This article discusses abdominal aortic emergencies. There is a common thread of risk factors and causes of these diseases, including age, male gender, hypertension, dyslipidemia, and connective tissue disorders. The most common presenting symptom of these disorders is pain, usually in the chest, flank, abdomen, or back. Computed tomography scan is the gold standard for diagnosis of pathologic conditions of the aorta in the hemodynamically stable patient. Treatment consists of a combination of blood pressure and heart rate control and, in many cases, emergent surgical intervention.
Key points
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Acute aortic syndrome is a group of diagnoses, including aortic dissection, intramural hematoma, and penetrating atherosclerotic ulcer. These have similar risk factors, including hypertension and dyslipidemia, as well as comparable presentations.
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Aortic aneurysm can be a precursor to dissection and rupture. Close surveillance and risk factor modification are key to prevention of aneurysm progression.
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Aortic endoleak and aortoenteric fistula can be either primary processes or, more commonly, a postoperative complication after aortic repair. Although some endoleaks can be managed conservatively, aortoenteric fistulas are surgical emergencies.
Introduction
The abdominal aorta is the continuation of the descending thoracic aorta. It begins at the aortic hiatus of the diaphragm at the level of the twelfth thoracic vertebrae and ends on the body of the fourth lumbar vertebrae where it divides into the 2 common iliac arteries. The abdominal aorta is broadly subdivided into suprarenal and infrarenal segments at the level of the renal arteries. The wall of the aorta is composed of 3 layers (tunicae): the intima, media, and adventitia. Advanced age, as well as degenerative processes (and those factors that accelerate them), such as atherosclerosis, fibrosis, and calcification of the aortic wall, impair its elasticity.
Introduction
The abdominal aorta is the continuation of the descending thoracic aorta. It begins at the aortic hiatus of the diaphragm at the level of the twelfth thoracic vertebrae and ends on the body of the fourth lumbar vertebrae where it divides into the 2 common iliac arteries. The abdominal aorta is broadly subdivided into suprarenal and infrarenal segments at the level of the renal arteries. The wall of the aorta is composed of 3 layers (tunicae): the intima, media, and adventitia. Advanced age, as well as degenerative processes (and those factors that accelerate them), such as atherosclerosis, fibrosis, and calcification of the aortic wall, impair its elasticity.
Acute aortic syndrome
Acute aortic syndrome (AAS) encompasses a constellation of conditions that have a similar presentation. These pathologic conditions include aortic dissection (AD), intramural hematoma (IMH), and penetrating atherosclerotic ulcer (PAU).
Each of these diseases is described in detail in the following sections. Common features of these conditions are discussed, including risk factors and classification systems used to categorize them.
Definition
Abdominal aortic dissection
AD occurs when there is a tear in the aortic intima, leading to separation of the media and the intima. (See aortic dissection at: https://radiopaedia.org/cases/aortic-dissection .) This is often preceded by medial degeneration or cystic medial necrosis. There are 2 theories that describe the pathogenesis of AD. The first theory is that there is a primary tear in the intimal layer and, during a subsequent hypertensive attack, blood enters the media at the location of the intimal tear and dissects into the media. The second theory is that the catalyst to dissection is rupture of the vasa vasorum with the development of an IMH, and that the intimal tear occurs as a result of increased wall stress.
AD can propagate in both an anterograde and retrograde manner. As an AD propagates in an anterograde fashion, it can spread to the iliac bifurcation. This usually occurs along the convexity of the aorta, which preferentially involves the left side of the aorta and can lead to occlusion of branching arteries (renal and brachiocephalic), leading to end-organ ischemia and necrosis.
Dissection can be classified as hyperacute (<24 hours), acute (2–7 days), subacute (8–30 days), and chronic (>30 days). Of the 3 conditions that define AAS, abdominal AD is the most common.
Intramural hematoma
IMH is defined as hemorrhage from the vasa vasorum into the media layer of the aortic wall in the absence of a demonstrable 2-lumen flow and primary intimal tear. IMHs comprise approximately 5% to 15% of AASs. Whereas classic AD more commonly affects the ascending aorta, IMH more commonly involves the descending aorta. Approximately two-thirds of IMHs degenerate into aneurysm or dissection, and IMH is often thought of as a precursor to AD. IMH can lead to AD in 28% to 47% of patients and aortic rupture in 21% to 47% of patients. Approximately one-third of IMHs resolve spontaneously.
