Journal Article

Structural connectivity differences in left and right temporal lobe epilepsy

Besson, Pierre, Valabregue, Romain, Colliot, Olivier, Baulac, Michel, Samson, Séverine, Dupont, Sophie, Dinkelacker, Vera, Leclerc, Xavier, Thivard, Lionel, Sammler, Daniela, Lehéricy, Stéphane

2014

Overview

Our knowledge on temporal lobe epilepsy (TLE) with hippocampal sclerosis has evolved towards the view that this syndrome affects widespread brain networks. Diffusion weighted imaging studies have shown alterations of large white matter tracts, most notably in left temporal lobe epilepsy, but the degree of altered connections between cortical and subcortical structures remains to be clarified. We performed a whole brain connectome analysis in 39 patients with refractory temporal lobe epilepsy and unilateral hippocampal sclerosis (20 right and 19 left) and 28 healthy subjects. We performed whole-brain probabilistic fiber tracking using MRtrix and segmented 164 cortical and subcortical structures with Freesurfer. Individual structural connectivity graphs based on these 164 nodes were computed by mapping the mean fractional anisotropy (FA) onto each tract. Connectomes were then compared using two complementary methods: permutation tests for pair-wise connections and Network Based Statistics to probe for differences in large network components. Comparison of pair-wise connections revealed a marked reduction of connectivity between left TLE patients and controls, which was strongly lateralized to the ipsilateral temporal lobe. Specifically, infero-lateral cortex and temporal pole were strongly affected, and so was the perisylvian cortex. In contrast, for right TLE, focal connectivity loss was much less pronounced and restricted to bilateral limbic structures and right temporal cortex. Analysis of large network components revealed furthermore that both left and right hippocampal sclerosis affected diffuse global and interhemispheric connectivity. Thus, left temporal lobe epilepsy was associated with a much more pronounced pattern of reduced FA, that included major landmarks of perisylvian language circuitry. These distinct patterns of connectivity associated with unilateral hippocampal sclerosis show how a focal pathology influences global network architecture, and how left or right-sided lesions may have differential and specific impacts on cerebral connectivity. •We computed the structural network of 39 temporal lobe epilepsy (TLE) patients.•Two strategies, pairwise connection analysis and network based statistics, were used.•Widespread disconnections were found in TLE patients with respect to controls.•Left TLE patients were much more affected than right TLE patients.•Left TLE showed a strongly lateralized fronto-temporal disconnection pattern.

• Publisher: Elsevier Inc,Elsevier Limited,Elsevier
• Subject: Adult / Brain / Connectivity / Connectome / Connectome - methods / Engineering Sciences / Epilepsy / Epilepsy, Temporal Lobe - etiology / Epilepsy, Temporal Lobe - physiopathology / Female / Functional Laterality - physiology / Hippocampal sclerosis / Hippocampus - pathology / Humans / Magnetic Resonance Imaging / Male / Medical imaging / Middle Aged / Nerve Net - physiopathology / Network based statistics / Sclerosis - complications / Sclerosis - pathology / Signal and Image processing / Studies / Surgery / Temporal lobe epilepsy