Diagnostic Imaging Pathways - Abdominal Aortic Aneurysm
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This pathway provides guidance on imaging patients with suspected or known abdominal aortic aneurysms.
Date reviewed: August 2015
Date of next review: 2017/2018
Published: March 2016
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The relative radiation level (RRL) of each imaging investigation is displayed in the pop up box.
| SYMBOL | RRL | EFFECTIVE DOSE RANGE |
 | None | 0 |
 | Minimal | < 1 millisieverts |
 | Low | 1-5 mSv |
 | Medium | 5-10 mSv |
 | High | >10 mSv |
Images
Image GalleryNote: These images open in a new page | ||
|---|---|---|
| 1a |  |
Abdominal Aortic and Right Iliac Artery Aneurysms Image 1a and 1b (Computed Tomography): Axial and reconstructed images of an abdominal aortic aneurysm. There is also a right iliac artery aneurysm which is partially occluded by thrombus. |
| 1b |  |
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| 2 |  |
Tortuous infra-renal abdominal aortic aneurysm with thrombosis of the rest of the sac. |
| 3 |  |
Infra-renal abdominal aortic aneurysm with involvement of both common and internal iliac arteries. |
| 4 |  |
A large abdominal aortic aneurysm is seen which has ruptured with intraluminal developing thrombus formation and intra and retroperitoneal haemorrhage. |
Teaching Points
Teaching Points
- Physical examination has a moderate sensitivity for the detection of AAA
- Ultrasound is highly accurate in detecting the presence or absence of AAA
- Depending on the size of the aneurysm, further management is based on repeat ultrasounds at variable intervals or referral for surgical intervention (AAA >5cm)
- CT angiography allows evaluation of the anatomy of the abdominal aortic aneurysm and associated structures prior to elective surgical repair
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Computed Tomography Angiography (CTA)
- Preoperative multi detector (MD) computed tomography angiogram (CTA) of an AAA is required if EVAR is planned
- CTA is reliable in assessing the anatomy and dimensions of AAAs as well as the extent of atheromatous or inflammatory changes in the aorta and iliac arteries 15
- The main features of interest include 1,16
- The dimensions and extent of the AAA and any associated iliac artery aneurysmal disease
- The diameter, length, angulation and shape of the neck of the AAA and its relationship to the renal and visceral arteries
- The calibre and tortuosity of the access (iliac and femoral) arteries
- The advantages of MDCT compared to single detector CT include 2-3 times faster scan speeds and reduced contrast dose. With MDCT the acquisition of raw volumetric data combined with thinner section slices allows the recreation of images in any plane while preserving spatial resolution, and improved three dimensional reconstruction with reduced artefact 16,17
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Recommendations for Surveillance of Abdominal Aortic Aneurysm (AAA)
- Recommendations for surveillance frequency and interval vary widely 1,2,3
- Time taken for an AAA of 4.0 cm or less to have a 10% chance of growing to 5.5 cm is at least 3 years. For men with an AAA of 4.0 cm or smaller, it takes more than 3.5 years to have a risk of rupture greater than 1%. Based on these results, the risk of AAA rupture or the need for aortic repair can be objectively determined and guide surveillance interval decision making 2
- The risk of an AAA <5.5cm in diameter rupturing is low (<1.6%/year). This rises to ~10%/year for AAAs >5.5cm 1,4,5
- The threshold for elective intervention is 5.5cm as, compared to surveillance, survival is not improved by elective repair of AAAs <5.5cm in diameter 1,6,7
- There is some evidence that this threshold should be 5cm in women 8
- Women had a 4-fold greater rupture risk for all AAA sizes and reached a rupture risk of greater than 1% in a much shorter time than men. Differences in anatomy, structure, sex, steroids, and smoking habits have all been suggested to play a role in the increased risk of rupture in women 2
- The clinical implication is that a lower AAA diameter threshold for surgery should be adopted for women, a recommendation already made by the joint council of the American Association for Vascular Surgery and Society for Vascular Surgery, but one not yet supported by randomized trial evidence 2
- Unless there are indications for surgery, surveillance using ultrasound is indicated in all AAAs <5.5cm
- Diameter measurements using ultrasound are reliable and reproducible to within 3mm 9
- The annual rate of AAA expansion varies considerably but generally increases with diameter 1,10
- 1-3 mm for 3.0-3.9cm AAAs
- 3-4mm for 4-4.4cm AAAs
- 4-5mm for 4.5-4.9cm AAAs
- Majority of patients with sub-aneurysmal aortic dilatation progress to true aneurysmal aortic dilatation, with almost half of these doing so within 5 years of follow-up. Furthermore, within 10 years of detection, a smaller proportion (approximately 4%) will progress to an aortic diameter that would be considered at or above the threshold for surgical intervention 11
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Ultrasound
- An abdominal aortic aneurysm (AAA) is present when the infra-renal aortic diameter is ≥3cm. An AAA of >5.5cm is considered large 1
