Rapidly progressive dementia caused by nonenhancing primary lymphoma of the central nervous system.

A 76-year-old woman had rapidly progressive dementia over 4 months. Proton density- and T2-weighted MR images of the head showed increased signal in the periventricular and subcortical white matter of both cerebral hemispheres and the brain stem. Enhancement was not seen after administration of contrast material. Because of the rapid progression of the dementia and increasing signal abnormalities within the cerebral white matter, the patient underwent a craniotomy with biopsies of the right frontal lobe. Pathologic specimens were positive for malignant large-cell lymphoma, B-cell phenotype. The MR appearance is atypical for primary lymphoma of the central nervous system.