While uncommon, acute aortic dissection (AAD) is a rare but catastrophic disorder. Aortic dissection is due to the separation of the layers of the aortic wall. A tear in the intimal layer results in the progression of the dissection (either proximal or retrograde) chiefly due to the entry of blood in between the intima and media. An acute aortic dissection is associated with very high mortality; the majority die even before reaching the emergency department. Patients with a chronic aortic dissection (more than two weeks) have a slightly better prognosis.
Classically described as a patient complaining of an abrupt onset of severe ‘tearing’ chest pain, presentations can often be more subtle. Physicians correctly suspect the diagnosis in as few as 15% to 43% of cases of verified AAD. If left untreated, mortality approaches 50% in the first 48 hours of onset. Despite a wealth of literature, a significant number of aortic dissections are missed in the emergency department.
There are two main anatomic classifications used to classify aortic dissection.
The Stanford system is more frequently employed. It classifies dissections into two types based on whether ascending or descending part of the aorta involved.
Type A involves the ascending aorta, regardless of the site of the primary intimal tear. Type A dissection is defined as a dissection proximal to the brachiocephalic artery.
Type B aortic dissection originating distal to the left subclavian artery and involving only descending aorta.
The DeBakey classification is based upon the site of origin of the dissection.
Type 1 originates in the ascending aorta and to at least the aortic arch.
Type 2 originates in and is limited to the ascending aorta.
Type 3 begins in the descending aorta and extends distally above the diaphragm (type 3a) or below the diaphragm (type 3b).
Ascending aortic dissections are almost twice as common as descending dissections.
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