What is the differential diagnosis based on the CT appearance?
The differential includes tumours (high grade glioma, metastasis, lymphoma (less likely)), infection (cerebral abscess), demyelination, resolving infarct / contusion, radiation necrosis.
Which of these need to be considered the diagnosis until it can be excluded?
A cerebral abscess needs to be considered (especially as it turns out this patient was febrile), as prompt surgical evacuation is required before it enlarges or ruptures into the ventricles or extra-axial space.
What is the next step in the assessment of this patient?
An MRI is required as it is usually able to confirm or exclude the diagnosis.
Centred on the grey-white matter junction of the right frontal lobe is a ring enhancing lesion (which is slightly hyperdense pre-contrast) surrounded by low density white matter change, consistent with vasogenic oedema. This has moderate local mass effect.
Low density in the left occipital region with volume loss is consistent with an old area of gliosis. No other abnormality.