Epstein Barr Virus (EBV)-associated primary central nervous system lymphoma (PCNSL) remains a major problem among AIDS patients. The clinical presentation is often clinically indistinguishable from toxoplasmic encephalitis. The method of choice for establishing the definitive diagnosis is brain biopsy. This procedure can be associated with a significant morbidity and mortality, and therefore less invasive means of diagnosing cerebral mass lesions have been studied.