Voxel‐based T2 Relaxation Rate Measurements in Temporal Lobe Epilepsy (TLE) with and without Mesial Temporal Sclerosis

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Abstract
Summary:  Introduction: Quantitative measurements of T2 relaxation in the hippocampus for focus lateralization in mesial temporal lobe epilepsy (mTLE) are well established. Less is known to what degree such relaxation abnormalities also affect regions beyond the ipsilateral hippocampus. Therefore, the aim of this study was to characterize extent and distribution pattern of extrahippocampal relaxation abnormalities in TLE with (TLE‐MTS) and without MRI evidence of mesial‐temporal sclerosis (TLE‐no). Methods: Double spin echo images (TE1/2: 20/80 ms) acquired in 24 TLE‐MTS and 18 TLE‐no were used to calculate relaxation rate maps. These maps were analyzed by SPM2 and by selecting regions of interest (ROI) in the hippocampus and several extrahippocampal brain regions. Results: In TLE‐MTS, the results of the SPM and ROI analysis were in good agreement and showed the most severe relaxation rate decreases in the ipsilateral hippocampus but also in other ipsilateral temporal regions, orbitofrontal, and parietal regions and to a lesser degree in contralateral frontal regions. The relaxation rate decreases in TLE‐no were confined to small regions in the ipsilateral anterior inferior and medial temporal lobe in the SPM analysis while ROI analysis showed additional regions in the ipsilateral hippocampus, amygdala, and anterior cingulate. Conclusion: TLE‐MTS showed extensive, widespread but predominantly ipsilateral temporal and also extratemporal T2 relaxation rate decreases. In contrast, the findings of the SPM and ROI analyses in TLE‐no suggested that if relaxation rate decreases are present, they are less uniform and generally milder than in TLE‐MTS. This further supports the hypothesis that TLE‐no is a distinct clinicopathological entity from TLE‐MTS and probably heterogeneous in itself.