Tuesday, February 7, 2023
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Abdominal Aortic Aneurysm Rupture Imaging

Overview

Abdominal aortic aneurysms (AAAs) are segmental dilatations of the aortic wall that cause the vessel to be larger than 1.5 times its normal diameter or that cause the distal aorta to exceed 3 cm. These can continue to expand and rupture spontaneously, exsanguinate, and cause death. AAA rupture is an important cause of unheralded deaths in people older than 55 years. (See also Abdominal Aortic Aneurysm Imaging and Abdominal Aortic Aneurysm.)

See the AAA image below.

Contrast-enhanced abdominal CT in an elderly patie

Contrast-enhanced abdominal CT in an elderly patient who presented with severe back pain but was hemodynamically stable. CT reveals an abdominal aortic aneurysm (AAA) with eccentric mural thrombus. A disruption of the calcific rim of the AAA toward the left quadrant appears with adjacent isoattenuating soft tissue anterior to the left psoas muscle. Clinical and radiologic findings are consistent with a diagnosis of contained AAA rupture with left retroperitoneal hematoma.

Guidelines and recommendations

The following are screening recommendations by Kaiser Permanente for AAA by ultrasonography in the general population
:

One-time screening for AAA by ultrasonography is recommended in men aged 65 to 75 years.

It is an option to limit AAA screening to men aged 65 to 75 years who have never smoked.

Routine screening for AAA in women is not recommended.

The following are screening recommendations by Kaiser Permanente for AAA in adults with a family history of AAA
:

For men aged 50 and older with a known positive family history of aortic aneurysm in a first-degree relative, AAA screening is recommended.

The guideline development team makes no recommendation for or against screening women with a positive family history of AAA.

Systematically collecting information on aortic aneurysm family history is not recommended.

Preferred examination

Ideally, in a hemodynamically stable patient, nonenhanced and enhanced helical or spiral CT of the thorax, abdomen, and pelvis should be expeditiously performed. This examination provides key information about the extent of aneurysmal disease, and it can be used to confirm and localize the site of rupture, as shown in the image below.

Contrast-enhanced abdominal CT in an elderly patie

Contrast-enhanced abdominal CT in an elderly patient who presented with severe back pain but was hemodynamically stable. CT reveals an abdominal aortic aneurysm (AAA) with eccentric mural thrombus. A disruption of the calcific rim of the AAA toward the left quadrant appears with adjacent isoattenuating soft tissue anterior to the left psoas muscle. Clinical and radiologic findings are consistent with a diagnosis of contained AAA rupture with left retroperitoneal hematoma.

In the patient with an unstable presentation, an emergency operation is indicated. Time may permit only rapid bedside ultrasonography (US) and Doppler study of abdominal aorta and iliac arteries to confirm the presence of aneurysms.

The maximal aneurysm diameter is adequately assessed by using B-mode ultrasonography, CT scanning, and MRI.
Aortography reveals only the lumen of the abdominal aortic aneurysm because laminated clot obscures the outer limit of the aneurysm wall. Therefore, it often causes underestimation of the true aortic diameter.

Key pathobiologic processes of AAA progression and rupture include neovascularization, necrotic inflammation, microcalcification, and proteolytic degradation of the extracellular matrix. Future ancillary imaging techniques may therefore employ the use of MRI with ultrasmall superparamagnetic particles of iron oxide that may identify and track hotspots of macrophage activity. Positron emission tomography (PET) with a variety of targeted tracers may detect areas of inflammation, angiogenesis, hypoxia, and microcalcification.

Screening

The U.S. Preventive Services Task Force (USPSTF) recommends one-time screening for AAA by ultrasonography in men aged 65 to 75 who have ever smoked (B recommendation; at least fair evidence). American College of Cardiology/American Heart Association guidelines include a class I, level B recommendation that patients with infrarenal or juxtarenal AAAs measuring 5.5 cm or larger undergo repair to eliminate the risk of rupture, and a class I, level A recommendation that patients with infrarenal or juxtarenal AAAs measuring 4.0 to 5.4 cm in diameter be monitored by ultrasound or CT scans every 6 to 12 months to detect expansion.
For women, the USPSTF issued a grade D recommendation againstroutine screening for AAA, since the available data show a low prevalence of large AAAs and no reduction in mortality in females.

In the Cardiovascular Health Study, aneurysm dilatation of 3 cm or greater on a single screening ultrasound exam identified 68% of all AAA repairs over the next 10 years and 6 of the 10 AAA-related deaths in 4% of the total population; dilatation of 2.5 cm or more identified 91% of all AAA repairs and 9 of the 10 deaths in 10% of the total population.

Postoperative follow-up

Little objective information is available to guide long-term surveillance after successful emergency repair of AAA rupture. There are data from the prospective Canadian Aneurysm Study in the 1990s, which found that in approximately 15% of patients who underwent elective open repairs, another thoracic or abdominal aneurysm was subsequently detected; a similar percentage of patients had significant iliac aneurysms (following tube AAA graft).
These findings led the investigators to recommend routine CT from thorax to pelvis after 5 years.

Patients who have undergone endovascular aneurysm repair require more frequent and lifelong follow-up. Imaging studies are typically performed 1, 6, and 12 months after EVAR and annually thereafter.
CT angiography is most commonly used.
However, studies have found contrast-enhanced ultrasound to be comparable to CT angiography.
MRI and magnetic resonance angiography have also been used for surveillance, as has digital subtraction angiography, although this technique is now not as necessary.
Intermittent surveillance of the thoracic aorta should be performed, particularly in patients with preexisting aortic ectasia or dilatation elsewhere or for patients (or their siblings) with connective tissue disease (eg, Marfan or Ehlers-Danlos syndromes), bicuspid aortic valve, or familial aortopathies.

Surveillance imaging should be considered especially for suggestive symptoms, even for grafts older than 10 years, because surgical polyester graft degradation is not uncommon and has been documented up to 4 decades postoperatively.

Limitation of techniques

CT or MRI can rapidly provide detailed information about the blood vessels and their surrounding structures for treatment planning; the choice between them can be based on which is faster locally. Occasionally, however, these examinations may require too much time for them to be suitable for use in patients whose condition is unstable. Also, when contrast material is used in conjunction with CT to delineate blood-filled structures, it poses a risk of acute renal failure, particularly in hypovolemic elderly patients who may already have baseline nephrosclerosis or diabetic nephropathy.

Sonography is a quick and convenient modality, but it is much less sensitive and specific for the diagnosis of aneurysmal rupture. The absence of sonographic evidence of rupture does not rule out this entity if clinical suspicion is high.

Patient education

For patient education information, see the Circulatory Problems Center, as well as Aortic Aneurysm.

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