Hypermetabolism on Pediatric PET Scans of Brain Glucose Metabolism: What Does It Signify?

When one is interpreting clinical 18F-FDG PET scans of the brain (excluding tumors) in children, the typical abnormality seen is hypometabolism of various brain regions. Focal areas of hypermetabolism are noted occasionally, and the usual interpretation is that the hypermetabolic region represents a seizure focus. In this review, I discuss and illustrate the multiple causes of hypermetabolism on 18F-FDG PET studies that should not be interpreted as seizure activity, as such an interpretation could potentially be incorrect. Various conditions in which focal hypermetabolism can be encountered on 18F-FDG PET studies include interictal hypermetabolism, Sturge-Weber syndrome, changes associated with brain plasticity after injury, Rett syndrome, hypoxic-ischemic brain injury, various inborn errors of metabolism, and autoimmune encephalitis. The radiologist or nuclear medicine physician interpreting clinical 18F-FDG PET studies should be aware of these circumstances to accurately assess the findings.