Imaging findings of this patient. a Chronological changes in brain magnetic resonance imaging (MRI), fluid attenuated inversion recovery (FLAIR; top row), and diffusion weighted imaging (DWI, bottom row) on an axial view. Eight days following the patient’s admission, a FLAIR image revealed a high signal lesion in the cerebral white matter, which was dispersed in the central bilateral frontal lobes. Signal elevations were also revealed on DWI. (left) Twenty-five days following the patient’s admission, the number of high signal white matter lesions increased on FLAIR and DWI, and the discrete lesions expanded. (middle) Fifty days following the patient’s admission, the lesion with an elevated FLAIR signal expanded further to cover the entire bilateral frontal lobes. On DWI, the patient’s lesions had altered signal facilitation in the center and a restricted signal along the edge with perilesional edema. (right). b T2-weighted magnetic resonance (MR) images (top row) demonstrated signal changes in the perivascular lesion. T1-weighted magnetic resonance imaging with contrast administration 25 days following the patient’s admission revealed enhanced vasculature (likely veins). (white arrow) Subsequently, a T2-weighted image taken 50 days after the patient’s admission revealed perivascular edema around the indicated blood vessel. (white arrowhead) Similar perivascular edema was identified in nearby blood vessels.