Abstracts

Rationale: Patients with frontal lobe epilepsy continue to have lower post surgical seizure freedom rates compare to patients with mesial- and neocortical-temporal lobe epilepsy. The goal of epilepsy surgery, seizure freedom, is achieved with complete removal of epileptogenic zone(s). During invasive intracranial EEG (ICEEG) monitoring, the epileptogenic zone is approximated by identifying ictal onset zone (IOZ). In the absence of identifiable lesion on MRI or multi-lesional MRI, the irritative zone (IrZ) identified by MEG can be used for concordance. Methods: Five consecutive patients with frontal lobe epilepsy and normal or multi-lesional MRIs were studied. All patients had MEG and ICEEG as their presurgical workup. IrZ, the anatomical area of abnormal interictal epileptiform activity, was identified by MEG. IOZ was identified by ICEEG. All five patients had epilepsy surgery with complete removal of their IOZ as identified by ICEEG. Results: Four of the five patients had normal MRIs and one had multi-lesional MRI due to tuberous sclerosis. Three of the five patients who had complete surgical removal of their IrZ in addition to their IOZ (concordance between surgical resection, IOZ and IrZ) had Engel outcomes 1 and 2. Two of the five patients had incomplete surgical removal of IrZ and complete removal of IOZ (discordance between surgical resection and Irz, but concordance between surgical resection and IOZ). They had Engel outcomes 3 and 4. Conclusions: In a subset of patients with frontal lobe epilepsy concordance between ICEEG and MRI is not feasible. This is either due to lack of lesion or multi-focality of lesions in MRI. In this group, removal of irritative zone identified by interictal MEG in addition to IOZ identified by intracranial EEG may lead to improved post-surgical outcomes.