Antemortem MRI detects atrophy related to hippocampal sclerosis pathology in the oldest‐old but side matters: The 90+ Study

Background Hippocampal sclerosis of aging (HS) is the neuropathological finding of neuronal death and gliosis in the hippocampus. HS is more prevalent, and associated with dementia, in the oldest‐old (those ≥90 years), but cannot be diagnosed during life. HS is often unilateral and can be missed if only one brain hemisphere is assessed, which is standard neuropathological practice but may hamper the development of biomarkers for HS. Here we examined hippocampal volumes from antemortem MRI in relation to bilaterally‐assessed HS at autopsy, accounting for side, in oldest‐old participants from The 90+ Study. Method We included participants with both autopsy and antemortem MRI data. All participants had neuropathological assessment of HS for both hemispheres. We performed hippocampal segmentation of antemortem 3D‐T1w MRIs using FreeSurfer, adjusting by intracranial volume. We compared total average (average of left and right), left, and right, hippocampal volumes between those with and those without HS. For HS participants we combined the hippocampal volumes from each hemisphere with HS into a single group and from each hemisphere without HS into a separate group, and compared these to the average hippocampal volumes from those without HS. We used Welch’s T‐tests for comparisons and report Cohen’s d effect sizes. Result Participant characteristics (N = 89) are shown in Table‐1. All HS was unilateral (Right = 6, Left = 4). Average total hippocampal volume was not significantly different between those with and those without HS (d = 0.51, P = 0.11, Figure‐1a). However, right hippocampal volumes were significantly related to right‐sided HS with a large effect size (P = 0.002, d = 1.02) and left hippocampal volumes had a large effect size for left‐sided HS (P = 0.17, d = 0.90, Figure‐1c), whereas this was not the case when HS was on the opposite side (P>0.3, d