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

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).

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.

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.

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.