4th June 2026

Aetiology

For an aortic dissection to occur, there must be medial degeneration alongside mechanical wall stress. 

Medial wall degeneration: Likely due to loss of elastic and interconnecting elastic fibres, associated with damage to the vasa vasorum. This damage leads to an entry site for the false lumen. Precipitants to medial wall degeneration include hypertension, connective tissue disorders and aortic aneurysms. 

Chronic hypertension changes the composition of the arterial wall by causing a thickening of the intimal layer via fibrosis and calcification. This thickening will lead to compromised nutrient and oxygen supply to the wall of the artery, alongside fibrosis obstructing vessels that supply the wall and the vasa vasorum. This will lead to necrosis of the elastic structures and smooth muscle cells in the wall, leading to a rigid wall unable to tolerate pulsatile forces, and therefore creating an easy area for aneurysms and dissections to occur.  

Mechanical aortic wall stress > Caused by sheer stress from blood flow, alongside hypertension. 

The 3 ways that blood may enter the media space are: through an atherosclerotic ulcer, which leads to a tear, via an intramural haematoma from damage to the vasa vasorum and via a new (de novo) intimal tear. Most tears occur in the ascending aorta because it is nearer to the outflow from the left ventricle, leading to high pressure on the aortic wall. 

Often, the true lumen of the blood vessel will decrease in size due to compression from the blood flow through the false lumen. Dissection can also occur without an initial tear.