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- Disruption of the media layer of the aorta with bleeding within the wall resulting in separation of aortic layers. Accumulating blood in false lumen of arterial wall leads to propagation of a dissection. Alternatively, dissections may begin as an intramural hematoma without intimal tear.
- Stanford classification (most widely used)
- Type A: involves ascending aorta, may progress to involve arch and descending aorta
- Type B: involves descending aorta
- DeBakey classification (based on origin site)
- Type I: originates in ascending aorta, propagates at least as far as aortic arch
- Type II: confined to ascending aorta
- Type IIIa: involves descending thoracic aorta from left subclavian artery to celiac artery
- Type IIIb: involves descending thoracic aorta from left subclavian and tracts distal to celiac artery
- Synonym(s): dissecting aneurysm; dissecting hematoma
Predominant age varies with cause. About 68% are male and 79% Caucasians (1). Older patients usually have atherosclerosis, whereas younger patients should be investigated for an underlying cause. Type A dissection occurs in patients with an average age of 60 years. Type B dissection patients are generally older. Patients with Marfan syndrome have a mean age of 36 years.Incidence
- 2 to 3.5/100,000 people per year
- True incidence unknown due to undiagnosed/misdiagnosed cases resulting in sudden death without subsequent autopsy
- 6,000 to 10,000 cases annually
- Present in 3 out of every 1,000 patients presenting to ED with chest and/or back pain
Etiology and Pathophysiology
- Etiologic classification:
- Sporadic (degenerative)
- Genetically mediated
- Although the exact sequence of events is controversial, an aortic dissection is likely the result of multiple pathologic processes. Stress on the aortic wall from hypertension; intimal damage with subsequent tear, rupture, or ulceration of atherosclerotic plaques; and the involvement of vasa vasorum and intramural hematoma may be contributory.
- The primary event usually involves a tear in the intima of the aorta. Blood subsequently passes through the tear dissecting the intima from the media and/or adventitia layers. This creates a false lumen that has the potential to propagate proximally or distally. Expansion of the false lumen with blood may cause compression of the true lumen, causing hypoperfusion of distal organs. In patients with inherited connective tissue disease, abnormal or deficient proteins lead to weakening of vessel walls. Bicuspid aortic valves may also lead to an acquired dysfunction of vascular walls and smooth muscle cells.
- Up to 20% of patients with thoracic aneurysm or dissection were found to have first-degree relatives with aneurysm or dissection.
- Studies have found that the TGFBR1, TGFBR2 genes are related to aneurysm and dissection in isolated cases and in patients with Marfan syndrome. Other research has found ACTA2 gene mutations to be involved in isolated and familial dissections and aneurysms.
- Identifying gene mutations in TGFBR1, TGBFR2, FBN1, ACTA2, MYH11, and COL3A1 in affected individuals can help identify family members at risk.
- Any condition that results in aortic medial degeneration. Most common associated factors: hypertension (~70% of patients), old age, atherosclerosis, previous cardiovascular surgery, particularly repair of aneurysm or dissection, Valsalva maneuvers, trauma or deceleration injuries
- 75% of patients with acute aortic dissection have underlying hypertension.
- Conditions associated with aortic media abnormalities:
- Genetic: Marfan syndrome, Ehlers-Danlos syndrome (type IV), Loeys-Dietz, Turner syndrome, familial thoracic aortic aneurysm, and dissection syndrome
- Inflammatory vasculitides: Takayasu arteritis, giant cell arteritis, Behçet arteritis
- Other: polycystic kidney disease, pregnancy
- Recreational drug use: tobacco use, cocaine, methamphetamine
- Trauma (catheters, motor vehicle accidents, vascular surgery, intra-aortic balloon pump)
- Medical management of precipitating risk factors such as hypertension, smoking cessation, lipid control (2)[C]
- Surveillance of aortic root and replacement when appropriate in patients with collagen disorders (e.g., Marfan, Ehlers-Danlos) (2)[C]. In addition, Marfan patients should receive β-blockade to reduce aortic dilatation (2)[B].
Commonly Associated Conditions
See “Risk Factors.”