Version May 2024
INTRODUCTION — Complications of aortic aneurysmal disease (thoracic and abdominal) are a leading cause of death in the United States, particularly in individuals aged >55 years [1]. Thoracic aortic aneurysm (TAA) represents approximately one third of aortic aneurysm admissions, with the remainder related to abdominal aortic disease [2]. The prevalence of TAAs is lower than the reported prevalence of abdominal aortic aneurysms (AAAs), but unlike AAA, which appears to be decreasing, the incidence of TAA is increasing. Enlargement of the thoracic aorta is an increasingly recognized condition that is diagnosed incidentally on imaging studies performed to evaluate unrelated conditions.
Most patients with TAA have no symptoms. Aneurysms that produce symptoms are typically very large and are at an increased risk for rupture, which is associated with high mortality rates. When symptoms do occur, patients can present with chest or upper back pain, or with symptoms related to compression of surrounding structures leading to nerve dysfunction, or arterial compression causing ischemia or thromboembolism.
This topic will review the clinical features and diagnosis of TAA. Pseudoaneurysm (false aneurysm) represents a collection of blood and connective tissue outside the aortic wall, the result of a contained aortic rupture, which may be due to one of a variety of pathologic processes such as penetrating aortic ulcer, aortic dissection, blunt aortic injury, or other acute aortic syndromes. These disorders are discussed elsewhere. (See "Overview of acute aortic dissection and other acute aortic syndromes" and "Overview of acute aortic dissection and other acute aortic syndromes", section on 'Definition and pathophysiology'.)
The management and outcome of TAA and AAA are discussed separately. (See "Management of thoracic aortic aneurysm in adults" and "Overview of abdominal aortic aneurysm".)
ANATOMIC ISSUES
Anatomy of the thoracic aorta — The aorta is the major arterial conduit conveying blood from the heart to the systemic circulation. It originates immediately beyond the aortic valve and ascends initially, then curves, forming the aortic arch, and descends caudally adjacent to the spine. The ascending thoracic aorta gives off the coronary arteries, and the aortic arch branches are typically the brachiocephalic trunk (ie, innominate artery, provides branches to the right carotid and right subclavian arteries), left carotid, and left subclavian arteries; however, aortic arch anatomy can vary (figure 1). The descending thoracic aorta provides paired thoracic arteries (T1-T12) and continues through the hiatus of the diaphragm (figure 2A-B) to become the abdominal aorta, which extends retroperitoneally to its bifurcation into the common iliac arteries at the level of the fourth lumbar vertebra.
Definition of TAA — A true aneurysm is defined as a segmental full-thickness dilation of a blood vessel having at least a 50 percent increase in diameter compared with the expected diameter [2-4]. True aneurysms involve all three layers of the arterial wall (intima, media, adventitia).
"Expected" thoracic aortic diameter varies according to the location within the aorta and also with body habitus, sex, and age [5]. Average diameters of the thoracic aorta identified on imaging (computed tomography, magnetic resonance) are given below for adult males and females for various locations in the thoracic aorta.
●Average aortic dimensions in a normal male (ie, no connective tissue disease)
•Aortic sinuses: 3.63 to 3.91 cm
•Ascending aorta: 2.86 cm
•Mid-descending aorta: 2.39 to 2.98 cm
•At diaphragm: 2.43 to 2.69 cm
●Average aortic dimensions in a normal female (ie, no connective tissue disease)
•Aortic sinuses: 3.5 to 3.72 cm
•Ascending aorta: 2.86 cm
•Mid-descending aorta: 2.45 to 2.64 cm
•At diaphragm: 2.40 to 2.44 cm
Nomograms of normal ascending aortic diameter by body surface area and age from a cohort of normal individuals (ie, no known aortic disease) are also provided for males and females (figure 3 and figure 4) [6-8]. Thoracic aortic measurements are standardized. (See 'Imaging standards' below.)
Some anatomic relationships may also be useful to help determine the "expected" diameter of the ascending aorta:
●The ascending should be roughly the size of the main pulmonary artery (ie, no pulmonary hypertension).
●The ratio between ascending aortic diameter and descending thoracic aorta (ie, no descending thoracic aortic aneurysm) is around 1.2:1 [9].
Classification — Thoracic aortic aneurysms are classified by location within the aorta, extent of aortic involvement, and morphology [2]. These categories help to stratify the approach to surgical management. (See "Management of thoracic aortic aneurysm in adults" and "Endovascular repair of the thoracic aorta".)
