Primary and secondary lymphoma of the central nervous system. Conventional and functional magnetic resonance imaging findings

Lymphomas, and their different radiological presentations have motivated recent publications in the Brazilian radiological literature. Primary lymphoma of the central nervous system (CNS) is becoming increasingly diagnosed both in immunocompetent and immunocompromised patients, and therefore recognition of the several imaging characteristics of such tumor in the conventional and functional imaging studies is essential. Currently, primary lymphoma represents 70% to 90% of all CNS lymphomas. It is the most common CNS tumor after meningioma and glioma. Central nervous system lymphoma is almost always a B-cell non-Hodgkin’s lymphoma. Its high cellularity and high nucleus to cytoplasm ratio result in some of the most known radiological characteristics of this tumor, such as hyperdensity on the computed tomography study, isointensity on the T2-weighted image, and restricted diffusion. In an excellent article published in the present issue of Radiologia Brasileira, Reis et al. describe some of the main radiological characteristics of primary and secondary CNS lymphomas at conventional magnetic resonance imaging as well as in the advanced imaging studies such as proton magnetic resonance spectroscopy, diffusionand perfusion-weighted magnetic resonance imaging studies. The authors discuss the different tumor presentations (focal × multifocal), as well as the most typical tumor locations (periventricular, in the basal ganglia and corpus callosum). Characteristics of primary and secondary lymphomas are described, with leptomeningeal involvement, as well as infiltration of perivascular Virchow-Robin spaces and involvement of the cranial nerves most commonly observed in secondary lymphoma. There are some other less common presentations of CNS lymphomas such as lymphomatoid granulomatosis, intravascular lymphoma and lymphomatosis cerebri, which may represent a diagnostic challenge to radiologists. Another impor-