Of the conditions of AAS, the risk of aortic rupture is higher in patients with IMH and PAU than in those with AD.
Penetrating atherosclerotic ulcer
PAU is defined as ulceration of an atherosclerotic plaque in the intimal layer of the aorta that extends into the media with rupture of the internal elastic lamina. Alternatively, PAU can be thought of as a localized dissection that is limited by extensive calcification associated with progressive atherothrombosis. PAU makes up approximately 2% to 7% of AAS. PAU is most commonly seen in patients with extensive atherosclerotic disease who are often 70 years or older. Complications of PAU include false aneurysm, aortoenteric fistula, AD, and aortic rupture. Ulcers with an initial diameter greater than 20 mm and a depth of greater than 10 mm are associated with a high risk of ulcer progression.
Of the conditions of AAS, the risk of aortic rupture is higher in IMH and PAU patients than in those with AD.
Causes and Risk Factors
Abdominal aortic dissection
One of the major risk factors for dissection is hypertension (prevalence ∼70%), especially in patients with poorly controlled blood pressure despite multidrug therapy. Chronic hypertension leads to intimal thickening, fibrosis, calcification, and extracellular fatty acid deposition, in addition to extracellular matrix degradation, elastolysis, and apoptosis. This leads to intimal disruption and thickening. This cascade leads to necrosis of smooth muscle cells and fibrosis of elastic structures in the aortic wall, which can lead to both aneurysm and dissection.
A history of connective tissue disease (Marfan syndrome, Ehlers-Danlos syndrome, Turner syndrome, Loeys-Dietz syndrome) is also a risk factor for dissection. Approximately 20% of cases of dissection are associated with a genetic disorder that affects the connective tissues. Moreover, those with connective tissue disorders can present at a younger age with AD compared with those with dissection without history of a connective tissue disorder.
There is a male predominance in AD; approximately 60% of patients with dissection are men. However, this predominance may equalize with time because research has shown that for patients older than 75 years, there is similar incidence of dissection for men and women. Additional risk factors include history of atherosclerosis; cigarette use; illicit drug use, in particular cocaine or amphetamine use; dyslipidemia; history of blunt trauma; recent aortic manipulation; or family history of aortic disease. Patients with inflammatory disorders, including autoimmune (eg, Behçet syndrome, polyarteritis nodosa) and infectious (eg, tuberculosis, syphilis), are at increased risk for development of AD, as well as rupture. AD has been reported in pregnancy, most commonly in the third trimester or early puerperium; however, many of these woman are hypothesized or known to have an underlying connective tissue disorder.
Intramural hematoma
Risk factors for the development of IMH include hypertension, vascular disorders, arteriosclerosis, trauma, and iatrogenic causes. Unlike in AD, patients with IMH are typically older in age, and IMH rarely occurs in those with Marfan syndrome. There is a greater prevalence of IMH in patients of Chinese, Korean, and Japanese descent compared with European and American patients.
Penetrating atherosclerotic ulcer
Age (>70 year old), atherosclerotic disease, coronary artery disease, hypertension, hyperlipidemia, history of cigarette use, and renal disease are all risk factors for development of a penetrating aortic ulcer. Moreover, compared with patients with AD, those with PAU are typically a decade older and have more extensive atherothrombotic degeneration their vessels.
Clinical Presentation
AD, IMH, and PAU can have similar clinical presentations and, as such, they are discussed together. There is a particular emphasis on AD because it makes up almost all AASs.
AD is the great mimicker because it can present with myriad of signs and symptoms that can be subtle and nonspecific. Studies have demonstrated that the diagnosis of dissection can be missed up to 40% of the time at symptom onset.
The most common presentation (∼90% of patients) is sudden onset and severe pain located in the chest, abdomen, flank, or back. Abruptness of pain symptoms for AD, as well as other aortic emergencies, is highly sensitive and is present in approximately 90% of affected patients. That being said, in about 5% of cases dissections may be painless. Although classic features of AD (ie, abrupt onset of severe chest or abdominal pain that is tearing or ripping in nature and radiates to the back) often increase the clinician’s suspicion for dissection. Those who present with painless dissections are often subject to delays in diagnosis and potentially worse outcomes.
