Can we increase the yield of FDG-PET in the preoperative work-up for epilepsy surgery?

Summary Purpose [ 18 F] Fluorodeoxyglucose Positron Emission Tomography (FDG-PET) is a semi-invasive, interictal method of localization of hypometabolic epileptic foci. FDG-PET can be useful in the clinical work-up prior to epilepsy surgery, especially in equivocal cases. We investigated whether we could increase the yield of presurgical FDG-PET in patients with difficult epilepsy requiring chronic subdural electrocorticography (ECoG). Methods We retrospectively studied patients with refractory focal epilepsy in whom there was uncertainty about the focus localization and who underwent FDG-PET and ECoG. Two experts (epileptologist and nuclear medicine radiologist) together systematically re-assessed the scans visually (PET RE ), blinded to their initial reports. Scans were also re-analyzed by comparing them to a normal control dataset with Statistical Parametric Mapping (SPM), using a liberal (PET SPM1 ), and strict (PET SPM2 ) statistical threshold. Regions with hypometabolism and regions containing the seizure onset zone (SOZ) in ECoG were marked as positive anatomical regions (PARs). We compared the concordance of these PARs for the different PET re-assessments. We calculated the sensitivity, specificity and accuracy of the PET results for the SOZ. The added value of the re-assessments was evaluated with emphasis on scans initially reported as negative. Results 41 Patients (63% extra-temporal) were included. PET RE identified the SOZ best, with a sensitivity of 62% and specificity of 93%. PET SPM1 had a sensitivity of 62% and specificity 69%, for PET SPM2 this was 35% and 85% respectively. The overlap between PET RE vs. PET SPM1 and vs. PET SPM2 was 71% and 37%. Visual re-assessment and PET SPM1 identified the SOZ in four out of five scans that were initially reported as negative. Conclusions Pre-surgical re-assessment of PET scans is worthwhile in epilepsy patients who undergo ECoG, especially when results were reported as negative before. Visual re-assessment itself has a higher combined specificity, sensitivity and accuracy than SPM analysis alone. SPM analysis could be used as a guide for visual (re-)assessment, because of its high sensitivity.