Spatial patterns of water diffusion along white matter tracts in temporal lobe epilepsy

Abstract

Objectives: Diffusion tensor imaging (DTI) tractography has shown tract-specific pathology in temporal lobe epilepsy (TLE). This technique normally yields a single value per diffusion parameter per tract, potentially reducing the sensitivity for the detection of focal changes. Our goal was to spatially characterize diffusion abnormalities of fasciculi carrying temporal lobe connections. Methods:We studied 30 patients with drug-resistant TLE and 21 healthy control subjects.Twenty-four patients underwent DTI toward the end of video-EEG telemetry, with an average of 50 Ϯ 54 hours between the last seizure and DTI examination. After manual dissection of the uncinate and inferior longitudinal and arcuate bundle, they were spatially matched based on their distance to the temporal lobe, providing between-subject correspondence of tract segments. We evaluated point-wise differences in diffusion parameters along each tract at group and subject levels.Results: Our approach localized increased mean diffusivity restricted to or more prominent within the ipsilateral temporal lobe. These abnormalities tapered off as tracts exited the temporal lobe. We observed that the shorter the interval between the last seizure and DTI, the higher the mean diffusivity (MD) of the ipsilateral tracts. Linear discriminant analysis of tract segments correctly lateralized 87% of patients. Conclusions:The centrifugal pattern of white matter diffusion abnormalities probably reflects astrogliosis and microstructure derangement related to seizure activity in the vicinity of the focus. The negative correlation between the interval from last seizure and MD suggests a role for postictal vasogenic edema. The ability to assess tracts segmentally may contribute to a better understanding of the extent of white matter pathology in epilepsy and assist in the presurgical evaluation of patients with TLE, particularly those with unremarkable conventional imaging results. Neurology ® 2012;79:455-462 GLOSSARY DTI ϭ diffusion tensor imaging; FA ϭ fractional anisotropy; FWHM ϭ full-width at half-maximum; MD ϭ mean diffusivity; TE ϭ echo time; TLE ϭ temporal lobe epilepsy; TR ϭ repetition time; WM ϭ white matter.

Epilepsy-related cytoarchitectonic abnormalities along white matter pathways

“…This study also extends the work of Concha et al ,38 where along-the-tract measures were assessed in the ILF, AF and UF using a manual segmentation routine with DTI in subjects with medically intractable TLE. In that work, it was argued that the changes in diffusion metrics could reflect astrogliosis and microstructural alterations related to the occurrence of seizures with potential effects of postictal vasogenic oedema.…”

The brain connectome as a personalized biomarker of seizure outcomes after temporal lobectomy

“…The main purpose of this study was to define a method to scrutinize and abridge the individual connectome in order to derive a personalized score of network abnormalities to be used toward outcome prediction. In this context, this goal and methodology is different from regional abnormalities demonstrated from previous groupwise studies from our group and others, indicating groupwise white matter loss, 23,24 connectivity abnormalities, [25][26][27][28][29][30] and neural network rearrangement in patients with TLE. 20,31,32 We assessed the area under the curve (AUC) for the receiver operating characteristic (ROC) curve for each possible connectome link (including only connections from the temporal to extratemporal regions, as described in e-Methods).…”

Multimodal investigation of epileptic networks

“…White matter insults in TLE are mostly ipsilateral to the SOZ and tracts closely connected to the affected temporal lobe are the most disturbed. Furthermore, fiber tracts remote from the temporal lobe are also affected, which supports the view of epilepsy as a brain network disease (Concha et al, 2012;Gross, 2011;Otte et al, 2012;Rodríguez-Cruces and Concha, 2015). To follow-up on our study on healthy controls, we performed tractography on patients with ICE.…”