From the Guidelines
An abdominal aortic aneurysm (AAA) is measured using medical imaging techniques that assess its maximum diameter, which is the primary metric for determining risk and treatment decisions, with the most common imaging methods including ultrasound, computed tomography (CT), and magnetic resonance imaging (MRI) 1. The measurement of AAA is crucial for determining the risk of rupture and guiding treatment decisions.
- The maximum diameter of the aneurysm is the primary metric used to determine the risk of rupture and the need for surgical intervention.
- Ultrasound is typically used for initial screening and routine monitoring due to its safety, accessibility, and lack of radiation.
- CT scans provide more detailed measurements and are considered the gold standard for pre-surgical planning, offering precise measurements of the aneurysm's diameter, length, and relationship to branch vessels 1.
- The diameter is measured perpendicular to the centerline or flow axis of the aorta, not simply the widest visible dimension.
- For accuracy, measurements should be taken from outer wall to outer wall, as this approach provides the most consistent results across different imaging modalities.
- The location of measurement is also important, with the maximum diameter typically occurring below the renal arteries but above the aortic bifurcation.
- Regular monitoring is essential for aneurysms below the surgical threshold (generally 5.5 cm for men and 5.0 cm for women), with measurement intervals determined by the current size and growth rate of the aneurysm 1. Key factors associated with the expansion and rupture of AAA include large aneurysm diameter, rapid growth, smoking, hypertension, high peak wall stress, and being female 1. Given the high mortality and morbidity associated with AAA rupture, imaging screening continues to play a crucial role in the management of AAA 1.
From the Research
Measurement of Abdominal Aortic Aneurysm
- An abdominal aortic aneurysm (AAA) is defined as a localized dilatation of the abdominal aorta of ≥ 3 cm 2
- The measurement of AAA is crucial for diagnosis, monitoring, and treatment planning
- Various imaging modalities are used to measure AAA, including:
- Ultrasound: mainstay imaging modality for AAA screening and surveillance 2
- Contrast-enhanced CT angiography: gold standard for preoperative imaging and image-based treatment planning in AAA repair 2
- Non-contrast MR angiography: allows for accurate monitoring of aortic diameters in AAA patients 2
- 3D imaging with multiplanar reformation and automatic centerline positioning: enables more accurate assessment of the maximum aortic diameter 2
Comparison of Imaging Modalities
- CT-based measurements of aneurysm size tend to be larger than ultrasound measurements 3
- CT-PCLF diameters are consistently larger than CT-PME and CT-AP measurements 3
- MRI provides the necessary information for the surveillance and preoperative evaluation of abdominal aortic aneurysms, including the measurement of outer dimension, diameter of the residual lumen, and length of the aneurysm 4
- CT plays a central role in the diagnosis, risk stratification, and management of most aneurysms, particularly those located distal to the proximal ascending aorta 5
Importance of Accurate Measurement
- Aortic diameters are the cornerstone of current clinical practice in aortic aneurysms 5
- Accurate measurement of AAA is critical for clinical decision making, as errors in measurement may generate errors in clinical decision making 5
- New biomechanical and metabolic information could potentially provide a more reliable prediction of the risk of aneurysm rupture 5