Imaging modalities in high-grade gliomas: Pseudoprogression, recurrence, or necrosis?

High grade gliomas (HGG) frequently recur regardless of treatment. Radiological detection of progressive disease (PD) is challenging due to the possibility of therapy-related MRI changes including: pseudoprogression (PP) and radiation necrosis (RN). Both may mimic PD. We undertook a literature review to examine existing data regarding imaging modalities and their ability to distinguish between PP, RN and PD. The review revealed 26 articles comparing the value of imaging modalities used to differentiate PP, RN and PD. Overall, conventional MRI and 18fluorine-fluorodeoxyglucose positron emission tomography (18F-FDG PET) were more sensitive, while thallium single photon emission CT (SPECT) was more specific in differentiating PD from PP and RN. However, further prospective studies comparing the clinical utility of MRI, PET, and SPECT are needed to establish the most reliable diagnostic tool for the differentiation of PP, RN and PD in HGG.