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Published: April 2014

Diseases of the Aorta

Gian M. Novaro

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Diseases of the aorta account for significant cardiovascular morbidity and mortality worldwide. The incidence of aortic diseases is expected to rise with the increasing age of the population. Diagnostic evaluation of aortic disorders has improved in the last 2 decades, allowing earlier diagnosis and therapeutic intervention. This chapter summarizes the major disease entities affecting the aorta, and reviews the current practice guidelines on their evaluation and management.1

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Anatomy

The aorta is the main conduit and reservoir of oxygenated blood in the body. A large elastic artery, it is composed of three layers: The intima is the innermost layer and includes the single-layered endothelium. The media is the thickest layer of the aortic wall and is composed of sheets of elastic tissue, smooth muscle cells, and collagen, which provide the aorta with its tensile strength and distensibility. The adventitia is the outermost layer; it is composed of loose connective tissue and contains the vasa vasorum, which constitutes the blood supply to the aortic wall.

Anatomically, the aorta is divided into subcomponents. The thoracic aorta consists of the aortic root, from the aortic annulus, including the sinuses of Valsalva, up to the level just above the sinotubular junction; the ascending aorta, from the sinotubular junction to the innominate artery, with an average diameter of 3 cm; the arch, from the innominate artery to the left subclavian artery; and the descending thoracic aorta, with an average diameter of 2.5 cm, which begins after the origin of the left subclavian artery. The abdominal aorta begins when the descending thoracic aorta passes through the diaphragm. The abdominal aorta (average diameter, 2.0 cm) is further classified as suprarenal or infrarenal.

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Pathologic Processes

Cystic Medial Degeneration

An important predisposing factor to diseases of the aorta, particularly the ascending aorta, is cystic medial degeneration. It is characterized by smooth muscle cell necrosis and apoptosis and by degeneration of elastic fibers within the media of the aortic wall. Cystic spaces form in these areas of degeneration; thus its name. This degenerative process also extends to the elastic components of the adventitial layer. The weakened aortic wall is prone to aneurysm formation and dissection. This degenerative process, which can be genetically determined, is typically seen in connective tissue diseases such as Marfan, Loeys-Dietz, and Ehlers-Danlos syndromes. However, varying degrees of degeneration can be seen in patients without these disorders, occurring as an idiopathic variant in familial syndromes or as an acquired form. Hypertension and advancing age are associated with the latter. Varying degrees of cystic medial degeneration can also be seen in the genetically inferior aortas seen in association with congenital abnormalities, including bicuspid or unicuspid aortic valves, aortic coarctation, and Turner’s and Noonan’s syndromes.

Atherosclerosis

Atherosclerosis appears to play a major role in diseases of the aortic arch, descending thoracic, and abdominal aorta. Atherosclerosis can result in weakening of the aortic wall, making it prone to aneurysm formation or dissection. The development of aortic atherosclerosis is associated with traditional cardiac risk factors of smoking, hypertension, hyperglycemia, and atherogenic lipoproteins. Atherosclerosis can also lead to the formation of complex atheromatous plaques, which are prone to embolization, resulting in cerebral and peripheral arterial occlusive events.

Inflammatory Disorders

Inflammatory disorders represent a third broad category as a predisposing factor causing aortic diseases. These occur in isolation or in the context of systemic disorders such as inflammatory vasculitides. They include infectious and noninfectious causes.

Trauma

Aortic injury from trauma usually occurs because of deceleration injuries. Traumatic dissection or laceration often occurs at the level of the left subclavian artery. Injury can result in the formation of a chronic pseudoaneurysm.

