Abstracts

Rationale: To characterize patterns of ictal high-frequency oscillations (HFOs) recorded by intracranial EEG and ictal clinical semiology in children with intractable localization-related epilepsy.Methods: We retrospectively studied 34 children (17 girls; 17 boys; mean age, 11 years; range, 2 to 17 years) who presented with intractable localization-related epilepsy, underwent extraoperative intracranial video EEG (1000 Hz sampling rate) and cortical resection between July 2004 and May 2007. We reviewed ictal epileptiform discharges on the raw EEG and performed multiple band frequency analysis (MBFA) to evaluate the frequency, distribution and patterns on power spectrograms of ictal HFOs. We analyzed spatial and temporal changes of ictal HFOs and clinical seizure patterns consisting of partial seizures, partial seizures followed by generalized tonic clonic seizures, partial seizures followed by clonic seizures and epileptic spasms.Results: Thirty-two patients underwent subdural grid and depth/strip electrodes. The other two patients had bilateral strip/depth electrodes. All 34 patients had seizures and ictal HFOs. We analyzed 41 seizures in 34 patients. Peak frequency ranged from 58 to 270 Hz (mean, 151 Hz). Power spectrograms revealed three patterns of ictal HFOs. A) Wide-band HFOs consisted of a mixture of various HFOs (5~270 Hz). We observed the wide-band HFOs in 20 patients with partial seizures alone and in 5 patients with partial seizures followed by clonic seizures. B) Modified wide-band HFOs consisted of brief (1-3 sec) wide-band HFOs and lack of middle range HFOs (30-90 Hz). Eight patients had the modified wide-band HFOs with slow waves on EEG during epileptic spasms. C) Sustained narrow-band HFOs consisted of an isolated HFOs (<30Hz band range) with paroxysmal electrodecremental event on EEG. Eight patients had the sustained narrow-band HFOs following wide-band HFOs with partial seizures evolving to secondarily generalized tonic clonic seizures. Conclusions: The wide-band HFOs were most often seen corresponding to partial seizures. The brief modified wide-band HFOs were seen at epileptic spasms. The sustained narrow-band HFOs reflected only when partial seizures became secondary generalized tonic clonic seizures. The patterns and time course of HFOs by MBFA identified the clinical expressions of seizures. The dynamic changes of ictal rhythms on intracranial EEG recordings reflected mechanisms of clinical manifestations of seizures.