I am no expert patty but i think the three different scans(mri,cat and bone)each have there own area of definition(tumour,tissue,bone)and i guess they will all show fluid but they dont all define tissue and tumour.Lymphatic fluid is mostly diagnosed by physcial exam(soft and spongy and leaves an impression when pressed as opposed to tissue scarring which is hard and tumour which doesn't leave a indentation when pressed If the tumour is anywhere around the trachea(windpipe)then as it grows it pushes the windpipe off centre and narrows the width,reducing the oxygen intake (a bit like pressing on it with your finger)so you may feel you are gasping for breath.I think the point is if the last scan identified where the new tumour is situated then they should know from your symptoms how it is developing.I cant imagine why they are not discussing this with you.Sorry i cant help more.

liz