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- Classically an intimal tear in the aorta resulting in hematoma formation. Accumulating blood in false lumen of arterial wall leads to propagation of a dissection. Alternatively, it may begin as an intrawall hematoma without intimal tear.
- Stanford classification (most widely used and frequently guides management)
- Type A: involves ascending aorta or ascending aorta and aortic arch regardless of site of intimal tear
- Type B: involves descending aorta
- Type non-A, non-B: isolated aortic arch involvement
- DeBakey classification (based on origin site)
- Type 1: originates in ascending aorta, propagates at least as far as aortic arch
- Type 2: involves only ascending aorta
- Type 3: originates in descending aorta, may propagate proximately to the arch or distally to the abdominal aorta
- Svensson classification
- Class 1: classic dissection with true and false lumen
- Class 2: intramural hematoma or hemorrhage
- Class 3: subtle dissection without hematoma
- Class 4: atherosclerotic plaque rupture and ulceration
- Class 5: iatrogenic
- 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.
3/100,000 people per year
- Diagnosed in 1/10,000 patients admitted to hospital
- Found in 1/350 patients at autopsy
- Numbers may be slightly higher due to unexplained deaths at home or in hospital without autopsy.
Etiology and Pathophysiology
- In most cases, dissection develops in the absence of an aneurysm, but the false lumen that can be created during dissection can later expand to form an aneurysm. 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. Histologic investigations of postmortem and biopsy specimens reveal cystic medial necrosis, especially in those patients with known preexisting aneurysms.
- 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. Expansion of the false lumen with blood may cause compression of the true lumen, causing hypoperfusion of distal organs.
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 and 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.
- Most common associated factors: hypertension (~70% of patients), old age, atherosclerosis, previous cardiovascular surgery, particularly repair of aneurysm or dissection
- Collagen abnormalities: Marfan syndrome, Ehlers-Danlos syndrome (particularly type IV)
- Recreational drug use: smoking, cocaine, methamphetamine
- Inflammatory vasculitis: Takayasu arteritis, giant cell arteritis, Behçet disease, syphilis
- Congenital cardiovascular anomalies (Turner syndrome, bicuspid aortic valve, coarctation of the aorta, Erdheim cystic medial necrosis, familial ectopia lentis, tetralogy of Fallot)
- Trauma (catheters, motor vehicle accidents, vascular surgery, intra-aortic balloon pump)
- Pregnancy (usually has underlying vascular pathology)
- 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.”