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Thoracic Aortic Aneurysms

By

Mark A. Farber

, MD, FACS, University of North Carolina;


Federico E Parodi

, MD, University of North Carolina School of Medicine

Last full review/revision Nov 2020| Content last modified Nov 2020
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A thoracic aortic diameter ≥ 50% larger than normal is considered an aneurysm (normal diameter varies by location). Most thoracic aortic aneurysms do not cause symptoms, although some patients have chest or back pain; other symptoms and signs are usually the result of complications (eg, dissection, compression of adjacent structures, thromboembolism, rupture). Risk of rupture is proportional to the size of the aneurysm. Diagnosis is made by CT angiography or transesophageal echocardiography (TEE). Treatment is endovascular stent grafting or surgery.

Thoracic aortic aneurysms (TAAs) are abnormal dilatations of the aorta above the diaphragm. TAAs account for one fourth of aortic aneurysms. Men and women are affected equally.

Locations of TAAs include

  • Ascending thoracic aorta (between the aortic root and brachiocephalic, or innominate, artery): 40%

  • Aortic arch (including the brachiocephalic, carotid, and subclavian arteries): 10%

  • Descending thoracic aorta (distal to the left subclavian artery): 35%

  • Upper abdomen—thoracoabdominal aneurysms (TAAAs): 15%

Complications

Etiology of Thoracic Aortic Aneurysms

Most thoracic aortic aneurysms result from

Infected (mycotic) TAAs result from hematogenous spread of systemic or local infections (eg, sepsis Sepsis and Septic Shock Sepsis is a clinical syndrome of life-threatening organ dysfunction caused by a dysregulated response to infection. In septic shock, there is critical reduction in tissue perfusion; acute failure... read more , pneumonia Overview of Pneumonia Pneumonia is acute inflammation of the lungs caused by infection. Initial diagnosis is usually based on chest x-ray and clinical findings. Causes, symptoms, treatment, preventive measures, and... read more ), lymphangitic spread (eg, tuberculosis Tuberculosis (TB) Tuberculosis (TB) is a chronic, progressive mycobacterial infection, often with a period of latency following initial infection. TB most commonly affects the lungs. Symptoms include productive... read more Tuberculosis (TB) ), or direct extension (eg, in osteomyelitis Osteomyelitis Osteomyelitis is inflammation and destruction of bone caused by bacteria, mycobacteria, or fungi. Common symptoms are localized bone pain and tenderness with constitutional symptoms (in acute... read more Osteomyelitis or pericarditis Pericarditis Pericarditis is inflammation of the pericardium, often with fluid accumulation. Pericarditis may be caused by many disorders (eg, infection, myocardial infarction, trauma, tumors, metabolic... read more Pericarditis ). Bacterial endocarditis Infective Endocarditis Infective endocarditis is infection of the endocardium, usually with bacteria (commonly, streptococci or staphylococci) or fungi. It may cause fever, heart murmurs, petechiae, anemia, embolic... read more Infective Endocarditis and tertiary syphilis Late or tertiary syphilis Syphilis is caused by the spirochete Treponema pallidum and is characterized by 3 sequential clinical, symptomatic stages separated by periods of asymptomatic latent infection. Common manifestations... read more Late or tertiary syphilis are uncommon causes. TAAs occur in some inflammatory disorders (eg, giant cell arteritis Giant Cell Arteritis Giant cell arteritis involves predominantly the thoracic aorta, large arteries emerging from the aorta in the neck, and extracranial branches of the carotid arteries. Symptoms of polymyalgia... read more , Takayasu arteritis Takayasu Arteritis Takayasu arteritis is an inflammatory disease affecting the aorta, its branches, and pulmonary arteries. It occurs predominantly in young women. Etiology is unknown. Vascular inflammation may... read more Takayasu Arteritis , granulomatosis with polyangiitis Granulomatosis with Polyangiitis (GPA) Granulomatosis with polyangiitis is characterized by necrotizing granulomatous inflammation, small- and medium-sized vessel vasculitis, and focal necrotizing glomerulonephritis, often with crescent... read more Granulomatosis with Polyangiitis (GPA) ).

Blunt chest trauma can cause a pseudoaneurysm (false aneurysm) due to injury to the aortic wall resulting in a communication between the arterial lumen and overlying connective tissue and blood leaking outside the confines of the aorta; a blood-filled cavity forms outside the vessel wall and seals the leak as it thromboses).

