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.
I know CT scans with contrast are the protocol for anuerysms in the abdomen and chest, don't know about the brain though.
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 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.