Discovering the aorta through ultrasound

ECHO images Tina Cullen. Text Genevieve Carbonatto

A 65 year old lady presented to the Emergency department with a 6 month history of  abdominal pain. The pain was vague and mainly located in her pelvis but at times was epigastric.

A bedside point of care ultrasound was performed.

This was the ultrasound of her  proximal aorta in the transverse plane

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The AP diameter of the proximal aorta is 4.84 cm

Ok so we have a AAA. How can we examine this aorta from it’s origin at the heart to it’s bifurcation using ultrasound? The challenge will be examining the aorta in the chest. The ribs, the sternum and the lungs are in the way. These are some of windows that may be used.

 

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Starting at the chest

PLAX view

Aortic root, proximal part of ascending aorta and descending aorta

With the index marker at 11.00 o’clock, the aortic root and the very proximal ascending aorta can be seen

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This is our patient’s parasternal view

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The ascending aorta is 3.58 cm which is at the upper limit of normal for this patient, if absolute measurements are used but if indexed to body surface area, this ascending aorta is significantly dilated.

If there is significant dilatation of the aortic root, aortic regurgitation will be present and may be significant. Colour Doppler will give you an idea of the degree of regurgitation

The aortic regurgitation is not significant in this patient as the ascending aorta is dilated but not the aortic root.

The descending aorta is also visible in the PLAX view as it passes posterior to the heart. Note the descending aorta is not seen in the above clips,  because of lack of depth. The descending aorta is seen deep to the left atrium (LA).  This is her PLAX including her aorta

The descending aorta is not always seen in transverse, at times it is seen as slightly oblique. The measurement of the aorta when it appears as round as possible is 7.21 cm. This clearly indicates a very dilated aorta at this point.

High parasternal view

By moving one rib space up from the PLAX view, moving closer to the sternum and using a little clockwise rotation a more dedicated view of the ascending aorta is achieved. In this view more of the aorta is visualised and less of the LV is seen.

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Her ascending aorta is above the upper limit of normal for her height and weight. It should be less than 3.5 cm. It is 3.90cm in diameter.

Parastenal short axis view

The aorta can be seen deep to the heart in the PSAX view

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When measured, the aorta is just over 5cm – clearly aneurysmal.

The suprasternal notch

With the index marker of the probe at 1 0’clock in the sternal notch, the arch of the aorta can be visualised

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The ascending aorta measures 3.6 cm, the arch, 3.8cm and the descending aorta at it’s widest point 5.1cm

The 5 chamber view

To get  the 4 chamber view the index marker points between 2 and 3 o’clock at the apex of the heart. Panning superiorly and anteriorly will reveal the aortic valve leaflets and aortic root. This is the 5 chamber view.

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By panning inferiorly and posteriorly from the 4 chamber view, the  descending aorta can be seen behind the heart.

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The aorta here measures 4.6 cm

Apical 2-chamber view

A very useful view to see the descending aorta is the Apical 2 chamber view. From the 4 chamber view rotate the probe anticlockwise to 1 o’clock then tilt the probe posteriorly with slight medial angulation and the aorta can be seen in it’s long axis

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The descending aorta is tortuous in this patient, so the aorta is seen in long axis and further away dips away. The maximum diameter of the descending thoracic aorta in this view is 5.2 cm

Right sternal edge

A dilated ascending aorta courses to the right and can be visualised using the right sternal edge view. With the patient rolled  onto their right lateral side, the probe is placed at the edge of the sternum in the 2nd or 3rd rib space. The probe index marker is at around 11 o’clock. Once the aorta is visualised then slowly rotate the probe clockwise to get the length of the aorta.

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The abdominal aorta

The examination of the abdominal aorta is straight forward compared to examining the aorta through the chest. Essentially the proximal, mid  and distal aorta are examined in the transverse  and  longitudinal planes.

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Proximal Aorta

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Size of aneurysm  in AP diameter is 4.85 cm

The aorta is aneurysmal proximally. It does not change in diameter proximally.

proximal-aorta

 

Size of aneurysm in the longitudinal view is 5.42 cm

Mid aorta

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Distal Aorta , bifurcation

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The right common iliac artery measures measures 4.1cm

Finally we have come to the end of our journey.  By using ultrasound we have found that this lady’s aneurysm starts at the ascending aorta seen in the high parasternal view to be 3.90 cm in diameter. The descending thoracic aorta seen in the PLAX view was 7.21 cm. In the short axis view, her descending aorta was 5.00 cm.  At the aortic arch her ascending aorta was 3.6 cm, at the arch it was 3.8 cm and the descending thoracic aorta was 5.1 cm.  From the 2 chamber view her descending aorta was 5.2 cm and it was clear that the aorta was tortuous at that point. The proximal abdominal aorta was 4.85 cm in the short axis, and a little more caudally 5.42 cm in the longitudinal view. Her mid aorta was 4.85 cm and at the bifurcation her right common iliac artery was 4.1 cm. These measurements are not exact. A CT angiogram is required for that, however with bedside ultrasound we have acquired a pretty good idea of how aneurysmal this aorta is from it’s origin to it’s bifurcation.

Teaching point: The abdominal aorta is relatively easy to identify and measure especially if it is aneurysmal. Knowing where to look for the thoracic  aorta using the basic cardiac windows is important. The suprasternal notch and the right parasternal view add to the examination of the aorta . This is especially  useful  if there is  concern regarding a possible thoracic aortic dissection. The most useful  windows to visualise the aorta from the chest are the PLAX view, the apical 2 chamber view, the suprasternal notch and the right sternal edge. Ultrasound cannot compete with CT . It may identify a dissection, will give you an idea of  how aneurysmal the thoracic aorta may be and will show you whether the aortic root is affected and whether it is causing aortic valve annular dilatation and aortic regurgitation.

 

 

 

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