Abstracts

High frequency oscillations (HFOs) in the frequency range of 80 Hz and higher has been investigated from ictal subdural EEG data in patients with intractable localization-related epilepsy. Multiple band frequency analysis (MBFA) provides high resolution of frequency changes and time courses in HFOs. We studied ictal HFOs from extraoperative video subdural EEG monitoring (SDEEG) using MBFA to characterize patterns of HFOs in children with intractable neocortical epilepsy. We retrospectively studied 8 children (3 girls and 5 boys; mean age, 14 years; range, 8 to 17 years) who presented with intractable neocortical epilepsy and underwent SDEEG consisting of 48 to 116 contacts (AD-TECH Medical instrument corporation, Racine, WI, USA). We recorded SDEEG for 48 to 144 hours with 1,000 Hz sampling rate (HARMONY 5.4, Stellate, Montreal, PQ, Canada). We analyzed 4 to 11 seizures by selecting SDEEG data epochs of 10 to 50 seconds including 5 seconds before the ictal EEG onset. We used MBFA using the software program Short Spectrum Eye (Gram, Saitama, Japan) for frequency and distribution analyses of HFOs. The power spectrograms of frequency bands between 5 Hz to 300 Hz were calculated with a frequency resolution of 2 Hz and a temporal resolution of 25 ms. We arranged all power spectrograms in the same order as subdural grid electrodes and evaluated the distribution of HFOs. Seven of 8 patients presented with regionally predominant ictal HFO changes (mean, 23 electrodes). We found two patterns of HFOs consisting of existence or absence of sustained narrow band of HFOs. Four of 7 patients had initial wide range of HFOs (up to 115 Hz) lasting 2 to 5 seconds before the clinical seizure onset, followed by a sustained narrow band of HFOs (mean, 101 Hz) during ictal symptom of partial seizures. The seizures in these 4 patients evolved into secondary generalization. The other three patients had wide range of HFOs (up to 214 Hz) before and after the clinical onset without following sustained narrow band of HFOs. They presented with brief partial seizures in cluster in one patient, epileptic spasms in 2, but they did not evolved into secondarily generalized seizures. The cortical resection areas in 7 patients included the region of predominant HFOs (mean maximum frequency, 138 Hz). They achieved good postsurgical outcomes. The remaining one patient had no regionally predominant ictal HFO changes. This patient has residual partial seizures after frontal cortical excision. MBFA characterized 2 patterns of ictal HFO changes between seizures with and without secondarily generalized in pediatric neocortical epilepsy. The regionally predominant ictal HFOs represented the ictal onset and ictal symptomatogenic zones.