Hey shelli,
When I was first diagnosed (2005) my vertebrobasilar arteries were quite affected (narrowed), my surgeon was hoping that the bloodflow from my direct bypasses would "force open" these arteries and it appears this has happened to a degree.. The "fix" is not simple, not in that area anyway, my dr was suggesting an indirect bypass of sorts by wrapping a long muscle around the brain stem and letting that blood supply grow through.. However this is for extreme posterior, right in the back of the brain, I'm not sure if that was what your dr may have been referring to - or just posterior blood vessels such as the PCOM arteries... Anyway, keep us posted...