Thoracic aortic aneurysm (TAA) is a life-threatening condition that causes significant short- and long-term mortality due to rupture and dissection. Aneurysm is defined as dilatation of the aorta of greater than 150% of its normal diameter for a given segment. For the thoracic aorta, a diameter greater than 3.5 cm is generally considered dilated, whereas greater than 4.5 cm would be considered aneurysmal.
Aneurysms may affect one or more segments of the thoracic aorta, including the ascending aorta, the arch, and the descending thoracic aorta. As many as 25% of patients with TAA also have an abdominal aortic aneurysm. Thoracic aortic aneurysm most commonly results from degeneration of the media of the aortic wall as well as from local hemodynamic forces.
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Descending thoracic aortic aneurysm with mural thrombus at the level of the left atrium.
Degenerative changes in the wall of the aorta lead to cystic medial necrosis. This causes damage to collagen and elastin, loss of smooth muscle cells, and increased amounts of basophilic ground substance in the medial (elastic) layer of the aorta. The ascending thoracic aorta is generally most affected by cystic medial necrosis, whereas a descending thoracic aneurysm is primarily a consequence of atherosclerosis.
In Marfan syndrome, abnormalities of the gene encoding for the synthesis of fibrillin have been implicated in the predisposition to form aneurysms. Mutations in the gene responsible for this structural lipoprotein found in the aortic wall have been found in patients who do not have Marfan syndrome but have aneurysms.
As many as 75% of patients with a bicuspid aortic valve have shown evidence for cystic medial necrosis, which may be because of inadequate fibrillin production. Other inherited forms of medial degeneration have been associated with defects in the genes for fibrillin and are associated with higher rates of thoracic aortic aneurysm (TAA).
Weakening of the aortic wall is compounded by increased shear stress, especially in the ascending aorta. This segment of the aorta is most exposed to the pressure of each cardiac systole (dP/dt) as well as the dynamic heart motion transmitted from each cardiac cycle. As local wall weakness causes dilatation of the aorta, wall tension increases (described by the Laplace law (T=PR), where wall tension equals the radius of a cylinder multiplied by the pressure within it). Small tears in the intimal (innermost) layer of the aorta can permit blood to penetrate the medial layer, leading to aortic dissection.
The incidence of aortic aneurysm is 5.9 cases per 100,000 person-years.[1]
Mortality/Morbidity
The cumulative risk of rupturing a thoracic aortic aneurysm (TAA) is related to aneurysm diameter. In a recent series of 133 patients with TAA, risk of rupture at 5 years was 0% for diameter less than 4 cm, 16% for diameter 4-5.9 cm, and 31% for aneurysms greater than 6 cm in diameter.[2]
Race
Thoracic aortic aneurysm is most common among whites.
Sex
Men are affected 2-4 times more frequently than women.
Patients with thoracic aortic aneurysm (TAA) may be asymptomatic. Forty percent may be found incidentally during workup for other processes. Symptoms vary according to the size, location, and changes in the aneurysm. Chest, back, and abdominal pain are common symptoms in patients who are symptomatic. Note the following:
Aortic root dilatation may lead to symptoms of congestive heart failure (CHF) due to aortic insufficiency.
Hoarseness may signify vagus or recurrent laryngeal nerve compression.
Wheezing, dyspnea, or cough suggests tracheal compression. Hemoptysis may be a sign of aneurysmal erosion into the trachea.
Dysphagia, hematochezia, or hematemesis may be caused by esophageal compression or aortoesophageal fistula.
Although atherosclerotic disease is often present in patients with thoracic aortic aneurysm (TAA), it may only play a minor causal role in the pathogenesis of aneurysm development. Note the following:
Aortic aneurysm is often associated with smoking and hypertension.
Marfan syndrome and Ehlers-Danlos syndrome are associated with an increased incidence of TAA and dilatation of the aortic root.
Aortic aneurysm has been associated with a number of rheumatologic disorders, such as giant cell arteritis, Takayasu arteritis, and psoriatic arthritis.
Syphilitic aortitis is an increasingly uncommon cause of thoracic aneurysm.
CT scanning, MRI, angiography, and transesophageal echocardiography are most often used to assess thoracic aneurysm in the emergent setting. The preferred method of assessment depends on the stability of the patient, the availability of radiographic modalities, and the preference of the surgeon. However, CT scanning is most commonly used in both emergent and outpatient settings to diagnose and follow thoracic aneurysm.
Chest radiography
Chest radiography should be obtained in the initial workup of patients with chest discomfort.
Findings may not demonstrate small aneurysms.
Findings suggestive of aneurysm include mediastinal widening, blurring of the aortic knob, and tracheal displacement. Pleural effusion is usually associated with aortic dissection rather than with a stable aneurysm.
