Prediction of Surgical Outcome by Interictal Epileptiform Abnormalities During Intracranial EEG Monitoring in Patients with Extrahippocampal Seizures

Abstract

Purpose: Ictal intracranial EEG recordings obtained during continuous preoperative monitoring are often used to localize the region of seizure onset for purposes of surgical resection in patients with extrahippocampal seizures. Whether interictal epileptiform abnormalities during long-term monitoring can predict surgical outcome in this group is not established.Methods: Intracranial EEGs of patients who underwent extrahippocampal resective epilepsy surgery were reviewed for interictal epileptiform abnormalities before medication discontinuation or first seizure occurrence. Interictal abnormalities were categorized as within or beyond the confines of surgical resection. We correlated these findings with the region of seizure onset, the pathologic substrate, and surgical outcome (by using Engel criteria) at I-year minimum follow-up.ResuZts: Of I3 patients with interictal epileptiform abnormalities, six patients had interictal epileptiform discharges extending beyond the confines of surgical resection. These pa-

MRS Studies of the Role of Altered Glutamate and GABA Neurotransmitter Metabolism in the Pathophysiology of Epilepsy

“…This observation raises the possibility of additional abnormal epileptogenic cortical regions with impaired seizure-terminating capabilities, i.e., increased cortical excitability. The presence of interictal epileptiform discharges extending beyond the area of resection correlates with poor surgical outcome in patients with extra-hippocampal epilepsy (Bautista et al, 1999). The observations are consistent with the hypothesis that increased cortical excitability beyond the epileptogenic region appears to contribute continued seizure activity.…”

High-frequency changes during interictal spikes detected by time-frequency analysis

“…Interictal epileptic spikes have always been an important diagnostic feature in patients with epilepsy (Bautista et al, 1999;Hufnagel et al, 2000). In presurgical diagnostics for patients with epilepsy, the brain areas which generate epileptic spikes are called the irritative zone (Rosenow and Luders, 2001).…”

Epileptiform synchronization in the rat insular and perirhinal cortices in vitro

“…is that interietal diseharges in TLE are pro-convulsive, sinee they often oeeur within the same epileptogenie zones that initiate ietal diseharges; interietal diseharges are therefore useful for loeating the epileptogenie zone by EEG (Bautista et aL, 1999;Avoli et aL, 2006). In addition, cases of TLE with frequent interietal spikes tend to be more severe than cases with infrequent interietal spikes (Rosati et al, 2003).…”