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Specific Disorders

Aortic Dissection

Aortic dissection comprises one of the more ominous acute aortic syndromes, which include the dissection variants of penetrating aortic ulcers, intramural hematomas, and symptomatic aneurysms.2 Aortic dissection involves splitting of the aortic wall within the media, which results in the formation of an aortic false lumen that courses along with a true lumen. The hallmark of aortic dissection is an intimal tear, which allows access of pulsatile high-pressure blood into the aortic media, separating it from the outer layers. Often, the so-called intimal flap (Fig. 1) is usually an intimal-medial flap. The initiating event of dissection may be a tear in the intima. Alternatively, primary rupture of the vasa vasorum can result in an intramural hematoma, which secondarily leads to an intimal tear as blood vents from the intramural space (Fig. 2). Regardless of the initiating event, the force of blood flow propagates the dissection antegrade (and, less commonly, retrograde) for a variable extent along the vessel, splitting the aortic wall, usually along the outer one third of the medial layer.

Classification

Dissections are classified by their location of origin and how far along they extend in the aorta. There are two important classification systems of dissection, the DeBakey and Stanford classifications (Table 1; Fig. 3). Dissections are also classified by their duration. Acute dissections are those of less than 2 weeks’ duration after the onset of symptoms; chronic dissections are those that have been present for longer than 2 weeks.

Table 1: Classification of Aortic Dissections
Type Extent of Aortic Involvement
DeBakey
I Originates in ascending aorta, propagates to involve descending aorta
II Confined to ascending aorta
IIIa Confined to descending thoracic aorta
IIIb Involves descending aorta, extending to abdominal aorta
Stanford
A Involves ascending aorta
B Restricted to descending aorta


Signs and Symptoms

Dissections typically manifest between the 5th and 7th decades of life, with a male preponderance.3 Patients typically present with the acute onset of pain, which occurs in up to 96% of cases. Pain is often most severe at its onset and described as a tearing, ripping, or stabbing sensation. Often, the pain is migratory, a crucial component of the history, reflecting propagation of the dissection. Involvement of the ascending aorta results in anterior chest or neck pain, with intrascapular or subscapular pain from involvement of the descending thoracic aorta, and lower back and left flank pain from thoracoabdominal aortic involvement. Hypertension on presentation is common, more so in distal dissection, although hypotension can be seen if complications have developed, particularly in proximal dissections. The dissection may compromise flow to the great vessels and lead to pulse deficits; these can be transient, because the dissection flap can oscillate. Actual blood pressure may not be appreciated if the arm used has compromise of the brachial circulation (pseudohypotension).

If the dissection involves the aortic root, commissural involvement of the aortic valve can lead to aortic regurgitation. Dilation of the root and aortic annulus, without leaflet involvement, can also lead to aortic valve regurgitation. A diastolic murmur is evident in these cases. Dissections can involve the ostia of the coronary arteries, resulting in acute myocardial ischemia and infarction (2%-3% of cases). The right coronary artery ostium is more commonly affected than the left main. The dissection can extend proximally into the pericardial space, resulting in pericardial effusion and tamponade, a common mechanism of syncope and hypotension in dissection. A pericardial friction rub can be a clue to the presence of hemopericardium. Rupture into the pericardial space represents a common mode of death in patients with aortic dissection. Malperfusion syndromes with acute lower extremity, renal, or mesenteric ischemia can be seen in descending aortic dissections. Focal neurologic deficits can occur with involvement of the great vessels. Compromise of spinal artery perfusion may result in paraparesis. Whereas chest pain and pulse deficits are usually described, it is important to recognize that less than 20% of patients present with these findings. Therefore, a high clinical suspicion for dissection is paramount.

