The most common site for acute aortic dissection is the beginning of the ascending aorta. About 90% are found within 10 centimeters of the aortic valve. The second most common site is just past the left subclavian artery.

Aortic dissection is classified using the Stanford classification or the DeBakey classification. The Stanford classification defines two types of dissection: type A and type B. Type A dissections involve the ascending aorta whereas type B dissections involve only the descending aorta. This classification is used to help determine treatment: Type A dissections require surgery, while type B dissection can often be managed medically.

The DeBakey Classification of Aortic Dissection

• Type I aortic dissection:
• Involves the ascending aorta, aortic arch, and the descending aorta
• Type II aortic dissection:
• Involves only the ascending aorta
• Type IIIa aortic dissection:
• Involves the descending aorta, originates distal to the left subclavian artery but extend toward the heart and toward the diaphragm
• Type IIIb aortic dissection:
• Involves the descending aorta, originates distal to the left subclavian artery and extends only distally and can extend below the diaphragm.