Abstracts

Rationale: Reduced ¹⁸FDG-PET in the hippocampus of mesial temporal sclerosis (MTS) was commonly seen in medial temporal lobe epilepsy (MTLE). The glucose metabolisms of the hippocampal subfields have not been well investigated.

Methods: Eighteen patients (4 male and 14 female, age at 15-58 years) who had epilepsy surgery for drug-resistant epilepsy (DRE) and pathology diagnosis of MTS were included. Both high resolution 3T MRI and ¹⁸FDG-PET were obtained before surgery. Automated segmentation of the hippocampal subfields was carried out by FreeSurfer 7.1.1. ¹⁸FDG-PET image was coregistered to the parcellated MRI. Hippocampal subfields were extracted for metabolic analysis. The regions of interest included CA1, CA3, CA4, granule cell and molecular layer of the dentate gyrus (GC-ML-DG), and subiculum. The registered ¹⁸FDG-PET images were corrected for partial effects. The standardized uptake value (SUV) of the ¹⁸FDG-PET images were normalized to the mean value for the whole gray matter. Asymmetry index was defined by ipsilateral-to-contralateral SUV ratios. Wilcoxon signed rank tests were used to compare the SUV between ipsilateral and contralateral side SUV and the asymmetry index of subfields in individuals. Clinical data were also obtained for partial correlation analysis. The false discovery rate was applied to select the significant differences with p values of less than 0.05.

Results: The CA1, CA3, CA4, subiculum, GC-ML-DG, and whole hippocampus showed significantly reduced hypometabolism on the ipsilateral side of MTLE (p < 0.001 for the subfields and whole hippocampus). Younger age of onset was significantly associated with ipsilateral lower SUV for CA1, CA3, CA4, GC-ML-DG, and whole hippocampus. The degree of reduced hypometabolism varies among the subfields. The asymmetry index of SUV was lower in the CA3, CA4 and GC-ML-DG compared to CA1 and subiculum (Table1).