Multi-scale structural alterations of the thalamus and basal ganglia in focal epilepsy as demonstrated by 7T MRI

Abstract

Focal epilepsy is characterized by repeated spontaneous seizures that originate from one or multiple epileptogenic zones (EZ). These epileptic activities rapidly propagate to other regions in the brain following a hierarchical organization defined by a decrease in epileptogenicity and the anatomical specificity of subnetworks, also known as EZ networks (EZN). More recently, analysis of intracerebral recordings showed that subcortical structures, and in particular the thalamus, play an important role in facilitating and/or propagating epileptic activity. This supports previously reported structural alterations of these structures. Nonetheless, between-patient differences in EZN (e.g., temporal vs. non-temporal lobe epilepsy) as well as other clinical features (e.g., number of EZs) might impact the magnitude and spatial distribution of subcortical structural changes. Here we used 7 Tesla MRI T1data to provide a comprehensive description of subcortical morphological (volume, tissue deformation, and shape) and longitudinal relaxation (T1) changes in focal epilepsy patients to evaluate the impact of the EZN and patient-specific clinical features. Our results revealed widespread morphometric alterations as well as reduction in T1, with volume acting as the dominant discriminator between patients and controls, while thalamic T1measures looked promising to further differentiate patients based on EZN. In particular, the observed differences in T1changes between thalamic nuclei indicated differential involvement of thalamic nuclei based on EZN. Finally, the number of EZs was found to best explain the observed variability between patients. To conclude, this work revealed multi-scale subcortical alterations in focal epilepsy as well their dependence on several clinical characteristics. Our results provide a basis for further, in-depth investigations using (quantitative) MRI and SEEG data and warrant further personalization of intervention strategies, such as deep brain stimulation, for treating focal epilepsy patients.

Mapping hippocampal and thalamic atrophy in epilepsy: A 7‐T magnetic resonance imaging study

“…Prior work at 3 T has demonstrated structural alterations in the hippocampus and thalamus of patients with epilepsy. 18,[36][37][38][39] Independently, hippocampal [10][11][12][13] and thalamic 20 alterations have also been reported at 7 T. We expand on this literature by leveraging 7-T structural neuroimaging of both the hippocampus and the thalamus. We found that all ipsilateral hippocampal subfields (CA1, CA2, CA3, DG) as well as some ipsilateral (CM, MD) and contralateral (AV, Pul, MD) thalamic nuclei were significantly atrophied in our epilepsy cohort relative to controls.…”

“…Using automated segmentation algorithms, 16,17 volumetric changes between epilepsy patients and controls have been shown across thalamic nuclei 18,19 . Recent work has also leveraged 7‐T magnetic resonance imaging (MRI) to explore thalamic structural changes in epilepsy 20 . Given the thalamus's relevance in deep brain stimulation (DBS) treatment of epilepsy, 21 understanding the patterns of atrophy across thalamic nuclei, as well as their relationship with other epileptogenic structures such as the hippocampus, is crucial for designing implant strategies in DBS and other neuromodulatory devices.…”