I can only speak from my experience, I have an aneurysm in the right carotid artery of my brain. I underwent an open craniotomy on 11/19/08, it was unsuccessful the Dr. Didn't have enough room to clip it, so therefore I was referred to another Dr. To have it coiled. On 12/23/08 I'm glad to say it was coiled successfully. The only side effects I had from the coiling were some severe headaches for several weeks and craniotomy ( spasms in the artery), both of which went away with time. I'm required to have an craniotomy every December for the next 5 years so that it can be monitored closely. There are risks either way you go, but there is even a greater risk if you do nothing. Hope this helps.
