A 40-year-old man is referred to the cardiology outpatient clinic from the ED where he had presented with a cough. A CXR had been performed and had demonstrated a widened mediastinum. A CT thorax was requested which demonstrated a 6.1 cm aneurysm in the ascending aorta. Therefore he was referred to you for further follow-up.
Which one of the following is true regarding the pathophysiology of aortic aneurysms?
Bicuspid aortic valves have a 1% prevalence and are seen in 6–10% of all dissections. They have a ninefold higher risk of dissection. This is due to cystic medial degeneration, impaired fibrillin-1, and lymphocytic infiltration in the aortic wall, and not to post-stenotic dilatation of the ascending aorta as had initially been thought. Kawasaki syndrome causes circumscript aneurysm formation, classically in coronary arteries, and typically occurs in children.
What is the likelihood that the man in question 1, who does not have a known predisposition to dissection, will die within a year as a result of this aneurysm?
The annual risk of complications of aortic aneurysms is related to aortic size. The risk of rupture and death increase significantly once aortic size increases above 6 cm (see Table below). The rate of thoracic aorta growth is 0.1 cm/year which is less than that of abdominal aortic aneurysms. The rate of growth is affected by aortic size and genetic disposition (e.g. Marfan syndrome). The 1-, 3-, and 5-year survivals for ascending thoracic aortic aneurysm are 65%, 36%, and 20%, respectively. Therefore surgical repair of ascending aortas is recommended when aortic size reaches 5.5 cm, or 4.5 cm if the patient has Marfan syndrome.
With regard to the pathogenesis of aortic aneurysm, which one of the following is the most important factor?
The most common cause of aneurysm formation is atherosclerosis, primarily related to hypertension. Marfan syndrome is a significant risk factor for aneurysm formation and dissection, and therefore the threshold for treating these aneurysms is lower than in the non-Marfan population.
In which one of the following conditions does cystic medial necrosis occur?
The aortic wall is composed of three layers—the adventitia, the media, and the intima. Aortic dissection occurs when these layers are interrupted, and blood flows typically between the media and adventitia. The media layer is composed of smooth muscle, collagen, and elastin, and thus conditions that affect the strength of this layer will predispose to aneurysm formation and dissection. Cystic medial necrosis occurs in Marfan syndrome, but it is also known to occur in other fibrillinopathies and is said to confer a more aggressive disease course. It occurs in 75% of patients with bicuspid aortic valve undergoing aortic valve surgery. Atherosclerosis results in reduced flow in the vasa vasorum and contributes to a cystic medial necrosis/degeneration-like condition.
Which one of the following is true about the genetics of aortopathies?
Marfan syndrome has dominant inheritance. Having a first-degree relative with the condition is a major criterion in the Ghent nosology for the diagnosis of the condition. Fifty per cent of patients with Turner’s syndrome have congenital cardiovascular disease, including bicuspid aortic valves, coarctation, and dilated ascending thoracic aorta. Routine screening for these pathologies has been advised by the ACC/AHA. Assessing aortic dilatation in patients with Turner’s syndrome is difficult owing to their small stature. However, if the definition of a dilated ascending aorta is taken as a ratio of ascending to descending aortic diameters of >1.5:1, then 33% of patients with Turner’s syndrome have dilated ascending aortas. Only the vascular form or Ehlers–Danlos type IV is associated with aortic aneurysm formation. The disease is caused by defects in the gene that encodes the synthesis of collagen III (COL3A1 gene). It is dominantly inherited, although it can present sporadically, and is characterized by joint hypermobility, lax skin, and tissue friability. 125 spot mutations for the fibrillin gene are known. Matrix metalloproteinase is important in extracellular metabolism and increased expression of the gene encoding this has been seen in patients with thoracic aortic disease.
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