Abstracts

RATIONALE: To assess if the size of the ictal generator has a prognostic value in terms of surgical outcome in patients with unilateral temporal lobe epilepsy investigated with scalp and depth electrodes.
METHODS: We retrospectively studied 25 patients with strictly unilateral temporal lobe epilepsy who underwent long-term EEG-video monitoring with scalp electrodes and subsequently with depth electrodes ( 64 channels ). Bilateral depth electrode implantation was performed stereotactically or using a 3D neuro navigational system, targeting : amygdala (25 pts), hippocampus (25 pts ) and parahippocampus ( 13 pts ). Surgical procedures included: anterior temporal lobectomy (7 patients ) and selective amygdalectomy hippocampectomy (18 patients ). Follow up after surgery ranged from 1-10 years ( mean : 4,5 years ). Engel`s classification was used to rate outcome.
RESULTS: Depth EEG findings: Focal onset ( most commonly hippocampal, amygdaloid and parahippocampal in respective order) was documented in 9/25 patients ( 36 %) ; regional onset ( most frequently amygdalo- hippocampal or hippocampal-parahippocampal ) was recorded in 12/25 ( 48% ) a lobar onset was seen in 4/25 patients ( 16% ). A good outcome ( Engel I or II ) was seen in 17 patients of these series ( 68% ) regardless the size of the ictal generator. In 4 of these patients, the size of the ictal generator was larger than the surgical removal ( SAH), including lobar onset (1), temporal neo-cortex involvement(1) and parahippocampus in addition to amygdala and hippocampus involvement ( 2 ). Only in 1/8 failures, the surgical removal was smaller than the ictal generator as documented by depth-EEG.
CONCLUSIONS: In a pure culture of patients with unilateral temporal lobe epilepsy as evidenced by depth electrode recordings, the size of the ictal generator within the mesial temporal lobe network, does not provide a prognostic implication regarding surgical outcome. Selective amygdalectomy - hippocampectomy is an effective surgical procedure even in patients with large ( regional and lobar ) ictal generators and therefore one could postulate that this technique produces a critical disconnection of the temporo- limbic network which results in elimination or significant reduction of seizures. One could explain the surgical failures assuming that this network is much larger than its electrographic expression on depth recordings, possibly involving subcortical structures in keeping with recent MRI changes.
[Supported by: Montreal Neurological Institute- Mc Gill Montreal Swiss EPI Center]