Resection of ictal high‐frequency oscillations leads to favorable surgical outcome in pediatric epilepsy

Abstract

Summary Purpose Intracranial electroencephalography (EEG) is performed as part of an epilepsy surgery evaluation when noninvasive tests are incongruent or the putative seizure-onset zone is near eloquent cortex. Determining the seizure-onset zone using intracranial EEG has been conventionally based on identification of specific ictal patterns with visual inspection. High-frequency oscillations (HFOs, >80 Hz) have been recognized recently as highly correlated with the epileptogenic zone. However, HFOs can be difficult to detect because of their low amplitude. Therefore, the prevalence of ictal HFOs and their role in localization of epileptogenic zone on intracranial EEG are unknown. Methods We identified 48 patients who underwent surgical treatment after the surgical evaluation with intracranial EEG, and 44 patients met criteria for this retrospective study. Results were not used in surgical decision making. Intracranial EEG recordings were collected with a sampling rate of 2,000 Hz. Recordings were first inspected visually to determine ictal onset and then analyzed further with time-frequency analysis. Forty-one (93%) of 44 patients had ictal HFOs determined with time-frequency analysis of intracranial EEG. Key Findings Twenty-two (54%) of the 41 patients with ictal HFOs had complete resection of HFO regions, regardless of frequency bands. Complete resection of HFOs (n = 22) resulted in a seizure-free outcome in 18 (82%) of 22 patients, significantly higher than the seizure-free outcome with incomplete HFO resection (4/19, 21%). Significance Our study shows that ictal HFOs are commonly found with intracranial EEG in our population largely of children with cortical dysplasia, and have localizing value. The use of ictal HFOs may add more promising information compared to interictal HFOs because of the evidence of ictal propagation and followed by clinical aspect of seizures. Complete resection of HFOs is a favorable prognostic indicator for surgical outcome.

Magnetic resonance imaging abnormalities in the resection region correlate with histopathological type, gliosis extent, and postoperative outcome in pediatric cortical dysplasia

“…The identification of the resection region was subjective but carefully performed and has been used successfully by our group in other studies. 11 Although all of our patients had at least 1 year of postsurgical follow-up, longer-term outcomes are not known for some patients.…”

“…11,23,29 In brief, our standard presurgical evaluation included a detailed history and clinical examination, scalp video-EEG monitoring, MRI, PET, ictal/interictal SPECT with SISCOM, and MEG. All patients underwent scalp video-EEG monitoring and MRI, but not all patients necessarily received all the noninvasive functional tests.…”

“…Intracranial electrographic data were used to identify the seizure-onset zone as detailed previously. 11,23 Surgical extent was determined based on preoperative testing, intracranial EEG, MRI results, and proximity to eloquent brain regions as described previously. 11,23 In general, standard craniotomy techniques were used to expose the desired cortical surface.…”

“…11,23 Surgical extent was determined based on preoperative testing, intracranial EEG, MRI results, and proximity to eloquent brain regions as described previously. 11,23 In general, standard craniotomy techniques were used to expose the desired cortical surface. The resection margin selected was determined by ictal onset zone using intracranial EEG (primary ictal onset zone plus secondary spread zone).…”

A Simple Statistical Method for the Automatic Detection of Ripples in Human Intracranial EEG

“…High frequency oscillations (HFOs) are a promising biomarker for the delineation of the seizure-onset zone in epileptic patients (Bragin et al 2010;Zijlmans et al 2012), and the removal of brain regions exhibiting HFOs has been correlated with a greater likelihood of seizure-free surgical outcome Fujiwara et al 2012). Pathological HFOs are broadly defined as spontaneous electrographic events of at least three to four full oscillations that are clearly distinguishable from the background signal, with frequencies ranging from 80-500 Hz (Buzsáki et al 1992;Jacobs et al 2012).…”