Abstracts

Rationale: This research aimed to investigate whether patients with unilateral mesial temporal lobe epilepsy (MTLE) who became seizure-free after surgery (Engel IA; Sz-Free Group) have different hippocampal volumetry when compared to patients who did not achieve seizure control (Engel IB-IVB; Not-Sz-Free Group). Also, to evaluate factors associated to more severe hippocampal atrophy (HA). Methods: We included 67 operated patients (34 Engel IA and 33 Engel IB-IVB) who had preoperative evaluation indicating unilateral MTLE and MRI visual analysis suggestive of HA and/or other signs of hippocampal sclerosis. Manual segmentation was performed in all patients and 30 healthy subjects using the software Display (http://www.bic.mni.mcgill.ca/software/Display/Display.html) and preoperative 3D-MRI (1mm thick). Clinical data were extracted retrospectively from medical records. Two-sample t-test was used for statistics. It was considered significant results those with p<0.05. Results: Z-score of affected hippocampus was -2.69±1.29 (Mean±SD) in Sz-Free Group and -2.39±1.45 in Not-Sz-Free Group (p=0.369). There was a significant difference between groups in Z-Scores of contralateral hippocampi (Sz-Free Group: 0.46±0.86, Not-Sz-Free Group: -0.41±1.14; p=0.001). Hippocampal volumetry correctly identified the affected side, as the smaller volume, in 65 of 67 patients (97%) and did not show atrophy in the remaining 2. Grouping all patients, smaller hippocampal volumes in the affected side were associated to history of meningitis (p=0.036) and absence of family history of epilepsy (p=0.028). Occurrence of tonic-clonic generalized seizures and febrile seizures in childhood were not associated to the degree of HA. Conclusions: Unfavorable surgery outcome for unilateral MTLE was associated to more atrophic hippocampus contralateral to operated side, which suggests that surgery is less effective when more widespread and severe atrophy exists, as demonstrated recently in other studies published by our group based on VBM analysis. This data also shows the usefulness of preoperative evaluation of hippocampal volumes, even when there is evident asymmetry. Hippocampal volumetry is an accurate method for identification of the affected side in patients presenting MTLE. Sporadic MTLE is associated to more intense HA than Familiar MTLE, what supports the theory that when there is no genetic predisposition, cerebral damage needs to be more severe to generate the epileptic discharges.