Abstract
Malignant central nervous system (CNS) tumors are often treated with radiation therapy, after which clinical and radiographic sequelae can lead to difficulties differentiating tumor recurrence from treatment effect. Magnetic resonance imaging (MRI) is often unable to distinguish between these two entities. The improved ability to delineate concerning foci could lead to earlier tumor detection with quicker access to new therapies and/or clinical trials; conversely, it could alleviate patient concerns in the case of radiation necrosis as the etiology. The utility of positron emission tomography with computed tomography (PET/CT) imaging with fluorodeoxyglucose (FDG) has been explored in CNS tumors in the past, as this imaging modality is widely used in oncologic practices. As there are concerns with false positive imaging in the case of cells with a high metabolic uptake due to causes other than malignancy (i.e. infection, inflammation), delayed FDG PET imaging has been proposed as a mechanism to reduce this confusion. Delayed FDG PET imaging has been explored in several adult and pediatric malignancies, including adult CNS tumors, though there are no current publications applying its use in pediatric CNS tumors. We present two cases of pediatric CNS tumors, where delayed FDG PET imaging helped in the early diagnosis of a recurrence through a distinguishing tumor from the treatment effect.