Abstracts

Rationale: In presurgical evaluation, invasive EEG (iEEG) recording can precisely define the topography of seizure onset and spread. The aim of the evaluation process is to allow complete removal of the epileptogenic zone, postoperative seizure freedom confirms its correct delineation. In this study, we analyzed if electrophysiological parameters such as size of seizure onset zone, morphology of ictal onset pattern (IOP) and velocity of propagation of ictal activity are associated with postoperative seizure freedom. Methods: We retrospectively assessed 305 seizures recorded with iEEG (subdural electrodes) from 83 patients with drug-resistant focal epilepsy. For each seizure, the size of the seizure onset zone (focal = 2 cm vs. regional), the IOP (well-defined patterns adapted from Perucca et al. 2014) and the latency to onset of propagation (time in sec until ictal activity was recorded by electrodes > 2 cm beyond the seizure onset zone). On the patient level, the association of these parameters with post-operative seizure freedom (Engel I), histopathology and topography of seizure onset zone was analyzed. On the seizure level, the association of clinical-EEG- and propagation latency with topography of seizure onset was examined. Results: Patients with focal (70%) vs. regional (37%) seizure onset had significantly more often post-operative Engel I seizure outcome (p < 0.05). The most common IOP was low amplitude fast activity (LAFA, 38.6% of patients, 51.8% of seizures), but we were unable to demonstrate a significant association of this parameter and of propagation latency with post-operative seizure freedom, histopathology or localization of the seizure onset zone. Seizures originating in temporo-mesial structures has a significantly longer clinic-EEG- and propagation latency (28 / 27 sec) compared to seizures arising in temporo-lateral structures (9 / 7 sec, p < 0.01) or the frontal lobe (4 / 5 sec, p < 0.01). Conclusions: Focal seizure onset was – in contrast to IOP (LAFA) and propagation latency – significantly associated with postoperative seizure freedom. Specific brain structures – in which seizures are arising – determine latency between clinical and electrophysiological seizure onset and of propagation of ictal activity to adjacent areas. Funding: No funding