What is the most likely diagnoses?
A high grade glioma (glioblastoma) or solitary metastasis are most likely.
What is the broader differential for this sort of lesion and what mnemonic is useful?
MAGIC DR L is a good way of remembering the differential for peripherally enhancing cerebral lesions. Metastasis, Abscess, Glioblastoma, Infarct (resolving), Contusion / haematoma (resolving), Demyelinating disease, Radiation necrosis, Lymphoma (in immunosuppressed patients).
Without the previous history of breast cancer, which entity would you think to be most likely? why?
A large solitary lesions seemingly centred in the white matter with extensive central necrosis in this age group is more likely to be a glioblastoma, especially if there isn't a history of malignancy elsewhere.
What investigations would be helpful in preoperatively distinguishing between a glioma and a metastasis?
MRI is most useful. MR spectroscopy and MR perfusion are both helpful and usually enable the distinction to be made.
A large heterogeneous mass is centred into the right temporal lobe, elevating the MCA vessels in the Sylvian fissure and resulting in uncal herniation which in turn pushes the midbrain towards the left.
The mass has central non-enhancing liquid density components, and irregular peripheral enhancement. It is surrounded by vasogenic pattern oedema.