Aneurysms of the thoracic aorta can be classified into four general anatomic categories; however, some aneurysms involve more than one segment [10]:
●Ascending aortic aneurysms arise anywhere from the aortic valve to the brachiocephalic trunk (ie, innominate artery; 60 percent)
●Aortic arch aneurysms include any thoracic aneurysm that involves the brachiocephalic vessels (10 percent)
●Descending aortic aneurysms are those distal to the left subclavian artery (40 percent)
●Thoracoabdominal aneurysms (10 percent)
Aneurysms that affect the thoracic and abdominal aorta (ie, thoracoabdominal aneurysms) have been classified according to Crawford and modified by Safi (figure 5) [11,12]:
●Type I arises from above the sixth intercostal space, usually near the left subclavian artery, and extends to include the origins of the celiac axis and superior mesenteric arteries. Although the renal arteries can also be involved, the aneurysm does not extend into the infrarenal aortic segment.
●Type II aneurysm also arises above the sixth intercostal space and may include the ascending aorta, but extends distal to include the infrarenal aortic segment, often to the level of the aortic bifurcation.
●Type III aneurysm arises in the distal half of the descending thoracic aorta, below the sixth intercostal space, and extends into the abdominal aorta.
●Type IV aneurysm generally involves the entire abdominal aorta from the level of the diaphragm to the aortic bifurcation.
●Type V aneurysm arises in the distal half of the descending thoracic aorta, below the sixth intercostal space, and extends into the abdominal aorta, but is limited to the visceral segment.
There are two major types of aneurysm morphology: fusiform, which is uniform in shape with symmetrical dilatation that involves the entire circumference of the aortic wall, and saccular, which is more localized and appears as an outpouching of only a portion of the aortic wall. Saccular aneurysms may be a manifestation of plaque hemorrhage and aortic ulceration or aortic wall infection and appear to have an increased risk for rupture [13,14]. (See "Overview of infected (mycotic) arterial aneurysm".)
CLINICAL PRESENTATIONS — Thoracic aortic aneurysm (TAA) disease is usually silent unless a complication occurs (eg, dissection, rupture). Complications of TAA, such as thoracic aortic dissection, may initially be attributed to another cause; thus, a high index of suspicion must be maintained in patients who present with chest pain [15,16].
Providers should ask specific questions about the individual's medical history as it pertains to the known risk factors for thoracic aortic disease. Patients should also be questioned about a history of aortic pathology in immediate family members as there is a strong familial component to acute thoracic aortic disease [17,18]. Risk factors associated with TAA are listed here and are discussed in detail elsewhere. (See "Epidemiology, risk factors, pathogenesis, and natural history of thoracic aortic aneurysm and dissection", section on 'Etiology and risk factors'.)
●Risk factors for atherosclerosis (eg, smoking, hypertension, hypercholesterolemia).
●Known aneurysm in the thoracic aorta or at other sites (eg, abdominal aortic aneurysm).
●Prior aortic dissection.
●High-risk conditions – Marfan syndrome (table 1), Loeys-Dietz syndrome, vascular Ehlers-Danlos syndrome, Turner syndrome, or other connective tissue disease. Patients with these conditions may have a known mutation in genes known to predispose to TAA (FBN1, TGFBR1, TGFBR2, ACTA2, and MYH11).
●Known aortic valve disease (eg, bicuspid aortic valve, aortic valve replacement, or aortic stenosis).
●Family history of aortic dissection or thoracic aortic aneurysm.
●Cerebral aneurysm.
Asymptomatic TAA — Most patients with aortic thoracic aneurysm have no symptoms related to the aneurysm when TAA is discovered [19]. The aneurysm may be discovered incidentally on echocardiography performed to evaluate an aortic murmur (ascending aneurysm), computed tomography (CT) scan for an unrelated condition (eg, lung nodule or pulmonary embolus), or as a result of a screening for TAA in a patient at risk for disease. (See 'Incidental TAA' below.)
Biomarkers of thoracic aortic disease — Multiple studies have attempted to identify biomarkers and gene expression profiles as potential screening tests for TAA; however, none of these studies, to date, identifies the presence of TAA with certainty [20-23].
Elevated D-dimer levels may reflect increasing deposition of thrombus within a thoracic aneurysm sac [24]; however, D-dimer is nonspecific and can be elevated in a variety of other thrombotic conditions [25,26]. D-dimer has been used primarily in patients who present with symptoms based on its negative predictive value. (See 'Laboratory studies' below.)
Other serum markers have been studied, including matrix metalloproteinases, cytokines, acute phase reactants, lipoproteins, homocysteine, and transforming growth factor beta, but none of these has proven useful [23].
