Given the cerebral findings, and lack of a primary on the body CT, what is your favoured diagnosis?
An aggressive ring enhancing lesion, which crosses the midline, is suspicious for a high grade glial series tumour, probably GBM. Ependymal involvement is a poor prognostic marker.
If there was marked central high DWI signal with corresponding low ADC values, does anything else enter your differential?
Increased restricted diffusion indicates reduced extracellular space, either due to swollen cells or too many cells per voxel. Tumours do not typically restrict (lymphoma and medulloblastoma do), so abscess should be considered. However, this is not the situation in this case.
What histopathological results from the biopsy might affect treatment?
MGMT is a DNA repair enzyme. If this is methylated (on genetic testing), then there is a better response to some chemotherapeutic (alkylating) agents. Low grade gliomas tend to be methylated, while higher grade gliomas, as in this case, are unmethylated, usually with limited response to chemotherapy. This patient proceeded to undergo radiotherapy alone.
Solitary 5 cm right frontal lobe mass, crossing the anterior corpus callosum. The mass also extends to the ependymal surface at the right lateral ventricle.
Thick enhancing wall with non-enhancing centre, probable necrosis. No central increased diffusion signal, excluding abscess formation.
Local white matter FLAIR hyperintensity with mass effect as on CT.
Appearances, with unremarkable staging CT and with the lesion crossing the midline, favour a high grade glial series tumour.