Welcome to Connect, @carol1965.
I can imagine it would be worrisome to receive any diagnosis related to aneurysms. Blister aneurysms are a rare but well-recognized form of cerebral vascular lesions. Here’s some information about blister aneurysm: https://www.intechopen.com/online-first/blister-aneurysms

Since they are typically found on the wall of the internal carotid artery (ICA), I’d like to bring in @lizang @tanyabray41 @roch @skk15 @perion to join this discussion and offer their insights.
You may also wish to view this discussion: https://connect.mayoclinic.org/discussion/internal-carotid-artery-aneurysm/

@carol1965, could you share a few more details? Do you have any symptoms?