Preferential involvement of thalamic nuclei in hippocampal sclerosis: A combined structural and diffusion tensor MRI analysis

초록

Purpose: The thalamus has been implicated in seizurepropagation in temporal lobe epilepsy and neuroimagingstudies have shown thalamic abnormality in patients withmesial temporal lobe epilepsy with hippocampal sclerosis(HS- MTLE). We investigated both macrostructural andmicrostructural changes of the thalamus in unilateral HS-MTLE patients by employing structural and diffusion ten-sor MRI analyses.Method: Structural and diffusion tensor MRIs were ob-tained from 47 patients with unilateral HS-MTLE (24 left,23 right) and 41 matched control subjects using a 3T MRscanner. Automated volumetry and shape analysis wereused to assess volumetric and shape changes of the thala-mus, respectively. Fractional anisotropy (FA) and meandiffusivity (MD) were analysed to evaluate microstruc-tural integrity changes within the thalamus. Structuralconnectivity between the sclerotic hippocampus and thal-amus was investigated using probabilistic tractography.Results: Compared to controls, both HS-MTLE patientsexhibited a significant volume reduction and regionalatrophy mainly localized to the medial and posterior as-pects of the ipsilateral thalamus. Compared to controls,both HS-MTLE patients showed significant FA decreasesand MD increases in ipsilateral hippocampus and ad-jacent temporal white matter, and medial and posteriorparts of the ipsilateral thalamus. Probabilistic tractogra-phy revealed a significant increase in structural connec-tivity between the sclerotic hippocampus and medial partof the ipsilateral thalamus in both HS-MTLE patients ascompared with controls.Conclusion: We have identified concomitant macrostruc-tural and microstructural abnormalities of medial andposterior parts of the ipsilateral thalamus in patients withunilateral HS-MTLE. In addition, we observed a paradoxi-cal overconnectivity between the sclerotic hippocampusand ipsilateral medial thalamus, suggesting that seizure-induced neuronal loss and axonal damage lead to the ab-errant connection between the pathologic hippocampusand thalamus. Our results provide converging evidencefor the involvement of mediodorsal and pulvinar thalamicnuclei in the epileptic network in HS-MTLE.