach.

RESULTS

In 14 of 19 patients (74%), complete resection was achieved, and in 5 patients significant tumor volume reduction was accomplished. Eight of 14 (57%) complete resections were achieved only by performing an intraoperative image update. Neurological deterioration was found permanently in 2 patients. After a mean follow-up of 43.8 ± 23.8 months, 15 patients (79%) became seizure free (Engel class Ia).

CONCLUSIONS

Despite the highly eloquent location of tumors causing intractable epilepsy, our multimodal approach led to complete resection in more than two-thirds of patients with an acceptable neurological morbidity and excellent long-term seizure control.

Mesenchymal stem cells promote oligodendroglial differentiation in hippocampal slice cultures

We have previously shown that soluble factors derived from mesenchymal stem cells (MSCs) induce oligodendrogenic fate and differentiation in adult rat neural progenitors (NPCs) in vitro. Here, we investigated if this pro-oligodendrogenic effect is maintained after cells have been transplanted onto rat hippocampal slice cultures, a CNS-organotypic environment. We first tested whether NPCs, that were pre-differentiated in vitro by MSC-derived conditioned medium, would generate oligodendrocytes after transplantation. This approach resulted in the loss of grafted NPCs, suggesting that oligodendroglial pre-differentiated cells could not integrate in the tissue and therefore did not survive grafting. However, when NPCs together with MSCs were transplanted in situ into hippocampal slice cultures, the grafted NPCs survived and the majority of them differentiated into oligodendrocytes. In contrast to the prevalent oligodendroglial differentiation in case of the NPC/MSC co-transplantation, naïve NPCs transplanted in the absence of MSCs differentiated predominantly into astrocytes. In summary, the pro-oligodendrogenic activity of MSCs was maintained only after co-transplantation into hippocampal slice cultures. Therefore, in the otherwise astrogenic milieu, MSCs established an oligodendrogenic niche for transplanted NPCs, and thus, co-transplantation of MSCs with NPCs might provide an attractive approach to re-myelinate the various regions of the diseased CNS.

Early diffusion-weighted MRI predicts regional neuronal damage in generalized status epilepticus in rats treated with diazepam

We applied diffusion-weighted MRI (DWI) in the pilocarpine-induced status epilepticus (SE) model to investigate the evolution of acute phase changes in brain diffusion with and without early anticonvulsive therapy correlated to long-term SE-induced neuronal cell loss. Hereby, DWI was performed before (baseline) and serially between 3 and 120 min after onset of SE in untreated and treated animals (n=15 in each group). Anticonvulsive-treated animals received 20 mg/kg diazepam at 15 min after onset of SE. Apparent diffusion coefficients (ADC) were calculated for the parietal, temporal and piriform cortex, thalamus, hippocampus and amygdala and compared to baseline. Neuronal cell loss was quantified at 2 weeks after onset of SE utilizing cresyle-violet-staining. The results of ADC-mapping demonstrated a significant transient increase in ADC (to 116+/-4% of baseline) in the very acute phase starting 3 min after SE onset, lasting for 10 min in both groups. In untreated animals, there was a significant gradual decline in ADC to 75+/-12% of baseline while this decline in diazepam-treated animals was significantly less pronounced (P<0.05) and ADC recovered to 93+/-6% of baseline. There was good correlation between neuronal cell loss in specific brain regions at 2 weeks after SE and maximal decrease in ADC (r>0.79). In conclusion, serial DWI is a sensitive noninvasive technique for early detection, monitoring and prediction of SE-induced neuronal alterations. Using ADC-mapping, verification of early anticonvulsive therapy in SE seems to be possible as there is good correlation between the maximal decrease in ACD in the acute phase of SE and late neuronal cell loss.

Evolution of MRI changes and development of bilateral hippocampal sclerosis during long lasting generalised status epilepticus

This report describes a previously healthy 28 year old patient with a 5 month period of intractable generalised status epilepticus (SE) of unknown aetiology with fatal outcome. Repeated magnetic resonance imaging (MRI) showed no pre-existing abnormality, but did show progressive cortical and hippocampal atrophy and T2 hyperintensity in both hippocampal formations, suggestive of progressive tissue damage. Post-mortem histopathological analysis revealed substantial neuronal cell loss including CA1 and CA4 sectors of the hippocampus compatible with bilateral hippocampal sclerosis. There was no evidence of systemic complications including arterial hypotension and hypoxia, hypoglycaemia, hyperpyrexia, or other confounding factors to account for these findings. This case provides further evidence of SE induced hippocampal damage in humans.