Other presenting symptoms, which can be nonspecific in isolation, include neurologic symptoms such as paresis, paraplegia, or syncope. Syncope, which occurs in approximately 13% of patients, can signal evidence of cardiac tamponade or stroke. Neurologic deficits (eg, paresis, paraplegia) occur more commonly with type A dissections and can be found in approximately 17% of patients with AD.
On physical examination, a pulse deficit, which is associated with increased in-hospital mortality, may also be noted. Pulse deficits occur in 19% to 30% of patients with type A dissection and 9% to 21% of patients with type B dissection. The commonly noted pulse deficits include decreased or absent right brachial pulse, right femoral pulse (15%), left femoral pulse (14%), left brachial pulse (12%), and left common carotid pulse.
One highly specific, although less sensitive, finding of dissection is auscultation of the murmur of aortic insufficiency. This murmur was appreciated in 12% of patients with type B AD and 44% of patients with type A dissection in the study population of the International Registry of Acute Aortic Dissection (IRAD) study. It was more common than other examination findings, including pulse deficit, cerebrovascular accident, or congestive heart failure. Less commonly on examination, patients may demonstrate gastrointestinal bleeding or hematuria or anuria. Ominous signs indicating evolution of the dissection include myocardial ischemia, cardiac tamponade, cardiogenic shock, acute aortic regurgitation, and mesenteric ischemia.
Hypertension is noted in over 60% of patients. Older patients (≥70 years) are more likely to be hypertensive at presentation. Conversely, younger patients (<40 years) more often present without hypertension. Approximately 34% of patients with AD are normotensive, defined as a systolic blood pressure (SBP) between 100 to 149 mm Hg, and approximately 8% of patients with dissection present with shock, defined as an SBP less than or equal to 80.
IMH and PAU can present as abrupt onset of chest, back, abdominal, and/or flank pain, mimicking AD. Pain is a more common presenting symptom in IMH compared with AD, although the pain quality of IMH and PAU is usually clinically indistinguishable.
Classification
The initial management of patients with AD always includes medical management and may include surgical intervention. The classification schemes (see later discussion) can help with clinical decision-making for clinical management.
The DeBakey classification system describes the site of the origin of the intimal tear and the extent of the dissection ( Table 1 ).
| Category | Description |
|---|---|
| I | Tear in the ascending aorta propagating distally to include at least the aortic arch and typically the descending aorta |
| II | Tear only in the ascending aorta |
| III | Tear in the descending aorta most often propagating distally |
| IIIa | Tear only in the descending thoracic aorta |
| IIIb | Tear extending below the diaphragm |
The Stanford classification system is used for AD, IMH, and PAU, and it describes the absence or presence of ascending aorta involvement ( Table 2 ).
| Type | Description |
|---|---|
| A | Dissection involving the ascending aorta irrespective of the site of tear |
| B | Dissection that does not involve the ascending aorta |
The Working Group on Aortic Diseases of the DEFINE project created a novel classification system for AD: the DISSECT mnemonic. The purpose of this new system is to provide a way to describe multiple characteristics of a dissection that are important in the decision-making pathway for dissection management. The group makes it clear that this new system supplements, rather than replaces, the traditional DeBakey and Stanford systems.
DISSECT mnemonic
D: dissection less than 2 weeks, 2 weeks to 3 months, or greater than 3 months from initial symptoms
I: intimal tear location (ascending aorta, arch, descending, abdominal, or unknown)
S: size of the aorta
SE: segmental extent
C: clinical complications; that is, cardiac tamponade, aortic valve compromise, rupture, or branch malperfusion
T: thrombosis and extent of the false lumen.
Diagnosis
The evaluation of a patient with suspected AAS should include a focused history and physical examination, particularly looking for risk factors, signs, or symptoms, as previously described.
Computed tomography with angiography
Computed tomography (CT) with angiography (CT-A) is the imaging modality of choice for the diagnosis and follow-up of aortic disease because it has a sensitivity and specificity of almost 100%. CT-A allows for the examination of the entire thoracic and abdominal aorta and their branches and evaluates nonaortic diseases.
