Central nervous system manifestations of systemic haematological malignancies and key differentials.

Central nervous system (CNS) involvement by haematological malignancies is uncommon, and generally associated with a poor prognosis. Neuroimaging plays a key role in the accurate diagnosis, including in the critical differentiation from other processes such as infection and treatment-related toxicity. This review illustrates a variety of manifestations of CNS involvement by haematological malignancies and relevant differential diagnoses. CNS involvement can be seen in lymphoma (both primary and secondary), Waldenström macroglobulinaemia, multiple myeloma, leukaemia, and the malignant histiocytoses. The typical patterns vary between the different disorders, for example, in the most common sites of involvement and the relative frequency of parenchymal and meningeal involvement. Adjacent structures may also be involved. Nevertheless, there is some overlap in the imaging appearances, with common features including pre-contrast hyperdensity on computed tomography (CT), diffusion restriction, and avid post-contrast enhancement. In the post-treatment context, it is also important to distinguish between disease relapse and post-treatment effects. This includes opportunistic infections and the effects of chemotherapy and/or radiotherapy, including toxic effects and radiotherapy-induced neoplasms.