The Facts
An aneurysm is a weak point in a blood vessel wall, most commonly in an artery. Blood pressure tends to push the weakened section of an arterial wall outward, forming a balloon-like projection. This condition by itself isn't especially harmful, but the artery is prone to rupture. A ruptured aneurysm breaks the artery and allows uncontrolled bleeding to occur, which can be fatal.
Aneurysms can form in different places. The most common type of aneurysm is an abdominal aortic aneurysm (AAA). The aorta is the body's largest artery, carrying blood from the heart to every organ except the lungs. It leaves the heart flowing upwards in the chest, makes a U-bend, and flows down the spine from the chest to the abdomen. Several branches leave the aorta in the abdomen, going to the kidneys, liver, and intestines. These branch points are prime sites for aneurysms.
Other locations for aneurysms are:
- the bottom of the brain - the most common type of cerebral aneurysm is called a berry aneurysm
- thoracic aortic aneurysm (the thorax is the chest)
- of the thoracic aneurysms, the most common subtype is the aneurysm of the ascending aorta (between the heart and the U-bend)
Abdomincal aortic aneurysms affect as many as 8% of the senior population. Men are 4 times more likely to have it than women and smokers are 4 times more likely to die of it than non-smokers. It's the 17th leading cause of death in the United States. People of African descent rarely develop aneurysms.
Causes
A person's risk of developing an aneurysm may be inherited. Ascending aortic aneurysms and berry aneurysms are especially likely to run in families. The men of an affected family are more likely to develop aneurysms than are the women. Scientists haven't yet identified the responsible genes in humans, though they have identified some in mice.
About half of all people with ascending aortic aneurysms are born with deformations known as Marfan's syndrome. Such people are unusually tall with long extremities. Abraham Lincoln is thought to have had Marfan's syndrome. They also have a weakness in the aortic wall, just where the aorta leaves the top of the heart.
Two other types of aneurysms are mycotic and atherosclerotic aneurysms. Mycotic aneurysms are caused by bacterial or fungal infection. Almost any such organism can damage the arteries, but the infection must be very deep and severe. Salmonella and syphilis both seem to have a special liking for arterial walls.
Atherosclerotic aneurysms are linked to the process that causes coronary artery disease - the buildup of fatty deposits on the inner wall of the arteries. In reality, the picture's not so clear. Even someone with severe atherosclerosis may not develop an aneurysm if they are not already genetically predisposed.
High blood pressure, high cholesterol, inactivity, smoking, and obesity, which are risk factors for heart disease, are also risk factors for aneurysms. Severe aneurysms are probably due to a combination of genes and poor cardiovascular health. Occasionally, aneurysms develop where stab or gunshot wounds have perforated an artery.
