Abstracts

Rationale: Hippocampal sclerosis (HS) is the most commonly observed imaging abnormality in temporal lobe epilepsy (TLE). The classic MRI hallmarks are hippocampal atrophy, T2 signal hyperintensity, and loss of hippocampal internal architecture clarity. We have previously characterized a feature of hippocampal morphology known as hippocampal dentation (HD), which refers to the ridged, tooth-like appearance of the undersurface of the hippocampus (HC) (Fig. 1). Beattie et al. 2017 showed there is dramatic variation in the degree of HD from highly bumpy to totally smooth among healthy controls, and more intriguingly, that the degree of HD on the left positively correlated with verbal memory (CVLT-LDFR) and right HD was positively correlated with visual-spatial memory (RCFT- Recognition). TLE patients commonly show deficits in either or both of these measures. As systematic study of HD and its memory correlates has not been done heretofore. In this work we review a dataset of HS patients with preoperative neuropsychological testing to assess the following: A) does the presence of HS affect the degree HD compared to the unaffected contralateral side, and B) does the pattern of HD correlate with memory performance in this population? Our a priori hypotheses are that HD will be markedly decreased in the epileptic HC compared to the contralateral HC, and that measures of memory performance will correlate more strongly to the degree of HD in the contralateral HC than the diseased epileptic HC in a hemisphere-specific pattern, that is, that verbal memory in left HS patients will be more strongly related to right HD and visual-spatial memory in right HS patient will be more strongly related to leftHD. Furthermore, we employ a novel method for generating ultra high resolution 3D renderings of the HC from common T1w images that aid in visualization of HD.  Methods: Fifty-eight HS patients were identified with neuropsychological data were retrospectively identified. The primary measures were Long Delay Free Recall of the CVLT and the recognition score of the Rey Complex Figure Task. T1w MPRAGE images with a resolution of ~1mm were interpolated up to 0.25mm and were processed using ASHS (Yushkevich 2014) to generate high resolution segmentations. 3D renderings were visualized using ITK-SNAP. The number of dentes on each side was counted using the 3D view and convention 3-plane views of the source image. The Wilcoxon Paired Signed Rank Test was used to compare the distribution of HD counts on the epileptic side vs contralateral side. A Pearson's Correlation Coefficient was calculated to test associations between HD and neuropsychometric measures.  Results: The distribution of counts of dentes was significantly different (p<0.0001) between epileptic and contralateral hippocampi (Fig 2a) with a median of 1 and 4 dentes respectively. Among left HS cases, LDFR was significantly correlated with right HD (p=0.0275) and not left HD (p=0.274), and among right HS cases RCTF Recognition was significantly correlated with left HD (p=0.0377) but not right HD (p=0.5886) (Fig.2b,c). All other analyses were not significant.  Conclusions: This is the first systematic study to describe loss of hippocampal dentation as a common MRI feature of HS. The results indicate that sclerotic hippocampi lose structural complexity (loss of dentation) instead of simply having a smaller skeletonized shape. Contralateral HD also explains a significant degree of the variability in memory performance among HS patients in a hemisphere-specific pattern. Future work will assess whether contralateral HD is predictive of post-operative memory outcomes.  Funding: NINDS R01NS094743