Abstracts

Rationale: Intra-operative electrocorticography (ECoG) is used in epilepsy surgery from many years, even though its real utility to optimize resection and its role in epileptologic outcome improvement have not been unequivocally defined yet. We present our case series of epileptic patients who underwent ECoG during epilepsy surgery. Our aim is to better define ECoG indications and utility.Methods: We collected the anatomo-electro-clinical data from a cohort of patients suffering from drug-resistant focal epilepsy, who underwent ECoG between 2009 and 2015. ECoG was performed with multi-contact grids to record the electrical activity of the surgically exposed cerebral cortex. ECoG findings were correlated to pre-surgical scalp EEG and MRI data, and to neuropathology and post-surgical outcome. Data from ECoG patients were compared to those from patients who did not undergo ECoG.Results: Thirty-one (24%) patients (mean age 29.7 y) underwent ECoG between 2009 and 2015, among a total of 130 patients operated on for drug-resistant epilepsy during the same period. Epilepsy was temporal in 16 patients, extratemporal in 15. MRI showed a lesion in 30 patients. The reason for ECoG was the presence of pre-surgical scalp EEG interictal and/or ictal activity not enough localized compared to the anatomic lesion and/or the presence of a lesion supposed to be more extended than showed by MRI. Another reason was proximity to functional areas. ECoG data contributed to modify the pre-surgical planning in 15 patients, performing more extended and “tailored” resections. For the aim of extending the resection, we considered reliable the perilesional or distant from the lesion ECoG interictal activities, present before and after the first part of resection. ECoG activities recorded only after the first part of the resection were not considered reliable. The main histological findings were focal cortical dysplasias (FCD I or II), glioneuronal/glial tumors, hippocampal sclerosis with or without associated FCD. Cortical areas removed on the basis of ECoG more often showed a histological alteration, but in some patients only an intense gliosis was observed, independent of disease duration or seizure frequency. The ECoG patients’ outcome was 83.8% in class I, 74% in class Ia, compared to 87.3% and 72.6% respectively for non-ECoG patients. When ECoG alterations persisted after resection, the outcome resulted non-optimal.Conclusions: Our data confirm the utility of ECoG in lesional epilepsy surgery, in spite of its limitations represented by the possibility to evaluate only the irritative zone. In the presence of poorly localized pre-surgical data, ECoG contributed to a “tailoring” of the resection. The absence of a histologic alteration, other than intense gliosis, in some cortical areas removed according to ECoG data, suggests the presence of possible perilesional epileptogenic networks. The good outcome in ECoG patients, comparable to non-ECoG patients, provided that ECoG alterations did not persist after resection, confirms ECoG utility.