COMPARISON BETWEEN TL-201-CHLORIDE AND TC-99(M)-SESTAMIBI SPET BRAIN IMAGING FOR DIFFERENTIATING INTRACRANIAL LYMPHOMA FROM NONMALIGNANT LESIONS IN AIDS PATIENTS

The aim of this study was to compare Tl-201-chloride and Tc-99(m)-sest amibi (MIBI) SPET brain imaging for differentiating brain lymphoma fro m other intracranial lesions in AIDS patients. Both studies were perfo rmed on the same day in 17 AIDS patients with intracranial enhancing l esions on either CT or MRI. Eleven patients underwent brain biopsy and six patients were followed clinically. We calculated the radiopharmac eutical uptake ratio of the lesion to that on the contralateral side w ith the guidance of CT or MRI findings. Ratios of 1.5 or more were con sidered to represent malignant lesions and ratios <1.5 were considered to represent benign lesions. Biopsy revealed four cases of lymphoma, four cases of toxoplasmosis and two cases of progressive multi-focal l eukoencephalopathy; one biopsy yielded necrosis. Both the MIBI and Tl- 201 studies yielded no false-negative cases of lymphoma (sensitivity 1 00%). Of the 13 non-lymphoma cases, the Tl-201 studies showed seven tr ue-negative cases (specificity 54%) and the MIBI studies showed nine t rue-negative cases (specificity 69%). The biopsies of the false-positi ve cases (toxoplasmosis) showed a pattern of healing after medical tre atment. We conclude that MIBI is more helpful than Tl-201 because of h igher specificity and equal sensitivity. The medical treatment of toxo plasmosis is a cause of false-positive Tl-201 and MIBI studies.