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Thoracic Aortic Aneurysms

By Mark A. Farber, MD, FACS, Professor of Surgery and Radiology, Division of Vascular Surgery;Director University of North Carolina Aortic Network, University of North Carolina;University of North Carolina ; Thaniyyah S. Ahmad, MD, MPH

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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 echocardiogram (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

Complications of TAAs include

  • Compression or erosion into adjacent structures

  • Leak or rupture

  • Thromboembolism

Aneurysms of the ascending aorta sometimes affect the aortic root, causing aortic valve regurgitation or occlusion of the coronary arterial ostia, causing angina, myocardial infarction, or syncope.

Etiology

Most thoracic aortic aneurysms result from

Risk factors for both TAAs and aortic dissections include prolonged hypertension, dyslipidemia, and smoking. Additional risk factors for TAAs include presence of aneurysms elsewhere in the body, infection, aortitis, and older age (peak incidence at age 65 to 70).

Congenital connective tissue disorders (eg, Marfan syndrome, Ehlers-Danlos syndrome, Loeys-Dietz syndrome) cause cystic medial necrosis, a degenerative change that leads to TAAs complicated by aortic dissection and by widening of the proximal aorta and aortic valve (annuloaortic ectasia), which causes aortic regurgitation. Marfan syndrome causes 50% of cases of annuloaortic ectasia, but cystic medial necrosis and its complications can occur in young people even if no congenital connective tissue disorder is present.

Infected (mycotic) TAAs result from hematogenous spread of systemic or local infections (eg, sepsis, pneumonia), lymphangitic spread (eg, TB), or direct extension (eg, in osteomyelitis or pericarditis). Bacterial endocarditis and tertiary syphilis are uncommon causes. TAAs occur in some inflammatory disorders (eg, giant cell arteritis, Takayasu arteritis, granulomatosis with polyangiitis).

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

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.

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 (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 and inflammatory stenosis of the coronary artery ostia, which may manifest as chest pain due to myocardial ischemia. Syphilitic aneurysms do not dissect.

Diagnosis

  • 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

Thoracic abdominal aneurysms enlarge an average of 3 to 5 mm/yr. 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 aneurysm of 5 to 5.9 cm, and 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, but rupture of smaller aneurysms may occur, especially in patients with connective tissue disorders or saccular aneurysms.

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

Treatment

  • Endovascular stent grafting or open surgical repair

  • Control of hypertension and other comorbidities

Medical management with optimal control of hypertension, hypercholesterolemia, 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 considered large if the diameter is > 5 to 6 cm or twice the native size of the ascending aorta. In the descending aorta, aneurysms are large if they are > 6 to 7 cm and open repair is planned and > 5.5 cm for endovascular repair. 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 yr. 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 using a beta-blocker and other antihypertensives if necessary. Smoking cessation 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 mo. 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 CTA, MRA, or TEE.

  • 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.

* This is the Professional Version. *