Journal of the American Society of Echocardiography
State-of-the-Art ReviewUltrasound Imaging of the Abdominal Aorta: A Comprehensive Review
Section snippets
Anatomy of the AA
The AA represents the continuation of the DTA, extending from the aortic hiatus in the diaphragm at the level of the 12th thoracic vertebra to its bifurcation into the common iliac arteries at the level of the fourth lumbar vertebra, typically 1 to 2 cm below the umbilicus. The AA runs to the left of the midline in the retroperitoneal space, anterior to the spine, and to the left of the inferior vena cava (IVC). It gives rise to single-branch arteries that arise anteriorly to supply the
Image Orientation
With the patient in a supine decubitus position, scanning from the subcostal window to the level of the umbilicus allows visualization of the AA in its entirety. The longitudinal view is obtained in the sagittal plane with the transducer positioned along the long axis of the AA and its notch pointing toward the patient's head (Figure 2, row 1). This view allows measurement of the anteroposterior (AP) diameter (front to back) of the AA and the length (cranial-to-caudal) of any structural
Expertise, Feasibility, and Reproducibility of Ultrasound Imaging of the AA
Ultrasound is a highly operator-dependent modality, and thus image acquisition and data interpretation rely on the expertise of the sonographer. Still, health care staff members with no expertise in abdominal imaging can achieve good performance in simple visualization of the AA after a short training period.11 The AA can be visualized in 86% to 97% of individuals undergoing routine transthoracic echocardiography (TTE).12,13 In a study of nonfasting patients undergoing TTE in the emergency
Spectral Doppler Interrogation of the AA
The flow profile in the AA varies depending on the segment being interrogated (i.e., proximal vs distal segment). PW and CW Doppler interrogation of the AA can be accomplished in the majority of individuals.
Abnormalities on 2D Imaging of the AA
The AA is closer to the transducer from the subcostal and abdominal windows than is the DTA from the transthoracic parasternal and apical windows. Moreover, unlike the DTA, the AA is often visualized in its entirety. Therefore, the detection by ultrasound of structural abnormalities such as atheromas, aneurysms, and dissection is higher in the AA than in the DTA.
Abnormalities on Spectral Doppler Interrogation of the AA
PW Doppler interrogation of the proximal AA is routinely performed as part of TTE. Disorders involving the aortic valve, the aorta and its branches, and the left ventricle alter the flow profile in the AA, often in a characteristic manner.
Saline Contrast
Patients with PDA associated with severe pulmonary hypertension typically demonstrate a small bidirectional or predominantly right-to-left shunt. The equalization of aortic and pulmonary artery pressures results in the loss of turbulent flow across the ductus and often leads to the PDA's being overlooked by color Doppler.51 A saline contrast study focused on the cardiac chambers would fail to demonstrate any right-to-left intracardiac shunting. Visualization of bubbles in the AA but not in the
Assessment of Aortic Stiffness
Arterial stiffness, or the resistance to deformation, is a marker of LV afterload. Compliance is the opposite of stiffness and refers to the absolute change in vessel lumen for a given change in pressure.53 Increased stiffness is one of the earliest measurable markers of adverse structural and functional alterations of the vessel wall.
Aortic stiffness is an independent predictor of major cardiovascular events and all-cause mortality. Aging, atherosclerosis, hypertension, diabetes mellitus, and
Imaging of the AA in Echocardiography versus Radiology or Vascular Laboratories
Comprehensive TTE includes imaging of the proximal AA from the subcostal window using 2D, color, and spectral Doppler interrogation. This limited imaging is mostly directed at assisting with the diagnosis and quantification of left-sided cardiac lesions and identifying any gross abnormalities of the proximal AA.
Several factors interfere with imaging of the entire AA in the echocardiography laboratory. Bowel gas, more prominent in nonfasting patients, adversely affects visualization of the AA
Point-of-Care Imaging of the AA
Point-of-care ultrasound is an established tool for focused bedside assessment of the AA as an extension to the physical examination. It is often used to expedite the diagnosis of conditions that require urgent management, including ruptured AAA and aortic dissection. Advantages of point-of-care ultrasound performed by emergency providers include its immediate availability and relatively high accuracy. Point-of-care ultrasound improves the detection rate of AAA over physical examination,58
Prognostic Value of Ultrasound Imaging of the AA
Imaging of the AA carries prognostic value when used as a screening tool for AAA. Randomized control trials and meta-analyses have uniformly demonstrated reduction in AAA-related mortality by screening men ≥65 years of age. Some studies have additionally shown a reduction in all-cause mortality, rate of AAA rupture, and emergent AAA repair.21,60, 61, 62, 63, 64 The outcome studies are summarized in Table 5.
Artifacts
Acoustic artifacts are occasionally encountered on ultrasound imaging of the AA. Physicians and sonographers should be aware of them to avoid misinterpretation and unnecessary diagnostic workup. A frequently observed artifact known as pseudothrombus consists of an intraluminal longitudinal echogenicity, typically noted at the level of the SMA, that simulates a mass or a thrombus (Figure 14A). The pseudothrombus is a reverberation artifact resulting from repeated reflection of the ultrasound
Limitations and Pitfalls
Bowel gas is the most common cause of failed ultrasound examination of the AA. Body habitus such as obesity, acute abdominal pain, ascites, abdominal distension, emergency situation, recent surgery, and the inability to control the pattern of respiration, all interfere with visualization of the AA. Fasting and the abstinence from habits that lead to air swallowing such as smoking and chewing gum for ≥8 hours before the examination reduce bowel gas and help improve image quality. Displacing
Conclusion
Ultrasound is the modality of choice for the initial assessment of disorders that involve the AA because of its numerous advantages and the absence of contraindications. The combination of 2D, color, and spectral Doppler with the “as needed” use of 3D imaging and ultrasound enhancing agents makes ultrasound a powerful imaging and diagnostic tool. When performed in the echocardiography laboratory, imaging of the proximal AA improves the diagnostic ability of TTE and provides added hemodynamic
References (66)
- et al.
