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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.
Behind the descending thoracic aorta is the vertebral column and the hemiazygos vein. To the right is the azygos veins and thoracic duct, and to the left is the left pleura and lung. In front of the thoracic aorta lies the root of the left lung, the pericardium, the esophagus, and the diaphragm.
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.
A thoracic aorta diameter greater than 3.5 cm is generally considered dilated, whereas a diameter greater than 4.5 cm is generally considered to be a thoracic aortic aneurysm. [4] Still, the average diameter in the population varies by for example age and sex.
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]
Aortic unfolding is an abnormality visible on a chest X-ray, that shows widening of the mediastinum which may mimic the appearance of a thoracic aortic aneurysm. [ 1 ] With aging, the ascending portion of the thoracic aorta increases in length by approximately 12% per decade, whereas the diameter increases by just 3% per decade.
Abrupt loss of function of the aortic valve results in acute aortic regurgitation (also known as acute aortic insufficiency) and loss in the normal diastolic blood pressure resulting in a wide pulse pressure and bounding pulses. The endocardium perfuses during diastole and so acute aortic regurgitation can reduce perfusion of the heart.
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]