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Three Part Question

In [patients with suspected AAA] is [Ultrasound or CT] better at [ruling in the diagnosis].

Clinical Scenario

A 59 year old man presents to the emergency department with a four hour history of worsening central abdominal pain. He has a history of vascular disease and you suspect an Abdominal Aortic Aneurysm. His vital signs remain stable and you wonder if ultrasound scan or CT would best confirm your diagnosis.

Search Strategy

PubMed
1. ultrasound AND computed tomography AND AAA.
2. Abdominal Aortic Aneurysm AND Ultrasound AND diagnos* English in the last 5 years in adults aged 45+ (In the last 5 years added to ensure that high quality multi slice CT was compared to ED Trained USS)

Search Outcome

Search 1: 133 papers of which 4 were relevant and one was excluded on the grounds of quality.
Search 2: 125 papers of which 3 were relevant, one of which had also been found in search 1.

Relevant Paper(s)

Author, date and country	Patient group	Study type (level of evidence)	Outcomes	Key results	Study Weaknesses
Wanhainen, Berggvist, Nov 2002 Sweden	61 patients comparison of US and CT measurement	Comparison of US and CT measurement	Difference in diameter of aorta when measured by USS when compared to CT	The difference and variability between US and CT varies depends on the diameter of the aorta and how it is measured	Study size
Taval VS, Graf CD, Gibbs MA. 2003 USA	125 patients with suspected AAA. prospective, observational study. Bedside ultrasound by EM physician followed by confirmatory test (radiology US/CT/MRI/laparotomy)	Prospective, observational study. Bedside ultrasound by EM physician followed by confirmatory test (radiology US/CT/MRI/laparotomy)	Presence of AAA defined as abdominal Aorta diameter > 3cm	EUS-AA in a symptomatic population for AAA is 100% sensitive and 98% specific.	Study size, no blinding.
Costantino TG, Bruno EC, Handly N, Dean AJ Nov 2005 USA	238 patients, Diagnostic cohort study. Operators were 3rd year EM residents.	Diagnostic cohort study. Operators were 3rd year EM residents.	AAA defined as > 3cm on USS	EM residents with appropriate training can accurately determine the presence of AAA	Size, operator skill, possible selection bias.
Bentz, Jones Oct 2006 Review (BestBET)	Review	Review	Review	ED bedside ultrasound is sensitive and specific	Only 4 papers reviewed.
Dent, Kendall, Boyle, Aug 2007 UK	120 patients prospective cohort study. All patients who underwent ED USS in 1 year were included.	Prospective cohort study. All patients who underwent ED USS in 1 year were included.	Presence of AAA > 3cm on USS or death from ruptured AAA.	Emergency ultrasound scanning by UK emergency physicians has high sensitivity (96.3%) and specificity (100%)for identifying AAA	Study size
Vidakovic R, Feringa HH et al. Oct 2007 Netherlands	146 patients, prospective study	prospective study	AAA defined as > 3 cm	Ultrasound can effectively identify patients with AAA. USS Sensitivity 90% and specificity 90% compared to CT	Size, operator skill.

Comment(s)

Three studies and one review (A BestBET – Accuracy of Emergency Department Ultrasound scanning in detecting AAA) looked at the accuracy of Emergency Medicine bedside ultrasound in the evaluation of AAA. All these papers showed that bedside ultrasound was both sensitive and specific for the diagnosis of AAA.

No papers directly compared the suitability of ultrasound vs CT.

However if a patient is being considered for operative treatment of the AAA then ultrasound alone has limitations. One paper listed the limitations as being:

Not accurate enough for pre operative evaluation

Not accurate in obese patients

In aneurysms with proximal extension assessment of thoracic aorta is difficult

Two other articles comment on the desirability of CT before operative intervention, suggesting that Ultrasound alone is insufficient for endovascular surgery planning and that CT should be mandatory before a patient goes to the operating theatre.

Clinical Bottom Line

In the hands of an experienced operator Emergency Department bedside ultrasound is both sensitive and specific; it is also quick, easy and cheap. If the patient is being considered for operative intervention then a CT should be considered.

References

1. Wanhainen A, Bergqvist D, Björck M Measuring the abdominal aorta with ultrasonography and computed tomography – difference and variability. Eur J Vasc Endovasc Surg. 2002 Nov;24(5):428-34
2. Taval VS, Graf CD, Gibbs MA. Prospective study of accuracy and outcome of emergency ultrasound for aortic aneurysm over two years. Acad Emerg Med. 2003 Aug;10(8):867-71.
3. Costantino TG, Bruno EC, Handly N, Dean AJ. Accuracy of emergency medicine ultrasound in the evaluation of abdominal aortic aneurysm. J Emerg Med. 2005 Nov;29(4):455-60.
4. Bentz S, Jones J. Towards evidence based medicine:bestBETS from the Manchester Royal Infirmary. Accuracy of emergency department ultrasound scanning in detecting abdominal aortic aneurysm. Emerg Med J. 2006 Oct;23(10):803-4.
5. Dent B, Kendall RJ, Boyle AA, Atkinson PR. Emergency ultrasound of the abdominal aorta by UK emergency physicians: a prospective cohort study. Emerg Med J. 2007 Aug;24(8):547-9.
6. Vidakovik R, Feringa HH, Kuiper RJ, Karagiannis SE, Schouten O, Dunkelgrun M, Hoeks SE, Bom N, Bax JJ, Neskovic AN, Poldermans D. Comparison with computed tomography of two ultrasound devices for diagnosis of abdominal aortic aneurysm. Am J Cardiol 2007 Dec15;100 (12):1786 91.