Volumetric and functional connectivity alterations of the thalamus and thalamic nuclei groups in drug-resistant focal epilepsy: A 7T MRI study

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PURPOSE: Through its global and extensive connections with multiple brain structures, the thalamus can play an important role in seizure propagation. This study investigated volumetric and functional connectivity alterations of the thalamus and more specifically the thalamic nuclei subgroups using 7T MRI in patients with MRI-negative drug-resistant focal epilepsy (DRE). METHODS: Twenty-nine patients with MRI-negative DRE and 49 healthy controls underwent 7T MRI, including T1-weighted and resting-state functional MRI sequences. Thalamic nuclei segmentations were derived using automated segmentation tools and split into anterior (ANT), medial, ventral, and posterior nuclei groups. Functional connectivity with the rest of the brain was assessed using degree centrality (DC). Linear regression models evaluated group differences and relationships with epilepsy characteristics while controlling for age and sex. Asymmetry indices assessed the ipsi- vs. contralateral differences in the patient cohort. RESULTS: Patients showed decreased bilateral medial and increased bilateral ventral relative volumes, alongside a right-sided ANT volume increase, compared with controls. DC was increased in the left posterior and ventral nuclei. Both volume and DC in the medial, ventral, and whole-thalamic ROIs were related to epilepsy duration, while ventral and whole-thalamic DC asymmetry distinguished patients by seizure type and seizure duration. CONCLUSIONS: Both structural and functional alterations of the thalamic nuclei groups in patients with DRE were observed. Ventral, medial, and posterior nuclei metrics show promise as imaging biomarkers of disease burden and seizure severity, thus encouraging further research into both structural and functional properties of thalamic nuclei in focal epilepsy.

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