Cause: underlying malignancy, collagen disease, cancer therapy, AIDS, immunosuppressive therapy in organ transplant

Organism: Toxoplasma, Nocardia, Aspergillus, Candida, Cryptococcus

• poorly defined hypodense zones with rapid enlargement in size + number, particularly affecting basal ganglia + centrum semiovale (poorly localized + encapsulated infection with poor prognosis)
• ring / nodular enhancement (sufficient immune defenses): Toxoplasma, Nocardia
• enhancement may be blunted by steroid Rx

AIDS may be associated with:

• thrombocytopenia, lymphoma, plasmacytoma, Kaposi sarcoma, progressive multifocal leukoencephalopathy