Use of thallium-201 brain SPECT to differentiate cerebral lymphoma from toxoplasma encephalitis in AIDS patients.

PURPOSE To determine whether thallium-201 brain single-photon emission CT could be used to make the distinction between central nervous system lymphoma and toxoplasma encephalitis, which may not be possible by routine MR and CT.

METHODS A total of 37 patients with acquired immunodeficiency syndrome who had intracranial mass lesions found during a 9-month prospective study by either MR or CT underwent further evaluation with Tl-201 brain single-photon emission CT.

RESULTS Twelve patients had increased intense focal Tl-201 uptake. All of these patients had either biopsy- or autopsy-proven lymphoma. Twenty-five of the patients studied had no Tl-201 brain uptake in the lesion(s); 24 of these patients had toxoplasma encephalitis on clinical follow-up. One patient with no Tl-201 uptake was found by cerebrospinal fluid analysis to have mycobacterium tuberculosis abscess.

CONCLUSION Patients with acquired immunodeficiency syndrome who have intracranial mass lesions on MR or CT may benefit from Tl-201 brain single-photon emission CT because it can help distinguish between lymphoma and infectious lesions such as toxoplasma encephalitis.