Primary Central Nervous System Lymphoma

The incidence of primary central nervous system lymphoma (PCNSL) has increased over the past several decades. The prevalence continues to remain higher in the immunocompromised than immunocompetent population. Despite advances in therapy, the prognosis remains poor with PCNSL. Early diagnosis and initiation of appropriate therapy is important for the long-term prognosis. Clinical presentations are variable, and neuroimaging plays a key role in suggesting the diagnosis. Computed tomography generally demonstrates iso- or hyperdense masses that homogeneously enhance. On magnetic resonance imaging, which is the study of choice, the lesions are typically iso- or hypointense on T1 and T2 sequences, and again enhance with contrast. The lesions may also demonstrate restricted diffusion on diffusion-weighted imaging, due to their dense cellularity. The cerebral hemispheres are the most common location, but the deep gray matter and corpus callosum are also frequently involved. Imaging patterns vary between immunocompetent and immunocompromised patients, with the latter group more likely to have multiple lesions and ring enhancement patterns related to central necrosis. Alternative imaging modalities may play a role in the diagnosis in certain circumstances. Numerous variations of PCNSL have been described, and are also discussed in this chapter.