Diagnostic Testing

The chest radiograph may be normal in cases of dissection. A well-recognized finding is mediastinal widening, present in about 60% of cases. Rupture into the pleural or pericardial space manifests as pleural effusions or an enlarged cardiac silhouette; the latter may also be present because of chronic aortic regurgitation. The electrocardiogram can be normal but often shows nonspecific ST-T wave changes. Involvement of the coronary artery ostia can result in ST-segment elevation, representing an acute myocardial injury pattern. Transthoracic echocardiography can on occasion identify a proximal or even distal dissection flap. Even if a flap is not seen, the presence of aortic dilation, aortic regurgitation, or an unexplained pericardial effusion (present in one third of patients) can be important clues in the diagnostic consideration of dissection in a patient with chest pain. More definitive diagnostic modalities include transesophageal echocardiography (TEE), computed tomography (CT), and magnetic resonance angiography (MRA; Fig. 4). Each has relative advantages and disadvantages, but all have excellent sensitivity and specificity (Table 2).4

Table 2 Comparison of Imaging Modalities for Aortic Dissection
Advantages Disadvantages
Transesophageal Echocardiography
Portability
Assesses valvular function
Assesses ventricular function
No contrast agent
“Blind spot”-ascending aorta where bronchi cross esophagus
Difficulty in assessing great vessels
Difficulty in diagnosing intramural hematoma
Invasive procedure
Computed Tomography
Assesses great vessels and branch vessels Lacks valvular and ventricular function assessment
Lacks portability
IV contrast agent required
Magnetic Resonance Angiography
Provides detailed resolution of aorta (i.e., intramural hematoma) in addition to assessing branch vessels
Contrast agent without nephrotoxicity
Lacks portability
Limited access to scanners
Cost
Angiography
Assesses coronary anatomy (controversial as to whether this should be done before surgery) Invasive
Risk and difficulty in accessing true lumen
Contrast agent required

Angiography is less commonly used for the primary diagnosis of aortic dissection. The choice of test is often dependent on expedited availability and expertise at the center in which the patient is evaluated. An important caveat is that in most patients, more than one test may be required. If clinical suspicion is high enough and the initial test is negative or equivocal, consideration should be given to performing another confirmatory test.

Treatment

Anti-impulse medical therapy (i.e., β-adrenergic blockade) should be initiated as soon as the diagnosis of dissection is considered, even while awaiting confirmatory diagnostic testing. In patients who are hypertensive, intravenous beta blockade and sodium nitroprusside are the treatment agents of choice. Beta blockade should be initiated before sodium nitroprusside to prevent a rise in cardiac contractility associated with isolated vasodilator use. In the absence of hypertension, beta blockers can be used alone. In those with ascending aortic dissections, these are temporizing agents while preparing for definitive surgical therapy. In patients with descending dissections, these agents are first-line therapy before longer acting oral agents are initiated. Intravenous nondihydropyridine calcium channel antagonists such as verapamil and diltiazem are alternatives for those patients who cannot tolerate beta blockers. Dissections that involve the ascending aorta (proximal, type A) require urgent surgical therapy (Fig. 5) because there is a very high early mortality rate (approaching 1%-2% per hour for the first 24-48 hours).

An important management point arises in patients who have pericardial effusion or tamponade in association with a proximal dissection. These patients should not undergo percutaneous pericardiocentesis unless they are in extremis. The evacuation of pericardial blood by such a route has been associated with aortic rupture and increased mortality, perhaps secondary to dissection extension or aortic rupture, or both, because blood pressure and contractility increase after tamponade resolution. Pericardial access should be obtained in the operating room, after the institution of cardiopulmonary bypass.

Dissections that involve the descending aorta (distal, type B) should initially be treated medically. Data suggest that medical therapy is the preferred initial treatment, with surgery guided by a complication-specific approach. This is because acute aortic surgery is associated with a high mortality and paraplegia rate (inadequate protection of the spinal arteries). Surgery should be considered for the following indications: evidence of organ ischemia secondary to compromise of the branch vessels (malperfusion syndromes); persistent pain; aneurysm formation, particularly if saccular; and retrograde dissection to a proximal extent. Alternatively, aortic fenestration, surgical or percutaneous, can also be considered for organ or limb malperfusion in carefully selected patients, as can endovascular stent grafting. Distal (type B) dissections in Marfan syndrome patients carry a poor prognosis and have thus led to recommendations of early aortic surgery.

