Thoracic aortic aneurysm

Thoracic aortic aneurysm (TAA) is the focal dilatation of the thoracic aorta to more than 1.5 times its normal diameter. TAAs are classified by location as affecting the ascending aorta, descending aorta, or aortic arch. Men of advanced age are at a higher risk of forming TAAs; other risk factors include trauma, connective tissue disorders, and hypertension. TAAs are frequently asymptomatic and therefore detected incidentally. If symptomatic, they may manifest with a feeling of pressure in the chest, thoracic back pain, and signs of mediastinal obstruction (e.g., difficulty swallowing). The initial test is often a chest x-ray, which may show a prominent aortic arch. CT with contrast is used to confirm the diagnosis and determine the extent of the aneurysm. Observation, close follow-up, and reduction of cardiovascular risk factors are indicated for small aneurysms whereas pronounced or rapidly expanding aneurysms require surgery. TAA rupture and dissection are life-threatening conditions that require emergency surgical repair to prevent cardiac tamponade, hemothorax, and death.

• Dilatation of all three layers of the aortic wall (intima, media, and adventitia) to > 150% of the normal diameter (a true aneurysm) ^[1]
  • Ascending aorta: approx. > 5.0 cm
  • Descending aorta: approx. > 4.0 cm

• Less common than abdominal aortic aneurysm (AAA) ^[2]
• Peak incidence: 60–65 years ^[3]
• Sex: ♂ > ♀ (∼ 3:1)

Epidemiological data refers to the US, unless otherwise specified.

The risk factors for TAA include:

• Arterial hypertension
• Smoking
• Advanced age
• Trauma
• Tertiary syphilis (due to obliterative endarteritis of the vasa vasorum) ^[4]
• Connective tissue diseases (e.g., Marfan syndrome, Ehlers-Danlos syndrome)
• Bicuspid aortic valve ^[5]
• Positive family history
• Aortitis: aortic wall inflammation ^[6][7]
  • Noninfectious (most common): giant cell arteritis, Takayasu arteritis, other inflammatory conditions
  • Infectious: bacterial , mycobacterial, fungal

• Ascending aorta (most common location) ^[8]
• Descending aorta (thoracoabdominal)
• Aortic arch

• Ascending thoracic aortic aneurysm: most often due to cystic medial necrosis
• Descending thoracic aortic aneurysm: typically a result of atherosclerosis
• Inflammation and proteolytic degeneration of connective tissue proteins; (e.g., collagen and elastin) and/or smooth muscle cells in high-risk patients → loss of structural integrity of the aortic wall → widening of the vessel
• The aneurysmatic dilatation of the vessel wall may cause disruption of the laminar blood flow and turbulence.
• Possible formation of thrombi in the aneurysm → peripheral thromboembolism

References:^[9]

Aortic aneurysms are mostly asymptomatic or have nonspecific symptoms. They are often discovered incidentally on imaging.

• Chest pressure
• Thoracic back pain
• Features of mediastinal compression/obstruction, such as:
  • Difficulty swallowing (esophagus)
  • Upper venous congestion (superior vena cava syndrome)
  • Hoarseness (recurrent laryngeal nerve)
  • Cough, wheeze, stridor (trachea)
  • Horner syndrome (sympathetic trunk)

Imaging ^{[10][11][12][13]}

Chest x-ray

• Indications: may be conducted as an initial imaging study in patients with chest pain and/or dyspnea
• Suggestive findings ^[10][11][13]
  • Abnormal aortic contour
  • Widened mediastinum
  • Tracheal deviation

CT angiography chest

• Indications: best confirmatory test for TAAs
  • Abnormal findings on chest x-ray, ultrasound, or echocardiography
  • Interventional planning and follow-up
  • Detailed evaluation of the extent, length, angulation, and diameter of the aneurysm
  • Evaluation of aortic branch involvement
• Supportive findings ^[11][12]
  • Dilatation of the aorta ^[10]
  • Possible mural thrombus (nonenhancing)
  • Possible dissection, perforation, or rupture

