Abstracts

Intraoperative electrocorticography (iECoG) was the method of choice for the determination of the amount of tissue to be resected in the early days of epilepsy surgery. By that time, almost no neuroimaging was available, except for pneumoencephalogram. Modern neuroimaging, especially MRI, made it possible to diagnose preoperatively the majority of the epileptogenic lesions. However, 15-20% of the patients with refractory epilepsy still have normal imaging findings. This paper discusses the present role of iECoG based on a series of 726 patients submitted to surgery.
We retrospectively reviewed the usefulness of iECoG in a series of 726 patients submitted to surgery for refractory epilepsy. There were 446 temporal , 75 frontal , 43 rolandic, 22 posterior quadrant, 15 parietal, 9 occipital and 4 insular cortical resections, 79 callosal sections and 33 hemispherectomies. Mean age at surgery was 24,7 years and mean follow-up time was 3,1 years. IECoG was routinely used during the first 250 procedures.
IECoG findings did not correlate with seizure[rsquo]s outcome after surgery in temporal lobe epilepsy. Although some of the early patients submitted to callosal sections received IECoG for documentation of the rupture of secondary bilateral synchrony, this also proved to have no correlation with outcome, and presently a maximized callosal section is preferred, without iECoG. Patients with normal neuroimaging invariably need prolonged chronic recordings with invasive electrodes (cECoG) and iECoG is not needed. Until recently, iECoG continued to be used as a method for the determination of the additional cortical margins to be resected during lesionectomy. However, additional cortical resection is more often limited by vascular and functional boundaries then by iECoG findings.
IECoG is being less and less used in epilepsy surgery. Although it is easy to be performed and analyze, decision-making should be usually based on limited interictal data (30-45 minutes of recording) obtained in anesthetized patients. More importantly, iECoG did not correlate with outcome in the majority of the surgical modalities presently carried out for refractory epilepsy. The better comprehension of the epileptogenic lesions and their pathophysiology would certainly lead to the disappearance of iECoG as a routine neurophysiological tool.
[Supported by: Sao Paulo Secretary of Health]