Abdominal aortic dissection
CT scans can be useful to evaluate the location of the intimal flap to guide surgical intervention. In addition, CT scanning can identify involvement of branch vessels and other nonaortic diseases. Also, CT scanning can assist in the differentiation between the false and the true lumen. The false lumen usually is rounded and biconvex in shape. Additionally, the false lumen may demonstrate the presence of a thrombus or other radiographic sign, such as the cobwebs sign (strands of media that appear as filling defects because they cross the false lumen) and the beak sign (a wedge of hematoma that permits propagation of the false lumen) ( Fig. 1 ).
Intramural hematoma
An IMH appears as a circular or crescentic hyperdensity (thickening >5 mm) of the aortic wall in the absence of detectable blood flow in the vessel wall. In addition, the aortic wall can be observed to be thickened, and there is no communication with the lumen or contrast flow into the aortic wall ( Fig. 2 ).
Penetrating atherosclerotic ulcer
On contrast-enhanced images, PAU appears as a localized, crater-like, contrast-filled out-pouching of the aorta through the intimal layer ( Fig. 3 ). Noncontrast CT scan imaging of a PAU appears as displacement of intimal calcifications.
Ultrasonography
This modality can be performed at the bedside, which is useful for the unstable patient. Additional benefits of ultrasound are that it is noninvasive, safe, accurate, and does not involve the use of radiation or potentially nephrotoxic contrast material. In the emergency department, the use of transabdominal ultrasound to evaluate the aorta has a sensitivity of 70% to 80% and a specificity of 100%.
Limitations of ultrasonography include that it provides a restricted field of view and that its accuracy is operator-dependent. It is also affected by patient characteristics, including body habitus.
MRI and magnetic resonance angiography
MRI is a sensitive imaging modality for the detection of AD. Other benefits of MRI or magnetic resonance angiography (MRA) are lack of ionizing radiation and that use of iodinated contrast medium is not needed. MRI is superior to CT scan with regard to ability to characterize tissue and fluid components, which is particularly important in the evaluation of inflammation-related edema and hematoma age. However, because MRI or MRA requires that the patient to be hemodynamically stable, and necessitates a longer amount of time to obtain as well as interpret, this modality is often not feasible.
Abdominal aortic dissection
MRI or MRA also provides detail regarding the location and extent of the area of dissection ( Fig. 4 ).
Intramural hematoma
On MRI, an IMH appears as a crescent-shaped area of eccentric thickening and has intermediate signal intensity in the acute setting. MRI is superior to CT scan with regard to ability to characterize tissue and fluid components, which is particularly important in the evaluation of inflammation-related edema and hematoma age.
Penetrating atherosclerotic ulcer
On MRI imaging, PAU appears as high intensity in the aortic wall in both T1-weighted and T2-weighted images. MRI is superior to CT scan with regard to the ability to characterize tissue and fluid components, which is particularly important in the evaluation of inflammation-related edema and hematoma age. However, due to the time needed to obtain and interpret the study, this modality is often not feasible.
Treatment
Patients who are diagnosed with AAS may require aggressive resuscitation to stabilize them for potential surgical intervention, as well as emergent cardiothoracic and vascular surgery consultation. In addition, medical treatment focused on anti-impulse therapy should be initiated. All patients diagnosed with AAS should be first treated medically in parallel with emergent surgical consultation for surgical intervention.
Medications used to treat AAS are aimed at anti-impulse therapy: controlling heart rate, blood pressure, and rate of increase of blood pressure dP/dT. Medical treatment involves administration of intravenous beta-blockade as the first-line treatment. Beta-blockers are used to lower heart rate and blood pressure. Esmolol is a short-acting beta-blocker medication that can be titrated to goal vital signs. Esmolol can be used for heart rate control but may not be effective for blood pressure control and thus often necessitates the use of a calcium channel blocker. Labetalol may also be used. Labetalol provides both beta-blockade and alpha-blockade, lowering blood pressure and reducing the change in pressure over time.
If the patient cannot tolerate beta-blockers, nondihydropyridine calcium channel blockers can be used. Caution is advised regarding the use of calcium channel blockers in patients who are hemodynamically unstable or have acute severe aortic regurgitation on examination. Opiate medications provide analgesia and also mitigate sympathetic release of catecholamines.
The goal SBP is 100 to 120 mm Hg, and the goal heart rate is 60 to 80 beats per minute, though no studies definitively demonstrate improved outcome with these targets ( Table 3 ).
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