Abstracts

Rationale: Refractory epilepsy is a significant problem in children often requiring neurosurgery. Identification of the ictal onset zone is critical for surgical success. In children, there is little published data on which ictal onset patterns (IOPs) are used to guide surgical decision-making and associated surgical outcomes. We aim to describe our experience with intracranial EEG (iEEG) in a pediatric population, focusing on IOPs and likelihood of surgical success. Methods: We performed a retrospective review of pediatric patients with refractory epilepsy who underwent iEEG monitoring followed by epilepsy surgery at our institution from January 1, 2001 to October 31, 2016. EEGs were reviewed by two epileptologists. IOPs were categorized. Results: 34 patients were identified that met inclusion criteria. Of these, data analysis has been completed for 12 so far (Table 1). Age range at time of iEEG and epilepsy surgery was 8-20 (mean 15.5) years. Greater than 354 seizures were recorded (3-100+ seizures per patient).Four distinct IOPs were seen with habitual seizures: A) Low voltage fast activity (LVFA) with spread to the adjacent electrodes (n=3 patients, 25%), B) Burst of LVFA followed by an electrodecrement (n=5 patients, 42%), C) Burst of rhythmic spike waves (RSW) followed by an electrodecrement (n=1 patient, 8%), D) RSW followed by LVFA (n=3 patients, 25%).LVFA was the most frequently seen single IOP at ictal onset, in 8 patients (66%). Burst of paroxysmal activity (RSW or LVFA) and subsequent electrodecrement was also seen often at ictal onset, in 6 patients (50%).When the area of the IOP was subsequently resected, favorable outcome was accomplished in 10 patients (Engel Class I); 2 patients had no benefit (Engel Class IV) and required repeat surgery.  One of these patients had 3 different IOPs with or without clinical correlation, and the other patient underwent partial resection due to the involvement of eloquent cortex.  The most common pathology was cortical dysplasia (CD), seen in the surgical substrates of 8 patients (67%), followed by gliosis in 3 (25%) and mesial temporal sclerosis in 1 (8%). LVFA was seen at the ictal onset in the majority of the patients with CD (5/8 patients, 63%). Conclusions: Intracranial ictal patterns present challenges to localize seizure onset. This pilot study is significant because it demonstrates that LVFA is the most common intracranial ictal onset pattern in children and is often associated with cortical dysplasia. Despite the variation in ictal EEG pattern, post-surgical outcome is favorable in the presence of stereotyped EEG findings and semiology.  The presence of multiple ictal onset patterns may predict unfavorable outcome.  Funding: None.