Diffusional kurtosis imaging reveals a distinctive pattern of microstructural alternations in idiopathic generalized epilepsy

Abstract

Objectives: Idiopathic generalized epilepsy (IGE) arises from paroxysmal dysfunctions of the thalamo-cortical network. One of the hallmarks of IGE is the absence of visible abnormalities on routine magnetic resonance imaging (MRI). However, recent quantitative MRI studies showed cortical-subcortical structural abnormalities in IGE, but the extent of abnormalities has been inconsistent in the literature. The inconsistencies may be associated with complex microstructural abnormalities in IGE that are not completely detectable using conventional diffusion tensor imaging methods. The goal of this study was to investigate white-matter (WM) microstructural abnormalities in patients with IGE using diffusional kurtosis imaging (DKI).

Materials and methods: We obtained DKI and volumetric T1-weighted images from 14 patients with IGE and 25 matched healthy controls. Using tract-based spatial statistics, we performed voxel-wise group comparisons in the parametric maps generated from DKI: mean diffusivity (MD), fractional anisotropy (FA), and mean kurtosis (MK), and in probabilistic maps of WM volume generated by voxel-based morphometry.

Results: We observed that conventional microstructural measures (MD and FA) revealed WM abnormalities in thalamo-cortical projections, whereas MK disclosed a broader pattern of WM abnormalities involving thalamo-cortical and cortical-cortical projections.

Conclusions: Even though IGE is traditionally considered a 'non-lesional' form of epilepsy, our results demonstrated pervasive thalamo-cortical WM microstructural abnormalities. Particularly, WM abnormalities shown by MK further extended into cortical-cortical projections. This suggests that the extent of microstructural abnormalities in thalamo-cortical projections in IGE may be better assessed through the diffusion metrics provided by DKI.

Keywords: diffusion tensor imaging; diffusional kurtosis imaging; idiopathic generalized epilepsy; magnetic resonance imaging; tract-based spatial statistics; voxel-based morphometry.