Gray, white matter concentration changes and their correlation with heterotopic neurons in temporal lobe epilepsy

Pattern of abnormalities on gray matter in patients with medial temporal lobe epilepsy and hippocampal sclerosis: An updated meta-analysis

Temporal lobe epilepsy (TLE) is a prevalent form of epilepsy originating in the temporal lobes. A common pathological feature is hippocampal sclerosis (HS), characterized by the loss of neuronal cells, which is associated with the typical temporal mesial lobe epilepsy (MTLE). In this study, we aimed to analyze gray matter alterations in patients with MTLE with right and left hemisphere HS using voxel-based morphometry and compare them with control groups. A meta-analysis was performed based on the guidelines contained in the Protocol Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA), using the MEDLINE database, with the keywords: "gray matter" AND "temporal lobe epilepsy " AND ("hippocampal sclerosis" OR "hippocampal abnormalities") AND ("voxel-based morphometry" OR "VBM" OR "voxel-wise"). Of the 14 articles included in the review, 8 were added by the method, in which the meta-analysis was performed. Our results indicate that in the right hemisphere, the hippocampus, caudate nucleus, parahippocampal gyrus, thalamus, dorsalis medial nucleus, insula, and right claustrum were most commonly implicated. In the left hemisphere, a significant pattern of gray matter loss was observed in the putamen, lentiform nucleus, uncus, Brodmann areas 20 and 23, cingulate gyrus, caudate nucleus, cerebellum, and cuneus compared to healthy controls.Our study highlights distinct patterns of gray matter alteration in MLTE-HS and suggests that these regions may contribute to changes in verbal memory and visuospatial impairment based on their anatomical and hemispheric locations. Our findings can be potentially helpful for future diagnostic markers, therapeutic targets, and insights into disease progression, better understanding of these findings.

Interhemispheric asymmetrical change in gray matter volume in patients with unilateral hippocampal sclerosis

Objectives

To clarify the interhemispheric asymmetrical change in gray matter volume (GMV) in unilateral hippocampal sclerosis (HS), we compared changes in GMV relative to normal subjects between the HS and contralateral or non-HS sides.

Material and Methods

Forty-five patients with unilateral HS and 30 healthy subjects were enrolled. We quantified changes in GMV in the patients with HS as compared to GMV in the normal subjects by introducing the Z-score (Z-GMV) in each region or region of interest in unilateral HS. Then, we assessed the asymmetrically decreased regions, that is, regions with significantly higher Z-GMV on the HS side than the contralateral or non-HS side. Z-GMV was calculated according to the two templates of 58 regions per hemisphere covering the whole brain by anatomical automatic labeling (AAL) and 78 regions per cerebral hemisphere using the Anatomy Toolbox.

Results

Seven and four regions in AAL and 17 and 11 regions in Anatomy Toolbox were asymmetrically decreased in the Left Hand Side (LHS) and Right Hand Side (RHS), respectively. Hippocampus and Caudate in AAL, five subregions of the hippocampus (CA1-3, Dentate Gyrus and hippocampus-amygdala-transition-area and 4 extrahippocampal regions including two subregions in amygdala (CM: Centromedial, SF: Superficial), basal forebrain (BF) (Ch4), and thalamus (temporal) in anatomy toolbox were common among LHS and RHS concerning asymmetrically decreased regions.

Conclusion

By introducing Z-GMV, we demonstrated the regions with asymmetrically decreased GMV in LHS and RHS, and found that the hippocampus and extrahippocampal regions, including the BF, were the common asymmetrically decreased regions among LHS and RHS.

Characterization of Hippocampal-Thalamic-Cortical Morphometric Reorganization in Temporal Lobe Epilepsy

Introduction

Brain cortico-subcortical connectivity has been investigated in epilepsy using the functional MRI (MRI). Although structural images cannot demonstrate dynamic changes, they provide higher spatial resolution, which allows exploration of the organization of brain in greater detail.

Methods

We used high-resolution brain MRI to study the hippocampal-thalamic-cortical networks in temporal lobe epilepsy (TLE) using a volume-based morphometric method. We enrolled 22 right-TLE, 33 left-TLE, and 28 age/gender-matched controls retrospectively. FreeSurfer software was used for the thalamus segmentation.

Results

Among the 50 subfields, ipsilateral anterior, lateral, and parts of the intralaminar and medial nuclei, as well as the contralateral parts of lateral nuclei had significant volume loss in both TLE. The anteroventral nucleus was most vulnerable. Most thalamic subfields were susceptible to seizure burden, especially the left-TLE. SPM12 was used to conduct an analysis of the gray matter density (GMD) maps. Decreased extratemporal GMD occurred bilaterally. Both TLE demonstrated significant GMD loss over the ipsilateral inferior frontal gyrus, precentral gyrus, and medial orbital cortices.

Significance

Thalamic subfield atrophy was related to the ipsilateral inferior frontal GMD changes, which presented positively in left-TLE and negatively in right-TLE. These findings suggest prefrontal-thalamo-hippocampal network disruption in TLE.

Thalamic medial dorsal nucleus atrophy in medial temporal lobe epilepsy: A VBM meta-analysis

Purpose

Medial temporal lobe epilepsy (MTLE) is associated with MTLE network pathology within and beyond the hippocampus. The purpose of this meta-analysis was to identify consistent MTLE structural change to guide subsequent targeted analyses of these areas.

Methods

We performed an anatomic likelihood estimation (ALE) meta-analysis of 22 whole-brain voxel-based morphometry experiments from 11 published studies. We grouped these experiments in three ways. We then constructed a meta-analytic connectivity model (MACM) for regions of consistent MTLE structural change as reported by the ALE analysis.

Key findings

ALE reported spatially consistent structural change across VBM studies only in the epileptogenic hippocampus and the bilateral thalamus; within the thalamus, the medial dorsal nucleus of the thalamus (MDN thalamus) represented the greatest convergence (P < 0.05 corrected for multiple comparisons). The subsequent MACM for the hippocampus and ipsilateral MDN thalamus demonstrated that the hippocampus and ipsilateral MDN thalamus functionally co-activate and are nodes within the same network, suggesting that MDN thalamic damage could result from MTLE network excitotoxicity.

Significance

Notwithstanding our large sample of studies, these findings are more restrictive than previous reports and demonstrate the utility of our inclusion filters and of recently modified meta-analytic methods in approximating clinical relevance. Thalamic pathology is commonly observed in animal and human studies, suggesting it could be a clinically useful indicator. Thalamus-specific research as a clinical marker awaits further investigation.