Abstracts

Rationale: MEG and ictal SPECT are two noninvasive approaches commonly used in the epilepsy presurgical evaluation process. In this study, we aim to investigate whether the noninvasive multimodal approach with MEG and ictal SPECT contributes to better seizure outcomes in patients with previously failed epilepsy surgery. Methods: In this retrospective study, we included a consecutive cohort who failed prior resective epilepsy surgery, underwent re-evaluation including MEG and ictal SPECT, and had new surgery subsequent to the re-evaluation. The relationship between resection and the localization from each test was determined, and its association with seizure outcomes was analyzed.Pre-surgical data before previous surgery such as electroencephalogram (EEG) (interictal, ictal), MEG, PET, SPECT and invasive EEG were obtained and analyzed. The following inclusion criteria were used: (1) intractable epilepsy as defined by ILAE classification; (2) prior resective epilepsy surgery (single or multiple); (3) re-evaluation including MEG and ictal SPECT; (4) resective epilepsy surgery following the re-evaluation as mentioned in (3); and (5) follow-up of 12 months after the surgery mentioned in (4).  Exclusion criteria were: (1) non-resective prior brain surgery (e.g., VNS, SEEG investigation, brain biopsy, craniotomy and drainage for intracranial hemorrhage, placement of shunts and aneurysm clipping); (2) (functional) hemispherectomy as a new surgery and (3) postoperative MRI or CT scan unavailable and of unsatisfactory quality for delineation of resection extent.The concordance between MEG and SPECT was defined as “sublobar”, “sublobar plus”, “lobar”, “multilobar ipsilateral” and “multilobar bilateral”. The concordance between scalp electroencephalogram (EEG) and MEG was performed at a lobar level. Results: From the 1512 patients screened, 158 patients had previous epilepsy surgery. Of which 46 patients were included in our study. Mean age of our cohort was 30 (range 2-54 year old) and mean duration of epilepsy was 20 years (range1-53 years). 32 out of 46 patients(70%) had extratemporal lobe epilepsy. 24 out of 46 patients (52%) had previous (failed) surgery at our institute. The difficulty of this group is further highlighted by 67% of patients having a non-contributory MRI and 22% had more than one previous surgery. Seizure-free rate after the re-surgery was 46% at 1-year follow up after the new surgery. The majority of the pathological findings from the new surgery consisted of focal cortical dysplasia [21/46 FCD type I (45%), 4/46 FCD type II (9%)].Twenty-six (56%) had a positive MEG and 34 (67%) had a successful ictal SPECT with mean injection time of 20 secs (range 4-185 secs) after EEG onset or clinical seizure onset if it preceded the EEG onset. 25 out of 34(73%) patients had ictal SPECT injection done during the typical seizure 30 seconds or more before the EEG offset.The resection of MEG foci significantly correlated with seizure-free outcome (p=0.003). The resection of hyperperfusion zones of ictal SPECT significantly correlated with seizure-free outcome in the subgroup of patients with injection time = 20 sec (p=0.03), but did not show significant correlation in the overall cohort (p=0.49). Patients whose MEG and ictal SPECT were concordant on a sublobar level had a significantly higher chance of seizure freedom (p=0.04). Conclusions: Our study emphasizes the importance of considering a multimodal presurgical evaluation including MEG and SPECT in all patients with a previously failed epilepsy surgery. MEG and ictal SPECT with early injection had good localization value in this challenging cohort. The importance of early injection for ictal SPECT is reinforced by our data. Both tests remain complementary to each other, as sublobar concordance between both correlated significantly with seizure freedom, and SPECT can provide essential information in MEG-negative cases and vice versa. Funding: None