Can ultrasound miss an abdominal aortic aneurysm?

Possibly: If the u/s was not performed for the express purpose of looking at the aorta, or if there were technical considerations like intestinal gas or body habitus that made imaging difficult, then AAA could be missed. Ct will never miss the finding.

Not likely: Some are not ideal if too much gas. Or poor prep or obesity , but usually are repeated if technical issue. The infra renal aorta and iliacs are well visualized in most.