Introduction
Background
Much has been written on the subject of aortic dissections, from the first well-documented case of aortic dissection, when King George II of England died while straining on the commode, to the first successful operative repairs by DeBakey in 1955, to modern techniques of diagnosing and repairing thoracic aortic dissections. More recently, this has come to light with the diagnosis of aortic dissection in Princess Diana, actor John Ritter, and Dr. DeBakey himself.
Aortic dissection is the most common catastrophe of the aorta, 2-3 times more common than rupture of the abdominal aorta. When left untreated, about 33% of patients die within the first 24 hours, and 50% die within 48 hours. The 2-week mortality rate approaches 75% in patients with undiagnosed ascending aortic dissection.
The establishment of the International Registry of Acute Aortic Dissection in 1996 which gathers information from 24 centers in 11 Countries has helped understand the complexity of Aortic Dissection.
Dissections of the thoracic aorta have been classified anatomically by 2 different methods. The more commonly used system is the Stanford classification, which is based on involvement of the ascending aorta and simplifies the DeBakey classification.
Patient with an ascending type A aortic dissection showing the intimal flap. Image courtesy of Kaiser-Permanente.
The Stanford classification divides dissections into 2 types, type A and type B.
- Type A involves the ascending aorta (DeBakey types I and II); type B does not (DeBakey type III).
- This system also helps delineate treatment. Usually, type A dissections require surgery, while type B dissections may be managed medically under most conditions.
The DeBakey classification divides dissections into 3 types.
- Type I involves the ascending aorta, aortic arch, and descending aorta.
- Type II is confined to the ascending aorta.
- Type III is confined to the descending aorta distal to the left subclavian artery.
- Type III dissections are further divided into IIIa and IIIb.
- Type IIIa refers to dissections that originate distal to the left subclavian artery but extend both proximally and distally, mostly above the diaphragm.
- Type IIIb refers to dissections that originate distal to the left subclavian artery, extend only distally and may extend below the diaphragm.
Thoracic aortic dissections should be distinguished from aneurysms (ie, localized abnormal dilation of the aorta) and transections, which are caused most commonly by high-energy trauma.
Pathophysiology
The essential feature of aortic dissection is a tear in the intimal layer, followed by formation and propagation of a subintimal hematoma. The dissecting hematoma commonly occupies about half and occasionally the entire circumference of the aorta. This produces a false lumen or double-barreled aorta, which can reduce blood flow to the major arteries arising from the aorta. If the dissection involves the pericardial space, cardiac tamponade may result.
Cystic medial necrosis
The normal aorta contains collagen, elastin, and smooth muscle cells that contribute the intima, media, and adventitia, which are the layers of the aorta. With aging, degenerative changes lead to breakdown of the collagen, elastin, and smooth muscle and an increase in basophilic ground substance. This condition is termed cystic medial necrosis. Atherosclerosis that causes occlusion of the vasa vasorum also produces this disorder. Cystic medial necrosis is the hallmark histologic change associated with dissection in those with Marfan syndrome.
Cystic medial necrosis was first described by Erdheim in 1929. Sources disagree over the accuracy of this term in elderly patients because the true histopathologic changes are neither cystic nor necrotic. Researchers have used the term cystic medial degeneration.
Early on, cystic medial necrosis described an accumulation of basophilic ground substance in the media with the formation of cystlike pools. The media in these focal areas may show loss of cells (ie, necrosis). This term still is used commonly to describe the histopathologic changes that occur.
Dissection sites
The most common site of dissection is the first few centimeters of the ascending aorta, with 90% occurring within 10 centimeters of the aortic valve. The second most common site is just distal to the left subclavian artery. Between 5% and 10% of dissections do not have an obvious intimal tear. These often are attributed to rupture of the aortic vasa vasorum as first described by Krukenberg in 1920.
Diseases leading to aortic dissection
Certain diseases, such as Marfan, Ehlers-Danlos, and other connective tissue diseases, affect the media of the aorta and make it prone to dissection. Pulsatile flow and high blood pressure contribute to propagation of the dissection.
Diseases that weaken the aortic wall predispose the patient to aortic dissection. Shearing forces separate the layers in the media of the aorta. Intimal rupture occurs at points of fixation along the aorta where hydraulic stress is maximal.
