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Abdominal aortic aneurysm (AAA), also known as a triple-a, is a localized enlargement of the abdominal aorta such that the diameter is greater than 3 cm or more than 50% larger than normal. They usually cause no symptoms except when ruptured.〔 Occasionally there may be abdominal, back or leg pain. Large aneurysms can sometimes be felt by pushing on the abdomen.〔 Rupture may result in pain in the abdomen or back, low blood pressure or a brief loss of consciousness.〔 AAAs occur most commonly in those over 50 years old, in men, and among those with a family history.〔 Additional risk factors include smoking, high blood pressure, and other heart or blood vessel diseases. Genetic conditions with an increased risk include Marfan syndrome and Ehlers-Danlos syndrome. AAAs are the most common form of aortic aneurysm.〔 Approximately 85 percent occur below the kidneys with the rest either at the level of or above the kidneys.〔 In the United States screening males with ultrasound who are between 65 and 75 years old and have a history of smoking is recommended. In the United Kingdom screening all men over 65 is recommended.〔 Australia has no guideline on screening. Once an aneurysm is found, further ultrasounds are typically done on a regular basis.〔 Not smoking is the single best way to prevent the disease. Other methods of prevention include treating high blood pressure, treating high blood cholesterol and not being overweight. Surgery is usually recommended when an AAA's diameter grows to >5.5 cm in males and >5.0 cm in females.〔 Other reasons for repair include the presence of symptoms and a rapid increase in size.〔 Repair may be either by open surgery or endovascular aneurysm repair (EVAR).〔 As compared to open surgery, EVAR has a lower risk of death in the short term and a shorter hospital stay but may not always be an option.〔 There does not appear to be a difference in longer term outcomes between the two. With EVAR there is a higher need for repeat procedures. AAAs affect between 2% and 8% of males over the age of 65. Rates among women are four times lower. In those with an aneurysm less than 5.5 cm the risk of rupture in the next year is less than 1%. Among those with an aneurysm between 5.5 and 7 cm the risk is about 10% while for those with an aneurysm greater than 7 cm the risk is about 33%. Mortality if ruptured is 85% to 90%.〔 During 2013, aortic aneurysms resulted in 152,000 deaths, up from 100,000 in 1990. In the United States AAAs resulted in between 10,000 and 18,000 deaths in 2009. ==Signs and symptoms== The vast majority of aneurysms are asymptomatic. However, as abdominal aortic aneurysms expand, they may become painful and lead to pulsating sensations in the abdomen or pain in the chest, lower back, or scrotum. The risk of rupture is high in a symptomatic aneurysm, which is therefore considered an indication for surgery. The complications include rupture, peripheral embolization, acute aortic occlusion, and aortocaval (between the aorta and inferior vena cava) or aortoduodenal (between the aorta and the duodenum) fistulae. On physical examination, a palpable and pulsatile abdominal mass can be noted. Bruits can be present in case of renal or visceral arterial stenosis.〔 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「abdominal aortic aneurysm」の詳細全文を読む スポンサード リンク
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