If it be that they leave behind a cell or two with surgery there is always a chance it will grow, that is the theory as to why I had AN in the same place twice (rather than just grew a brand new one in the same place).
I myself will never know if they got it all this time or not as my intention is to never have another MRI, I do not ever want to hear those words again "you have a brain tumor", I do not intend to have "follow up" MRI's to check if they got it all or not, I don't want to know they didn't and the surgeon said he did so I won't have another MRI unless there is another reason to do so under which circumstances I will tell the doctor I don't want a look at they pic's and I don't want to know if they is an AN in there on either side. My regrowth didn't have to be removed because of the physical aspect of it rather what it was doing to me psychologically knowing it was in there and growing.
Kathleen