Disrupted anatomic white matter network in left mesial temporal lobe epilepsy

Abstract

her PhD at the University of Alberta studying white matter pathology in epilepsy. SUMMARYObjective: Brain imaging studies have shown widespread structural abnormalities in patients with temporal lobe epilepsy (TLE) within and beyond the affected temporal lobe, suggesting an altered network. Graph theoretical analysis based on white matter tractography has provided a new perspective to evaluate the connectivity of the brain. The alterations in the topologic properties of a whole brain white matter network in patients with TLE remain unknown. The purpose of this study was to examine the white matter network in a cohort of patients with left TLE and mesial temporal sclerosis (mTLE) compared to healthy controls. Methods: Anatomic brain networks of 16 patients with left mTLE were compared to those of 21 healthy controls. A white matter structural network was constructed from diffusion tensor tractography for each participant, and network parameters were compared between the patient and control groups. Results: Patients with left mTLE exhibited concurrent decreases of global and local efficiencies and widespread reduction of regional efficiency in ipsilateral temporal, bilateral frontal, and bilateral parietal areas. Communication hubs, such as the left precuneus, were also altered in patients with mTLE compared to controls. Significance: Our results demonstrate white matter network disruption in patients with left mTLE, supporting the notion that mTLE is a systemic brain disorder. KEY WORDS: Diffusion tensor imaging, Graph theory, Temporal lobe epilepsy, Network, Tractography, Diffusion tensor imaging.Temporal lobe epilepsy (TLE) is the most common focal epilepsy syndrome. Most TLE cases are associated with mesial temporal sclerosis (MTS), where hippocampal atrophy and/or T2 hyperintensity is observed on magnetic resonance imaging (MRI). Recently, quantitative MRI studies have provided new structural information in TLE by demonstrating extensive abnormalities within and beyond the temporal lobe, including reduced gray matter concentration/atrophy, 1 decreased cortical thickness, 2 and abnormal white matter in the temporal, frontal, and parietal lobes. The language and memory impairments seen in patients with TLE have also been related to altered blood oxygen level-dependent (BOLD) activation during memory and language tasks compared to healthy controls in functional MRI (fMRI) studies. 4 The growing knowledge of the brain structural and functional changes related to TLE has led to the notion that TLE is a network disorder that affects large neural networks involved in normal brain function.5 With the implementation of graph theoretical analysis on brain functional and structural measurements, features of the brain as an integrated system can be quantified to infer its capacity of information integration and segregation. 6 Graph theoretical analysis enables the abstraction and examination of the brain topologic architecture and properties at the network level, which provides a macroscopic perspective rather than the p...

Disrupted Brain Functional Organization in Epilepsy Revealed by Graph Theory Analysis

“…Previous studies have examined brain efficiency in both functional networks (Vlooswijk et al, 2011;Wang et al, 2014;Zhang et al, 2011) and structural networks in epilepsy (Bernhardt et al, 2011;Liu et al, 2014). However, these findings have remained conflicting potentially due to various factors such as different data processing approach and heterogeneous study population.…”

Disrupted Global and Regional Structural Networks and Subnetworks in Children with Localization-Related Epilepsy

“…In a subsequent study, 10 the same authors did not find an association between the clustering coefficient and path length measures of structural or functional connectivity with a computerized visual searching task in children with FLE. Liu et al 30 did not find any association among characteristic path length, global efficiency, and local efficiency with neurocognitive function including IQ, auditory verbal learning, and visual memory, as well as with age at seizure onset and duration of epilepsy in adults with left mesial TLE. We did not find any associations between graph network measures and IQ scores.…”

“…Differences in findings could be related to different populations of FLE, with our patient population having a wider age range and possibly more severe epilepsy relative to the patients in the study by Vaessen et al 10 Disruption in the global structural network has also been identified in childhood absence epilepsy 28 and adults with TLE. 29,30 Patients with localization-related epilepsy showed reduced regional efficiency affecting multiple regions in the frontal, temporal, and occipital lobes. Liu et al 30 also found that adult patients with left mesial TLE have significantly reduced regional efficiency in multiple regions in the temporal, frontal, and parietal lobes.…”

“…29,30 Patients with localization-related epilepsy showed reduced regional efficiency affecting multiple regions in the frontal, temporal, and occipital lobes. Liu et al 30 also found that adult patients with left mesial TLE have significantly reduced regional efficiency in multiple regions in the temporal, frontal, and parietal lobes. We have found more regions of reduced nodal efficiency in the FLE than in the TLE subgroup, which may be due to the rapid spread of seizure activity as a result of the extensive network of connections of the frontal lobe and more frequent seizures in FLE [31][32][33] or, alternatively, an inherently more extensive abnormal regional efficiency from an underlying etiology that predispose to FLE.…”

“…Adult patients with TLE have also shown reduced structural connectivity between the temporal and frontal cortices, including the orbitofrontal cortex. 29,30 The WM tracts connecting the frontal lobe to the temporal and occipital lobes have demonstrated smaller volumes in children with FLE compared with controls, 34 indicating impaired structural connections between the frontal and temporal and occipital lobes. Vaessen et al 4 found that the clustering coefficient was significantly positively correlated with IQ, and path length was negatively correlated with IQ in adults with cryptogenic localizationrelated epilepsy.…”