Part 1
There are any number of things that can cause this presentation. We perform an MRI brain in both patients and and this is what we see:
In both cases there is a lesion that has very high signal on T2WI.
Which sequence will help us determine whether these lesions contain fluid or something else that is T2 hyperintense (e.g. blood or fat)?
FLAIR
Correct, if the lesion completely loses its signal on FLAIR we can be confident that it is filled with fluid.
T1WI
T1WI would be able to tell us whether the lesion contains acute haemorrhage or fat as the signal will be high, but it doesn't exclude old haemorrhage.
SWI
SWI will be able to pick up any acute haemorrhage or haemosiderin deposition but it is not the best sequence to confirm fluid.
CE-T1WI
CE-T1WI will tell us whether there are any enhancing components but it is not the best sequence to confirm fluid.