Abstracts

Rationale: 2-deoxy-2[F-18]fluoro-D-glucose positron emission tomography (FDG-PET) is commonly used to assist localization of epileptic foci in children with intractable epilepsy. However, objective identification of metabolic abnormalities on pediatric PET remains difficult due to the lack of age-matched healthy controls. Adult healthy controls have been used with some success using statistical parametric mapping, but this approach has not been validated in children below 6 years of age. An alternative approach is to utilize a "pseudo-control" group from pediatric PET databases, including PET scans of epileptic children showing a normal metabolic pattern, as originally used by Chugani et al. (Ann Neurol, 1987;22:487-97). A more recent study demonstrated that this approach could improve specificity of detecting metabolic abnormalities (Archambaud et al., EJNMMI Res, 2013; 2013;3:2). The purpose of the present study was to generate and characterize a large pseudo-control pediatric PET group across a wide age range (1-18 years) that could be used in both asymmetry- and voxel-based objective pediatric PET analyses. Methods: From a pediatric database of 1500 PET scans acquired using a single PET/CT scanner at the Children's Hospital of Michigan (Detroit) between 2006 and 2013, we first identified 185 scans reported to have a normal glucose metabolic pattern. After reviewing electro-clinical data, MRI and PET images, we selected interictal PET scans of children with non-lesional MRI and absence of frequent epileptiform activity on EEG. On all selected PET scans, FDG uptake was measured in bilateral cortical and subcortical regions. Cortico-thalamic FDG uptake ratios and left/right asymmetries were calculated and compared between genders and correlated with age, clinical seizure variables, and antiepileptic drug treatment. Results: A total of 64 children (33 boys) were selected with a mean age of 9.05.2 years (range: 1-18 years). The mean duration of epilepsy was 3.73.2 years; the most common seizure frequency was less than one per month (n=20). Handedness showed a normal distribution (with 10% of the patients being left-handed). Cortico-thalamic FDG uptake ratios in the 64 children showed a non-linear variation with age, variably increasing between age 1 to 5 years in different regions, then reaching a plateau, largely corresponding to previously reported maturational changes on PET in different pediatric groups (Chugani et al., Science, 1986;231:840-3; Hua et al., J Nucl Med 2015;56:575-9). Mean regional cortical and subcortical left /right asymmetries were the lowest in the frontal cortex (0%) and the highest in the parietal cortex (4%), with lower values on the left side, regardless of handedness (Table 1). The highest variability of asymmetries was seen in the temporal cortex and hippocampus (Table 1). Left/right asymmetries of regional FDG uptake showed no correlation with age, seizure variables, handedness, and number of antiepileptic medications. Mean left/right hippocampal asymmetries were greater in boys as compared to girls (p=0.02). Conclusions: While cortico/thalamic ratios show a previously described age-related change, metabolic asymmetries in this pediatric epilepsy group with normal MRI and glucose metabolic pattern are stable above 1 year of age but show regional variations. Only hippocampal metabolic asymmetries showed a gender difference, with a higher asymmetry in boys. FDG-PET scans of this large, carefully selected pediatric pseudo-control group can be used in studies for both asymmetry- and voxel-based objective PET analysis to identify focal glucose metabolic abnormalities in children with epilepsy across a wide age-range of 1-18 years. Funding: None