Would abdominal aorta aneurysm show up on a abdominal x-ray?

Not reliable test. If an abdominal aortic aneurysm (AAA) has been present for a long time, calcium deposits in wall of the AAA may be visible on x-ray but this is unreliable. An ultrasound or ct scan are better, excellent, studies to diagnose an aaa.
Infrequently . Most abdominal aortic aneurysms will not show up on a plain x-ray. In fact, these may not even show up on a fluoroscopic angiogram (an xray taken with special dye that shows the outline of blood flow in an artery). The best screening test is a duplex ultrasound of the abdomen. Infrequently, an aneurysm will be calcified and be seen on plain x-ray -- but many more will be missed on x-ray alone!