Aortic dissection is the formation of a dissection of the aortic wall, which was previously called aortic dissection aneurysm. It refers to the rupture of the aortic intima caused by various reasons. Blood enters the middle layer of the aortic wall through the rupture of the intima and forms a hematoma, which leads to the stratification of the blood vessel wall and the separation of the peeled intima to form a "double-lumen aorta". However, Coady reported that 8% to 15% of cases did not have intima tearing, which may be caused by bleeding in the middle layer of the aortic wall, also known as intramural hematoma. The dilation of the aortic cavity is not the dilation of the aortic wall, which is different from an aortic aneurysm.