Table 3:

MRI Features of PML

Features
LocationSubcortical white matter U-fibers
Predilection for frontal lobe > occipital lobe > parietal lobe
SizeSmall, <3 cm when asymptomatic
In symptomatic patients, lesions are often large (>3 cm)
MorphologyPunctate lesions often identified in asymptomatic PML
Symptomatic PML typically demonstrates more confluent and diffuse lesions
Microcysts
No associated edema or mass effect
T1WI and T2WIFLAIR hyperintensity with corresponding T1 hypointense lesions
T1 hypointesity is less pronounced in asymptomatic PML
DWIHyperintensity on DWI
T1 postcontrast30% will demonstrate linear or punctate enhancing lesions; if nodular or rim enhancement is present, active MS plaque or IRIS should be considered
SWILow signal intensity in U-fibers
Differential diagnosisMS plaque
Acute disseminated encephalomyelitis
Tumefactive lesion
Ischemic changes
Posterior reversible encephalopathy syndrome