Additional imaging

• MR angiography chest with and without IV contrast
  • Indication: Consider as an alternative to CTA. ^[12]
    • In stable patients who should avoid ionizing radiation
    • For serial follow-ups
  • Supportive findings: similar to CTA
  • Disadvantages
    • Prolonged duration
    • Less accurate than CTA in allowing for the visualization of branch vessel involvement ^[12]
• Transthoracic echocardiography ^[12]
  • Indications
    • Rapid assessment in hemodynamically unstable patients
    • Evaluation for concomitant heart disease
  • Supportive findings
    • Dilatation of the aorta
    • Possible cardiac pathology
    • Signs of coronary artery disease ^[14]
• Transesophageal echocardiography: allows for more accurate assessment than TTE ^[12]
  • Indication: intraoperative monitoring
  • Disadvantages
    • Less accurate than CTA in allowing for the visualization of branch vessel involvement
    • Limited visualization of pathologies above the gastroesophageal junction
• Catheter angiography (aortography) ^[13]
  • Indications
    • Evaluation and possibly treatment of coexisting coronary artery disease
    • Assessment of aortic lumen and branch vessels
  • Supportive findings: contrast column in the lumen of the aneurysm
  • Disadvantages
    • May mask the actual diameter of the aneurysm ^[11]
    • Thrombus-filled discrete aneurysms might be missed. ^[13]

• See “Differential diagnoses of chest pain.”
• See “Abdominal vs. thoracic aortic aneurysm.”

The differential diagnoses listed here are not exhaustive.

Approach

• Unstable patients (e.g., in the case of rupture): emergency TAA repair (see “Thoracic aortic aneurysm rupture”)
• Symptomatic patients: urgent TAA repair
• Asymptomatic patients
  • Aneurysm surveillance
  • Elective TAA repair when size or growth thresholds are passed
• All patients: conservative management with reduction of cardiovascular risk factors

Invasive treatment: TAA repair ^[10]

General indications

• TAA rupture
• Symptomatic TAA
• Asymptomatic TAA when size or growth thresholds are passed

Indications for asymptomatic patients

The decision to perform elective TAA repair in asymptomatic patients depends on the size and expansion rate of the aneurysm. In all patients, the risks and benefits of aneurysm resection should be weighed carefully. ^[8]

Procedures ^[10]

Open surgical repair (OSR) is recommended for patients with TAA of the ascending aorta and aneurysms involving the aortic arch. For patients with descending thoracic or thoracoabdominal aortic aneurysms, thoracic endovascular aneurysm repair (TEVAR) or OSR can be performed.

Open surgical repair (OSR) ^[10]

Open surgical repair is a major operation with high associated morbidity and mortality. ^[8]

• Indications: preferred in young patients with few comorbidities and low surgical risk and patients with connective tissue disorders ^[8]
  • Symptomatic TAAs involving the ascending aorta or the aortic arch
  • Consider as an alternative in symptomatic TAAs involving the descending aorta (see indications for TEVAR below).
  • Consider in asymptomatic TAAs.
• Complications: 40% of all patients experience a perioperative complication ^[8]
  • Paralysis (due to spinal cord injury or ischemia)
  • Renal and mesenteric ischemia

Thoracic endovascular aneurysm repair (TEVAR) ^[10]

• Indications:
  • Degenerative or traumatic descending aortic aneurysms
• Contraindications
  • Absence of a sufficiently long (2–3 cm) “landing zone” for the stent graft
  • Absence of adequate vascular access sites
• Procedure: Under fluoroscopic guidance, an expandable stent graft is placed via the femoral or iliac arteries intraluminally at the site of the aneurysm.
• Complications ^[10][16]
  • Ischemia of the bowel, kidneys, spinal cord
  • Access site complications, e.g., infection, bleeding, hematoma
  • Embolic cerebral ischemia
  • Endoleak
  • Graft migration
  • Need for reintervention
• Other: requires lifelong postoperative surveillance

Additional procedures

Concomitant diseases may require additional procedures, e.g., CABG, valve replacement or repair.

• Identify coronary anatomy and possible CAD before repair of the ascending aorta.
• In end-organ ischemia or stenosis, ancillary revascularization is recommended.

Perioperative care

• See “Perioperative care for AAA repair.”

Surveillance after repair ^[12]

• CTA chest abdomen pelvis with IV contrast
  • Initially: within the first month then at 3–12 months
  • Then every 6–12 months depending on the stability of findings
• MRA chest/abdomen/pelvis with IV contrast: in patients with MR-compatible stent grafts (e.g., nitinol)

Conservative management

All patients should receive conservative treatment to reduce the risk of further aneurysm expansion or rupture. Regular aneurysm surveillance via CT or MR is recommended for patients in whom the diameter of the aneurysm has not reached the threshold defined as the indication for repair.

