Abstracts

Rationale: Previous studies have shown that patients with TLE can have a broad spectrum of hippocampal shape changes, including atrophy ipsilateral as well as contralateral to the seizure onset region. However, specific local changes within the hippocampus remain incompletely characterized. Here we used MRI-based large-deformation high-dimensional mapping (HDM-LD) to assess local hippocampal shape changes in patients with TLE with and without significant global atrophy.Methods: Forty-seven patients with unilateral temporal lobe epilepsy confirmed with video-EEG and thirty-two age, gender and handedness matched healthy controls were studied. High-resolution T1-weighted structural images were acquired in a 3T MRI scanner. HDM-LD was used to derive hippocampal surface estimates for each subject. Local measures of surface expansion/contraction were calculated at the vertex level for each surface and corrected for multiple comparisons with a cluster-based empiric noise estimation. Local deformation estimates were then entered into a general linear model with contrasts comparing TLE patients to controls, as well as TLE patient subgroups (left vs. right TLE, high vs. low global hippocampal atrophy).Results: Compared to the control group, 23 patients had high atrophy in the ipsilateral hippocampus (HIGH atrophy group, mean volume 1913 mm3), while 24 had low atrophy (LOW atrophy group, mean volume 2702 mm3). Consistent with previous studies, the HIGH atrophy group showed significant and extensive local surface contraction ipsilateral to the seizure focus, as well as less prominent but significant contraction in the contralateral medial hippocampal body and head (p<.05). Interestingly, patients with LOW global atrophy also showed a bilateral pattern of surface contraction localized to the medial hippocampal body and head, similar to the contralateral hippocampi of patients with HIGH atrophy. No statistically significant difference was noted in the hippocampal atrophy between the thirty left TLE patients (ipsilateral mean volume 2336 mm3, contralateral mean volume 2619 mm3) and the seventeen right TLE patients (ipsilateral mean volume 2282 mm3, contralateral mean volume 2473 mm3).Conclusions: These findings are suggestive of two broad patterns of hippocampal surface changes in patients with temporal lobe epilepsy: one that results in extensive surface contraction, and is characteristic of patients with significant global hippocampal atrophy, and another with more localized, bilateral changes, seen in patients with minimal global atrophy. While the former pattern may reflect a direct effect of the pathologic process also involved in epileptogenesis, the latter may instead be indicative of seizure propagation to the medial temporal region. The local hippocampal surface changes we observed may be helpful in identifying patients with temporal lobe seizures with medial vs. neocortical onset.