What is the most likely diagnosis?
The location and the fact that it is a number of weeks since onset suggests that this represents a subacute infarct of haemorrhage.
What is the differential diagnosis?
The differential is that of a peripherally enhancing lesion and includes GBM, metastasis, radiation necrosis and demyelination although the last two are very unlikely given the history and age.
A region of irregular peripheral enhancement involves the left lentiform nucleus and internal capsule.