Metabolism of the developing brain: Retrospective [¹⁸F]FDG analysis in a pediatric cohort.

Objectives: During development, the brain undergoes anatomical and functional changes that include a series of organizational events such as proliferation of neurons and their migration to specific loci. The metabolic evolution of the maturing brain from birth has not been extensively studied. Furthermore, the advent of PET imaging and various metabolic radiotracers can enhance our understanding of anatomical, functional, and organizational changes that occur in the developing brain. It is the aim of this retrospective study to delineate these metabolic changes in a cohort of pediatric patients undergoing [¹⁸F]FDG PET/CT scintigraphy.

Methods: IRB approval was obtained. We retrospectively identified patients aged 0-21 years who underwent FDG PET/CT which included the entire brain. Suboptimal studies due to poor pre-procedural preparation or patients with underlying brain pathology were excluded. Nuclear medicine imaging software (HybridRecon, Hermes Med Solutions, Stockholm) was used to interrogate brain regions (frontal, parietal, occipital, temporal lobes, brain stem, thalamus, basal ganglia) obtaining SUV measurements; measurement of liver, blood pool, soft tissue, heart, and brown fat were also obtained. An adult cohort without underlying brain pathology was used as control.

Results: 97 studies in 55 children (27M; 28F) and 5 controls (2M; 3F) were analyzed. SUV_max of each brain region shows a general upward trend over the first 2 decades. By linear regression, the greatest effect was found in the occipital lobe followed by parietal lobe, basal ganglia, frontal lobe and thalamus. Smaller increases in FDG consumption over time were observed in the temporal lobe and brain stem. Although a clear trend was observed, there was large variability between different subjects and within different scans of the same subject. Conclusion: Metabolic changes occurring in the brain in relation to cognitive and behavioral maturational milestones are essential in understanding structural and functional morphologies in both normal and especially disease states. Our in-vivo study confirms in man the results of many animal investigations which have demonstrated that cerebral oxygen and glucose consumption in developing rats follow a sigmoid rise between birth and adulthood as the immature brain uses ketone bodies as substrates for energy metabolism and biosynthesis, sparing glucose which is in low supply in the early developmental period. The point at which the brain transitions between metabolic substrates in specific regions may have far reaching implications in normal and pathologic development and should be a basis for future investigations.