Case 1: Cellular infiltrate consisting of lymphocytes.

A closer look reveals atypical lymphocytes, with a slight condensation around the vessels.

A bit less cellular here. Image

Primary diffuse large B-cell lymphoma is the most common primary intracranial neoplasm in immunosuppressed patients (e.g. HIV, or post-transplant). Primary refers to the fact that these tumors arise within the CNS, whereas secondary DLBCL refers to extracranial CNS that secondarily involves. These tumors are strongly associated with EBV (>90% of cases). Mean CD4 count is usually less than 50/ul. Prognosis is generally poor.

On MRI, DLBCL may present as fairly discrete ring-enhancing lesions. Multiple lesions can be common. Histologically, the atypical lymphocytes infiltrate through the brain parenchyma and may accumulate around blood vessels. The lymphocytes express B-cell markers as well as BCL-6 and EBER.

→Of all the CNS lymphomas, diffuse large B-cell lymphoma is the most common subtype.

→Strongly associated with immunosuppression (e.g. HIV) and EBV infection.