Section Editor: Sandy Cheng-Yu Chen, M.D.
Taipei Medical University Hospital, Taipei, Taiwan
CNS lymphoma is a malignant neoplasm, primarily composed of B lymphocytes, which tends to involve the leptomeninges, corpus callosum, periventricular white matters, and the subcortical nuclei. The dense cellularity of the tumor accounts for its isodensity or hyperdensity on non-contrast CT scan. On MRI the tumor often appears hyerintense on DWI (arrow, A) and well-enhanced after gadolinium injection on T1WI (arrows, B). In this case the histopathology revealed infiltration of brain tissue by the large tumor cells, particularly in the perivascular space (figure C).