Hi Jane,
This is only my opinion, so take it for the 2 cents its worth.... we know MRI's on AN's have a +/- 2mm, so as you did not state what the size difference was between the 9 mos and 5 months later (what it is now), I cannot directly reply. Yes, it may swell just a hint bit more, but also, does the size differential fall in line with the +/-2mm? As for the necrosis, well, for me (and only me), that is the key.
You note you don't have the report yet, so let me ask you this... was the MRI done at the same location as the past MRI's? Did you ask for a copy of the report? Maybe when the report comes in, it may note "more rim enhanced growth" (necrosis) or some other wording to help put you at ease. For me, difficult to state since it sounds like you glanced at your films unless the MRI tech/radiologist noted something in particular to you.
Again, just my 2 cents... bet someone else has thoughts worth more.
Phyl