P339 Long-term electrocorticographic monitoring and pathological high-frequency oscillations in tumor-related epilepsy
Objective Removal of brain tissue generating pathological high-frequency oscillations (pHFOs) has been related to better seizure outcome than resection of seizure onset zone. However, there is still a lack of understanding what oscillations are to be considered pathological. Methods A female patient (age 53) with 10 year duration of temporal lobe tumor-related epilepsy was admitted to Polenov’s Neurosurgery Institute for tumor resection. The patient underwent a two-staged surgery with subdural implantation of a grid electrode (4 × 5) over the temporal lobe to identify the epileptogenic zone (EZ). During the second stage wideband intraoperative electrocorticography (iECoG) was recorded (up to 500 Hz, sampling frequency 2000 Hz, Mitsar-EEG 202 amplifier). Results Electrocorticographic monitoring data were subjected to visual analysis in traditional frequency range (0.5–70 Hz). Six of 20 electrodes were marked as EZ electrodes. The distance between tumor margin and EZ electrodes reached 1–2.5 cm. Subpial resection of this zone was arranged. During the surgery iECoG data in 0.5–70 Hz frequency band were uninformative, while in 80–500 Hz range bursts of fast ripples (250–500 Hz, 100 μV, extended up to 3 s) were recorded over the marked EZ electrodes. The tumor and EZ were completely resected. Discussion Observed data demonstrate that HFOs coincide with EZ marked during long-term monitoring. The patient is seizure-free for 5 months at the moment, though a more prolonged follow-up is required. Conclusion Wideband iECoG recordings might give us more essential information in case of tumor-related epilepsy. As is shown, fast ripples may be a valid marker of EZ. Significance Pathological HFOs show promise for optimising epilepsy surgery in tumor-related epilepsy.