Planning of invasive intracerebral Stereo-EEG (sEEG) in non-lesional focal drug resistant epilepsy is challenging and accurate spatial information about the organization of the epileptic focus is needed. Planning of sEEG is even more demanding, if patients with non-lesional epilepsy underwent prior epilepsy surgery.

Between 10/2019 and 10/2022 in 14 patients with non-lesional focal epilepsy with suspected monofocal epilepsy based on electro-clinical findings from non-invasive video-EEG-monitoring underwent sEEG implantation based on multimodal imaging. Four patients underwent prior epilepsy surgery and two of them prior invasive subdural EEG. All patients underwent multimodal diagnostics including high-resolution 3 T epilepsy MRI, MRI morphometry. A subgroup of patients underwent functional imaging using source imaging or FDG-PET. sEEG was planned considering findings from all available methods coregistered within the sEEG planning system.

Nine (± 2) sEEG electrodes were implanted per patient considering the primary hypothesis and usually several secondary hypotheses of the epileptic focus. No bleeding complication occurred. In sEEG recordings a focal seizure onset could be identified in 11/14 patients, and all of these patients underwent subsequent epilepsy surgery. Eighty percent (9/11 patients) had Engel 1 postsurgical outcome, 2/11 patients had Engel 2 postsurgical outcome. In 2/14 patients a multifocal epilepsy was diagnosed based on sEEG findings and only in 1/14 patients the epileptic focus could not be identified.

In patients with non-lesional focal epilepsy and suspected monofocal epilepsy sEEG diagnostics considering advanced multimodal imaging is highly successful identifying the seizure onset zone. After identification and exclusion of multifocal epilepsy patients based on sEEG findings epilepsy surgery in patients with identified monofocal seizure onset zone often results in seizure-free postsurgical outcome.