Biopsy proven CNS lymphoma. Features of this CNS neoplasm are:

• the great majority are diffuse large B-cell, non-Hodgkin lymphomas
• usually supratentorial
• usually hyperdense on CT and showing restricted diffusion on DWI/ADC (high cellularity)
• periventricular and subependymal locations are typical 

The involvement of the corpus callosum in this way has a few differentials to be considered: PCNSL, glioblastoma, and metastasis. 

Also in this case, a further right extra-axial lesion over the pterion has featured in keeping with a meningioma.