Radiographic presentation of multifocal PCNSL, characterized by distinct MRI sequences. (A) T1 postgadolinium image demonstrates an enhancing mass involving the left frontal lobe (arrows) with central necrosis and surrounding vasogenic edema. On spectroscopy the mass demonstrated increased tumor metabolites, lactate, and choline (not shown). (B) An apparently isolated, second homogeneously enhancing mass (arrow) is identified inferiorly, involving splenium of the corpus callosum. (C) No enhancing foci are detected in white matter between the 2 distinct lesions. (D) Diffusion-weighted imaging demonstrates foci of reduced or restricted diffusion (arrows), suggestive of dense cellularity, in the superior aspect of the frontal mass. (E) Restricted diffusion within the enhancing lesion involving the corpus callosum, strongly suggestive of lymphoma. (F) Extensive T2/FLAIR signal hyperintensity (arrows) extending from the frontal mass posteriorly to the corpus callosal lesion, consistent with nonenhancing lymphoma dissemination involving the cerebral hemisphere.