Can Ictal F18-FDG PET/CT Drawing Epileptogenic Zone in Refractory Focal Epilepsy? Histopathological and Outcome Correlation

Unlike interictal Positron Emission Tomography (PET), ictal PET is not regularly used in the study of refractory focal epilepsy, and its usefulness in presurgical evaluations, and prognosis value have not been established. The aim is to present six patients with epilepsy whose PET/CT brain scans showed focal hypermetabolism, and analyze their correlation with the histopathological findings and clinical results. We reviewed 146 18F-FDG PET/CT scans performed on patients with refractory focal epilepsy. Only those cases with hypermetabolic foci which were subsequently surgically resected were selected. The epidemiological and clinical data were reviewed in addition to the brain MRI, Electroencephalography (EEG), video-EEG monitoring, intraoperative Electrocorticography (ECoG), histopathology, and postsurgical outcome. The PET findings were correlated with the clinical characteristics of the seizures, the EEG, brain MRI, ECoG, and histopathology. Seven PET/CT scans carried out on six patients showed well-defined hypermetabolic foci (three temporal, four extratemporal). There was a high correlation between the clinical lateralization, EEG/ECoG findings, and hypermetabolic foci located by PET. An MRI correctly identified the resected histopathological lesion in five cases and it was negative in two. Three patients had Focal Cortical Dysplasia (FCD), one had FCD with areas of polymicrogyria, one had temporal lobe cavernoma associated with hippocampal sclerosis, and one had a focal subcortical heterotopia. Mean postsurgical follow-up was 29.1 months (range: 16-24 months) and all patients were seizure free during this period. This small series of patients who underwent surgery for intractable focal epilepsy have shown good correlation between the ictal F18-FDG PET/CT scan and the electroclinical and pathological findings. These results suggest that hypermetabolic foci showed in PET/CT provides a reliable estimation of epileptogenic zone. Focus size underestimation in one case suggest the need of doing an interictal PET before surgery.