Screening for abdominal aortic aneurysm during transthoracic echocardiography: a systematic review and meta-analysis
Eur J Vasc Endovasc Surg
(2018) - et al.
Ultrasound measurement for abdominal aortic aneurysm screening: a direct comparison of the three leading methods
Eur J Vasc Endovasc Surg
(2014) - et al.
Ultrasound measurement of the luminal diameter of the abdominal aorta and iliac arteries in patients without vascular disease
J Vasc Surg
(1993) - et al.
Usefulness of transesophageal echocardiography in the evaluation of celiac trunk and superior mesenteric artery involvement in acute aortic dissection
J Am Soc Echocardiogr
(2021) - et al.
Intra- and interobserver variability in ultrasound measurements of abdominal aortic diameter. The Tromsø Study
Eur J Vasc Endovasc Surg
(1998) - et al.
Effectiveness of screening for abdominal aortic aneurysm during echocardiography
Am J Cardiol
(2014) - et al.
Screening for abdominal aortic aneurysm during transthoracic echocardiography in a hypertensive patient population
J Am Soc Echocardiogr
(1997) - et al.
The cardiac cycle is a major contributor to variability in size measurements of abdominal aortic aneurysms by ultrasound
Eur J Vasc Endovasc Surg
(2012) - et al.
Clinical validation of three-dimensional ultrasound for abdominal aortic aneurysm
J Vasc Surg
(2020) - et al.
Contrast enhanced ultrasound can replace computed tomography angiography for surveillance after endovascular aortic aneurysm repair
Eur J Vasc Endovasc Surg
(2016)
Three-dimensional ultrasound in the management of abdominal aortic aneurysms: a topical review
Eur J Vasc Endovasc Surg
Three-dimensional ultrasound improves the accuracy of diameter measurement of the residual sac in EVAR patients
Eur J Vasc Endovasc Surg
Pseudoaneurysm of the abdominal aorta in pregnancy
Eur J Obstet Gynecol Reprod Biol
Mobile thrombi in the abdominal aorta in cases of lower extremity embolic arterial occlusion: value of extended transthoracic echocardiography
Am Heart J
Duplex ultrasound of the abdominal aorta—a neglected tool in aortic dissection
Clin Radiol
Recommendations for evaluation of the severity of native valvular regurgitation with two-dimensional and Doppler echocardiography: a report from the American Society of Echocardiography developed in Collaboration with the Society for Cardiovascular Magnetic Resonance
J Am Soc Echocardiogr
An integrated approach to the quantification of aortic regurgitation by Doppler echocardiography
Am Heart J
Aortic flow velocity patterns in chronic aortic regurgitation: implications for Doppler echocardiography
J Am Soc Echocardiogr
A simple Doppler echocardiographic method for estimating severity of aortic regurgitation
Am J Cardiol
Abdominal aortic Doppler waveform in patients with aorto-iliac disease
Eur J Vasc Endovasc Surg
Aortic stiffness: current understanding and future directions
J Am Coll Cardiol
Correlates of aortic distensibility in chronic aortic regurgitation and relation to progression to surgery
J Am Coll Cardiol
Point-of-care ultrasound performed by a medical student compared to physical examination by vascular surgeons in the detection of abdominal aortic aneurysms
Ann Vasc Surg
Population screening and intervention for vascular disease in Danish men (VIVA): a randomised controlled trial
Lancet
Screening for abdominal aortic aneurysm in asymptomatic adults
J Vasc Surg
Pulse-wave Doppler interrogation of the abdominal aorta: a window to the left heart and vasculature
Echocardiography
Recommendations for cardiac chamber quantification by echocardiography in adults: an update from the American Society of Echocardiography and the European Association of Cardiovascular Imaging
J Am Soc Echocardiogr
2014 ESC guidelines on the diagnosis and treatment of aortic diseases
Eur Heart J
Comparison of three ultrasound methods of measuring the diameter of the abdominal aorta
Br J Surg
Systematic approach towards reliable estimation of abdominal aortic aneurysm size by ultrasound imaging and CT
BJS Open
AIUM practice parameter for the performance of diagnostic and screening ultrasound examinations of the abdominal aorta in adults
J Ultrasound Med
Frequency of incomplete abdominal aorta visualization by emergency department bedside ultrasound
Acad Emerg Med
Reproducibility of ultrasound measurement of the abdominal aorta
Br J Surg
Cited by (8)
ACR Appropriateness Criteria® Pulsatile Abdominal Mass, Suspected Abdominal Aortic Aneurysm: 2023 Update
2023, Journal of the American College of RadiologyAbdominal Aortic Aneurysms (Etiology, Epidemiology, and Natural History)
2022, Anesthesiology ClinicsCitation Excerpt :However, effective ultrasound measuring is operator dependent, and computed tomography remains the gold standard for quantifying aneurysm size and instability64(Fig. 1). Diameters measured on computed tomography are typically approximately 5 mm greater than those measured with ultrasound; the former allows aortic diameter measurement in any plane, whereas the latter is limited to anterior-posterior and transverse planes.65 Three-dimensional computed tomography reconstructions are now created to aid in surgical planning for repair (Fig. 2).
An Approach to Point-Of-Care Ultrasound Evaluation of the Abdominal Aorta
2023, Journal of Visualized ExperimentsHead to toe ultrasound: a narrative review of experts’ recommendations of methodological approaches
2022, Journal of Anesthesia, Analgesia and Critical Care
Conflicts of Interest: None.