I'm just a medical writer with zero expertise in this area, but I've been assuming GL had an abdominal aneurysm. I think another poster referred to it as this too. If this was the case, I guess I don't really understand why the doctor hasn't used the specific name (other than the fact that in general they're giving out no details). Anyway, there's some general information about abdominal aneurysm on the Guidant web site:
http://www.guidant.com/condition/aaa/condition.shtml