Use of fluorodeoxyglucose-positron emission tomography for the differentiation of cerebral lesions in patients with acquired immune deficiency syndrome.

Intracranial mass lesions comprise approximately half of all acquired immune deficiency syndrome (AIDS)-related neurological complications. Although toxoplasmosis and lymphoma are the most common causes of these lesions, diagnosis and treatment can be delayed because computerized tomography and magnetic resonance imaging studies cannot accurately differentiate between them. The authors retrospectively studied nine patients with AIDS in whom, after a 6-hour fast, [18F]-fluorodeoxyglucose (FDG)-positron emission tomography (PET) scanning demonstrated intracranial mass lesions. The FDG uptake within each lesion was classified as either increased or not increased. In six patients there was no increase in FDG uptake, which suggested a diagnosis of toxoplasmosis, and lymphoma was suggested in two patients in whom increased FDG uptake was demonstrated. In a patient with two lesions, one lesion was shown to have increased FDG uptake whereas the other was shown to have no increased FDG uptake. All patients in whom a diagnosis of toxoplasmosis was made were started on antimicrobial therapy. Two patients died of other AIDS-related complications before repeated neuroimaging could be performed to assess treatment response, one patient refused to undergo further treatment or follow up, and two patients responded well to treatment. One patient with toxoplasmosis did not respond to the drugs. Analysis of a biopsy sample of the lesion confirmed the diagnosis; however, the patient died shortly thereafter. The two patients with FDG-PET-diagnosed lymphoma began corticosteroid therapy and improved considerably. In the patient in whom PET demonstrated two different FDG uptakes, a biopsy sample was obtained that confirmed the diagnosis of lymphoma; this patient was started on corticosteroid therapy and improved. A safe and reliable diagnostic tool, FDG-PET scanning can be used to differentiate causes of human immunodeficiency virus-related intracranial mass lesions. When available, this diagnostic study should be conducted before initiating empirical treatment or obtaining a stereotactically guided brain biopsy sample.