Neuroimaging example of PCNSL. MRI of the brain showing an expansive mass lesion in the right frontal lobe, which is hypointense in noncontrasted T1 scans (A), isointense with respect to cortex in T2-weighted images (C), with reduced average diffusion coefficient (B), and homogeneous contrast enhancement in contrasted T1 weighted scans (D arrows). Lesion is surrounded by modest edema (A arrows). CT and MRI findings are attributed to the high cell density and scant cytoplasm. Enhancement along the Virchow-Robin spaces, although not constant, is a highly specific feature of PCNSL.