THE NEUROIMAGING features of progressive multifocal leukoencephalopathy (PML) are characterized by decreased attenuation on computed tomographic scans and an increased signal on T2-weighted magnetic resonance imaging scans, with lesions most often involving periventricular and subcortical white matter in parieto-occipital or frontal lobes and occasionally the posterior fossa, with rare enhancement and absence of mass effect.1 We describe a patient diagnosed as having PML by the findings of brain biopsy and cerebrospinal fluid polymerase chain reaction in whom the diagnosis was initially not considered because of the mass effect demonstrated on neuroimaging scans.
Finelli PF. Mass Effect in Progressive Multifocal Leukoencephalopathy. Arch Neurol. 1998;55(8):1148-1149. doi:10.1001/archneur.55.8.1148