i think some people can be born with that defect and i'm pretty sure u need an mra which means an angiogram instead of imaging.if u are worried about it than i would request an mra instead cause u don't wasnt to miss something.
My mom had an aneurism and it didn't show up on the scan...we requested that they do a sample of her spinal fluid, which showed that she needed immediate brain surgery. She would have died if we didn't do the spinal fluid test.
Hope this helps!
I know CT scans with contrast are the protocol for anuerysms in the abdomen and chest, don't know about the brain though.
I know for a fact that they do not always show up on MRI's or CAT scans because I had one that clotted itself off and it does not show up on any tests but yet they know positively that it happened because it happened while I was in the hospital after having child birth, I suffer to this day from the effects of that anuerysm and many doctors and pain management doctors and neurologist give me a hard time for wanting medication to help me with pain and seizures that I have since that day, they think it is all fake because narcotics won't stop the pain completely unless they knock me out, I don't want to be knocked out I just want my pain to be at a reasonable level to live with.