Screening for abdominal aortic aneurysm

INTRODUCTION — An aneurysm is a focal dilation of a blood vessel with respect to the original or adjacent artery. An abdominal aortic aneurysm (AAA) is defined as a dilated aorta with a diameter at least 1.5 times the diameter measured at the level of the renal arteries. In most individuals, the diameter of the normal abdominal aorta is approximately 2.0 cm (range 1.4 to 3.0 cm). For practical purposes, an AAA is diagnosed when the aortic diameter exceeds 3.0 cm [1].

The majority of aneurysms never rupture, but when they do, sudden death from retroperitoneal or intraperitoneal exsanguination is usual unless surgery or endovascular repair is performed immediately. Acute AAA rupture is one of the most dramatic emergencies in medicine, particularly because it often masquerades as another problem. In the United States, ruptured AAA is estimated to cause 4 to 5 percent of sudden deaths [2].

Screening is a strategy of performing a test to detect a problem in an asymptomatic person. The decision to screen an individual for AAA must take into consideration the likelihood that an AAA will be detected and that the discovery of an AAA will result in an action that will reduce the risk of AAA rupture and death. The concept of screening is distinct from the incidental discovery of a previously undiagnosed AAA when abdominal and pelvic ultrasonography, computed tomography (CT), and magnetic resonance imaging (MRI) are used to evaluate abdominal and back symptoms. (See "Management of asymptomatic abdominal aortic aneurysm", section on 'Introduction' and "Management of asymptomatic abdominal aortic aneurysm".)

Issues related to screening for AAAs will be reviewed here. Details regarding the clinical manifestations, diagnosis, and treatment of AAAs are presented separately. (See "Clinical features and diagnosis of abdominal aortic aneurysm" and "Management of asymptomatic abdominal aortic aneurysm", section on 'Introduction'.)

EPIDEMIOLOGY AND RISK FACTORS — The epidemiology and risk factors related to abdominal aortic aneurysm (AAA) are discussed in detail elsewhere. (See "Epidemiology, risk factors, pathogenesis, and natural history of abdominal aortic aneurysm", section on 'Risk factors for the development of AAA'.)

In summary, the most important risk factors for AAA are older age, smoking, male sex, and family history of AAA:

●The prevalence of AAAs is low in individuals under the age of 50 but then increases significantly with age [1,3,4]. Most screening studies show that AAA occurs in approximately 3 to 5 percent of men over the age of 60, although some studies have reported a prevalence as high as 9 percent [5-10]. However, most of these aneurysms are ≤4.0 cm in diameter. Aneurysms over 4.0 cm in diameter are present in about 1 percent of men between the ages of 55 and 64; the prevalence increases by 2 to 4 percent per decade thereafter [3,4].

●AAAs occur less commonly in females than in males [11,12]. A meta-analysis of eight studies of women 60 years of age or older performed since 2000 found that the prevalence in women ranges from 0.37 to 1.53 percent and that the prevalence increases with age from 0.43 percent in those between 61 and 70 years, to 1.15 per cent in those between 71 and 80 years, to 1.68 per cent in those over the age of 80 years [13].

●There is a dose-dependent association between smoking and risk for developing AAA, from an odds ratio (OR) of 2.6 for those who smoke <0.5 pack per day (PPD) for 10 years to an OR of 12.1 for those smoking >1 PPD for >35 years [14]. The lifetime risk for AAA is 10.5 percent in persons who currently smoke [11].

●A positive family history also increases the risk of AAA by two- to fourfold [15-18].

Other predictors of AAA include hypertension, coronary artery disease, and peripheral artery disease, whereas diabetes is negatively associated with AAA [5].

NATURAL HISTORY AND MANAGEMENT — Observations regarding the natural history of abdominal aortic aneurysms (AAAs) include the following (see "Management of asymptomatic abdominal aortic aneurysm", section on 'Aneurysm diameter and rupture risk'):

●Aneurysms less than 4.0 cm in transverse diameter are unlikely to rupture in the next five years [19-21].

●The five-year overall cumulative rupture rate of incidentally diagnosed aneurysms in population-based samples is 25 to 40 percent for aneurysms larger than 5.0 cm, compared with 1 to 7 percent for aneurysms 4.0 to 5.0 cm [19,22-24].

●The 30-day case-fatality rate previously was reported as 45 to 50 percent when emergency surgical repair was performed on patients with ruptured aneurysms who survive long enough to come to medical attention. More contemporary studies, which were undertaken to compare endovascular to surgical repair, have reported 35 to 40 percent day mortality rates, with no significant difference between the method of repair [25-27].

