• Clinical science

Thoracic aortic aneurysm

Abstract

Thoracic aortic aneurysm (TAA) is a focal dilatation of the thoracic aorta to more than 1.5 times its normal diameter. TAAs are classified by location as either ascending or descending aneurysms or aneurysms of the aortic arch. Male patients 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 present with a feeling of pressure in the chest, thoracic back pain, and signs of mediastinal obstruction (e.g., difficulty swallowing). Whereas a chest x-ray is the best initial test and may show a prominent aortic arch, a CT with contrast is used to confirm the diagnosis and to 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. Surgical treatment involves open resection of the aneurysm with graft placement or, increasingly, endovascular stent placement. The prognosis is markedly worse if dissection or free rupture of the aneurysm occurs. In manifested rupture presenting with severe chest pain and possible loss of consciousness, there is no time for detailed assessment and emergency surgical repair must be performed to prevent cardiac tamponade, hemothorax, and death.

Definition

  • Dilation of all three layers of the aortic wall (intima, media, and adventitia) to > 50% of the normal diameter)[1][2]
    • Diameter: > 3.5 cm (see also aneurysm)

Epidemiology

  • Less common than abdominal aortic aneurysm (AAA) [3]
  • Peak incidence: 60–65 years
  • Sex: > (∼ 3:1)
  • More common in white populations

References:[1]

Epidemiological data refers to the US, unless otherwise specified.

Etiology

Classification

References:[2]

Pathophysiology

  • Ascending; thoracic aortic aneurysm: most often due to cystic medial necrosis [1]
  • Descending; thoracic aortic aneurysm: typically a result of atherosclerosis [1]
  • Inflammation and proteolytic degeneration of connective tissue proteins and/or smooth muscle cells in high-risk patients → loss of structural integrity of the aortic wall → widening of the vessel [7]
  • 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:[2]

Clinical features

Aortic aneurysms are mostly asymptomatic or have nonspecific symptoms. Therefore, they are often incidental findings on ultrasound or CT scan. Rupture or dissection of the aneurysm is a life-threatening condition (see “Complications” below).

References:[2][9]

Diagnostics

  • Chest x-ray: may be useful as an initial test in TAAs
  • CT with contrast: best confirmatory test for TAAs
    • Determines the extent, length, angulation, and diameter of the aneurysm
    • Can detect a thrombus in the aneurysm
    • Can detect free or contained rupture in the chest wall
    • Useful for preoperative planning
    • Disadvantages: exposure to radiation and contrast material; costly, time-consuming process; not suitable for hemodynamically unstable patients [10]
  • Other imaging
    • MRI: similar findings as on CT scan
    • Transthoracic or transesophageal echocardiography
    • Arteriography [11]

References:[1][12][2]

Differential diagnoses

The differential diagnoses listed here are not exhaustive.

Treatment

Conservative[13]

  • Reduction of cardiovascular risk factors
    • Optimal blood pressure levels (< 120–80 mm Hg)
    • Cessation of smoking

Surgical

Whether elective surgical repair is undertaken in asymptomatic patients depends on the size and expansion rate of the aneurysm. In symptomatic patients, the risks and benefits of aneurysm resection should be weighed carefully. In acutely symptomatic patients (e.g., in the case of rupture), an emergency operation is inevitable.

  • Indications for repair[14]
    • Asymptomatic
      • Diameter: ascending aneurysm ≥ 5.5 cm; descending aneurysm ≥ 6.5 cm [15]
      • Aneurysm expanding rapidly: ≥ 1 cm per year
    • Symptomatic : carefully consider whether the risk of rupture outweighs the surgical risks
    • Acutely symptomatic : emergency operation
  • Procedure: open or endovascular stent grafting repair[2]

Complications

  • Embolism: from thrombotic material of the aneurysm
  • Aortic dissection
  • Rupture
    • Risk factors: large diameter, rapid expansion, trauma
    • Clinical features of rupture
    • Diagnosis
      • No time for detailed assessment
      • Immediate surgery may be the investigation of choice
    • Therapy: emergency surgical repair (prosthetic graft placement)
    • Complications: bleeding into the mediastinumcardiac tamponade (rapidly fatal); left hemothorax
    • Prognosis: high mortality rate

References:[1][12][2]

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