22 Interpreting Aortic Ultrasound

Normal Ultrasound Findings

• Size and Shape: The aorta should be cylindrical, with a diameter varying from 2 to 3 cm depending on the segment.
• Pulsatile Nature: The aorta should show pulsatile movement synchronized with the cardiac cycle.

Abnormal Findings

• Aortic Aneurysms: Appear as focal or diffuse dilations of the aorta. Criteria include a diameter of 3 cm or more. Thrombus within the aneurysm can also be detected.
• Aortic Dissections: Characterized by the presence of an intimal flap and the formation of a true and false lumen.

Types of Aortic Aneurysms

Abdominal aortic aneurysms (AAAs) fall into two primary categories:

• Fusiform Aneurysms: This more common type is characterized by a symmetrical expansion affecting the entire aortic circumference, often associated with risk factors like smoking and hypertension.
• Saccular Aneurysms: Less prevalent, saccular aneurysms are identified by localized bulging on one side of the aortic wall, typically linked with inflammation or infection.

In terms of sonographic imaging:

• Fusiform Aneurysms typically present with symmetrical and concentric aortic dilation in ultrasound images, although occasional asymmetric appearances can be observed.
• Saccular Aneurysms are distinguished from fusiform aneurysms in ultrasound images by the presence of discontinuities and interruptions in the layers of the aortic wall.

Aortic Pathologies

• Aneurysms: Most AAAs occur distal to the renal arteries (infrarenal). The AAA is diagnosed when the aorta’s diameter exceeds 3.0 cm.
• Dissections and Occlusions: Doppler ultrasound is useful in detecting aortic occlusions by recognising the absence of blood flow and estimating the severity of stenosis.

Longitudinal view of Abdominal Aorta Aneurysm. Adapted from “65 AAA US longutudinal view” by International Emergency Medicine Education Project is licensed under CC BY 4.0

Image Criteria for Evaluation

• Diameter Measurement: Aortic diameter is assessed by measuring the outer-to-outer wall distance in both transverse and longitudinal perspectives.
• Wall Characteristics: Examine the aortic wall for uniform thickness, hypoechoic regions, or calcifications.
• Lumen Evaluation: Should be anechoic; the presence of thrombus or plaque alters this appearance.
• Pathology Detection: Aneurysms are typically defined as a focal dilation exceeding 3 cm, while dissections involve the visualization of an intimal flap.

Pearls and Pitfalls in Aortic Ultrasound

• Measurement Accuracy: Measure the aorta’s diameter accurately to prevent underestimating aneurysm size.
• Avoid inferior vena cava (IVC) Confusion: Identifying the aorta’s branches can assist in distinguishing between these two vessels.

• Bowel Gas Interference: May obstruct views, requiring patient repositioning or varying probe angles.

Case Studies

• Case 1: A patient with an aortic aneurysm showing a dilated aorta with a mural thrombus.

Abdominal Aorta Aneurysm with Mural Thrombus. Adapted from “66 AAA US transvers view thrombus” by International Emergency Medicine Education Project is licensed under CC BY 4.0