Management options for patients with an asymptomatic AAA include surgery, endovascular repair with stent grafts, and watchful waiting. (See "Management of asymptomatic abdominal aortic aneurysm" and "Endovascular repair of abdominal aortic aneurysm" and "Management of asymptomatic abdominal aortic aneurysm", section on 'Introduction'.)

SCREENING TESTS — Asymptomatic abdominal aortic aneurysms (AAAs) can be detected on physical examination or by imaging studies. Abdominal ultrasonography is considered the screening modality of choice for AAAs because of its high sensitivity and specificity as well as its safety and relatively low cost.

Abdominal ultrasonography — Ultrasonography has been used as the screening modality in the large randomized trials of screening for AAA. With a sensitivity of 95 to 100 percent and a specificity of nearly 100 percent [28-31], ultrasonography has superb test characteristics for diagnosing and following an AAA. (See "Clinical features and diagnosis of abdominal aortic aneurysm", section on 'Imaging asymptomatic patients'.)

Physical examination — Physical examination in a patient with an AAA may reveal a pulsatile mass in the epigastrium; the aorta bifurcates at the umbilicus [32]. (See "Clinical features and diagnosis of abdominal aortic aneurysm", section on 'Abdominal palpation'.)

Use of abdominal palpation for screening purposes has been evaluated in several populations. Using ultrasonography as the gold standard, the sensitivity of abdominal palpation varies depending on the size of the aneurysm and the patient’s body habitus [32,33]. Sensitivity increases with the size of the aneurysm and decreased abdominal girth. In a review of 15 studies of patients not known to have AAA, pooled analysis found that the sensitivity was 29 percent for AAAs 3.0 to 3.9 cm, 50 percent for aneurysms 4.0 to 4.9 cm, and 76 percent for aneurysms 5.0 cm or greater. In another study, sensitivity was 91 percent in subjects with an abdominal girth <100 cm and 53 percent for patients with a girth of >100 cm [32]. Physical examination findings require imaging verification.

Other imaging modalities — AAAs may be seen incidentally on plain films of the abdomen, abdominal computed tomography (CT), and magnetic resonance imaging (MRI). Both CT and MRI are highly accurate tests for AAAs but are not generally performed for screening as they are more expensive than abdominal ultrasonography, expose the patient to radiation in the case of CT scanning, and are often lengthier and more difficult for the patient in the case of MRI. However, nearly two-thirds of aneurysms leading to endovascular or surgical repair are detected as incidental findings on imaging studies (most often CT or MRI) that are performed for other indications [2]. (See "Clinical features and diagnosis of abdominal aortic aneurysm", section on 'Diagnosis'.)

EFFECTIVENESS OF SCREENING

Effectiveness — One-time screening with ultrasound for abdominal aortic aneurysm (AAA) has been shown to be effective in reducing AAA-related mortality and AAA rupture in men 65 years and older [34-39]. AAA screening is also associated with increased elective AAA operations and decreased emergency AAA operations.

The effectiveness of one-time screening in women has not been demonstrated. It is also not known whether rescreening in men is effective.

The effectiveness of utilizing the Centers for Medicare and Medicaid Services (CMS) criteria for screening has been evaluated in a retrospective review [40]. This study was based on the eligibility criteria for coverage by CMS, which are for a one-time screening with ultrasound in males between 65 and 75 years of age who smoked at least 100 cigarettes, and in males or females with a family history of AAA [41,42]. These criteria are based on the US Preventive Services Task Force (USPSTF) recommendations [43]. In the observational study of patients in the United States using the National Inpatient Sample from 2004 to 2015, 68 percent of 65,125 patients who presented with ruptured AAAs and 59 percent of 461,191 patients who had repairs of AAAs did not meet CMS criteria for screening [40]. Of the patients who did not qualify, 63 percent were over 75 years of age, 24 percent were less than 65 years, and 36 percent were women. It is possible, however, that AAA would have been detected earlier in men over the age of 75 had screening been conducted between ages 65 and 75.

●One-time ultrasound screening in men – A 2016 systematic review evaluated the effect of one-time ultrasound screening compared with no screening/usual care in men age 64 to 83 years [35]. In pooled analysis of four randomized trials including approximately 125,500 men [8,10,12,44-47], one-time ultrasound screening reduced AAA-related mortality beginning three to five years after screening (absolute risk reduction [ARR] 0.13 percent, risk ratio [RR] 0.57, 95% CI 0.44-0.77), and persisting at 13 to 15 years (ARR 0.47 percent, RR 0.58, 95% CI 0.39-0.88). Total mortality was not significantly reduced at three to five years (RR, 0.94, 95% CI 0.88-1.02), but the effect became marginally significant at longer follow-up times and persisted up to 13 to 15 years of follow-up. There were twice as many elective operations for AAA and half as many emergency AAA operations in the invited-to-screening group compared with the control group at all time intervals measured, up through 15 years after screening [35].

