Primary CNS lymphomas (PCNSL) are relatively uncommon tumors, accounting for 2.5% of all brain tumors. There are multiple subtypes of primary CNS lymphomas including AIDS related diffuse large B-cell lymphoma, EBV-positive diffuse B-cell lymphoma, MALT lymphoma of the dura and intravascular lymphoma. Al subtypes share relatively similar radiographic features. PCNSL present as solitary (60-70%) or multiple (30-40%) lesions with a predilection for the periventricular white matter, although they can also arise in the cortex or deep grey matter; the latter being more common in low-grade lesions. 

Epidemiology

PCNSL is usually diagnosed in patients over the age of 50 with a relatively short duration of symptoms (weeks to months). The disease is diagnosed twice as much in men. There is a strong correlation with immunodeficient states including HIV/AIDS. 

MRI features

T1: T1 imaging typically shows a signal hypointense to grey matter.

T1 C+ (Gd): typical high-grade tumours show intense homogeneous enhancement while low-grade tumours have absent to moderate enhancement. Peripheral ring enhancement may be seen in immunocompromised patients (HIV/AIDS) 

T2: T2 imaging is highly variable, the majority of lymphomas are iso to hypointense to grey matter: isointense: 33%, hypointense: 20%. A hyperintense signal is present in 15-47% of tumors and is more common in tumors with necrosis. 

DWI/ADC: Lymphomas tend to show restricted diffusion with ADC values lower than normal brain. 

MR perfusion: Perfusion in lymphomas is only modest, if any.