Loss of hippocampal dentation in hippocampal sclerosis and its relationship to memory dysfunction

Abstract

Summary Objective Hippocampal dentation (HD) is a “toothlike” morphological feature observed on the inferior aspect of the human hippocampus. It has been found that HD varies dramatically in healthy adults and is positively associated with verbal and visual memory. In this work, we evaluate the loss of HD and its association with memory dysfunction in patients with temporal lobe epilepsy (TLE) who have hippocampal sclerosis (HS). Methods Fifty‐eight unilateral HS patients with neuropsychological data were identified from a retrospective database. T1‐weighted magnetization‐prepared rapid acquisition gradient echo images (~1 mm resolution) were upsampled to .25 mm and were processed using ASHS software to obtain ultra‐high‐resolution segmentations and three‐dimensional renderings. Dentes were counted on the epileptic and contralateral sides, and associations were tested between dentation on the epileptic versus contralateral sides and measures of verbal and visuospatial memory with respect to the dominant versus nondominant hemisphere. Results The median number of dentes in epileptic hippocampi was significantly lower than in contralateral hippocampi (p < .0001). Among cases with HS in the dominant hemisphere, verbal memory was significantly correlated with contralateral nondominant hemisphere dentation (r = .43, p = .04). Similarly, among cases of HS in the nondominant hemisphere, visual memory was significantly correlated with contralateral dominant hemisphere dentation (r = .48, p = .04). All other analyses were not significant. Significance This is the first study characterizing dentation in TLE patients with HS and its memory correlates. There is marked loss of dentation in sclerotic hippocampi compared to the unaffected contralateral hippocampi. Material‐specific measures of memory performance are paradoxically correlated with dentation contralateral to the side with HS, suggesting that contralateral functional capacity explains some of the variation in memory across TLE patients. HD is an important variable to consider in understanding memory loss in TLE.

Larger and more dentated hippocampal structure is associated with better memory in the oldest-old

“…A simple dentation count score alone might not most accurately and descriptively represent the structure of hippocampal dentation. The pending development of an objective quantitative method could help mitigate this limitation of subjectivity by more objectively scoring hippocampal dentation (Ramaniharan et al, 2020).…”

“…T-1 weighted MRI images were used to assign a score for hippocampal dentation by viewing the structure of the hippocampus in three dimensions (Fleming Beattie et al, 2017). Although high-resolution multispectral imaging using a combination of T1 and high-resolution T2 scans has been recommended for accurate scoring and to identify more detailed features of dentation, the use of only T1 scans has been suggested for determining counts of dentation with visual ratings along the hippocampus (Fleming Beattie et al, 2017), (Kilpattu Ramaniharan et al, 2022). The subjective dentation score from Kilpattu Ramaniharan et al (2022) was done for each participant by counting the number of hippocampal dentes in both the left and right hemispheres.…”

“…Although high-resolution multispectral imaging using a combination of T1 and high-resolution T2 scans has been recommended for accurate scoring and to identify more detailed features of dentation, the use of only T1 scans has been suggested for determining counts of dentation with visual ratings along the hippocampus (Fleming Beattie et al, 2017), (Kilpattu Ramaniharan et al, 2022). The subjective dentation score from Kilpattu Ramaniharan et al (2022) was done for each participant by counting the number of hippocampal dentes in both the left and right hemispheres. The program 3D Slicer was used to view the T-1 weighted images in the sagittal plane (Fedorov et al, 2012).…”

“…Additionally, the relationship between hippocampal dentation and hippocampal volume was not significant (Fleming Beattie et al, 2017). A more recent study examined dentation and episodic memory performance in adults with healthy hippocampi and in adults with hippocampi lesioned due to temporal lobe epilepsy (age = 36.64 11.28) In lesioned hippocampi, dentation positively correlated with hippocampal volume; dentation and volume trended toward significance in healthy hippocampi (Kilpattu Ramaniharan et al, 2022). Until now, hippocampal dentation and episodic memory have not been studied in the oldest-old adult cohort.…”

Development of an objective method to quantify hippocampal dentation

“…This finding is the opposite of what is found in healthy controls and suggests that prominent HD may be a marker of functional reserve or reorganization of material‐specific memory function to the contralateral side. Similarly, dominant hemisphere HD was significantly correlated with visual memory in the non‐dominant hemisphere HS patients (Kilpattu Ramaniharan et al, 2022 ). This was the first published report characterizing HD in a disease cohort and demonstrated HD to have a significant structural and functional correlations with hippocampal disease, suggesting the possibility that HD may have correlates in other forms of hippocampal pathology as well.…”