An elevated hemidiaphragm may suggest phrenic nerve compression from mass effect, but this finding is exceedingly rare compared with the other findings listed.
Thoracic CT scanning
Intravenous contrast-enhanced CT scanning is the procedure of choice for diagnosis.
Its sensitivity is 96-100%, and its specificity is 99% for detecting aneurysms.
CT scanning is useful in evaluating aneurysm size, proximal and distal extension, presence or absence of dissection, and in seeking other pathology within the chest.
Use caution in patients with an allergy to the contrast agent or in those with renal failure.
Use caution in moving patients who are potentially unstable to the CT scanner.
Contrast angiography
Contrast angiography is useful in assessing complex aortic pathology and identifying anatomy of branch vessels.
Its sensitivity is 85% and its specificity is 95% in detecting aneurysms.
Aortic dissection may not be detected, especially if thrombosis is present in the false lumen.
Use caution in patients with an allergy to the contrast agent or in those with renal failure.
Use caution in moving patients who are potentially unstable to the angiography suite.
Magnetic resonance angiography
Magnetic resonance angiography is useful in assessing the aortic anatomy, the size of the aneurysm, the dissection, and the branch vessels.
Its sensitivity is 100% and its specificity is 100% in detecting aneurysms.
Magnetic resonance angiography does not require the administration of iodinated radiologic contrast material.
This study requires longer image acquisition times than other modalities.
Use caution in moving patients who are potentially unstable to the MRI scanner, where distance from the emergency department is compounded by difficulties in hemodynamic monitoring within the scanner.
Transesophageal echocardiography
Transesophageal echocardiography is increasingly used to assess the anatomy of the aorta and its valves and the presence of dissection.
Its sensitivity is 98% and its specificity is 99% in depicting aneurysms.
Transesophageal echocardiography may be performed rapidly at the bedside.
ECG is useful in evaluating patients with chest discomfort or dyspnea.
Findings may demonstrate strain or ischemia when a proximal aneurysm distorts the anatomy of the aortic valve or the coronary artery. Myocardial infarction may also be present.
In patients with symptoms suggestive of thoracic aortic aneurysm (TAA), prehospital care should consist of ensuring adequate airway and breathing, providing oxygen via a nonrebreather mask, placing 2 large-bore intravenous lines, and providing continuous cardiac monitoring.
Patients who are unstable (often those with a ruptured aneurysm or dissection) may require airway protection, mechanical ventilation, and aggressive fluid resuscitation. Timely communication between prehospital care providers and the receiving hospital is important in ensuring that the proper resources are available and brought to bear rapidly.
Placing 2 large-bore intravenous lines, administering 100% oxygen, and providing a cardiac monitor
Monitoring urine output
Consider alternate diagnoses. Until the diagnosis of thoracic aortic aneurysm (TAA) is established, be vigilant for other causes of symptoms, such as myocardial infarction (MI), aortic insufficiency, CHF, or pulmonary embolus.
Provide aggressive blood pressure control. Beta-blockers and nitrates are commonly used.[3]
For patients who are hemodynamically unstable, provide the following:
Placing an arterial line in the right radial artery (or in the left radial artery, if the systolic blood pressure on the left is higher), especially in patients who may have dissection or in those who are receiving intravenous nitroprusside and/or esmolol
Immediately consult with a cardiac surgeon (for ascending aorta or arch) or with a vascular surgeon (for descending aorta) for patients who are hemodynamically unstable or for patients with symptoms of a thoracic aneurysm. Anesthesia and operating room personnel need to be contacted in cases where emergent operative procedures are indicated.
Consult with a vascular surgeon or a cardiac surgeon and a radiologist to determine the optimal studies for assessing the anatomy of the thoracic aneurysm.
The goal of medical therapy is to reduce the pulse pressure (dP/dt) within the aorta. Reducing the heart rate, the blood pressure (BP), pain, and anxiety are the mainstays of therapy.
Clinical Context:
Ultra–short-acting beta1-blocker particularly useful in patients with labile arterial pressure because it can be abruptly discontinued if necessary. Typically used in conjunction with nitroprusside. May be useful as a means to test beta-blocker safety and tolerance in patients with history of obstructive pulmonary disease who are at uncertain risk of bronchospasm from beta blockade. Elimination half-life is 9 min. The objective is a target heart rate of 55-65 bpm.
Clinical Context:
Selective beta1-adrenergic receptor blocker that decreases automaticity of contractions. During IV administration, carefully monitor BP, heart rate, and ECG. When considering conversion from IV to PO dosage forms, use ratio of 2.5 mg PO to 1 mg IV metoprolol.
Clinical Context:
Class II antiarrhythmic nonselective beta-adrenergic receptor blocker. Has membrane-stabilizing activity and decreases automaticity of contractions. Not a first-line agent in the treatment of hypertensive emergencies. Do not administer IV in hypertensive emergencies.
