MRI PATTERNS OF PROGRESSIVE MULTIFOCAL LE UKOEUCEPHALOPATHY

Progressive Multifocal Leukoencephalopathy is a demyelinating disease. MRI shows high signal intensity areas on T2w sequence and low intensi ty aeras on T1w sequence, without enhancement after intravenous contra st injection. The involvement of arcuate fiber (U fibers) creates a sh arp border with the cortex. There is no mass effect. Involvement of pa rieto-occipital areas is frequent. The lesions may be uni or bilateral , single or multiple; bilateral lesions are asymmetric. This typical a ppearance on MR images occurs in 90 % of the patients with PML. Some a typical patterns may occur: focal hemorrhage, atrophy, faint periphera l enhancement and involvement of deep gray matter (basal ganglia). In most cases, the clinical and MR features provide the diagnosis. The ma in differential diagnosis, in MRI, is HIV-leukoencephalitis, but lesio ns are diffuse, less intense on T2w sequence and not visible on T1, wi thout involvement of the arcuate fibers. Stereotactic biopsy should be performed only for atypical lesions, particularly in case of predomin ant involvement of deep gray structures.