Aortic Dissection in Younger Adults

Dissections occurring in younger patients (younger than 40 years) typically occur in the context of connective tissue disorders such as Marfan syndrome, Loeys-Dietz, congenital bicuspid aortic valve, prior aortic surgery, or the peripartum period.5 During late pregnancy and the peripartum period, it is believed that the physiologic effects of pregnancy along with the potential weakening of the arterial wall can lead to a heightened risk of dissection.

Chronic Aortic Dissection

Patients with chronic dissection (present for >2 weeks) have survived the period of increased mortality. They can often be managed medically, even in the presence of a proximal dissection. However, their aortas often dilate and are at higher risk for aneurysm formation because of the thinner aortic wall remaining after dissection. A complication-specific approach can be used for chronic dissection patients to guide elective surgical therapy—recurrent pain, aneurysm formation, particularly if saccular, and retrograde dissection extension to the ascending aorta. Serial follow-up imaging (usually CT or MRA), initially at short intervals, is vital in these patients because of their weakened aortic walls.

Iatrogenic Aortic Dissection

Special mention should be made of iatrogenic dissections. Angiographic catheters and guidewires can disrupt the intima and result in dissections anywhere along the aorta’s course. These typically result in retrograde dissections, and the false lumens generally thrombose spontaneously. They often can be managed medically unless the dissection is extensive. Dissections can also occur during aortic cross-clamping or cannulation during cardiac surgery; these are usually type A, proximal dissections. Such dissections are usually diagnosed and treated urgently and successfully at the time of surgery.

Intramural Hematoma and Penetrating Aortic Ulcer

Intramural hematoma and penetrating aortic ulcer differ from classic dissection by the absence of an intimal flap. Recent advances in diagnostic imaging modalities have led to an increased awareness and better understanding of these entities.

Intramural hematoma consists of a noncommunicating blood collection in the aortic wall. Unlike a true dissection, there is no loss of intimal continuity, no entry tear, and thus no intimal flap. The pathophysiology may be related to rupture of the aortic vasa vasorum. By TEE, intramural hematoma is characterized by the absence of a dissection flap, a regional crescent-shaped thickening of the aortic wall, usually more than 0.7 cm, and central displacement of intimal calcium (Fig. 6). At times, intramural echolucencies representing noncommunicating pockets of blood can be seen. Distinguishing an intramural hematoma from severe atheroma, a thrombosed false lumen, or an aneurysm with mural thrombus can be difficult. Angiography is of limited diagnostic accuracy in the evaluation of hematomas, because it fails to image the aortic wall. If the clinical history is concerning, a negative TEE should not represent the final diagnostic evaluation. CT and MRA are highly accurate imaging modalities and are often used as an initial or complementary study in the evaluation of hematomas. Intramural hematomas can communicate with the adventitial space, lead to rupture, or progress to overt dissection with an intimal tear. However, when small in size, they may also have a more benign course and gradually resolve with medical therapy and blood pressure control.

Penetrating aortic ulcer develops when an atheromatous plaque erodes into the aortic media. The advanced atherosclerotic burden prevents the erosion from extending longitudinally along the vessel wall, as in classic dissection. The ulcer is apparent on imaging modalities as an ulcer crater or contrast-filled outpouching (Fig. 7). Depending how far into the aortic wall the plaque erosion occurs, there can be formation of an intramural hematoma, saccular aneurysm, pseudoaneurysm, or even complete aortic rupture.

Clinical Presentation

Patients with these acute aortic syndromes often present with the same chest or back pain, or both, as patients with classic dissection. There may be a higher incidence of rupture than that seen with classic dissections. Compared with intramural hematomas, patients with penetrating ulcers are usually older and tend to have more aortic atherosclerosis. Isolated intramural hematomas tend to occur more often in the ascending aorta, whereas intramural hematomas associated with penetrating aortic ulcers are located more commonly in the descending aorta, where atherosclerosis is more prevalent.

