Abstracts

Rationale: One of the milestones of a successful outcome after epilepsy surgery is a complete resection of the epileptogenic region. It is well known, in the pre-surgical evaluation, that Magnetic Resonance Imaging (MRI) and Videoelectroencefalography (VEEG) are the essential features to guide optimal surgical resection and to predict a good post-surgical outcome. Nevertheless, no sufficient data has been addressing the relation between the nature of the neuropathology lesion and seizure outcome.  The goal of the present study was to investigate the follow-up outcome after epilepsy surgery according to neuropathology diagnosis in focal epileptogenic lesions. Methods: We retrospectively reviewed 508 patients operated for medically refractory epilepsy at the Ribeirão Preto Epilepsy Surgery Center of Hospital das Clínicas de Ribeirão Preto (HCRP) between 1996 and 2017. The patients were divided into groups according to the neuropathology type: Hippocampal Sclerosis (HS) (n=339), Focal Cortical Dysplasia (FCD) type I (n=24), type II (n=28) and type III (n=21), Gliosis (n=44), Long-term epilepsy-associated tumors (LEAT) (n=11) other tumors (n=16), and others (Cavernous Angioma (n=6), Dual pathology (1), Tuberous Sclerosis (TS) (1), Rasmussen (n=1), Malformations of Cortical Development (MCD) (n=6), Sturge-Weber (n=1), normal (n=1), and 8 patients whose neuropathology was not found. Patient's clinical and neuropathological data were correlated with their Engel class postsurgical outcomes (seizure free vs. nonseizure free).  Results: The mean follow-up time was 9,6 years (varying from 1-21 years). At the time of the last follow-up visit, 73,7% of HS patients were seizure free, 37,5% of FCD I, 67,9 % of FCD II, 66,7 % FCD III, 47,7% of gliosis, 72,7 % of LEAT, 50% other tumors. The difference of seizure-free outcome between FCD I (37,5%) and FCD II (67,9%) was significant (Fisher test, p=0,049). This difference was not due to an increased frequency of normal MRI in one of the FCD group (FCD I 17% vs. FCD II 14%, Fisher test, p=1). From the cerebral topography, the percentage of seizure-free in the frontal lobe was 44,4%, 71,3% in the temporal lobe, 73,7% in the occipital lobe, and 46,4% in the parietal lobe.  Conclusions: In this series of 508 patients, the neuropathology diagnosis was able to predict good seizure outcome in the cases of HS and FCD type II. The better seizure-free outcome of FCD II over FCD I could not be attributed to a lower frequency of normal MRI in the FCD type II group. These findings suggest that different neuropathological entities may underlie distinct epileptogenic circuits, which can have diverse outcomes after focal resection.Reference: Roessler et al. Neurosurgical Focus, 40(3): E15,2016 Funding: Financial support: CNPq (N# 466995/2014-8)and FAPESP (N# 2016/17882-4) grants.