Abstracts

Rationale: The thalamus has been implicated in seizure propagation in temporal lobe epilepsy and a number of neuroimaging studies have repeatedly confirmed thalamic abnormality in patients with mesial temporal lobe epilepsy with hippocampal sclerosis (HS-MTLE). However, involvement of specific thalamic nuclei in HS-MTLE remains to be determined. We therefore investigated both macrostructural and microstructural alterations within the thalamus in patients with unilateral HS-MTLE by using multimodal MRIs that took into account morphometric, integrity, and connectivity characteristics.Methods: Structural and diffusion tensor MRIs were acquired from 47 patients with unilateral HS-MTLE (24 left, 23 right) and 41 matched control subjects using a 3T MR scanner. Automated volumetry and shape analysis were used to assess volumetric change and shape deformation of the thalamus, respectively. Fractional anisotropy (FA) and mean diffusivity (MD) were analyzed in a whole-brain manner to evaluate microstructural integrity changes within the thalamus. Structural connectivity between the sclerotic hippocampus and thalamus was investigated using probabilistic tractography of diffusion tensor MRI. All statistical analyses were fully corrected for multiple comparisons by using either Bonferroni correction or familywise-error correction.Results: Compared to controls, both HS-MTLE patients exhibited a significant volume reduction and regional shape deformation (inward movement of vertices) mainly localized to the medial and posterior aspects of ipsilateral thalamus (corrected P < 0.05). Compared to controls, both HS-MTLE patients showed significant FA decreases and MD increases in ipsilateral hippocampus and adjacent temporal white matter, and medial and posterior parts of the ipsilateral thalamus (corrected P < 0.05). Probabilistic tractography revealed a significant increase in structural connectivity between the sclerotic hippocampus and medial part of the ipsilateral thalamus in both HS-MTLE patients as compared with controls (corrected P < 0.05).Conclusions: We have identified concomitant macrostructural and microstructural abnormalities of medial and posterior parts of the ipsilateral thalamus in patients with unilateral HS-MTLE. In addition, we have observed a paradoxical overconnectivity between the sclerotic hippocampus and ipsilateral medial thalamus, which may suggest that seizure-induced neuronal loss and axonal damage could lead to the development of aberrant connections between the pathologic hippocampus and thalamus. These convergent data provide evidence for the involvement of mediodorsal and pulvinar thalamic nuclei in the epileptic network in HS-MTLE.