Abdominal aorta is significantly atherosclerotic however not significantly dilated.

Significant means important, of consequence.

If the aortic atherosclerosis is important, it warrants further description. Things like location (infrarenal, diffuse), calcified or soft plaque, visceral vessel ostial involvement etc. should be reported. (If there is no contrast, then I think “calcified” is better than “atherosclerotic”, since you can’t assess non calcified atheromas.)

Saying the aorta is not significantly dilated gives the impression that it is dilated. If it is dilated, is it mildly dilated? If it’s not dilated, then say something like “the aorta is not dilated”, or “aorta had normal caliber” or “no aneurysm”.

rewrite: The infra-renal aorta is moderately calcified but not dilated.