Abstracts

Rationale: Hippocampal sclerosis (HS) constitutes the major part of drug-resistant epilepsies; however its bilateral type received little attention and is accepted as a challenge for planning epilepsy surgery. We aimed to investigate the differences in clinical, EEG findings and post-operative outcomes of bilateral HS (BHS) patients in comparison to the unilateral ones (UHS). Methods: Patients diagnosed with mesial temporal lobe epilepsy between the years 1987-2014 in our center and with at least one EEG analysis were evaluated. All cranial MRIs were investigated by an experienced neuroradiologist for the two major criteria of HS diagnosis, namely atrophy and hyperintensity of the involved site(s). Patients with clear-cut UHS with suspicion of the involvement the other side underwent 3 Tesla MRI, and were included after confirmation of the BHS. Patients with HS but with seizures originating from additional lesions and patients without neuropathological confirmation of HS after the operation were excluded. Clinical, etiological and all available electrophysiological data were evaluated by two epileptologists, retrospectively and the groups with UHS and BHS were compared statistically. Post-operative seizure outcomes were grouped according to the Engel classification. Results: A total of 127 patients; 31with BHS and 96 with UHS were included (Table 1). Five patients with BHS did not have drug-resistant course. Forty-eight patients were operated (9 with BHS and 39 with UHS) and postoperative follow-up periods did not differ significantly (63,2+36,7 months versus 68,9+43,5 , respectively). Bilateral interictal epileptic foci over the temporal lobes were observed in 15 patients out of 31 patients with BHS. Four patients with BHS had interestingly normal EEG recordings. Video-EEG monitoring (VEM) analysis done in 20 BHS patients showed bilateral onset in 6, left sided onset in 4 and right sided seizure onset in 5 of them, whereas the remaining were nonlocalized. Six out of 9 BHS patients needed invasive monitoring for the operation and 4 of them remained seizure-free. The post-operative outcomes of the groups did not differ significantly as seen in the Table. Six out of 9 patients were in Engel IA, two in Engel 3A, and the last case with switch-off lateralization in VEM in Engel 4A. Furthermore, all but one of BHS patients did not show any deterioration in post-operative neuropsychological testing. Conclusions: Our study showed that BHS is a highly heterogeneous group, showing similarities as well as differences from UHS. History of status epilepticus, mental retardation, febrile status epilepticus and abnormal neurological findings are statistically more common in BHS when compared to UHS. Although only a minority of BHS cases showed a benign course, drug-resistant BHS patients might show good post-operative outcome, when preoperative diagnostic investigations are appropriately planned.