Table 1.
Lesion Type | Common Clinical Features | Common Radiographic Features |
---|---|---|
Tumor progression | Nodular growth on sequential imaging ≥3 mo apart Progression in systemic disease |
Rounded with either homogeneous or ring enhancement and clear delineation of lesion edge Perilesional edema Higher rCBV on perfusion imaging Higher Cho/Cr and Cho/NAA on MRS FDG PET of limited value Potential role for amino acid PET |
ICI-related pseudoprogression | Growth within weeks of ICI initiation Regression on sequential imaging separated by ≤3 mo Clinical stability |
Can be indistinguishable from tumor progression |
Radiation necrosis | More often found ≥6 mo after radiation therapy Increased incidence after ICI therapy May spontaneously regress on longitudinal imaging even if presenting with symptoms |
Rim-enhancing pseudopodic lesion with central necrosis on T1-postcontrast Perilesional edema of previous SRS target on FLAIR Lower rCBV on PWI Lower Cho/Cr and Cho/NAA on MRS |
Demyelinating lesion | History of autoimmune disease History of high-dose or high-brain volume radiation therapy Little to no growth on longitudinal imaging |
T2 hyperintense, T1 hypointense Little to no surrounding edema Juxtacortical, periventricular Homogenous enhancements; however, heterogeneous, nodular, ring-like (typically open ring), or tumefactive patterns may be found |
Cho, choline; CNS, central nervous system; Cr, creatine; FDG, 18F-2-fluoro-2-deoxy-D-glucose; FLAIR, fluid-attenuated inversion recovery; ICI, immune checkpoint inhibitor; MR, magnetic resonance; MRS, magnetic resonance spectroscopy; NAA, N-acetyl aspartate; PET, positron emission tomography; PWI, perfusion-weighted imaging; rCBV, relative cerebral blood volume; SRS, stereotactic radiosurgery.