Of the images rolling the patient into a left lateral

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of the images, rolling the patient into a left lateral decubitus position may help mechanically shift the bowel out of the way of the ultrasound beam. ² Jiggle the probe with gentle pressure over the offending bowel to encourage peristalsis and afford a clearer view of the aorta. ² Try imaging the transverse aorta from an angle. If bowel gas obscures the right side of your screen, move the probe to your left and angle the beam toward the aorta to visualize it from an angle. As long as the beam remains transverse, this should not alter the size of the aorta as it appears on the screen ( Figure 5.13 ). Can’t see the aorta at all? ² Have the patient roll onto his or her left side, and use the liver as an acoustic window to try and view the aorta this way. ² Increase the depth to the maximum to see if you can find the vertebral shadow. 124 Diagnostic ultrasound Abdominal aorta ultrasound
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Abnormal images AAA Figure 5.14 is a transverse view of the mid-abdominal aorta in an elderly patient presenting with back pain. The depth markers on the screen reveal that this is larger than 3.0 cm in diameter, and therefore aneurysmal. Note that the blackened center (lumen) is the only area through which blood flows. The thickened outer dimension of the aorta is the result of a clot and athero- sclerotic plaque that are adherent to the wall. Figure 5.13 Probe angles to avoid bowel gas when imaging the abdominal aorta. Figure 5.14 AAA with thrombus (*) and lumen (L) visible as well as vertebral body shadow (V). Diagnostic ultrasound 125 Abdominal aorta ultrasound
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Figure 5.15 Thrombus (*) and lumen (L) within aorta are visible above vertebral body shadow (V). In this image hemorrhage from leaking AAA is evident as well (arrow). (A) (B) Figure 5.16 The same AAA seen in ( A ) transverse and ( B ) longitudinal views. 126 Diagnostic ultrasound Abdominal aorta ultrasound
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In the next examples of AAA ( Figures 5.15 and 5.16 ), lumen clot is visualized as a somewhat more heterogeneous gray lining of the aorta. Caution must be used when measuring the diameter so as not to be fooled into measuring only the patent lumen but to include the luminal clot in the diameter measure- ment. It should be appreciated that the aorta is actually significantly larger than the vertebral shadow, which is a visual clue that the diameter is likely dilated. Figure 5.17 shows a longitudinal view of an abdominal aortic aneurysm. It is easy to appreciate the fusiform shape in these views. Aortic dissection CT is a much more accurate test for dissection, and only rarely will bedside ultrasound be able to image the flap of an aortic dissection. However, if images similar to those in Figures 5.18 to 5.20 are seen (in particular, the Figure 5.17 Longitudinal view of proximal AAA with the celiac (C) and superior mesenteric (S) arteries branching off. In this view an aortic dissection flap (arrow) is evident as well.
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