The patient went on to have a brain biopsy (right frontal lobe) 

Histology

MICROSCOPIC DESCRIPTION
The sections  of  cerebral  white  matter are  mildly  hypercellular,  with focally prominent perivascular  lymphocytic cuffing.   There are diffusely increased astrocytes  through the tissue, as well  as a light scattering of macrophages and  activation of microglial  cells.  The  lymphocytes cuffing vessels are predominantly small CD3-positive T cells.  Within some of these vessels are large atypical  lymphoid cells with a  high proliferative index on the Ki67 stain.   Occasional single large atypical  B-cells are present within  perivascular   parenchyma.   The  features  are consistent  with a diagnosis of intravascular large B cell lymphoma.
 
DIAGNOSIS

Right frontal white  matter biopsies  - large B-cell  non-Hodgkin lymphoma, consistent with intravascular large B-cell lymphoma.