A novel geometry‐based analysis of hippocampal morphometry in mesial temporal lobe epilepsy

Hippocampal volumetry is an essential tool in researching and diagnosing mesial temporal lobe epilepsy (mTLE). However, it has a limited ability to detect subtle alterations in hippocampal morphometry. Here, we establish and apply a novel geometry‐based tool that enables point‐wise morphometric analysis based on an intrinsic coordinate system of the hippocampus. We hypothesized that this point‐wise analysis uncovers structural alterations not measurable by volumetry, but associated with histological underpinnings and the neuropsychological profile of mTLE. We conducted a retrospective study in 204 individuals with mTLE and 57 age‐ and gender‐matched healthy subjects. FreeSurfer‐based segmentations of hippocampal subfields in 3T‐MRI were subjected to a geometry‐based analysis that resulted in a coordinate system of the hippocampal mid‐surface and allowed for point‐wise measurements of hippocampal thickness and other features. Using point‐wise analysis, we found significantly lower thickness and higher FLAIR signal intensity in the entire affected hippocampus of individuals with hippocampal sclerosis (HS‐mTLE). In the contralateral hippocampus of HS‐mTLE and the affected hippocampus of MRI‐negative mTLE, we observed significantly lower thickness in the presubiculum. Impaired verbal memory was associated with lower thickness in the left presubiculum. In HS‐mTLE histological subtype 3, we observed higher curvature than in subtypes 1 and 2 (all p < .05). These findings could not be observed using conventional volumetry (Bonferroni‐corrected p < .05). We show that point‐wise measures of hippocampal morphometry can uncover structural alterations not measurable by volumetry while also reflecting histological underpinnings and verbal memory. This substantiates the prospect of their clinical application.