Imaging description

Progressive multifocal leukoencephalopathy (PML) is a demyelinating disorder of the brain caused by the JC virus (JCV). PML is most frequently seen in HIV/AIDS patients and patients with hematological malignancies [1]. On MRI, characteristic features of PML include unifocal or multifocal areas of hyperintensity on T2-weighted/FLAIR images, and corresponding areas of hypointensity on T1-weighted images with no associated mass effect or enhancement on post-contrast T1-weighted images [2]. Lesions can be patchy or confluent and involve the subcortical white matter including the U-fibers and the cerebellum (Fig. 20.1). The middle cerebellar peduncle is a common site of involvement (Fig. 20.2).

Diffusion-weighted imaging (DWI) may show variable signal; increased DWI signal corresponds to the sites of active infection [3]. Rarely, multiple sclerosis patients receiving natalizumab (a monoclonal antibody) may develop PML, which may show post-contrast enhancement. The diagnosis of PML is established by demonstrating the JCV DNA in CSF or brain biopsy.