Investigations
1st investigations to order
aortic ultrasound
Test
If the patient has a suspected ruptured or symptomatic AAA, get immediate help from a senior colleague to organise immediate imaging (with either bedside aortic ultrasound or contrast-enhanced computed tomography angiography [CTA]).[3][42] Do not delay diagnosis and management of a ruptured AAA while waiting for the results of imaging.[69]
Guidelines differ in their recommendations for diagnostic imaging for suspected ruptured or symptomatic AAA. In the UK, the National Institute for Health and Care Excellence (NICE) recommends bedside aortic ultrasound as first line.[42] Contrast-enhanced CTA is recommended as first-line imaging, over bedside aortic ultrasound, by some guidelines.[3][42][69]
Discuss the patient with a regional vascular service if:[42][69]
AAA is confirmed on bedside aortic ultrasound
OR
Bedside aortic ultrasound is not immediately available or is non-diagnostic but AAA is still suspected.
Bedside ultrasound can confirm the presence and size of an AAA, but cannot definitively rule out a ruptured AAA.[69]
A normal-sized aorta viewed on ultrasound in the presence of severe hypotension does not exclude the diagnosis of ruptured AAA or other abdominal pelvic aneurysm.[69] Consider contrast-enhanced CTA for these patients. See Computed tomography angiography (CTA) below.
However, ultrasound confirmation of AAA in a patient with symptoms or signs of rupture supports the diagnosis of a ruptured AAA.[69]
Aortic ultrasound is also used for:
Surveillance of asymptomatic AAA to guide treatment decisions with either surgical repair or conservative management[3][42]
Follow-up after surgery with endovascular aneurysm repair (EVAR) (using colour duplex ultrasound).[42]
The ultrasound is performed perpendicular to the aortic axis as oblique views may overestimate the true aortic diameter.[2] Size of aneurysm is measured inner-to-inner maximum anterior-posterior aortic diameter.[42]
Unfortunately, ultrasound offers little utility in imaging aneurysms close to the origins of, or proximal to, the renal arteries.[79][80]
Investigations to consider
computed tomography angiography (CTA)
Test
Once the diagnosis of AAA is made, contrast-enhanced CTA is used to assess the extent and anatomy of disease and to assist with operative planning (open or endovascular).[3][42][77]
It is the first choice for pre- and intraoperative planning; 0.5 mm slices are desirable and 3D reconstruction is essential for accurate planning.[82]
It is useful in diagnosing aortic aneurysms close to the origins of, or proximal to, the renal arteries.[80][81]
Contrast-enhanced CTA is the recommended definitive imaging modality for AAA rupture, and is also recommended as first-line imaging, over bedside aortic ultrasound, by some guidelines.[3][42][69] Do not delay diagnosis and management of a ruptured AAA while waiting for the results of imaging.[69]
CTA should be performed in a haemodynamically stable patient, and preferably after transfer to a regional vascular centre if the clinical diagnosis of ruptured AAA is clear without CTA.[3][42][69]
It should also be considered for definitive diagnosis of ruptured AAA if a normal-sized aorta is viewed on ultrasound in the presence of severe hypotension.[69] In this scenario, ultrasound does not exclude the diagnosis of ruptured AAA or other abdominal pelvic aneurysm.[69]
CTA is also important for follow-up after surgical repair with EVAR.[3][42]
Result
AAA is defined as abdominal aortic dilation of >1.5 times the expected anterior-posterior diameter of that segment, given the patient's sex and body size; the most commonly adopted threshold is a diameter of 3 cm or more[3][4]
signs of AAA rupture include retroperitoneal haematoma, discontinuity of the aortic wall, or extravasation of contrast into the retroperitoneal cavity[13][81]
cross match
Test
Indicated if ruptured or symptomatic AAA is suspected.
Result
necessary for blood transfusion
clotting screen
Test
Indicated if ruptured or symptomatic AAA is suspected.
Result
baseline levels
erythrocyte sedimentation rate (ESR)/C-reactive protein (CRP)
Test
Suggests inflammatory AAA.[3]
Result
elevated
FBC
Test
May show anaemia if there is haemorrhage due to ruptured AAA.
Leukocytosis and a relative anaemia on FBC with positive blood cultures are indicative of infectious AAA.
Result
leukocytosis, anaemia
blood cultures
Test
Leukocytosis and a relative anaemia on FBC with positive blood cultures are indicative of infectious AAA.
Result
positive
positron emission tomography-computed tomography (PET-CT)
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