Genetic testing may reveal mutations in genes associated with syndromes known to have a high risk for TAA. These genes include FBN1, TGFBR1/2, ACTA2, and MYH11. The role of these genes in the pathogenesis of TAA and the role of genetic testing in specific high-risk conditions associated with TAA are discussed elsewhere. (See "Epidemiology, risk factors, pathogenesis, and natural history of thoracic aortic aneurysm and dissection", section on 'Pathogenesis' and "Genetics, clinical features, and diagnosis of Marfan syndrome and related disorders", section on 'Screening relatives' and "Genetics, clinical features, and diagnosis of Marfan syndrome and related disorders", section on 'Role of genetic testing'.)
Clinical markers of thoracic aortic disease — Clinical markers associated with thoracic aortic aneurysm include bicuspid aortic valve, intracranial aneurysm, inguinal hernia, aortic arch branching anomalies (eg, bovine aortic arch, isolated left vertebral artery), and a positive family history of aortic aneurysm or dissection. Such clinical markers make it possible to identify patients at risk for thoracic aortic disease. (See "Epidemiology, risk factors, pathogenesis, and natural history of thoracic aortic aneurysm and dissection", section on 'Etiology and risk factors'.)
A finding of simple renal cysts during abdominal imaging studies may also give a clue to the presence of thoracic aortic aneurysm. A retrospective review identified the prevalences of simple renal cysts among patients with known ascending aneurysm, descending aneurysm, type A dissection, and type B dissection as 37.5, 57.0, 44.1, and 47.3 percent, respectively [27]. These prevalences were significantly higher than a control population for simple renal cyst, which was 15.3 percent.
Symptomatic TAA — Patients can present initially with symptoms related to rapid expansion, which increases the risk for rupture, or complications such as aortic dissection or rupture. Once TAA becomes symptomatic, surgical intervention is usually indicated regardless of aneurysm diameter to minimize the risk of rupture if rupture has not already occurred [28]. (See "Management of thoracic aortic aneurysm in adults", section on 'Indications for repair'.)
Patients presenting with sudden onset of severe chest, back, and/or abdominal pain, particularly younger patients, should be questioned about a history of and examined for physical features of Marfan syndrome, Loeys-Dietz syndrome, vascular Ehlers-Danlos syndrome [29], Turner syndrome, bicuspid aortic valve, or other connective tissue disorders associated with thoracic aortic disease. (See 'Physical examination' below.)
Patients generally do not develop symptoms until TAA has expanded enough to cause compression or distortion of other intrathoracic structures, erosion into adjacent bone, or symptoms related to complications, such as aortic dissection, or rupture. The most common symptom is pain, which can occur in the chest or abdomen. Other symptoms depend upon the location of the aneurysm.
●Ascending aorta/aortic arch – Ascending aneurysms can present with heart failure due to aortic regurgitation from aortic sinus dilatation and annular distortion. In addition, compression of a coronary artery can result in myocardial ischemia or infarction, while a sinus of Valsalva aneurysm can rupture into the right side of the heart, producing a continuous murmur and, in some cases, heart failure. (See "Acute aortic regurgitation in adults" and "Auscultation of cardiac murmurs in adults".)
Large aneurysms affecting the transverse and descending arch can cause dysphagia from esophageal compression, hoarseness from left recurrent laryngeal nerve or left vagus nerve compression, or hemidiaphragmatic paralysis from phrenic nerve compression [10,13,30].
Wheezing, cough, hemoptysis, dyspnea, or pneumonitis can occur if there is compression of the tracheobronchial tree. Compression of the central veins or superior vena cava (SVC) can lead to thromboembolism or superior vena cava syndrome (swelling of the neck, face, or upper extremities) from SVC occlusion.
Patients can also present with acute neurologic complaints due to aneurysmal compression of aortic arch branch vessels or arterial thromboembolism.
●Descending aorta – Compared with ascending aneurysms, descending aortic aneurysms are less likely to lead to symptoms until the aneurysm has become very large, given the capacity of the thoracic cavity. The aneurysm may erode into the adjacent spine, causing back pain. Pain can also be related to intercurrent dissection of the aneurysm, which can also produce visceral or extremity ischemia. (See "Clinical features and diagnosis of acute aortic dissection".)
Rupture — The most serious complication of thoracic aortic aneurysm is rupture, most often into the left chest or pericardium, presenting as severe chest pain and hypotension or shock (image 1). Descending TAA can rupture into the adjacent esophagus, producing aortoesophageal fistula and presenting with hematemesis.
