We report a patient with a progressive brainstem syndrome, who on magnetic
resonance imaging had large bilateral, symmetrical, contrast-enhancing, inf
ratentorial space-occupying lesions. Biopsy of one of the lesions revealed
this unusual appearance to be due to a primary central nervous system (CNS)
lymphoma of B-cell type. Symmetry of lesions may be a clue to the diagnosi
s, perhaps reflecting the mechanism by which CNS lymphomas spread, fur J Ne
urol 6:721-723 (C) 1999 Lippincott Williams & Wilkins.