Hi, sorry to hear that, it must be concerning for you.
I've just posted my post year MRI discussion in the thread " swelling post gamma." My AN has swelled, by 3.5mm, then gone done a bit but still larger by 2.5 mm on pre treatment size, now at 17mm.
I had linac SRS single dose in the UK. I asked the neurosurgeon if the AN can swell, go down but then swell up again. He said yes.
I asked if mine was cystic but he evaded answering that, but said basically if the tumour has swelled then gone down a bit, you can get cystic degeneration although he didn't see any on my MRI. Swelling causes fluid build up, ie oedema and when it goes down you are left with some fluid where the this has happened. I hope I got that right!
So I suppose if it swells again , it could be fluid. Although one worries what is swelling and what is growth. Hope yours is not growth. Let us know how you get on.
Alison x