Laboratory studies — Most patients who present with acute chest complaints will undergo initial laboratory testing that includes a complete blood count, electrolytes, blood urea nitrogen and creatinine, D-dimer, and markers of cardiac ischemia. These studies may help guide management of the patient diagnosed with TAA. In patients who present with systemic manifestations (eg, fever, weight loss), an elevated white blood cell count may indicate aortic infection or inflammation, and laboratory evidence of disseminated intravascular coagulation (elevated D-dimer) can be related to a large thoracoabdominal aneurysm (image 2) [31,32]. Anemia may point toward acute blood loss as the cause of shock, and elevated lactic acid levels help assess the severity of ischemia that may be due to TAA rupture or arterial occlusion. A negative D-dimer can be used to rule out aortic dissection in patients who present with chest pain, but it does not exclude the presence of an aneurysm. (See "Overview of acute aortic dissection and other acute aortic syndromes" and "Clinical features and diagnosis of acute aortic dissection", section on 'D-dimer'.)
ECG findings — Patients with symptoms of chest pain typically undergo electrocardiography (ECG). Electrocardiography may reveal findings consistent with myocardial infarction in patients with ascending aortic aneurysm, but this is less common. Signs of myocardial hypertrophy due to longstanding hypertension or valvular disease are more common, although nonspecific. Unless the patient is at high risk for aortic rupture or aortic dissection, myocardial infarction should be treated as a primary cardiac event. (See "Diagnosis of acute myocardial infarction".)
PHYSICAL EXAMINATION — Patients with risk factors and/or acute symptoms consistent with thoracic aortic aneurysm (TAA) should undergo a physical examination that includes vital signs and a careful and complete cardiovascular examination with bilateral upper extremity blood pressures, auscultation looking for any aortic murmurs or vascular bruits, pulse deficits or other signs of arterial ischemia, focal neurologic deficits, or signs of central venous compression (facial or upper extremity swelling).
Vital signs in symptomatic patients may be normal or demonstrate sinus tachycardia, or moderate-to-severe hypotension. Fever associated with TAA may indicate an infected aneurysm. In patients with ruptured TAA, femoral and pedal pulses may be diminished or absent depending upon the patient's blood pressure, the presence of peripheral artery disease, or thromboembolism. If lower extremity pulses are not easily identified, a handheld continuous wave Doppler can be used to locate them. If palpable or Dopplerable pulses in the feet are identified (dorsalis pedis, posterior tibial), it is helpful to mark the location of the vessels for later comparison.
Physical characteristics of associated high-risk conditions include the following:
●Marfan syndrome – Physical features include tall stature, scoliosis, pectus deformities, elongated skeletal features, hyperflexibility, and ocular abnormalities such as ectopia lentis (ie, dislocated lens) (table 2 and table 1). The diagnostic criteria are discussed elsewhere [33]. (See "Genetics, clinical features, and diagnosis of Marfan syndrome and related disorders", section on 'Diagnosis of MFS'.)
●Loeys-Dietz syndrome – This syndrome has many overlapping physical features in common with Marfan syndrome; however, several features are routinely described with Loeys-Dietz syndrome but not Marfan, including bifid uvula, hypertelorism, and cervical arterial tortuosity [34]. Other severe manifestations may include cleft lip and palate, and cervical spine deformity leading to instability. Arteriopathy is widespread, occurring in peripheral vascular beds as well. (See "Genetics, clinical features, and diagnosis of Marfan syndrome and related disorders", section on 'TGFBR1 or TGFBR2 mutation: Loeys-Dietz syndrome'.)
●Familial TAA is associated with livedo reticularis, iris flocculi, congenital mydriasis (ACTA2 mutation), and peripheral vascular malformation [29,35].
IMAGING DIAGNOSIS — A diagnosis of thoracic aortic aneurysm (TAA) relies on aortic imaging to confirm the presence of the aneurysm [2,36-38]. When complications associated with TAA are a concern, aortic imaging is a priority and should not be delayed for extensive physical examination or laboratory or electrocardiogram (ECG) studies.
Incidental TAA — Chest radiography is a common way that asymptomatic TAA is detected in asymptomatic patients (image 3 and image 4). The most common features on chest radiograph that are consistent with TAA are listed below, and these findings should prompt further evaluation using cross-sectional imaging to define the diameter and extent of the aneurysm [39,40]. (See 'Choice of imaging technique' below.)
●Widening of the mediastinal silhouette
●Enlargement of the aortic knob
●Displacement of the trachea from midline
●Other features include displaced aortic calcification, aortic kinking, and opacification of the aorticopulmonary window
TAA may also be discovered incidentally on echocardiography, CT (image 5 and image 6 and image 7), or magnetic resonance (MR) imaging of the chest performed for an unrelated condition [41-43], or routine follow-up surveillance (image 8 and image 9). TAA that is incidentally diagnosed on transthoracic echocardiography (TTE) or transesophageal echocardiography (TEE) should be evaluated further with CT or MR.
