Pseudoprogression in low-grade glioma

Pseudoprogression (PsP) is a common phenomenon seen after radiotherapy (RT) for primary brain tumors. PsP is a post-treatment related effect that is identified by increased enhancement on T1-weighted MRI, or increased hyperintensity on T2/FLAIR, with subsequent stabilization or resolution without any intervention. This imaging finding may or may not be accompanied by clinical symptoms, and the timing of this phenomenon is thought to be subacute, or in the initial 3–6 months post-treatment. The mechanism of PsP is unclear but proposed to be due to treatment-induced endothelial cell death and subsequent disruption of the blood-brain barrier; this alteration in the blood-brain barrier contributes to the increased uptake of gadolinium seen on MRI and vasogenic edema on T2/ FLAIR (1). PsP can be thought of as being on a spectrum of post-treatment effects that include mild, transient imaging changes not concerning for progression, PsP, or radiation necrosis.