Abstracts

Rationale: Resective epilepsy surgery is considered at the earliest in refractory epilepsy patients (a group that consists of 30% of all epilepsy patients) as resection may offer a cure or significantly decrease the seizure burden and tremendously improve quality of life in epilepsy patients. Patients with conventional temporal lobe epilepsies have a higher probability of being seizure free post resection following scalp EEG evaluation but intracranial EEG promises greater localization of the seizure onset zone and greater probability of success post resection even in these patients. Extratemporal epilepsies and dual pathology epilepsies show poorer responses to surgical resections following scalp EEG evaluation and may be amenable to better outcomes using intracranial EEG as well. We aimed to analyze surgical outcomes following evaluation using scalp and intracranial EEG in patients to help define treatment algorithms to help predict the need for invasive testing to improve outcomes for future patients. Methods: 83 patients undergoing EEG evaluation for epilepsy surgery at the Univ of Pennsylvania hospital over the last few years were included in the study. Chart reviews were performed to assess their treatment decision making and outcomes. They were divided using type of EEG evaluation (Groups 1 and 2 for scalp EEG only and intracranial EEG) and surgical outcomes (Groups A and B for good – Engel 1 & 2 - and bad – Engel 3 & 4 - outcomes respectively) into 4 groups – 1A, 1B, 2A and 2B. Various characteristics and outcomes for these groups were studied to help evaluate the usefulness of intracranial EEG in these patients. Results: 5 patients with intracranial EEG implantation experienced seizure freedom post implantation without respective surgery – ‘implantation effect’. 5 patients had had prior unsuccessful resections with scalp EEG and became seizure free after resections following intracranial EEG. Temporal and extratemporal epilepsies both showed good response to the use of intracranial EEG to guide resection.Patients with bitemporal onset, multiple foci, eloquent cortex involvement tended to have poorer outcomes in spite of the use of intracranial EEG but were able to derive some benefit from the use of RNS, VNS and other modalities. Conclusions: Intracranial EEG improves localization and surgical outcomes, especially in extratemporal epilepsies and temporal mimics, and provides greater diagnostic information to enable the use of other modalities like VNS / RNS. It also provides better localization in patients that have had prior resections and permits tailored resections in addition to offering cortical functional mapping as an added benefit. Stereotactic EEG may offer greater localization ability over conventional grids / strips / depth leads but this needs to be confirmed with more data from greater numbers of patients. Conventional temporal lobectomies must probably be performed after intracranial EEG as well to confidently rule out temporal mimics. The potential benefits of ‘implantation effect’ also add extra weight to favor increased use of intracranial EEG. The use of other testing modalities in diagnosis and prognostication will continue to influence decision making in surgical epilepsy. Funding: None