In patients found to have TAA on the basis of advanced imaging studies performed for an unrelated condition, the pattern of aortic dilation may provide clues to the potential underlying disorder. Marfan syndrome and Loeys-Dietz syndrome lead to aneurysms of the ascending aorta and sinuses of Valsalva and are associated with lumbosacral dural ectasia [33]. Bicuspid valve disease can involve the aortic sinuses, but aneurysms are more commonly located in the mid–ascending aorta. (See 'Determining TAA etiology' below.)
Imaging asymptomatic, high-risk patients — Consensus guidelines recommend aortic imaging in certain patient groups at high risk for TAA (image 10) [2]. Patients with genetic mutations known to predispose to aortic aneurysms or aortic dissection (TGFBR1, TGFBR2, FBN1, ACTA2, or MYH11) should undergo complete aortic imaging (thoracic and abdominal aorta) at the time of their medical diagnosis. (See 'Choice of imaging technique' below.)
Considerations for imaging in specific diseases are found in separate topic reviews:
●Marfan syndrome – (See "Management of Marfan syndrome and related disorders", section on 'Monitoring MFS' and "Genetics, clinical features, and diagnosis of Marfan syndrome and related disorders", section on 'Imaging those at risk for aortic enlargement'.)
●Loeys-Dietz syndrome – (See "Management of Marfan syndrome and related disorders", section on 'Monitoring Loeys-Dietz and related syndromes'.)
●Turner syndrome – (See "Clinical manifestations and diagnosis of Turner syndrome".)
●Bicuspid aortic valve – (image 11) (See "Bicuspid aortic valve: General management in adults", section on 'Surveillance'.)
●Takayasu disease – (See "Clinical features and diagnosis of Takayasu arteritis", section on 'Imaging'.)
Imaging symptomatic patients — Chest radiography may be useful in the initial evaluation of patients with chest pain or other thoracic symptoms as it may establish a clear alternative diagnosis that will obviate the need for definitive aortic imaging. (See "Evaluation of the adult with chest pain in the emergency department".)
Although chest radiography may demonstrate features consistent with TAA, it cannot reliably distinguish an aneurysm from a tortuous aorta, and many aneurysms are not apparent on the chest radiograph [10]. The frequency with which this occurs was illustrated in a series of 36 patients presenting with acute onset of chest or back pain within the prior 14 days who were found to have nondissecting TAAs; radiographic abnormalities were detected in only 22 (61 percent) [39]. A negative study should not delay definitive aortic imaging in those where a suspicion of TAA or aortic dissection is high, or in patients at high risk for TAA. For this reason, as well as better imaging detail, CT angiography is obtained in virtually all symptomatic patients suspected of having TAA (image 1 and image 12 and image 13 and image 14). (See 'Choice of imaging technique' below.)
Choice of imaging technique — When thoracic aortic aneurysm is suspected, we suggest imaging the entire aorta. Disease of the abdominal aorta can occur in up to 20 percent of cases [44,45]. The study should also be of sufficient detail to assess branch vessel involvement [2] . The advantages and disadvantages of the available imaging techniques to evaluate the thoracic aorta are given in the table (table 3).
CT or MR angiography are the optimal imaging tests to detect TAA, determine aortic diameter or any changes in diameter, define aortic and branch vessel anatomy (image 15 and image 16), identify rupture (image 17 and image 14), or identify dissection (image 18) [10,46,47]. Digital subtraction arteriography (DSA) provides sharper resolution of luminal characteristics and may be better for evaluating branch vessel pathology (image 19 and image 20 and image 21), but multislice CT and MR show sufficient detail under most circumstances. Contrast arteriography is also unable to determine the true aneurysm diameter and is invasive. For patients with connective tissue disorders, conventional catheter-based arteriography risks arterial injury or dissection and should be used with caution.
The choice of imaging technique depends upon the clinical circumstance. CT is used more often in acutely symptomatic patients due to availability, efficiency, and proximity to the emergency department. Under emergency circumstances, MR may not be immediately available. However, the lack of ionizing radiation makes MR a more useful tool for patients who require repeated thoracic aortic imaging, such as those with known TAA or syndromes known to predispose to TAA.
