Generally, The mean normal value for the aortic root annulus in men is 2.6 cm and for the proximal ascending aorta 2.9 cm . The upper normal limit for the ascending aorta is 2.1 cm/m2 (note per m2), so a value beyond 4 cm is regarded as an aneurysm, a lower value as ectasia. The normal value for the descending aorta is 1.6 cm/m2 for BSA, and aneurysm is present when a value of 3 cm is exceeded. The aortic arch is inbetween those two structures. I wasn't able to find exact references because these values aren't commonly reported here. The fact that there is dilation of the brachiocephalic is concerning, but not as dangerous as the ascending dilation because these vessels typically aren't at risk for rupture. At this point, you should continue to get the periodic screenig. Since I am not an expert in the field of arotic arch disease, I will ask a colleague of mine to comment on these findings and will get back to you.
Just wanted to add the exact wording from the report in case it makes any difference:
"The aortic arch between the brachiocephalic and right common carotid measures 3.2 cm."
Thanks again!