Contrast-Enhanced Fast MRI in Differentiating Brain Toxoplasmosis and Lymphoma in AIDS Patients

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Abstract
Dynamic contrast-enhanced MRI was used to investigate space-occupying lesions of the brain in 22 AIDS patients without prior neurologic disease. Final diagnoses were toxoplasmosis in 13 patients (19 lesions), primary lymphoma in 7 patients (9 lesions), and both diseases in two (2 lesions, respectively). Dynamic contrast-enhanced MRI was done by using a heavily T1-weighted GE sequence (TR/TE 100/5, 80 degrees flip angle) performed before and repeatedly for a period of 15 min after intravenous bolus injection of Gd-DOTA (0.1 mmol/kg). Signal enhancement of the lesions and normal brain was measured as the difference of signal intensity before and after intravenous administration of contrast medium. Lymphomas displayed significantly greater enhancement (mean 67%; SD 18%) than toxoplasmosis did (mean 34%; SD 16%; p < 0.001) on FLASH images. The enhancement ratios of the two lesions were significantly (p < 0.01) different between 30 and 600 s after injection. The difference between toxoplasmosis (mean 49%; SD 17%) and lymphoma (mean 69%; SD 26%) enhancement ratios on delayed SE images was less significant (p = 0.04). Preliminary evidence suggests that dynamic sequences increase the specificity of MR in distinguishing between toxoplasmosis and lymphoma, and this has important clinical implications.

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