Treatment

As with aortic dissection, anti-impulse medical therapy should be initiated as soon as the diagnosis of a dissection variant is considered. Intravenous beta blockade and, if needed for blood pressure control, sodium nitroprusside are the treatment agents of choice. For the dissection variants involving the ascending aorta, prompt surgical intervention is considered the treatment of choice, similar to classic proximal aortic dissection. However, there are data indicating that certain patients with small intramural hematomas in the ascending aorta may be managed medically. Recent data suggest that penetrating ulcer-like findings in an area of intramural hematoma can identify high-risk patients. Symptoms of sustained or recurrent pain or findings of an increasing pleural effusion are suggestive of disease progression and favor surgical intervention. Guidelines and management strategies continue to evolve in this patient population.

For the dissection variants involving the descending aorta, especially intramural hematomas without penetrating ulcers, medical therapy is the preferred initial treatment. However, some have argued that there should be a lower threshold for surgical intervention than for classic distal dissection, particularly when clinical signs of instability are present. The presence of a severely bulging hematoma or a deeply penetrating ulcer may warrant surgical or endovascular repair. The development of a saccular aneurysm or pseudoaneurysm should merit consideration for surgical repair. For those treated medically, serial imaging studies are warranted to assess for progression or increase in aortic diameter, in which case surgical repair or endovascular stent graft placement may be considered.

Thoracic Aortic Aneurysm

An aortic aneurysm is present when there is dilation of the aorta, typically at least 1.5 times its normal reference diameter in an adjacent segment. This dilation can involve the entire circumference of the aortic wall (fusiform) or a localized protrusion of one of the walls (saccular). Ectasia is characterized by dilation less than 1.5 times the normal reference diameter.

The incidence of thoracic aortic aneurysm (TAA) is estimated at 10 cases per 100,000 person-years. The leading causes include the risk factors of hypertension and smoking, the genetic syndromes of congenital bicuspid aortic valve, Marfan syndrome (Fig. 8), idiopathic annuloaortic ectasia (Fig. 9), Loeys-Dietz, Ehlers-Danlos, familial thoracic aortic aneurysm syndrome, and acquired types such as in ankylosing spondylitis syphilis, and trauma. Descending TAA may extend distally and involve the abdominal aorta, creating a thoracoabdominal aneurysm. Patients are often asymptomatic at time of presentation, and the TAA may be diagnosed by an imaging modality ordered for other clinical indications. Physical findings may also be absent. When signs and symptoms occur, they are often the result of mass effect. The enlarging aorta can compress nearby structures, such as the superior vena cava, trachea, esophagus, and recurrent laryngeal nerve. This can result in the superior vena cava syndrome, stridor, dysphagia, and hoarseness, respectively. Progressive dilation of the aortic root can lead to aortic regurgitation, which may produce symptoms of congestive heart failure. Enlargement of the aortic sinuses can lead to narrowing of the coronary artery ostia, which may lead to myocardial ischemia and even infarction. Blood flow can be static in large aneurysms, predisposing to atheroma and thrombus formation and distal embolization.

Noninvasive Imaging

TAAs are often noted incidentally on chest x-ray as a widened mediastinum or a prominent aortic knob. Transthoracic echocardiography is the most common modality for initial diagnosis and monitoring dilation of the aortic root. CT scanning and MRA are the preferred techniques to define the entire thoracic aorta and its branch vessels accurately and measure the TAA precisely. Because the thoracic aorta may be tortuous, care must be taken not to measure off-axis axial cuts; these can overestimate the true cross-section as compared with the actual orthogonal diameter.

