Volumetric analysis of hippocampal subregions in migraine without aura: an exploratory study on mechanisms underlying migraine chronification.

BACKGROUND: Previous neuroimaging studies on migraine have reported inconsistent hippocampal volumetric changes, potentially due to insufficient consideration of subregion heterogeneity. Exploring the alterations in hippocampal subregions may help reveal the mechanisms underlying migraine chronification. This study aims to investigate the role of volume changes in these subregions in migraine chronification. METHODS: Structural T1-weighted MRI scans were performed on 42 patients with episodic migraine (EM), 22 patients with chronic migraine (CM), and 65 healthy controls (HCs). Hippocampal subregion volumes were quantified using FreeSurfer-based segmentation, and group comparisons were performed with relevant covariates included and false discovery rate (FDR) correction applied to control for multiple comparisons. RESULTS: No hippocampal subregion volume differences survived FDR correction at 0.05. However, trend-level volumetric variations were observed across the three groups, including the bilateral whole hippocampus, subiculum, cornu ammonis (CA) 1, molecular layer, as well as the left granule cell and molecular layer of the dentate gyrus (GC-ML-DG) and CA4. Subsequent exploratory pairwise comparisons showed that (1) compared with HCs, CM patients exhibited trend-level smaller volumes in the bilateral whole hippocampus, subiculum, CA1, and molecular layer; and (2) compared with EM patients, CM patients showed trend-level reductions in the bilateral whole hippocampus, molecular layer, CA1, as well as in the left subiculum, GC-ML-DG, and CA4. CONCLUSION: No significant volumetric differences in hippocampal subregions were detected among the three groups. Exploratory findings suggest trend-level alterations in several hippocampal subregions, including CA1, CA4, molecular layer, GC-ML-DG, and subiculum in CM patients. These preliminary findings may suggest potential links to pain perception, emotion, memory, and cognition during migraine chronification.