Frequency
United States
The true incidence of dissection is difficult to estimate. Most estimates are based on autopsy studies. Population-based studies estimated the incidence at roughly 6-10 new aneurysms per 100,000 person-years. Evidence of dissection is found in 1-3% of all autopsies.1
Mortality/Morbidity
- From 1-2% of patients with aortic dissection die per hour for the first 24-48 hours.
- Aortopathy may be present in heritable diseases such as Marfan syndrome, Ehlers-Danlos syndrome, annuloaortic ectasia, familial aortic dissections, adult polycystic kidney disease, Turner syndrome, Noonan syndrome, osteogenesis imperfecta, bicuspid aortic valve, coarctation of the aorta, and connective tissue disorders. It is also seen in heritable metabolic disorders such as homocystinuria and familial hypercholesterolemia.
- Incidence is increased in pregnancy and syphilis. Thoracic aortic dissection also is associated with crack cocaine use and iatrogenic causes, such as cardiac catheterization.
Race
Aortic dissection is more common in blacks than in whites and less common in Asians than in whites.
Sex
The male-to-female ratio is 3:1.
Age
Approximately 75% of dissections occur in those aged 40-70 years, with a peak in the range of 50-65 years.
Clinical
History
No one sign or symptom can positively identify acute aortic dissection (AAD). An estimated 38% of acute aortic dissections are missed on initial evaluation.2,3,4
There are no validated clinical decision rules to help identify acute aortic dissection (ADD). The diagnosis is best made when there is high clinical suspicion given the overall evaluation of the patient, including the history, physical examination, and supporting tests including ECG, laboratory studies, and radiology.
". . . spontaneous tear of the arterial coats is associated with atrocious pain, with symptoms, indeed, in the case of the aorta of angina pectoris and many instances have been mistaken for it" William Osler, 1910.
- Chest pain is the most common presenting symptom in patients with an aortic dissection. Consider thoracic aortic dissection in the differential diagnosis of all patients presenting with chest pain.
- The pain usually is described as ripping or tearing. The description of ripping or tearing has been shown to have a likelihood ratio for aortic dissection of 1.2 and 10.8.
- The sudden onset of chest pain has been shown to have a sensitivity of 84%.
- This description is not universal, and some patients present with only mild pain, often mistaken for musculoskeletal conditions, located in the thorax, groin, or back.
- The pain of aortic dissection typically is distinguished from the pain of acute myocardial infarction (AMI) by its abrupt onset.
- Aortic dissection should be considered strongly in all patients reporting acute, sudden, and severe chest pain that is maximal at onset.
- The truly sudden onset of chest pain is seen in few other conditions. In 1926, Spiegel and Wassermann found that acute stretching of the aortic wall produces pain.5
- The nervi vascularis, bundles of nerve fibers found in the aortic adventitia, are involved in the production of pain.
- A retrospective chart review of 83 patients with a thoracic aortic dissection revealed that only 40% of alert patients were asked the basic questions about their pain. Remember to cover the P, Q, R, S, and T (pain, quality, radiation, severity, and timing) of pain in all able patients. Assess the following characteristics of pain:
- Severity
- Character
- Timing, including rate of onset, duration, and frequency of episodes
- Migration, including aggravating or alleviating factors and associated symptoms
- The description of the pain may indicate where the dissection arises.
- Anterior chest pain and chest pain that mimics AMI usually are associated with anterior arch or aortic root dissection. This is caused by the dissection interrupting flow to the coronary arteries, resulting in myocardial ischemia.
- Pain that is described in the neck or jaw indicates that the dissection involves the aortic arch and extends into the great vessels of the arch.
- Tearing or ripping pain that is felt in the intrascapular area may indicate that the dissection involves the descending aorta. The pain typically changes as the dissection evolves.
- Aortic dissection is painless in about 10% of patients. Painless dissection is more common in those with neurologic complications from the dissection and those with Marfan syndrome.
