T2 hyperintensity and expansion straddling the midline is centred on the genu and anterior body of the corpus callosum, with signal abnormality extensively involving the frontal lobes bilaterally, the left insular and anterior temporal lobe, as well as bilaterally tracking inferiorly along the internal capsules. The lesion contains patchy areas of restricted diffusion. Although there are wispy areas of equivocal enhancement, there is no solid nodular enhancing component.
On diffusion studies, there is no cerebral blood volume (CBV) increase (not showed). Spectroscopy demonstrates an unusual trace with marked metabolite lesion but no associated lactate peak (not showed).
There is localised mass effect on frontal sulci and suprasellar cistern, but no uncal or descending transtentorial herniation.
IMPRESSION: Unusual constellation of findings. On morphologic grounds, lesion straddling the anterior corpus callosum would be most consistent with a glioblastoma, possibly ex-oligodendroglioma given presence of calcification on CT. The absence of significant enhancement and cerebral blood volume (CBV) increase would be atypical, although can be seen secondary to high-dose steroid therapy. The spectroscopy trace is very unusual for tumour, but the morphologic features and distribution still strongly favour GBM over alternate pathologies such as ischaemia.