Symptoms and Signs of Thoracic Aortic Aneurysms

Most thoracic abdominal aneurysms are asymptomatic until complications (eg, thromboembolism, rupture, aortic regurgitation, dissection) develop. However, compression of adjacent structures can cause back pain (due to compression of vertebra), cough (due to compression of the trachea), wheezing, dysphagia (due to esophageal compression), hoarseness (due to left recurrent laryngeal or vagus nerve compression), chest pain (due to coronary artery compression), and superior vena cava syndrome Regional spread Lung carcinoma is the leading cause of cancer-related death worldwide. About 85% of cases are related to cigarette smoking. Symptoms can include cough, chest discomfort or pain, weight loss... read more Regional spread .

Erosion of aneurysms into the lungs causes hemoptysis or pneumonitis; erosion into the esophagus (aortoesophageal fistula) causes massive hematemesis.

Dissection manifests with tearing chest pain, often radiating to the back between the shoulder blades.

Thromboembolism may cause stroke, abdominal pain (due to mesenteric ischemia), or extremity pain.

Ruptured TAA that is not immediately fatal manifests with severe chest or back pain and hypotension or shock. Exsanguination due to rupture most commonly occurs into the pleural or pericardial space.

Additional signs include Horner syndrome Horner Syndrome Horner syndrome is ptosis, miosis, and anhidrosis due to dysfunction of cervical sympathetic output. (See also Overview of the Autonomic Nervous System.) Horner syndrome results when the cervical... read more Horner Syndrome (miosis, ptosis, anhidrosis) due to compression of sympathetic ganglia, palpable downward pull of the trachea with each cardiac contraction (tracheal tug), and tracheal deviation. Visible or palpable chest wall pulsations, occasionally more prominent than the left ventricular apical impulse, are unusual but may occur.

Syphilitic aneurysms of the aortic root classically lead to aortic regurgitation Aortic Regurgitation Aortic regurgitation (AR) is incompetency of the aortic valve causing backflow from the aorta into the left ventricle during diastole. Causes include valvular degeneration and aortic root dilation... read more Aortic Regurgitation and inflammatory stenosis of the coronary artery ostia, which may manifest as chest pain due to myocardial ischemia. Syphilitic aneurysms do not dissect.

Diagnosis of Thoracic Aortic Aneurysms

  • Incidental x-ray finding

  • Confirmation by CT angiography (CTA), magnetic resonance angiography (MRA), or transesophageal echocardiography (TEE)

Thoracic aortic aneurysms are usually first suspected when a chest x-ray incidentally shows a widened mediastinum or enlargement of the aortic knob. However, chest x-ray has poor sensitivity for TAA and is not a reliable diagnostic tool (eg, in patients with chest pain and suspected aortic aneurysm). Chest x-ray abnormalities, or symptoms and signs suggesting an aneurysm, should be followed up with a cross-sectional imaging test; choice among these tests is based on availability and local experience.

If rupture is suspected, TEE (for ascending dissection) or CTA, depending on availability, should be done immediately. Chest CTA can delineate aneurysm size and proximal or distal extent, detect leakage, and identify coincidental pathology. MRA may provide similar detail. Transthoracic echocardiography (TTE) can delineate size and extent and detect leakage of aneurysms of the ascending but not descending aorta. TEE cannot show the entire thoracic aorta, but it can be extremely useful in detecting the entry point in aortic dissection.

Contrast angiography historically has been the standard imaging test. It does provide the best image of the arterial lumen, but it provides no information on extraluminal structures (ie, as an alternative diagnosis). Additionally, angiography is invasive and has a significant risk of renal and extremity atheroembolism and contrast nephropathy.

Aortic root dilation or unexplained ascending aorta aneurysms warrant serologic testing for syphilis. If a mycotic aneurysm is suspected, bacterial and fungal blood cultures are done.

Prognosis for Thoracic Aortic Aneurysms

Thoracic abdominal aneurysms enlarge an average of 3 to 5 mm/year. Risk factors for rapid enlargement include larger size of aneurysm, location in the descending aorta, and presence of mural thrombi.

Annual rupture risk is

  • 2% for aneurysms < 5 cm

  • 3% for aneurysms of 5 to 5.9 cm

  • 8 to 10% for aneurysms > 6 cm

The risk appears to rise abruptly as TAAs reach 6 cm in diameter. Median diameter at aneurysm rupture is 6 cm for ascending aneurysms and 7 cm for descending aneurysms; smaller aneurysms also may rupture, especially in patients with connective tissue disorders or saccular aneurysms.