The evaluation of the aortic sinuses can be suboptimal with cross-sectional imaging given the asymmetry of the sinuses and artifact caused by cardiac motion [10,48]. Thus, it is reasonable to obtain transthoracic echocardiography (TTE) or transesophageal echocardiography (TEE) to further evaluate the aortic valve or other abnormalities or disease that may alter management [49,50]; TTE is the preferred initial study but can be technically limited. TEE is recommended rather than TTE or cross-sectional imaging in patients with acute symptoms who are hypotensive. Provided TTE adequately visualizes the affected aortic segments, the lower cost and risk of TTE make it the most useful imaging modality for long-term monitoring. (See "Clinical features and diagnosis of acute aortic dissection", section on 'Cardiovascular imaging'.)
Imaging standards — As the aorta dilates, it becomes more tortuous and presents challenges for obtaining accurate measurements from radiographic studies. Reports of rapid expansion often relate to variabilities in technique and measurement errors generated by comparing nonequivalent aortic segments or tangential measurement of aortic diameters [51-57]. It is important to take into account the margin of error for the imaging modality chosen [55,56,58]. When determining the rate of TAA expansion, a comparison should be made with the earliest study available so that changes over time can be better appreciated and differences in measurement variabilities minimized [59]. The American College of Cardiology/American Heart Association guidelines suggest the following standards for imaging the thoracic aorta [2]:
●Measurements of aortic diameter should be taken at reproducible anatomic landmarks such as the aortic sinuses, sinotubular junction, ascending, arch, and specific locations of the descending aorta.
●For CT and MR imaging, external aortic diameter should be measured perpendicular to the axis of blood flow when taking measurements using CT or MR.
●For measurements taken by echocardiography, the internal diameter should be measured perpendicular to the axis of blood flow.
●For aortic root measurements, the widest diameter, typically a "sinus-sinus measurement," should be used regardless of imaging modality (CT, MR, echocardiography).
A study compared echocardiographic measurement taken using diastolic leading-edge-to-leading-edge versus systolic inner-edge-to–inner-edge techniques in a large cohort of healthy adult individuals [54]. Although there was a significant difference in aortic diameter measurement between these two conventions, the difference was very small and correlations were excellent, suggesting that the difference is not clinically significant.
DETERMINING TAA ETIOLOGY — Thoracic aortic aneurysm/dissection can be degenerative, related to genetically mediated disorders (nonsyndromic or syndromic) or due to other causes (eg, chronic dissection, aortitis [Takayasu, giant cell, seronegative arthropathy, infection]). (See "Epidemiology, risk factors, pathogenesis, and natural history of thoracic aortic aneurysm and dissection", section on 'Etiology and risk factors'.)
The clinical presentation and physical examination offer clues to the etiology of thoracic aortic aneurysm and dissection (TAAD), which is important because the etiology impacts morbidity and mortality and affects the management of the aneurysm, such as the appropriate threshold for repair, and associated conditions that may have a bearing on determining the method of repair when it is indicated.
Degenerative versus genetically mediated — Degenerative thoracic aneurysm, typically affecting the descending aorta and sometimes in continuity with abdominal aortic aneurysm, is driven by factors in common with atherosclerosis, including older age, smoking, and hypertension. These risk factors are not commonly associated with genetically mediated disease. Rather, genetically mediated disease presents in younger patient populations, with up to 20 percent of patients having a family history of a thoracic aortic dilation [60,61].
Syndromic versus nonsyndromic — Genetically mediated TAAD can be described as syndromic or nonsyndromic. With nonsyndromic conditions, abnormalities are limited to the cardiovascular system; individuals do not exhibit external features of connective tissue disorders. External phenotypic features associated with syndromic conditions are given above. (See 'Physical examination' above and "Genetics, clinical features, and diagnosis of Marfan syndrome and related disorders", section on 'Differential diagnosis'.)
●Syndromic conditions include Marfan syndrome and related syndromic disorders such as Loeys-Dietz syndrome, vascular Ehlers-Danlos syndrome, Shprintzen-Goldberg syndrome, aneurysm-osteoarthritis syndrome, cutis laxa with aneurysm, and Turner syndrome.
●Nonsyndromic conditions include familial thoracic aortic aneurysm/dissection and bicuspid aortic valve with aneurysm.
In patients found to have TAA on imaging, gene analysis may also be needed in those with physical features associated with genetic conditions because of overlapping phenotypic characteristics, and to evaluate their relatives (algorithm 1). Up to 20 percent of patients with a TAA will have another first-degree relative with thoracic aortic disease. Aortic imaging is recommended for first-degree relatives of patients with familial thoracic aortic aneurysm and/or dissection to identify those with asymptomatic disease. If one or more first-degree relatives of a patient with known thoracic aortic aneurysm and/or dissection are found to have thoracic aortic dilatation, aneurysm, or dissection, then imaging of second-degree relatives is reasonable. Patients with intracranial aneurysm, a family history of sudden death, patients with persistent atypical chest pain, and relatives of patients with degenerative TAA or AAA may also benefit from aortic imaging. (See "Management of thoracic aortic aneurysm in adults", section on 'Counseling and other evaluation'.)
