A thoracic aortic aneurysm (TAA) is a dilatation of the part of the main artery of the body (aorta) in the chest region. As the aorta exits the heart, it goes upward (ascending part), and then changes direction downward (descending part), in effect forming the aortic arch. TAA can occur in all of these parts. In some cases, the dilatation can progress to rupture or lead to the development of a dissection. Aortic dissection happens when the flow of blood disrupts the wall of the vessel and creates a false lumen inside the vessel wall. Previously, it had been thought that TAA and abdominal aortic aneurysm (AAA) are similar in pathogenesis. Nowadays, it has become clear that although these diseases share a similar manifestation, they have different risk factors and pathophysiology. In TAA, the genetic influence is more important, while in AAA, the conventional risk factors play a more important role (smoking, high blood pressure, diabetes mellitus, male sex).
The prevalence of thoracic aortic aneurysm and dissection (aortopathies) is estimated at approximately 6 per 100,000There are multiple reasons why a dilatation in the thoracic aorta may arise. Most commonly, the development of an aortopathy has been linked to abnormalities in elastin and collagen — the main structural proteins in the aortic wall. There are multiple inheritable syndromes that increase the risk for an aortopathy (see Genetics section). Other risk factors include cigarette smoking, high blood pressure, diabetes mellitus, male sex, and increased age (most patient are above 65).[9]
The genetic component of the risk for a thoracic aortic aneurysm (and potential dissection) is very important. It has been estimated that 20% of affected individuals have a first-degree relative with a dilated portion of the thoracic aorta. Also, it is twice as common for siblings to have a TAA, as it is in abdominal aortic aneurysm. We know genotypes of hereditary aortopathies in approximately 40% of the cases. The affected genes generally fall into one of 3 categories, coding for connective tissue proteins; smooth muscle proteins; transforming growth factor-beta (TGF-beta) signaling pathway.
A familial thoracic aortic aneurysm can arise either as a part of a syndrome (with signs and symptoms outside of the cardiovascular system being present) or as a so-called ‘nonsyndromic’ TAA. The most common syndromes associated with a TAA are Marfan syndrome, Loeys-Dietz syndrome, and the vascular variant of Ehler-Danlos syndrome. The nonsyndromic TAAs are known as familiar TAAs, and TAAs associated with a bicuspid aortic valve. Usually, the aortic valve has three cusps, but some people only have two. This is associated with increased incidence of multiple cardiovascular pathologies.
Aneurysm of the thoracic aorta may be asymptomatic, and only discovered as an incidental finding in an examination focused on a different disease (ultrasound, CT, MR). It can also present with nonspecific symptoms like cough, hoarse voice, and chest pain. If, however, aortic dissection occurs, the presentation is acute and severe. Typical symptoms include sudden severe chest pain, which can radiate to the back. Patients have often described a tearing sensation in their chest. This can be accompanied by loss of consciousness, shortness of breath, and a weak pulse.
Diagnosis of an aneurysm is often made as an incidental finding in an imaging study, as a part of a routine examination. Due to the strong genetic component of the disease, relatives of an individual with a confirmed diagnosis are also screened for the development of an aneurysm. The standard method for describing a TAA is an echocardiographic study, i.e. ultrasound. There are novel methods of detection under development, such as specific biomarkers analyzed from the blood by qRT-PCR.[2]
The therapy of a thoracic aortic aneurysm can be either conservative, through the elimination of risk factors, monitoring, and medication; or surgical. The medication used is usually beta-blockers, and angiotensin II receptor blockers and their aim is to slow the process of dilation of the vessel. Surgical repair may be indicated either as a preventative measure, based on multiple factors (mainly the size of the dilation) or as an emergency intervention . There are two methods for repair — open abdominal, or endovascular. The choice between these two is made based on the patient’s anatomy, individual risk factors, and personal preference.
Due to the high importance of the genetic component in the pathogenesis of the disease, there is unfortunately no definitive prevention. If an aortopathy is present in a first-degree relative, screening is recommended. Eliminating risk factors, such as cigarette smoking, and managing one’s fat levels in the blood may be of benefit. The most significant treatable risk factor for aortic dissection is high blood pressure.
Thoracic aortic aneurysms have a tendency to increase in size. As the size increases, so does the risk of a rupture. Although the methods of diagnosis, as well as treatment, improve, the 5-year survival rate for untreated large TAAs is approximately 20%. If a rupture occurs, the mortality reaches 97%.
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