Survival rate of patients with untreated large TAAs is 65% at 1 year and 20% at 5 years. TAAA rupture has a mortality of 97%.

Treatment of Thoracic Aortic Aneurysms

  • Endovascular stent grafting or open surgical repair

  • Control of hypertension and other comorbidities

Medical management with optimal control of hypertension, dyslipidemia, diabetes, and respiratory disease is the appropriate treatment until surgery is indicated. Treatment is endovascular stent grafting when anatomically possible and open surgical repair for more complex aneurysms. Immediate control of hypertension is essential.

Ruptured TAAs, if untreated, are universally fatal. They require immediate intervention, as do leaking aneurysms and those that cause acute dissection or acute valvular regurgitation.

Surgery involves a median sternotomy (for ascending and aortic arch aneurysms) or left thoracotomy or thoraco-retroperitoneal exposure (for descending and thoracoabdominal aneurysms) and replacement with a synthetic graft. With emergent open surgery, 1-mo mortality rate is about 40 to 50%. Patients who survive have a high incidence of serious complications (eg, renal failure, respiratory failure, severe neurologic damage).

Transcatheter-placed endovascular stent grafts (endografts) for descending TAAs and TAAAs are being used more frequently as a less invasive alternative to open surgery.

Elective surgery is indicated for aneurysms that are

  • Large

  • Rapidly enlarging (> 0.5 cm/year)

  • Causing bronchial compression

  • Causing aortobronchial or aortoesophageal fistulas

  • Symptomatic

  • Traumatic

  • Mycotic

Aneurysms of the ascending aorta are generally considered large if the diameter is > 5.5 cm or twice the native size of the ascending aorta or if the aortic size index (aortic diameter in relation to body surface area) is ≥ 2.75 cm/m2. In the descending aorta, aneurysms are generally considered large if they are > 6 cm. In patients with Marfan syndrome, large aneurysms are those that are ≥ 4.5 to 5 cm in any location.

Treatment of mycotic aneurysms is aggressive antibiotic therapy directed at the specific pathogen. Generally, these aneurysms must also be surgically repaired.

Although open surgical repair of an intact TAA improves outcome, mortality rate may still exceed 5 to 10% at 30 days and is 40 to 50% at 10 years. The mortality rate is lower with endovascular stent grafts. Risk of death increases greatly if aneurysms are complicated (eg, located in the aortic arch or thoracoabdominal aorta) or if patients are older or have coronary artery disease, symptoms, or preexisting renal insufficiency. Perioperative complications (eg, stroke, spinal injury, renal failure) occur in about 10 to 20%.

Asymptomatic aneurysms that do not meet criteria for elective surgical or endovascular repair are treated with aggressive blood pressure control Treatment Hypertension is sustained elevation of resting systolic blood pressure (≥ 130 mm Hg), diastolic blood pressure (≥ 80 mm Hg), or both. Hypertension with no known cause (primary; formerly, essential... read more Treatment using a beta-blocker and other antihypertensives if necessary. Smoking cessation Smoking Cessation Most smokers want to quit and have tried doing so with limited success. Effective interventions include cessation counseling and drug treatment, such as varenicline, bupropion, or a nicotine... read more is essential. Dyslipidemia, diabetes, and respiratory diseases should all be treated. Patients require frequent follow-ups to check for symptoms and serial CT or ultrasonography every 6 to 12 months. Imaging frequency depends on aneurysm size.

Key Points

  • Thoracic aortic aneurysm (TAA) is a ≥ 50% increase in diameter of the thoracic aorta.

  • TAAs may dissect, compress, or erode into adjacent structures, cause thromboembolism, leak, or rupture.

  • Median diameter at aneurysm rupture is 6 cm for ascending aneurysms and 7 cm for descending aneurysms.

  • Diagnosis is often first suspected based on an incidental x-ray or CT finding, and confirmed using CT angiography, magnetic resonance angiography, or transthoracic echocardiography.

  • Treat small, asymptomatic TAAs with aggressive management of blood pressure and dyslipidemia and smoking cessation.

  • Treat larger or symptomatic TAAs with endovascular stent grafting when anatomically possible and open surgical repair for more complex aneurysms.

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