Abstracts

Rationale: In most cases of focal pharmaco-resistant epilepsy investigated by intracerebral EEG a key problem is the assessment of the extend of the Epileptogenic Zone (EZ) and its organization. Indeed, the EZ may disclose features that may range from a simple focal organization corresponding to the site of a lesion to a more complex facet commonly described as a “epileptogenic network” extending out of the lesional site. This distinction is particularly relevant in developmental lesions as focal cortical dysplasias (FCD), dysembryoplastic neuroepithelial tumors (DNET) and may be determining for surgical strategy and prognosis Methods: To gain insight into the EZ organization we have developed a new tool, which is able to quantify the epileptogenicity of each anatomical structure explored by SEEG electrodes. We computed an “Epileptogenicity Index” (EI) that combines both spectral and temporal parameters respectively related to the propensity of a brain area to generate rapid discharges and the time for this area to get involved into the seizure process. We determined this EI from signal recorded in distinct brain structures including the lesional site in patients investigated by SEEG (stereoelectroencephalography) and suffering from focal pharmaco-resistant epilepsy associated with FCD or DNET. Results: We studied the type of EZ organization (focal versus network) and looked for a correlation with clinical data and post-surgical outcome. We could demonstrate that the number of structures displaying a high EI score is a significant prognostic factor for a worse post-operative outcome with a higher probability of persistant seizures after surgery. Conclusions: The determination of EI in several brain structures throughout SEEG technique is a new and usefull tool for quantification of the EZ and its extend, and could help for more accurate surgical resection.