The aorta is the largest artery in the body and is responsible for carrying the blood away from the heart to the rest of the body. The section of the aorta that descends through the chest is called the thoracic aorta and is divided into three sections: the aortic arch, the ascending aorta and the descending thoracic aorta. A weakening and bulging of the artery is termed an aneurysm. Thoracic aortic aneurysms are more common among Caucasians, affect males two to four times more frequently than females and are typically diagnosed between the ages of 60 to 65 years old.
Atherosclerosis
According to the Cleveland Clinic, thoracic aortic aneurysms affect about 15,000 people in the United States each year. The most common cause of a thoracic aortic aneurysm is clogging or hardening of the arteries, which is termed atherosclerosis. Atherosclerosis is a common disorder of the arteries and occurs when fatty material, cholesterol and minerals build up in the walls and harden to form plaque. As the area within the artery becomes reduced for blood flow, pressure builds up against the weakened arterial walls and bulges form, which may rupture with time. Risk factors include diabetes, heavy alcohol use, high blood cholesterol levels, smoking and hypertension.
Chronic Hypertension
Aside from being a risk factor of atherosclerosis, chronic hypertension can be a direct cause of thoracic aortic aneurysms if the blood pressure is severe enough. The high normal limit of blood pressure is generally considered to be 135/85 mmHg. Multiple readings taken that are consistently above these numbers constitute high blood pressure. Factors that affect blood pressure include hydration levels, diet, stress, kidney function, hormone levels and conditions of blood vessels. Smoking, diabetes, alcohol abuse and obesity are the main risk factors for hypertension.
Connective Tissue Disorders
In Marfan syndrome, abnormal encoding of the gene responsible for the synthesis of fibrillin causes connective tissue problems, which has been linked to predisposition of aortic aneurysms. Ehlers-Danlos syndrome is another connective tissue disorder that has been associated with an increased incidence of aortic dilation and aneurysm. By definition, an aneurysm is a focal or diffuse dilation of an artery with a diameter at least 50 percent greater than normal size.
Previous Dissection
A dissection is defined as an intimal tear that causes separation of the aortic walls, and is another condition that may cause a thoracic aortic aneurysm. A traumatic injury or complications from previous surgery can lead to aortic dissections.
Trauma
Rarely does trauma, such as a severe fall or motor vehicle accident, cause a thoracic aortic aneurysm. As stated above, dissections are more common. Although, as a person ages, the risk of developing aortic aneurysms increases, so it would be possible for trauma to cause an aortic aneurysm.
Syphilis
Syphilis is an infectious, sexually transmitted disease caused by the bacteria, Treponema pallidum. Syphilis has three main stages: primary, secondary and tertiary. Tertiary syphilis is the final stage where the infection spreads to the brain, nervous system, heart and blood vessels. Complications of untreated tertiary syphilis do include aneurysms of the thoracic aorta, which is called a syphilitic aneurysm, but syphilis has been a disease on the decline for many years.
References
- "Circulation"; Thoracic and Abdominal Aortic Aneurysms; E.M. Isselbacher; February 2005
- Cleveland Clinic: Aortic Aneurysm
- Medline Plus: Thoracic Aortic Aneurysm
- Stanford Hospital: Thoracic Aortic Aneurysm
- "Essentials of Skeletal Radiology"; Terry Yochum D.C.; 2002
