What does this mean. on cta ? the right brachiocephalic artery and the left common carotid artery share a common trunk, anatomical variant?

This is a normal variant of the arteries Mentioned above. They both come off of a common larger artery. This is of no critical concern. Good luck.

Most likely the way you were born. Different than most as the Left common caroric usually comes off aorta separately from artery to the left arm. You might have s "steal" response when you exercise your Left arm as this can draw blood away from you L brain. If BP the same in both arms & no TIAs/dizziness with L arm exercise likely OK. Google branches off arota and look at images. Dicuws