Pathophysiology

Predisposing factors for aortic dissection

Aortic dissection occurs following a tear in the intimal layer of the aorta with subsequent anterograde or retrograde flow of blood within the outer third of the tunica media. It is thought that this occurs because of medial degeneration and certain conditions predispose to this.

Notably, essential hypertension is by far the most common risk factor, being present in approximately 70% of cases. It causes weakening of the tunica media layer of the aorta.

Marfan syndrome is associated with an inherited connective tissue disorder resulting in a weakened aortic media and progressive aortic dilatation. Marfan syndrome is likely to be present in 50% of cases of dissection presenting under the age of 40.

Bicuspid aortic valve is associated with aortic root dilatation and with a congenitally weakened aortic wall.

Intimal tear

The channel created by the dissection process is called the false lumen and occasionally the blood may re-enter the true lumen through a more distal tear in the intima.

The majority of intimal tears occur in the ascending aorta due to greater pressure on the aortic wall as it is closer to the left ventricular outflow.

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Dissection

Once the dissection process occurs, blood tracks through the media to varying degrees and may dissect down from the aortic root to the bifurcation of the common iliac arteries in a matter of seconds. This typically causes maximum pain at this time.

The image demonstrates an aortic dissection from the ascending aorta extending to the bifurcation of the common iliacs.

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Location of the primary aortic tear