Aortitis — Compared with degenerative or genetically mediated TAA, aortitis (infectious, noninfectious) as a cause of thoracic aortic aneurysm is much less common. Aortic wall inflammation results in the aortic wall degradation and subsequent expansion, which is often a delayed manifestation of the disease. Aortic wall infection can be due to bacterial inoculation, bacteremia, septic embolism, or contiguous infection. Noninfectious aortitis may be related to Takayasu arteritis, giant cell arteritis, immunoglobulin G4-related disease-related aortitis, ankylosing spondylitis, relapsing polychondritis, or Cogan syndrome [62]. In one review, noninfectious aortitis was diagnosed in 2.8 percent of TAA aneurysm repair surgical specimens over a five-year period [63]. The clinical presentation of thoracic aortic aneurysm in patients with aortitis may include constitutional symptoms such as malaise, fever, and weight loss. Other clinical manifestations and the natural history of disease leading to aneurysm formation are reviewed separately. (See "Overview of infected (mycotic) arterial aneurysm" and "Treatment of Takayasu arteritis", section on 'Surgical management of vascular complications' and "Cogan syndrome" and "Clinical manifestations of relapsing polychondritis" and "Treatment of giant cell arteritis", section on 'Imaging surveillance for patients with large vessel involvement'.)
Prior aortic dissection — Thoracic aortic aneurysm that develops from progressive expansion of the weakened aortic wall from a prior aortic dissection is more typically asymptomatic and identified during serial imaging examination. However, individuals who are lost to follow-up may present symptomatically. (See "Management of chronic type B aortic dissection".)
Imaging characteristics of underlying disorders — Imaging features may provide clues as to the underlying disorder leading to TAA. The pattern of aortic dilatation may be informative. With Marfan syndrome and related disorders, the main cardiovascular abnormality is aneurysm of the aortic root, which can extend into the proximal portion of the ascending aorta, appearing as a pear-shaped deformity sometimes referred to as annuloaortic ectasia (image 8 and image 10 and image 22) [60]. By contrast with nonsyndromic conditions, ascending aneurysmal dilation is more uniform and can extend to include the aortic arch vessels. Other etiologies may also be suggested on imaging studies, such as giant cell arteritis (image 23) or poststenotic aneurysm (image 24 and image 25).
Bicuspid aortic valve (BAV) aortopathy may involve the aortic root but more commonly (type I, type II) leads to aneurysm located in the mid-ascending aorta. Type III bicuspid aortopathy, which is rare [64], resembles Marfan annuloaortic ectasia, but the valvular anatomy will provide the distinction. Additionally, the presence of lumbosacral dural ectasia discovered in the aneurysm patient should trigger the evaluation of an underlying disease such as Marfan syndrome or Loeys-Dietz syndrome. (See "Clinical manifestations and diagnosis of bicuspid aortic valve in adults", section on 'Prevalence of aortic dilation and aneurysm'.)
Aneurysms can also be described as fusiform or saccular (image 5 and image 26), which may also be related to etiology. The shape of the aneurysm also has implications for endovascular repair. Saccular aneurysms are more commonly encountered in the thoracic compared with abdominal aorta and may be indicative of a false aneurysm due to a penetrating aortic ulcer or aortic infection. Alternatively, saccular aneurysm may represent a ductus aneurysm [65].
DIFFERENTIAL DIAGNOSIS — Other aortic pathologies can produce symptoms in the chest similar to those of thoracic aortic aneurysm (TAA), including thoracic aortic dissection and thoracic aortic pseudoaneurysm due to erosion of ulcerated plaque. The pain from aortic dissection is described as sharp, ripping, tearing, or searing in quality, often beginning in the chest or neck, then migrating into the back and abdomen over time. The intensity of the pain with dissection is typically severe. Aortic dissection may affect other arch vessels leading to other symptoms (cerebral embolism, upper extremity ischemia) that will not typically be present in patients with TAA. In patients with ulcerated aortic plaque, the symptoms may be indistinguishable from those of ruptured TAA. (See "Clinical features and diagnosis of acute aortic dissection".)
Thoracic aortic imaging will differentiate these etiologies. It is important to recognize abnormalities of aortic morphology (dissection, traumatic injury, pseudoaneurysm) even when aortic diameter is within normal limits. If there is any question that aortic pathology may involve the abdominal aorta, simultaneous chest and abdominal imaging should be obtained rather than thoracic imaging alone.
