gms | German Medical Science

Objective: MRI-negative drug-resistant epilepsy presents a challenge when it comes to surgical planning, and surgical outcome is worse than in cases with an identifiable lesion. Whereas in temporal lobe epilepsy a standardized resection approach is applicable in many cases, the surgical management of extratemporal lesions is always individual. Here, we present a strategy for surgical planning in patients with extratemporal MRI-negative epilepsy focus and report our histological findings and patient outcomes.

Methods: Patients undergoing epilepsy surgery in the Department of Neurosurgery of the University Hospital Erlangen between 2012 and 2020 were included in the study. Inclusion criteria were: (1) failure to identify a structural lesion on preoperative high-resolution 3 Tesla MRI with a standardized epilepsy protocol and (2) preoperative EEG diagnostics revealing an extratemporal epilepsy focus.

Results: We identified 8 patients corresponding to the inclusion criteria. Second look MRI analysis by an experienced neuroradiologist including the most recent analysis algorithm utilised in our clinic revealed a possible lesion in two patients. One of the patients with a clear focal cortical dysplasia (FCD) finding on a second look was excluded from further analysis. Of the other 7 patients, in one patient invasive EEG was performed with subdural electrodes, whereas the other 6 were subjected to depth electrode EEG. Magnetoencephalography (MEG) was performed preoperatively in all but one patient. An MEG focus was implemented in the resection planning in 3 patients. FDG PET was performed in all, but only implemented in the surgical planning in one patient. Preoperative fMRI was integrated in the surgical planning in order to identify eloquent brain regions. Intraoperative MRI was utilized for resection control and lead to continued resection in two patients. Histopathological evaluation revealed one non-lesional case, four cases of FCD and two cases with mild developmental malformation. All patients with depth electrodes EEG analysis had Engel 1A outcome on follow-up whereas one case with subdural electrode monitoring had Engel 1B outcome.

Conclusion: We describe a multimodal approach for preoperative planning and surgical treatment of extra -temporal MRI-negative epilepsy, based on invasive electrode EEG and intraoperative MRI resection control, which in our series lead to a favorable epilepsy outcome in all patients.