Reduction of cardiovascular risk factors ^[10]

• Blood pressure management
  • Optimal blood pressure goal to reduce aortic wall stress: the lowest blood pressure that the patient can tolerate ^[10]
    • Less than 140/90 mm Hg in patients without diabetes
    • Less than 130/80 mm Hg in patients with diabetes or CKD
  • Preferred agents:
    • Beta blockers (e.g., propranolol , metoprolol )
    • ACE inhibitor (e.g., lisinopril , enalapril )
    • Angiotensin receptor blocker (e.g., losartan , candesartan ) ^[10][17]
• Smoking cessation
• Lipid profile optimization: in patients with atherosclerotic aortic aneurysms
  • Target LDL cholesterol: < 70 mg/dL
  • Preferred agent: statin (e.g., atorvastatin )
• Lifestyle modification ^[18]
  • No participation in most competitive sports
  • No heavy weight lifting

Aneurysm surveillance

• Embolism: caused by thrombotic material of the aneurysm
• Aortic valve regurgitation: due to aortic root dilation
• Aortic dissection
• Thoracic aortic aneurysm rupture

We list the most important complications. The selection is not exhaustive.

Risk factors ^[10]

• Large aneurysm diameter
• Rapid aneurysm expansion
• Trauma
• Smoking

Clinical features ^[10][13]

It is difficult to tell TAA apart from other causes of acute aortic syndrome using clinical features alone.

• Contained rupture
  • Severe chest pain (may be indistinguishable from acute MI)
  • Possible abdominal pain in patients with thoracoabdominal aneurysms
  • Patients are often hemodynamically stable.
• Free rupture
  • Possible loss of consciousness
  • Severe chest and possible abdominal pain
  • Hypotension
  • Acute respiratory failure
  • Hemoptysis
  • Gastrointestinal bleeding
  • Cardiac tamponade and cardiogenic shock
  • Cardiac arrest (secondary to profound hypovolemia)

More than half of patients with TAA rupture die before reaching the emergency department! ^[13]

Diagnostics ^[10][12][13]

• Initial evaluation
  • Hemodynamically unstable patients: no time for detailed assessment
    • Proceed directly to OR; POCUS or formal bedside TTE may be considered if it does not delay treatment.
  • Hemodynamically stable patients: Obtain CTA of the chest, abdomen, and pelvis with IV contrast.
    • Supportive findings
      • Extravasation of contrast
      • Contained rupture: perivascular hematoma sealed off by surrounding structures
      • Free rupture: massive hematoma
• Additional diagnostic evaluation to consider (once patient has been stabilized)
  • ECG: to rule out STEMI as a differential diagnosis
  • Laboratory studies: There are no laboratory findings specific to TAA rupture.
    • CBC: ↓ hemoglobin, ↓ hematocrit, and ↓ red blood cell count in severe hemorrhage
    • ABG: metabolic acidosis in cases of shock
  • See “Chest pain” for workup and differential diagnoses.

Treatment

Initial stabilization ^[19]

• As soon as TAA rupture is suspected, obtain an immediate cardiothoracic surgery consult.
• Start continuous telemetry, consider invasive blood pressure monitoring.
• Manage hypotension.
  • Start fluid resuscitation, giving blood products as soon as they are available.
  • Refractory hypotension: Start vasopressors and consider POCUS to assess for pericardial effusion. ^[10]
• For patients with acute respiratory failure, start oxygen therapy and consider cautious intubation.
• Initiate IV pain management.
• Reassess frequently, as patients may rapidly decompensate.

Interventions such as intubation and opioid analgesia may worsen hypotension!

Patients are at risk of massive transfusion-associated reactions; give blood products in a balanced ratio, use inline blood warming devices, and screen for electrolyte imbalances.

Emergency surgical repair ^[20]

• OSR
• TEVAR may be considered in patients with rupture of the descending thoracic aorta. ^[20]

Complications

• Bleeding into the mediastinum → cardiac tamponade (rapidly fatal)
• Left hemothorax

Prognosis

• Free rupture has a high mortality rate. ^[13]

• Obtain surgery consult.
  • Immediate surgery consult for emergency repair if ruptured aneurysm is suspected; transfer to OR immediately.
  • Urgent surgery consult for repair if symptomatic but nonruptured TAA is suspected; consider imaging for preprocedural planning (if patient is hemodynamically stable).
• Make patient NPO.
• Establish IV access with two large-bore peripheral IV lines.
• Check CBC, type and screen, obtain patient consent for blood transfusion, and order pRBCs (prepare for massive transfusion protocol).
• Start IV fluid resuscitation using blood products as soon as available.
• Consider use of vasopressors.
• Manage associated complications, e.g., hypoxia.
• Initiate pain management.