Abstracts

Rationale: Some patients suffer from bitemporal epilepsy which is an unfavorable condition as surgery is contra-indicated and few therapeutic options can be proposed. This retrospective study focused on the precise localization of the Epileptogenic Zone (EZ) in patients suffering from bitemporal epilepsy, to determine in particular the relative involvement of hippocampal and peri-hippocampal regions in this kind of epilepsy. Methods: All patients displaying bitemporal epilepsy, and explored by Stereo-Electro-Encephalography (SEEG) in our centre, were analysed. Bitemporal epilepsy was defined as : 1) simultaneous seizure onset in both temporal lobes, and/or 2) independant seizures arising from right and left temporal lobe, and both recognized by the patient as usual seizures. The seizures recorded during SEEG were either spontaneous seizures or stimulation-induced seizures. We analysed ictal EEG of all recorded seizures in our patients and we used the 'Epileptogenicity Index', a method previously described (Bartolomei et al, Brain 2008 Jul;131(Pt 7):1818-30 ; Aubert et al, Brain 2009 Nov;132(Pt 11):3072-86) that accounts for both the propensity of a brain area to generate rapid discharges and the time for this area to get involved in the seizure. These results were compared with those of patients suffering from unilateral temporal epilepsy, but who had temporal electrodes bilaterally implanted during the SEEG. Results: In patients with bitemporal epilepsy, EZ encompassed both subhippocampal regions (perirhinal, entorhinal cortices) and hippocampi. Conclusions: This study raises the question of whether the involvement of these subhippocampal regions may be a pejorative prognostic factor (higher risk for the development of bitemporal epilepsy ?). It also helps in delineating the EZ in these peculiar form of epilepsy and could be useful for the determination of the most appropriate target for non-surgical procedures such as chronic temporal lobe stimulation, in the future.