Intraoperative electrocorticography: variants of periodic patterns in the structural epilepsy

The results of intraoperative electrocorticography for patients with the structural epilepsy are influenced by two main factors: the action of general anesthetic and the mechanisms of epileptogenesis. Under the general anesthesia, there is a dose-dependent suppression of the bioelectrical activity of the brain; you could even register the “outburst-diminution” and “outburst-suppression” types of the periodic patterns. The study was carried out to classify the variants of periodic activity registered on the intraoperative electrocorticogram for patients with a structural epilepsy. The work was carried out during the examination and surgical treatment of the two groups of patients: 1) 19 patients (men/women — 10/9, 19–45 years old) with focal drug-resistant epilepsy; 2) 19 patients (men/women — 8/11, 28–68 years old) with structural epilepsy associated with the intracerebral tumors. All patients underwent surgical removal of the epileptic focus under a neurophysiological control. Surgical interventions were performed under the sevoflurane-based inhalation anesthesia in doses from 1.0−1.5 MAC (minimum alveolar concentration). Periodic activity on intraoperative electrocorticography was represented with the “outburst-suppression” type of patterns and patterns containing epileptiform discharge graph elements: “discharge- postdischarge depression,” “outburst-suppression” with discharges against the background of depression, “small electrical elements” with epileptiform discharges. The presence of discharge graph elements in the periodic patterns has a neurophysiological correlation with a drug-resistance in the structural epilepsy.