Brain mets or scar tissue?

Hi,
I have had brain mets 3 times (2001,2002 and 2004). The first two times I had a cranionomy. They were both single lesions (3cm and 7mm). the last time was a year ago and it was a 5mm lesion which I had stereotactic surgery which went well except now I have scar tissue. The scar tissue is increasing and the doctors are unsure if it is brain mets or scar tissue. I have no s/e, no mass effect, no edema. Has this happened to anyone else? My doctors tell me it can happen and the only way to know for sure is a biopsy. Help!!