Clinical Context:
Causes peripheral vasodilation by direct action on venous and arteriolar smooth muscle, thus reducing peripheral resistance. Commonly used IV because of rapid onset and short duration of action. Easily titratable to reach desired effect. Light sensitive; both bottle and tubing should be wrapped in aluminum foil. Prior to initiating, administer beta-blocker to counteract physiologic response of reflex tachycardia that occurs when nitroprusside is used alone. This physiologic response increases shear forces against aortic wall, thus increasing dP/dT.
These agents are used to reduce arterial pressure. Short-acting IV beta blockade and nitrates are very effective in reducing the dP/dt, especially in the ascending aorta. Consider calcium channel blockade in patients with contraindications to beta blockade.
Clinical Context:
DOC for narcotic analgesia because of reliable and predictable effects, safety profile, and ease of reversibility with naloxone. Like fentanyl, morphine sulfate is easily titrated to desired level of pain control. If administered IV, may be dosed in a number of ways; commonly titrated until desired effect obtained.
Unstable patients with thoracic aortic aneurysm (TAA) usually require medical or surgical ICU admission for careful hemodynamic monitoring.
Patients who are symptomatic require admission, as do those in whom a final diagnosis is uncertain.
Some patients with complicating conditions, such as Marfan syndrome or another cardiovascular disease, may require admission for medical stabilization and for more urgent surgical repair, even if they are asymptomatic at presentation.
Indications for surgical repair include the following:[4]
Rupture
Acute dissection (ascending requires urgent intervention, whereas descending is managed medically or surgically, if vascular complications arise)
Symptomatic states, including pain, mediastinal organ compression, or aortic insufficiency severe enough to cause CHF or a dilated hypokinetic left ventricle
Rapid aneurysm growth rate
Absolute size (5.5 cm for ascending aortic aneurysm, 6.0 cm for descending aortic aneurysm; in patients with Marfan syndrome, 5.0 cm for ascending aortic aneurysm, 6.0 cm for descending aortic aneurysm)
Surgical and other interventional options for TAA repair include the following:[3]
Open approaches using cardiopulmonary bypass, hypothermia, and grafting
Endovascular stent grafting may be an option when TAA is limited to the descending aorta.
Complications of repair include paraplegia, renal failure, and intraoperative mortality.
Patients with TAA who are symptomatic should only be transferred via advanced life support (ALS) system if the sending facility is unable to provide appropriate operative care.
Bret P Nelson, MD, Associate Professor of Emergency Medicine, Director of Emergency Ultrasound, Department of Emergency Medicine, Mount Sinai School of Medicine
Disclosure: Serve(d) as a director, officer, partner, employee, advisor, consultant or trustee for: Medical advisory board for EyeLife.<br/>Received consulting fee from Simulab for consulting.
Coauthor(s)
Eric M Isselbacher, MD, MSc, Associate Professor of Medicine, Harvard Medical School; Associate Director, Massachusetts General Hospital Heart Center; Co-Director, Thoracic Aortic Center, Massachusetts General Hospital; Director, MGH Healthcare Transformation Lab
Disclosure: Nothing to disclose.
Theodore I Benzer, MD, PhD, Assistant Professor in Medicine, Harvard Medical School; Director of the ED Observation Unit, Director of Toxicology, Chair of Quality and Safety, Department of Emergency Medicine, Massachusetts General Hospital
Disclosure: Nothing to disclose.
Specialty Editors
Francisco Talavera, PharmD, PhD, Adjunct Assistant Professor, University of Nebraska Medical Center College of Pharmacy; Editor-in-Chief, Medscape Drug Reference
Disclosure: Received salary from Medscape for employment. for: Medscape.
Gary Setnik, MD, Chair, Department of Emergency Medicine, Mount Auburn Hospital; Assistant Professor, Department of Emergency Medicine, Harvard Medical School
Disclosure: Medical Director for: SironaHealth.
Chief Editor
Erik D Schraga, MD, Staff Physician, Department of Emergency Medicine, Mills-Peninsula Emergency Medical Associates
Disclosure: Nothing to disclose.
Additional Contributors
Edward Bessman, MD, MBA, Chairman and Clinical Director, Department of Emergency Medicine, John Hopkins Bayview Medical Center; Assistant Professor, Department of Emergency Medicine, Johns Hopkins University School of Medicine
Safi HJ, Miller CC. Thoracic vasculature. Townsend CM, Beauchamp DR, Evers MB, et al, eds. Sabiston Textbook of Surgery: The Biological Basis of Modern Surgical Practice. 16th ed. Philadelphia, Pa: WB Saunders Co; 2001.
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