- Most AAAs are asymptomatic and detected incidentally at the time of physical examination or imaging (usually ultrasound or CT scanning) for symptoms related to other pathology
- Physical examination has moderate overall sensitivity (68%) for the detection of AAA but is highly sensitive for diagnosis of AAAs large enough to warrant elective intervention in patients who do not have a large girth 12
- Ultrasound is highly accurate in detecting an AAA 13
- Intramural thrombus seen on any imaging is a common feature of AAAs
- There is evidence that population screening men aged 65 years and over using ultrasound can reduce the mortality from AAA. 1,14 However screening has yet to be introduced into Australia
References
References
Date of literature search: August 2015
The search methodology is available on request. Email
References are graded from Level I to V according to the Oxford Centre for Evidence-Based Medicine, Levels of Evidence. Download the document
- Moll FL, Powell JT, Fraedrich G, Verzini F, Haulon S, Waltham M, et al. Management of abdominal aortic aneurysms clinical practice guidelines of the European society for vascular surgery. Eur J Vasc Endovasc Surg. 2011;41 Suppl 1:S1-s58. (Guidelines). View the reference
- RESCAN Collaborators, Bown MJ, Sweeting MJ, Brown LC, Powell JT, Thompson SG. Surveillance intervals for small abdominal aortic aneurysms: a meta-analysis. JAMA. 2013;309(8):806-13. (Level I evidence). View the reference
- Brady AR, Thompson SG, Fowkes FG, Greenhalgh RM, Powell JT. Abdominal aortic aneurysm expansion: risk factors and time intervals for surveillance. Circulation. 2004;110(1):16-21. (Level II evidence). View the reference
- Lederle FA, Johnson GR, Wilson SE, Ballard DJ, Jordan WD, Jr., Blebea J, et al. Rupture rate of large abdominal aortic aneurysms in patients refusing or unfit for elective repair. JAMA. 2002;287(22):2968-72. (Level II evidence). View the reference
- Powell JT, Gotensparre SM, Sweeting MJ, Brown LC, Fowkes FG, Thompson SG. Rupture rates of small abdominal aortic aneurysms: a systematic review of the literature. Eur J Vasc Endovasc Surg. 2011;41(1):2-10. (Level II evidence). View the reference
- The United Kingdom Small Aneurysm Trial Participants. Long-term outcomes of immediate repair compared with surveillance of small abdominal aortic aneurysms. N Engl J Med. 2002;346(19):1445-52. (Level I evidence). View the reference
- Lederle FA, Wilson SE, Johnson GR, Reinke DB, Littooy FN, Acher CW, et al. Immediate repair compared with surveillance of small abdominal aortic aneurysms. N Engl J Med. 2002;346(19):1437-44. (Level I evidence). View the reference
- Pleumeekers HJ, Hoes AW, Mulder PG, van der Does E, Hofman A, Lameris JS, et al. Differences in observer variability of ultrasound measurements of the proximal and distal abdominal aorta. J Med Screen. 1998;5(2):104-8. (Level III evidence). View the reference
- Norman PE, Powell JT. Abdominal aortic aneurysm: the prognosis in women is worse than in men. Circulation. 2007;115(22):2865-9. (Review article). View the reference
- Powell JT, Sweeting MJ, Brown LC, Gotensparre SM, Fowkes FG, Thompson SG. Systematic review and meta-analysis of growth rates of small abdominal aortic aneurysms. Br J Surg. 2011;98(5):609-18. (Level II evidence). View the reference
- Wild JB, Stather PW, Biancari F, Choke EC, Earnshaw JJ, Grant SW, et al. A multicentre observational study of the outcomes of screening detected sub-aneurysmal aortic dilatation. Eur J Vasc Endovasc Surg. 2013;45(2):128-34. (Level III evidence). View the reference
- Fink HA, Lederle FA, Roth CS, Bowles CA, Nelson DB, Haas MA. The accuracy of physical examination to detect abdominal aortic aneurysm. Arch Intern Med. 2000;160(6):833-6. (Level III evidence). View the reference
- Kuhn M, Bonnin RL, Davey MJ, Rowland JL, Langlois SL. Emergency department ultrasound scanning for abdominal aortic aneurysm: accessible, accurate, and advantageous. Ann Emerg Med. 2000;36(3):219-23. (Level II evidence). View the reference
- Fleming C, Whitlock EP, Beil TL, Lederle FA. Screening for abdominal aortic aneurysm: a best-evidence systematic review for the U.S. Preventive Services Task Force. Ann Intern Med. 2005;142(3):203-11. (Level I evidence). View the reference
- Burrill J, Dabbagh Z, Gollub F, Hamady M. Multidetector computed tomographic angiography of the cardiovascular system. Postgraduate Medical Journal. 2007;83(985):698-704. (Review article). View the reference
- Hellinger JC. Endovascular repair of thoracic and abdominal aortic aneurysms: pre- and postprocedural imaging. Tech Vasc Interv Radiol. 2005;8(1):2-15. (Review article). View the reference
- Budovec JJ, Pollema M, Grogan M. Update on multidetector computed tomography angiography of the abdominal aorta. Radiol Clin North Am. 2010;48(2):283-309, viii. (Review article). View the reference
Information for Consumers
Information for Consumers
Information from this website |
Information from the Royal Australian and New Zealand College of Radiologists’ website |
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Consent to Procedure or Treatment Radiation Risks of X-rays and Scans Computed Tomography (CT) Angiography |
Contrast Medium (Gadolinium versus Iodine) Iodine-Containing Contrast Medium Radiation Risk of Medical Imaging During Pregnancy Radiation Risk of Medical Imaging for Adults and Children |
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