Abstracts

Rationale: In patients with refractory focal epilepsy, ictal single photon emission computed tomography (SPECT) is a commonly used presurgical study to help identify the seizure focus and guide placement of intracranial electrodes for invasive monitoring. With this retrospective study, we sought to determine the combined utility of ictal SPECT (IS) and intracranial monitoring (ICM) in localizing seizure onset and predicting postsurgical outcome. Forty consecutive patients who had IS followed by ICM were evaluated to determine how often IS seizure localization was congruent with ICM seizure localization. Congruency between IS and ICM localization was correlated with post-surgical outcome in those patients with at least two year follow-up.Methods: After IRB approval, we queried the Vanderbilt epilepsy surgical database from 1999-2012 for adult and pediatric patients who had both IS and ICM and identified 40 patients. Studies were considered congruent if ICM seizure onset included the IS focus. Two year post-operative data was looked at in 26 patients, and 24 had documented post-operative follow-up. Postsurgical seizure outcome was determined for these patients using the Engel classification system. In addition, the latency to IS injection after seizure onset and seizure characteristics were determined for each patient. Results: Congruency between IS data and ICM data was seen in 17 (42.5%) patients and incongruency in 23 (57.5%) of the 40 patients. Additional IC electrodes were placed in 7 patients in the incongruent group compared with 2 in the congruent group. Secondary seizure generalization was seen in 6 patients in the incongruent group compared to 4 in the congruent group. All but 2 patients underwent a surgical procedure after ICM ictal localization. 15 patients (62.5%) had class I/II outcome of which 9 (60.0%) had congruent data. 9 patients (37.5%) had class III/IV outcome of which 2 (22.2%) had congruent data between IS and ICM (Table 1). The latency to IS injection did not vary significantly among the groups.Conclusions: Overall, this study shows that incongruency of IS and ICM seizure localization is a poor prognostic factor for seizure control after surgery. The poor outcome could be due to a number of factors including difficulty in localizing a deep ictal focus with ICM, insufficient coverage of the epileptogenic zone, multiple epileptogenic zones and/or incomplete resection of the epileptogenic zone due to overlap with eloquent cortex.