Medical Treatment

There are data indicating that beta blockade can slow the rate of thoracic aneurysm expansion in patients with Marfan syndrome, resulting in improved survival. Although the data are extrapolated to those without Marfan syndrome, it would seem reasonable to recommend such therapy while TAA patients are being medically followed. In a recent study, angiotensin receptor blocker therapy was found to slow the progression rate of aortic root dilation in Marfan patients.6 As a result, it is also reasonable to use angiotensin receptor blockers, along with beta blockers, in patients with TAA.

Marfan Syndrome, Thoracic Aortic Aneurysms, and Pregnancy

Women with Marfan syndrome or a known thoracic aortic dilation have an increased risk of aortic dissection during pregnancy, particularly during the third trimester. The risk of dissection greatly increases if the aortic root diameter is more than 4.0 cm or if there is evidence of rapid aortic root dilation during pregnancy. If elective prepartum surgical repair is not performed, beta blockade should be used during pregnancy. Close echocardiographic follow-up (monthly or bimonthly) and cesarean section delivery should be considered if the aortic root size exceeds 4.0 cm or rapid aortic dilation is evident.7

Indications for Surgical Treatment

Dissection and rupture are the most-feared complications of TAA, and prevention of these conditions is the purpose of elective surgical aortic repair. Size is clearly a risk factor and the principal harbinger for dissection and rupture. In one series, the annual rate of dissection or rupture was 2% for TAAs smaller than 5 cm, 3% for TAAs 5.0 to 5.9 cm, and 7% for those larger than 6 cm. Therefore, prophylactic surgical intervention should be considered before the TAA reaches a size that predisposes to aortic instability. Although the optimal timing of prophylactic aortic surgery remains uncertain, recommendations for surgical repair are 5.5 cm for a degenerative ascending TAA and 6.0 cm for a descending TAA. Patients with Marfan syndrome, Loeys-Dietz, bicuspid aortic valve, or family history of premature aortic instability should be considered for earlier repair (perhaps at 4.5-5.0 cm and 5.5-6.0 cm for ascending and descending TAAs, respectively). Rapid enlargement of the aorta (>0.5-1.0 cm/year) or symptom development has also been advocated as indications for surgery. Although not approved for use in the ascending aorta, endovascular stent grafting should be considered when descending TAA are 5.5 cm. The decision for operative repair must take into account the patient’s medical comorbidities, and a risk-to-benefit ratio must be individualized for each patient. Patients who are at otherwise low medical risk may be considered for elective intervention at smaller aortic sizes.

Abdominal Aortic Aneurysm

The incidence of abdominal aortic aneurysm (AAA) is estimated at 36/100,000 person-years. AAA represents the most common form of arterial aneurysm. Seventy-five percent of AAAs are infrarenal. Atherosclerosis is the dominant risk factor in the development of an AAA. Additional risk factors associated with AAA are male gender (four to five times more common in men), increasing age, smoking, and hypertension. There is a clear familial predisposition to AAA, and relatives of affected patients have up to a 30% increased risk for developing an AAA. Asymptomatic AAA is often diagnosed on physical examination by abdominal palpation. The most common symptom is pain, which is usually steady. The pain may be a localized abdominal pain or may radiate to the back, flank, or groin. Sudden onset of severe abdominal and back pain suggests rupture, representing a surgical emergency. Fewer than one third of patients with rupture present with the classic triad of pain, pulsatile abdominal mass, and hypotension. Atheroembolism may be the first manifestation of an AAA.

Noninvasive Imaging

Ultrasonography, CT scanning, aortography, and MRA have all been used in the initial diagnosis, sizing, and monitoring of AAA. Ultrasonography represents the most practical method of screening and serial monitoring, whereas CT scanning and MRA remain superior for accurately detailing the morphology and extent of the AAA. When AAA is initially diagnosed, the rate of dilation cannot be determined; therefore, the next serial study should be performed in 6 months. In general, for an AAA smaller than 4.0 cm, yearly surveillance imaging is recommended, for an AAA 4.0 to 5.0 cm, imaging every 6 to 12 months, and for an AAA larger than 5.0 cm, imaging every 3 to 6 months. Although predictors of dilation are lacking, a baseline AAA size seems to be the best predictor. Larger aneurysms expand at higher rates than smaller ones.

