Brain MRI of progressive multifocal leukoencephalopathy after cardiac transplantation

T2-weighted (A) and FLAIR (B) images show hyperintensity in a confluent bifrontal pattern. Pre-contrast T1- weighted image (C) shows hypointensity in the lesion. Post-contrast T1-weighted image (D) demonstrates enhancement along the periphery, or advancing edge, of this lesion, suggesting a region of more active disease. The diffusion-weighted image (E) shows hyperintensity along this leading edge. The corresponding ADC map (F) shows diffuse increase in signal intensity suggesting facilitated water diffusion; however, there have been reports of restricted diffusion at the periphery (refer to text).