Thoracic Aortic Aneurysm and Aortic Dissections Background: The aorta, the largest artery in the body, is responsible for pumping blood out of the heart and into the organs of the body. The aorta projects upward from the heart through the chest (thoracic aorta), and then arches downward into the abdomen (abdominal aorta). An aortic aneurysm is a widening, bulge, or ballooning out of a portion of the aorta, usually a weak spot in the aortic wall, causing the vessel to progressively expand to at least 1.5 times beyond its normal diameter of one inch. With gradual enlargement, the aneurysm can lead to either dissection or rupture. Dissection is when the blood enters the wall of the aorta and splits it in two.
What are the different classifications of aortic aneurysms? Aortic aneurysms are commonly classified according to their anatomical location. While thoracic aortic aneurysms involve the ascending aorta, arch or descending aorta; abdominal aortic aneurysms affect the part of the aorta in the abdominal cavity. A third type involves thoracoabdominal aneurysms that originate in the descending aorta and extend to the abdominal aorta. In some cases an aneurysm may lead to a dissection. A dissecting aneurysm indicates that the inner wall of the aorta develops a tear and then down the inside of the aorta due to the pressure of the blood flowing over it. Ninety-five percent of aortic dissections originate either within the ascending or descending aorta and fewer than 5% originate in the abdominal aorta or aortic arch. The major factors predisposing an individual to aortic dissection include hypertension, previous aortic surgeries, trauma, aortic inflammatory diseases, or genetic disorders, such as Marfan syndrome. The focus of Dr. Milewicz's study involve thoracic aortic aneurysms (TAA).

What are the clinical features of TAA?
The symptoms of TAA often do not surface until the aneurysm is quite large. However, once enlarged, the aneurysm can cause the aorta to put pressure on the surrounding organs in the chest. Clinical features may include:

• Upper back pain
• Coughing and wheezing
• Hoarse voice
• Difficulty swallowing
• Swelling (edema) in the neck or arms
• Horner's syndrome (constricted pupil, drooping eyelid and dry skin on one side of the face)

What causes TAA?
TAA is primarily associated with medial necrosis, characterized by degeneration and loss of elastic fibers, smooth muscle cells, and collagen in the middle layer of the aorta and the associated formation of mucous-filled cysts. While medial necrosis does occur as part of the normal aging process of the aorta, it can be accelerated by hypertension and genetic alterations that predispose individuals to this aortic disease.
The causes of TAA are based on many factors, including environmental, physiological and genetic influences. One of the main causes includes arteriosclerosis (hardening of arteries), a condition in which fatty deposits are laid down in the walls of arteries, which are less elastic and weaker as a result. Major risk factors for arteriosclerosis are smoking and high blood pressure, although this also probably runs in families.
Other possible causes of TAA include:

• Trauma to the aorta from a car accident is an example
• Marfan syndrome, a hereditary condition
• Syphilis, a sexually transmitted disease

What is the inheritance pattern of the disorder?
Recent familial aggregation studies have indicated that there is a higher prevalence of TAA in first-degree relatives of TAA patients than in the general population. These studies indicate that up to 20% of TAA patients requiring surgery have other affected family members. This evidence strongly supports the hypothesis that genetic factors influence the formation of nonsyndromic TAA. Furthermore, in the majority of families TAA is inherited in an autosomal dominant manner with a marked variability in the age of onset.

How common is TAA?
Aortic aneurysms remains the 13th major cause of death in the United States, accounting for nearly 15, 000 deaths annually. Aortic dissection is the most common acute illness of the aorta, with more than 2,000 new cases in the USA every year.

What is the treatment?
Timely diagnosis can result in early intervention and dramatic improvements. If an aneurysm or dissection is suspected, an ultrasound scan is usually carried out. Other scans such as computerized tomography (CT) and magnetic resonance imaging (MRI) may also be performed in order to determine the exact position of an aortic aneurysm in the chest. The treatment of an aortic aneurysm depends upon the severity of the aneurysm or dissection.

What is the current research being done with TAA?
Studies are just beginning to clarify the genes that predispose individuals without known syndromes to TAA. Current research has identified two genomic loci for familial TAA located at 5q 13-14 and 11q 23-24. With future characterization of genes, the early identification of individuals at risk for aortic aneurysms and dissections will inevitably aid in the pathogenesis of the disorder. In addition, identification of defective genes will allow future predisposition testing for at-risk family members.

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Related web sites

• Researchers Map Location for Aortic Aneurysm Gene
• More Tests For Aortic Aneurysms?
• Scientific References for TAA
• Gene Tests
• OMIM - Aortic Aneurysm, Thoracic
• OMIM - Aortic Aneurysm, Familial Thoracic 1
• OMIM - Aortic Aneurysm, Familial Thoracic 2