Medical Treatment

Beta blockade with careful control of hypertension appears to have an impact on delaying the rate of AAA expansion. Smoking should be discontinued, because rupture risk is greater in active smokers.

Indications for Surgical Treatment

Mortality from an AAA is primarily related to rupture. As with thoracic aneurysms, increasing size is the harbinger of rupture risk. Aneurysms smaller than 4 cm have a 0% to 2% risk of rupture over 2 years, those larger than 5 cm have a 22% risk of rupture over 2 years, and those larger than 6 cm show the sharpest rise in risk. An aortic diameter of 5.0 to 5.5 cm is recommended as an indication for prophylactic surgery in asymptomatic AAA patients. Although AAAs are less common in women, when present, they are at greater risk of rupture and have a smaller aortic diameter than in men. Thus, it is recommended that women undergo prophylactic AAA repair at 4.5 to 5.0 cm.8 Aneurysms that expand rapidly (>0.5-1.0 cm/year) are also associated with an increased risk of rupture and are thus considered for elective surgical repair. Inflammation is present in up to 10% of AAAs. There appears to be a familial tendency, and inflammation often occurs in the context of smoking. Patients present with constitutional symptoms and have an elevated sedimentation rate in addition to the classic symptoms of pain. CT scanning or MRA can identify the inflammatory component. Treatment is aortic surgery.

Endovascular Stent-Graft Repair

An alternative therapeutic option for AAA repair is the percutaneous placement of an endovascular stent-graft. The endovascular stent-graft is placed within the aneurysmal segment of the aorta, bridging the normal segments and excluding the aneurysm. In the last 5 to 10 years, the endovascular approach has been used in the majority of AAA repairs in the United States. Compared with open surgical repair, early perioperative mortality is significantly lower with endovascular stent grafting but the 2- to 5-year mortality is similar.9 Additionally, long-term surveillance imaging is currently required after stent-graft placement due to the occurrence of endoleaks and persistent sac enlargement. Nonetheless, the procedure remains an attractive alternative to conventional surgical repair.

Atheromatous Aortic Disease

Atherosclerotic plaques (Fig. 10) in the aorta can give rise to cerebral and peripheral embolic events. TEE, in particular, has been a valuable imaging modality for assessing the presence and extent of these plaques.10 Plaques thicker than 4 mm, or those with mobile components, appear to be strongly associated with subsequent embolic events. Treatment strategies for patients with such atheromatous plaques have not been evaluated in sufficient numbers in a prospective randomized fashion. However, there is the suggestion that lipid-lowering therapy and antiplatelet therapy or anticoagulation with warfarin may have benefit for some patients. Earlier reports of a potential association between warfarin and the cholesterol embolization syndrome have produced some reluctance to use such anticoagulant therapy in these patients, but the risk appears to be very low. The potential role of aortic replacement or removal of an atheroma remains to be defined. It has become increasingly common for cardiac surgeons to assess the aorta before instituting cardiopulmonary bypass. The presence of significant plaque may alter the cross-clamp site or may even lead to endarterectomy or aortic replacement at the time of surgery.

Cholesterol Embolization Syndrome

This syndrome represents a distal showering of atheromatous emboli, typically from the descending aorta. The syndrome can be seen in patients undergoing diagnostic angiography, but it can also occur spontaneously. There is a reported association between warfarin anticoagulation and these events, albeit at a very low rate. Patients most often present with livedo reticularis and blue toes in the presence of palpable pulses. Renal insufficiency can occur, and may not be reversible. Transient eosinophilia is often present. Treatment is supportive. If the atheroma arose from an AAA, then surgical intervention can help prevent future events.