SOCIETY GUIDELINE LINKS — Links to society and government-sponsored guidelines from selected countries and regions around the world are provided separately. (See "Society guideline links: Aortic and other peripheral aneurysms".)
INFORMATION FOR PATIENTS — UpToDate offers two types of patient education materials, "The Basics" and "Beyond the Basics." The Basics patient education pieces are written in plain language, at the 5th to 6th grade reading level, and they answer the four or five key questions a patient might have about a given condition. These articles are best for patients who want a general overview and who prefer short, easy-to-read materials. Beyond the Basics patient education pieces are longer, more sophisticated, and more detailed. These articles are written at the 10th to 12th grade reading level and are best for patients who want in-depth information and are comfortable with some medical jargon.
Here are the patient education articles that are relevant to this topic. We encourage you to print or e-mail these topics to your patients. (You can also locate patient education articles on a variety of subjects by searching on "patient info" and the keyword(s) of interest.)
●Basics topics (see "Patient education: Thoracic aortic aneurysm (The Basics)")
SUMMARY AND RECOMMENDATIONS
●Thoracic aortic aneurysm – A thoracic aortic aneurysm (TAA) is defined as a permanent localized dilation of the thoracic aorta having at least a 50 percent increase in diameter compared with the expected normal diameter for that aortic segment. Normal diameters for the thoracic aorta are given in the text above. Aneurysms of the thoracic aorta are classified by the segment of the aorta that is involved. (See 'Introduction' above.)
●Clinical presentations – Patients with thoracic aneurysms are often asymptomatic at the time of presentation. When present, symptoms are usually due to compression of adjacent structures, which may lead to chest, back, flank, or abdominal pain. Depending upon the aneurysm location, pulmonary symptoms or signs of nerve compression (eg, hoarseness, diaphragm paralysis) can also occur. Other symptoms may be due to aortic regurgitation or thromboembolism to nearly any vascular bed (eg, coronary, cerebral, renal, mesenteric, lower extremity, and, rarely, spinal cord). The most serious complications of thoracic aortic aneurysm are aortic dissection and rupture, which is most often into the left intrapleural space or intrapericardial space. Rupture is associated with severe pain and hypotension or shock. (See 'Clinical presentations' above.)
●Diagnosis – The definitive diagnosis of TAA relies on advanced aortic imaging to confirm the presence of the aneurysm and characterize the diameter and extent.
•Incidental TAA – TAA is commonly detected as an incidental finding on chest radiography, echocardiography, and CT. TAA produces a widening of the mediastinal silhouette, enlargement of the aortic knob, or displacement of the trachea from midline. Plain chest radiography cannot distinguish TAA from a tortuous aorta and therefore when TAA is suspected based on radiographic findings, advanced imaging (CT, echocardiography) is necessary to confirm the diagnosis. (See 'Imaging symptomatic patients' above.)
•High-risk patients – Most patients with genetic mutations (eg, Marfan syndrome, Loeys-Dietz syndrome, Turner syndrome) known to predispose to aortic aneurysm/dissection should undergo complete aortic imaging (thoracic and abdominal aorta) at the time of their medical diagnosis. (See 'Imaging symptomatic patients' above.)
•Symptomatic patients – Chest radiography may be useful in the initial evaluation of patients with chest pain or other thoracic symptoms. When suspicion for TAA/dissection is high, negative radiography should not delay definitive aortic imaging.
●Imaging modalities – The choice of imaging technique depends on the clinical circumstance. The advantages and disadvantages of the available imaging techniques for TAA are given in the table (table 3). CT is used more often, particularly in acutely symptomatic patients, to detect TAA, determine its size, define aortic and branch vessel anatomy, and rule out an associated aortic dissection. The evaluation of the aortic sinuses can be suboptimal with cross-sectional imaging. Thus, it is reasonable to obtain transthoracic echocardiography (TTE) or transesophageal echocardiography (TEE) to further evaluate the aortic valve or other abnormalities or disease that may alter management. Transesophageal echocardiography (TEE) is preferred over TTE for examination of the entire aorta, particularly in emergency situations and for imaging when coexistent dissection is suspected.
ACKNOWLEDGMENTS — The UpToDate editorial staff acknowledges Y Joseph Woo, MD and Christina L Greene, MD, who contributed to an earlier version of this topic review.
The UpToDate editorial staff also acknowledges Emile R Mohler, III, MD (deceased), who contributed to an earlier version of this topic review.
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