What are the key radiological and clinical features of Progressive Multifocal Leukoencephalopathy (PML) in immunosuppressed patients, and how does it differ in presentation between AIDS and non-AIDS patients?

Progressive Multifocal Leukoencephalopathy (PML) is a demyelinating disease caused by reactivation of the JC virus in immunosuppressed patients, such as those with AIDS, organ transplants, or hematological malignancies. It presents with high T2 and low T1 signal lesions in the subcortical and deep white matter, often without mass effect or contrast enhancement. In non-AIDS patients, lesions commonly affect the occipital lobes, while in AIDS patients, any brain region may be involved. Key diagnostic features include asymmetric, multifocal lesions and the absence of mass effect. Clinical pearls include rapid progression to neurological decline and death within months. Common mimickers include multiple sclerosis and gliomatosis cerebri, which may show contrast enhancement or mass effect, unlike PML.