An aortic aneurysm is an enlargement (dilatation) of the aorta to greater than 1.5 times normal size. They usually cause no symptoms except when ruptured. Occasionally, there may be abdominal, back, or leg pain. The prevalence of abdominal aortic aneurysm ("AAA") has been reported to range from 2 to 12% and is found in about 8% of men more than 65 years of age. The mortality rate attributable to AAA is about 15,000 per year in the United States and 6,000 to 8,000 per year in the United Kingdom and Ireland. Between 2001 and 2006, there were approximately 230,000 AAA surgical repairs performed on Medicare patients in the United States. The etiology remains an area of active research. Known causes include trauma, infection, and inflammatory disorders. Risk factors include cigarette smoking, advanced age, dyslipidemia, hypertension, and coronary artery disease. The pathophysiology of the disease is related to an initial arterial insult causing a cascade of inflammation and extracellular matrix protein breakdown by proteinases leading to arterial wall weakening. They are most commonly located in the abdominal aorta, but can also be located in the thoracic aorta. Aortic aneurysms result from a weakness in the wall of the aorta and increase the risk of aortic rupture. When rupture occurs, massive internal bleeding results and, unless treated immediately, shock and death can occur. Screening with ultrasound is indicated in those at high risk. Prevention is by decreasing risk factors, such as smoking, and treatment is either by open or endovascular surgery. Aortic aneurysms resulted in about 152,000 deaths worldwide in 2013, up from 100,000 in 1990. Classification Aortic aneurysms are classified by their location on the aorta. An aortic root aneurysm, or aneurysm of the sinus of Valsalva. Thoracic aortic aneurysms are found within the chest; these are further classified as ascending, aortic arch, or descending aneurysms. Abdominal aortic aneurysms, "AAA" or "Triple A", the most common form of aortic aneurysm, involve that segment of the aorta within the abdominal cavity. Thoracoabdominal aortic aneurysms involve both the thoracic and abdominal aorta. Thoracoabdominal aortic aneurysms comprise some or all of the aorta in both the chest and abdomen, and have components of both thoracic and abdominal aortic aneurysms. The Crawford classification describes five types. Signs and symptoms Most intact aortic aneurysms do not produce symptoms. As they enlarge, symptoms such as abdominal pain and back pain may develop. Compression of nerve roots may