How large must the thoracic and abdominal aortas be to be called aneurysmal?
Any artery dilated by more than 50% of its normal caliber is called aneurysmal. Most authorities define an aortic aneurysm as an aorta that is greater than or equal to 4 cm in diameter in the thoracic aorta and 3 cm in diameter in the abdomen. The aorta should normally decrease in size as it extends distally, and any focal dilation should be considered abnormal.
