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Abdominal aortic aneurysms are commonly divided according to their size and symptomatology. An aneurysm is usually defined as an outer aortic diameter over 3 cm (normal diameter of the aorta is around 2 cm), [43] or more than 50% of normal diameter. [44] If the outer diameter exceeds 5.5 cm, the aneurysm is considered to be large. [42]
English: Abdominal ultrasound in the axial plane at the level of the navel of a 31 year old man, showing normal anatomy. It uses compression to decrease the distance to the aorta for better visualization, resulting in flat shapes of the inferior mesenteric vein and the inferior vena cava .
Coming out of the heart, the thoracic aorta has a maximum diameter of 40 mm at the root. By the time it becomes the ascending aorta, the diameter should be < 35–38 mm, and 30 mm at the arch. The diameter of the descending aorta should not exceed 25 mm. [8] [9] The arch of the aorta lies within the mediastinum.
An aortic aneurysm is an enlargement (dilatation) of the aorta to greater than 1.5 times normal size. [1] Typically, there are no symptoms except when the aneurysm dissects or ruptures, which causes sudden, severe pain in the abdomen and lower back. [2] [3] The etiology remains an area of active research.
An aneurysm is usually defined as an outer aortic diameter over 3 cm (normal diameter of the aorta is around 2 cm), [17] or more than 50% of normal diameter that of a healthy individual of the same sex and age. [9] [18] If the outer diameter exceeds 5.5 cm, the aneurysm is considered to be large. [16] The common iliac artery is classified as: [19]
As the blood moves into the aortic arch, the area with the highest velocity tends to be on the inner wall. Helical flow within the ascending aorta and aortic arch help to reduce flow stagnation and increase oxygen transport. [4] As the blood moves into the descending aorta, rotations in the flow are less present.
The aorta normally has three small pouches that sit directly above the aortic valve (the sinuses of Valsalva), and an aneurysm of one of these sinuses is a thin-walled swelling. Aneurysms may affect the right (65–85%), non-coronary (10–30%), or rarely the left (< 5%) coronary sinus. [ 1 ]
Thoracic aortic aneurysm is defined as a cross-sectional diameter exceeding the following cutoff: 4.5 cm in the United States [7] 4.0 cm in South Korea [8] A diameter of 3.5 cm is generally considered dilated. [7] However, average values vary with age and size of the reference population, as well as different segments of the aorta.