State-of-the-Art Review
Ultrasound Imaging of the Abdominal Aorta: A Comprehensive Review

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Highlights

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    Ultrasound is the modality of choice for initial evaluation of disorders of the AA.

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    Ultrasound of the AA provides important anatomic and hemodynamic information.

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    Imaging of the proximal AA is an integral part of comprehensive TTE.

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    2D, color, PW, CW Doppler, 3D, and contrast are ultrasound tools to assess the AA.

Ultrasound is the imaging modality of choice for the initial evaluation of disorders that involve the abdominal aorta (AA). The diagnostic value of ultrasound resides in its ability to allow assessment of the anatomy and structure of the AA using two- dimensional, three-dimensional, and contrast-enhanced imaging. Moreover, ultrasound permits evaluation of the physiologic and hemodynamic consequences of abnormalities through Doppler interrogation of blood flow, thus enabling the identification and quantification of disorders within the AA and beyond its boundaries. The approach to ultrasound imaging of the AA varies, depending on the purpose of the study and whether it is performed in a radiology or vascular laboratory or in an echocardiography laboratory. The aim of this review is to demonstrate the usefulness of ultrasound imaging for the detection and evaluation of disorders that involve the AA, detail the abnormalities that are detected or further assessed, and outline its value for echocardiographers, sonographers, and radiologists.

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)

  • C. Lowe et al.

    Three-dimensional ultrasound in the management of abdominal aortic aneurysms: a topical review

    Eur J Vasc Endovasc Surg

    (2016)
  • K. Bredahl et al.

    Three-dimensional ultrasound improves the accuracy of diameter measurement of the residual sac in EVAR patients

    Eur J Vasc Endovasc Surg

    (2013)
  • Z. Zegarac et al.

    Pseudoaneurysm of the abdominal aorta in pregnancy

    Eur J Obstet Gynecol Reprod Biol

    (2011)
  • P.C. Spittell et al.

    Mobile thrombi in the abdominal aorta in cases of lower extremity embolic arterial occlusion: value of extended transthoracic echocardiography

    Am Heart J

    (2000)
  • E.A. Thomas et al.

    Duplex ultrasound of the abdominal aorta—a neglected tool in aortic dissection

    Clin Radiol

    (1990)
  • W.A. Zoghbi et al.

    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

    (2003)
  • J. Zarauza et al.

    An integrated approach to the quantification of aortic regurgitation by Doppler echocardiography

    Am Heart J

    (1998)
  • S.C. Reimold et al.

    Aortic flow velocity patterns in chronic aortic regurgitation: implications for Doppler echocardiography

    J Am Soc Echocardiogr

    (1996)
  • K. Takenaka et al.

    A simple Doppler echocardiographic method for estimating severity of aortic regurgitation

    Am J Cardiol

    (1986)
  • G. Styczynski et al.

    Abdominal aortic Doppler waveform in patients with aorto-iliac disease

    Eur J Vasc Endovasc Surg

    (2010)
  • J.L. Cavalcante et al.

    Aortic stiffness: current understanding and future directions

    J Am Coll Cardiol

    (2011)
  • R.A. Wilson et al.

    Correlates of aortic distensibility in chronic aortic regurgitation and relation to progression to surgery

    J Am Coll Cardiol

    (1992)
  • T. Mai et al.

    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

    (2018)
  • J.S. Lindholt et al.

    Population screening and intervention for vascular disease in Danish men (VIVA): a randomised controlled trial

    Lancet

    (2017)
  • M.U. Ali et al.

    Screening for abdominal aortic aneurysm in asymptomatic adults

    J Vasc Surg

    (2016)
  • B.M. Fadel et al.

    Pulse-wave Doppler interrogation of the abdominal aorta: a window to the left heart and vasculature

    Echocardiography

    (2014)
  • R.M. Lang et al.

    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

    (2015)
  • R. Erbel et al.

    2014 ESC guidelines on the diagnosis and treatment of aortic diseases

    Eur Heart J

    (2014)
  • M. Gürtelschmid et al.

    Comparison of three ultrasound methods of measuring the diameter of the abdominal aorta

    Br J Surg

    (2014)
  • S.M. Tomee et al.

    Systematic approach towards reliable estimation of abdominal aortic aneurysm size by ultrasound imaging and CT

    BJS Open

    (2021)

  • AIUM practice parameter for the performance of diagnostic and screening ultrasound examinations of the abdominal aorta in adults

    J Ultrasound Med

    (2021)
  • M. Blaivas et al.

    Frequency of incomplete abdominal aorta visualization by emergency department bedside ultrasound

    Acad Emerg Med

    (2004)
  • L. Beales et al.

    Reproducibility of ultrasound measurement of the abdominal aorta

    Br J Surg

    (2011)

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    2021 Published by Elsevier Inc. on behalf of the American Society of Echocardiography.