A 77-year-old woman presented with worsening cognitive impairment, nausea and vomiting. Computed
tomography (CT) of the head revealed a high-density mass that symmetrically filled both lateral ventricles. Magnetic
resonance imaging (MRI) showed an enhanced mass with T1 and T2 prolongation and restricted diffusion on diffusion
weighted imaging (DWI). Diagnosis was delayed until a post-mortem examination, which revealed the mass as a primary
central nervous system lymphoma (PCNSL). A high-intensity tumor on DWI with lateral ventricle involvement should
raise the possibility of PCNSL.