Inflammatory Aortitis

Giant Cell Arteritis

Giant cell arteritis is an inflammatory disease that affects the temporal arteries, producing local tenderness and headaches. Patients affected are typically older than 55 years, and women are affected twice as often. The most devastating consequence is blindness. Although temporal arteritis is the hallmark of this disorder, there can be involvement of the thoracic aorta and the great vessels. This can lead to branch vessel occlusion, aneurysm formation, or even dissection. Corticosteroid treatment is the mainstay of therapy. With the development of advanced aortic involvement, surgical treatment may be required.

Takayasu’s Arteritis

Takayasu’s arteritis is an inflammatory disorder of the aorta that typically affects women younger than 40 years. Its prevalence is higher in Asian and African populations than in those of European or North American descent. A subacute inflammatory phase of the illness is manifested by constitutional symptoms. Later, there is occlusive inflammation of the aorta and branch vessels, with segmental narrowing apparent. Symptoms of arterial insufficiency may be present, depending on the vessels involved. Acquired coarctation can occur, leading to hypertension, as can aneurysm formation. Treatment is corticosteroids. For occlusive lesions not responsive to steroids, surgical bypass or endovascular stenting is warranted.

Syphilitic Aortitis

Syphilitic aortitis represents a manifestation of tertiary syphilis, which can occur 10 to 30 years after the initial infection. This inflammation results in a weakening of the vessel wall and can lead to aneurysm formation, usually saccular. Syphilitic aortitis most commonly affects the ascending aorta and hence can result in aortic regurgitation. The arch may also be affected. Involvement of the descending aorta occurs less often.

Other Types of Inflammatory Aortitis

Aortitis can also be seen in other systemic inflammatory diseases, such as reactive arthritis, ankylosing spondylitis, rheumatoid arthritis, Wegener’s granulomatosis, and enteropathic arthropathies. A common genetic underpinning of these conditions is the HLA-B27 genotype, which often plays a role in cases of lone aortic regurgitation, ascending aortic dilation, and conduction system disease. Treatment involves addressing the underlying disorder, with surgery as needed for aneurysmal or aortic valvular complications.

Mycotic Aneurysms

Bacteremia (from endocarditis, trauma, intravenous drug abuse) can result in infection within a weakened aneurysmal arterial wall. Persistent fevers after treatment of the inciting event should raise concern for an infected aneurysm. Mycotic aneurysms more commonly involve the abdominal aorta. Atheromatous plaques can, although uncommonly, also become infected (bacterial aortitis), serving as a nidus for infection and requiring prolonged antibiotic therapy.

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Summary

  • An important predisposing factor to diseases of the aorta, particularly the ascending aorta, is cystic medial degeneration.
  • Aortic dissection is one of the more ominous acute aortic syndromes, which also include the dissection variants of penetrating aortic ulcer, intramural hematoma, and symptomatic aneurysm.
  • Dissections that involve the ascending aorta (proximal, type A) require urgent surgical therapy, whereas dissections that involve the descending aorta (distal, type B) should be initially treated medically with surgery guided by a complication-specific approach.
  • In thoracic aortic aneurysm, recommendations for surgical repair are 5.5 cm for an ascending TAA and 6.0 cm for a descending TAA. Patients with Marfan syndrome, Loeys-Dietz, bicuspid aortic valve, or family history of unstable aortic disease should be considered for earlier repair (4.5-5.0 and 5.5-6.0 cm for ascending and descending TAAs, respectively).
  • In abdominal aortic aneurysms, an aortic diameter of 5.0-5.5 cm is recommended as an indication for prophylactic surgery in asymptomatic patients. In shorter women and men, prophylactic AAA repair is recommended at 4.5-5.0 cm.
  • Atherosclerotic plaques in the aorta can give rise to cerebral and peripheral embolic events. Plaques thicker than 4 mm, or those with mobile components, appear to be strongly associated with subsequent embolic events.

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References

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