I haven't looked at your pics but atrophy is caused by aging... it's common. Atrophy can also be caused by MS. I bet there are a lot of other things that also cause atrophy.
The only way you would know that the brain is atrophied or shrinking is to compare it to prior MRIs. That is why baselines are so important.
I wouldn't worry about atrophy until you see a doc and am told there's a problem.
Off to look at your pics -
Lulu
Oh, that's a comfort LOL. What would cause that?
(the atrophy)
Hey, they look like MRI scans to me! I see some lesions, but not a whole bunch of them. Looks like you might have a bit of atrophy - there's a lot of space between the brain and skull.