- Presenting signs and symptoms in acute thoracic aortic dissection include the following:
- Anterior chest pain - Ascending aortic dissection
- Neck or jaw pain - Aortic arch dissection
- Interscapular tearing or ripping pain - Descending aortic dissection
- Chest pain
- Myocardial infarction
- Neurologic symptoms
- Syncope
- Stroke symptoms
- Altered mental status
- Limb paresthesias, pain, or weakness
- Hemiparesis or hemiplegia
- Horner syndrome
- Dyspnea
- Dysphagia
- Orthopnea
- Anxiety and premonitions of death
- Flank pain if renal artery is involved
- Dyspnea and hemoptysis if dissection ruptures into the pleura
Physical
- Blood pressure may increase or decrease.
- Hypertension may result from a catecholamine surge or underlying essential hypertension.
- Hypotension is an ominous finding and may be the result of excessive vagal tone, cardiac tamponade, or hypovolemia from rupture of the dissection.
- A blood pressure differential of greater than 20 mm Hg was an independent predictor of aortic dissection. A pressure differential of greater than 20 mm Hg should increase the suspicion of aortic dissection, but it does not rule it in. Significant interarm blood pressure differentials may be found in 20% of people without aortic dissection.
- Neurologic deficits are a presenting sign in up to 20% of cases.
- The most common neurologic findings are syncope and altered mental status.
- Syncope is part of the early course of aortic dissection in about 5% of patients and may be the result of increased vagal tone, hypovolemia, or dysrhythmia.
- Other causes of syncope or altered mental status include strokes from compromised blood flow to the brain or spinal cord and ischemia from interruption of blood flow to the spinal arteries.
- Peripheral nerve ischemia can manifest with numbness and tingling in the extremities.
- Hoarseness from recurrent laryngeal nerve compression also has been described.
- Horner syndrome is caused by interruption in the cervical sympathetic ganglia and presents with ptosis, miosis, and anhidrosis.
- Superior vena cava syndrome, caused by compression of the superior vena cava from a large distorted aorta, may occur.
- Dyspnea may be caused by congestive heart failure or tracheal or bronchial compression.
- Dysphagia from compression of the esophagus may be present.
- Findings suggestive of cardiac tamponade, such as muffled heart sounds, hypotension, pulsus paradoxus, jugular venous distension, and Kussmaul sign, must be recognized quickly.
- Other diagnostic clues include a new diastolic murmur, asymmetrical pulses, and asymmetrical blood pressure measurements. Pay careful attention to carotid, brachial, and femoral pulses on initial examination and look for progression of bruits or development of bruits on reexamination.
- Physical findings of a hemothorax may be found if the dissection ruptures into the pleura.
Causes
Aortic dissection is more common in patients with hypertension, connective tissue disorders, congenital aortic stenosis or bicuspid aortic valve, and in those with first-degree relatives with history of thoracic dissections. These diseases affect the media of the aorta and predispose it to dissection.
- Aortopathy may be due to the following heritable diseases:
- Marfan syndrome
- Ehlers-Danlos syndrome
- Annuloaortic ectasia
- Familial aortic dissections
- Adult polycystic kidney disease
- Turner syndrome
- Noonan syndrome
- Osteogenesis imperfecta
- Bicuspid aortic valve
- Coarctation of the aorta
- Connective tissue disorders
- Metabolic disorders (eg, homocystinuria, familial hypercholesterolemia)
- Hypertension or pulsatile blood flow can propagate the dissection.
- An estimated 50% of all cases of aortic dissection that occur in women younger than 40 years are associated with pregnancy.
- Syphilis may cause aortic dissection.
- Crack cocaine use may precipitate aortic dissection.
- Iatrogenic causes of aortic dissection include cardiac catheterization.
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Further Reading
Keywords
aortic dissection, thoracic aortic dissection, dissection of the thoracic aorta, aortic aneurysm, aortic tear, tear in the aortic wall, Stanford classification, DeBakey classification, cystic medial necrosis, atherosclerosis, Marfan syndrome, Ehlers-Danlos syndrome, adult polycystic kidney disease, Turner syndrome, Noonan syndrome, osteogenesis imperfecta, bicuspid aortic valve, coarctation of the aorta, connective-tissue disorders, homocystinuria, familial hypercholesterolemia, syphilis, crackcocaine use, cardiac catheterization, myocardial infarction, syncope, cerebrovascular accident
