Abstracts

Rationale: Epilepsy surgery is an effective treatment for many patients with refractory epilepsy with seizure freedom rates of 60-80% in temporal lobe epilepsy and 50-60% in extra-temporal epilepsy. Intracranial EEG (iEEG) monitoring using either subdural grid and strip electrodes (SDE), and/or stereoelectroencephalograpy (SEEG) is utilized to study the epileptogenic network and define seizure onset zone prior to performing definitive surgery. Some patients may require multistage iEEG, either during one hospitalization or over the course of multiple hospitalizations, to achieve good outcomes. Rationale for performing multistage iEEG during the same hospitalization include incomplete localization, multifocality and mapping of eloquent cortex. Multistage iEEG over different hospitalizations is usually performed in cases of previous surgical failure. The reasons for failed epilepsy surgery include incomplete localization of the epileptogenic network, incomplete resection, or activation of a new epileptogenic focus due to surgery or due to an inherent tendency to develop new epileptogenic foci. In this study, we examined the reasons for multistage iEEG at our center.

Methods: This is a retrospective chart review of 8 patients who underwent multistage iEEG either during the same hospitalization or during different hospitalizations at the University of Nebraska Medical Center. We obtained data and compared both groups.

Results: Two patients had two-stage iEEG during the same hospitalization, and 7 patients had two-stage iEEG during different hospitalizations. Among the two patients who had single hospitalization, one had SEEG followed by SDE for localization of epileptic foci and language. The other patient had 2-stage SEEG where additional electrodes were placed for precise localization of epileptogenic foci. This patient had a prior non-diagnostic SDE during a different hospitalization. Among the seven patients who had iEEG during different hospitalizations, the indications were non-diagnostic first iEEG and failure of the epilepsy surgery due to insufficient resection margin, presence of a wide epileptic network or generation of new seizure foci. The first iEEG monitoring was done with SDE in 6 patients and old-fashioned depth electrode in 1 patient. The second iEEG monitoring was done with SEEG in 6 patients and SDE in 1 patient. There were minimal post-operative complications in both groups after both stages of surgery, except one patient had an infection of her old-fashioned depth electrodes during the first surgery in 1986.

Conclusions: Multistage iEEG during the same hospitalization is a safe procedure with similar complication rates as during different hospitalizations and can safely expedite the process of iEEG evaluation with good outcomes. Indications for multistage iEEG during same hospitalization can include eloquent cortex mapping, tailored resections, and more precise localization of epileptogenic zone.

Funding: None