Aortic aneurysms

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What are the common pathologies affecting the thoracic aorta?

• Aneurysm and dissection are the most common pathologies affecting the thoracic aorta. The incidence of aneurysm is probably underestimated. A Swedish population study demonstrated incidence of 16.3 per 100,000 per year in men and 9.1 per 100,000 per year in women, with trends demonstrating an increase in diagnoses. Congenital aortic diseases that may present in adulthood include coarctation and Kommerell’s diverticulum, characterized by aneurysmal dilatation of an anomalous subclavian artery. Thoracic aortic disease is often found incidentally during cross-sectional imaging performed for other causes. Inflammatory conditions of the aorta include aortitis, such as Takayasu, giant cell, and isolated aortitis, as well as infectious aortitis. The most common pathogen isolated in infectious aortitis is Staphylococcus ; less commonly, gram-negative organisms (including Salmonella ), tuberculous, or syphilis are encountered.

2

What is the definition of aneurysm?

• Arterial aneurysm is generally defined as greater than 50% increase in diameter compared to the normal expected diameter. Abdominal aortic aneurysms (AAAs) are defined by an aortic diameter greater than 3 cm. In true aneurysms, all three layers (intima, media, adventitia) are present. Pseudoaneurysms, or false aneurysms, are characterized by contained disruption of the aortic wall and all three layers are not present. Examples of thoracic and abdominal aneurysms are shown in Figs. 56.1 and 56.2 .

  
  

3

What is the most common pathologic cause of thoracic aortic aneurysm (TAA)?

• The pathologic processes causing aneurysm in the ascending and descending aorta are varied, reflecting the unique embryologic origins of vascular smooth muscle cells proximal and distal to the ligamentum arteriosum. Aneurysm of the ascending aorta is most often attributed to medial degeneration with disruption and loss of elastic fibers and proteoglycan deposition. Wall shear stress and chronic uncontrolled hypertension are frequent contributing factors. Aneurysm of the descending aorta is more commonly associated with atherosclerotic disease. Medial degeneration is also found in genetically triggered causes of aneurysm such as Marfan syndrome. Risk factors for thoracic aneurysm include age, male gender, hypertension, family history of aneurysm, and other known atherosclerotic disease risks. Major risk factors for AAA include male gender, age greater than 65 years, and smoking.

4

Which genetic conditions predispose patients to aortic aneurysm and dissection?

• Connective tissue disorders, including Marfan, Loeys-Dietz, and Vascular Ehlers-Danlos syndromes, are associated with medial degeneration, leading to increased incidence of TAA, more rapid aneurysm growth, and dissection at smaller diameters. A large number of aortic dissections are associated with bicuspid aortic valve aortopathy. Patients with Turner syndrome are also more prone to aneurysm and dissection, and this condition is often associated with bicuspid aortic valve disease and coarctation.

5

What findings in other organ systems may suggest the possible presence of thoracic aortic aneurysm?

• Findings in other organ systems that suggest the possible presence of TAAs include:

• Abdominal aortic aneurysm

• Renal cysts

• Intracranial aneurysm

• Hyperextensible joints

• Lens dislocation

• Musculoskeletal anomalies like scoliosis and pectus excavatum

• Arthritis

6

How fast does an aortic aneurysm grow?

• Aneurysms expand exponentially: the larger the aneurysm, the more rapid the growth. On average, the descending thoracic aorta grows faster than the ascending thoracic aorta (10–30 mm/year vs. 7–10 mm/year). The annual growth rates of aneurysms in patients with chronic dissections are significantly higher, ranging from 0.24 cm/year for small (4.0 cm) aneurysms to 0.48 cm/year for large (8.0 cm) aneurysms.

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What are the survival rates for untreated thoracic aortic aneurysms?

• Survival rates for TAAs without surgical repair are:

• 65% at 1 year

• 36% at 3 years

• 20% at 5 years

  • Aneurysm rupture occurs in 32% to 68% of patients not treated surgically, with rupture accounting for 32% to 47% of all deaths. It is estimated that less than one-half of patients with rupture actually arrive to the hospital alive. The mortality rates for aneurysmal rupture are 54% at 6 hours and 76% at 24 hours. Because death is the most likely outcome after unexpected rupture, more patients should be encouraged to undergo elective repair, and those managed conservatively should have risk factors aggressively controlled.

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