The following photos are taken from a stereotactic brain biopsy from the right frontal lobe of a 22-year-old man with AIDS. He complained of progressive headaches, and brain MRI found many non-enhancing lesions in the subcortical and deep white matter. Figures 1-2 are smear cytology, figures 3-4 are frozen section, and figure 5-12 are from paraffin sections at various magnifications. What are your differential diagnoses?