A 2019 meta-analysis of five studies, including the four studies mentioned above, and the Viborg Vascular (VIVA) study [37], comprising 175,085 men age 64 to 83 years with a mean 10.6 years of follow-up found that ultrasound screening reduced AAA-related mortality (RR 0.65; 95% CI, 0.48-0.89), all-cause mortality [38] (RR 0.97, 95% CI 0.96-0.99), and emergency AAA repair (RR 0.64, 95% CI 0.46-0.91). The number needed to screen to prevent one AAA-related death per 10 years ranged from 209 to 769 individuals [38].

●Repeat ultrasound screening in men – The effectiveness of repeat ultrasound screenings compared with one-time screening is uncertain. In one pooled analysis of three observational studies in which men with aortic diameter <30 mm were invited to rescreening at variable intervals (ranging from two to five years) [48-50], the AAA incidence was 2.3 percent (95% CI 0.4-4.1 percent) at 4 to 10 years of follow-up [35]. A systematic review by the USPSTF found that during rescreening of individuals with aortas <3.0 cm, 0 to 2 percent and 0 to 15 percent grew to >5 cm at 5 and 10 years, respectively, and that AAA-related mortality at 5 to 12 years was <3.0 percent [39].

●One-time ultrasound screening in women – Only one study has evaluated population-based ultrasound screening versus no screening for AAA in women [51]. Screening had no effect on AAA-related mortality (0.06 versus 0.04 percent) after five years of follow-up or AAA rupture (0.2 versus 0.2 percent) at 10-year follow-up. (See 'Epidemiology and risk factors' above.)

Screening high-risk populations — A positive smoking history identifies a higher-risk population, particularly in older males, and may provide a means to narrow the screening group.

A modeling study found that one-time screening of men aged 65 to 74 years with a history of ever smoking would account for 89 percent of the anticipated reduction in AAA-related mortality [52]. Modeling studies have also found that screening strategies that incorporate only the risk factors of age, sex, and lifetime smoking history outperform strategies that consider other risk factors. In a retrospective observational study, adherence to the USPSTF criteria that include smoking was associated with a higher proportion of ultrasound studies positive for AAA, and the AAAs detected were smaller than those of a group selected with less adherence to these guidelines [53]. The efficacy of screening for AAA in populations using other risk factors (eg, family history, hypertension) has not been well studied [35].

Cost-effectiveness — An early cost-effectiveness analysis based upon relatively short-term (four-year) follow-up of the Multicentre Aneurysm Screening Study (MASS) trial data suggested a high cost for a quality-adjusted life-year (QALY) over the initial four years [54]. Subsequent data indicate incremental cost-effectiveness with longer follow-up, as would be anticipated with major expense upfront for surgical intervention and sustained long-term benefit [45,55-58]. Cost-effectiveness still remains in modeling studies that account for the decreasing prevalence of AAA and newer surgical approaches [57-59].

Based on seven-year follow-up in one study, cost-effectiveness in men was estimated at USD $7600 per life-year gained based on all-cause mortality and $19,500 per life-year gained based on AAA mortality [55]. In a nationwide screening study from Sweden, data were obtained from 302,957 men representing 84 percent of those invited to participate in screening from 2006 through 2014 [60]. The prevalence of screening-detected AAA was 1.5 percent. After a mean of 4.5 years, 29 percent of patients with AAA had undergone endovascular or surgical repair. Screening significantly reduced the incidence of AAA-specific mortality (mean 4 percent per year of screening). The number needed to screen to prevent one premature death was 667, and the number needed to repair to prevent one premature death was 1.5. With a total population of 9.5 million, the Swedish national AAA-screening program was predicted to prevent 90 premature deaths from AAA annually and gain 577 QALYs. The incremental cost-efficiency ratio was estimated to be EUR €7770 (USD $8634) per QALY.

HARMS FROM SCREENING — Abdominal ultrasonography has no known inherent risks. Potential harms from screening for abdominal aortic aneurysm (AAA) include psychological distress and adverse outcomes from management of the AAA, such as increased number of procedures among patients with small AAAs [61,62].

Psychological distress — Psychological harm from screening may be a concern in patients found to have small AAAs that do not require immediate intervention. Several studies found no adverse effect of screening on quality of life (QOL) [63-65]. In a relatively small study from Denmark, men who were randomized to screening initially had lower QOL scores than those not invited to screening. Following screening, their QOL increased beyond that of the controls; however, men found to have a small AAA had lower QOL scores than those not undergoing screening, mainly related to poorer health perception [66]. Lower QOL scores persisted during the period of conservative management but improved in those who underwent surgical repair. In the Multicentre Aneurysm Screening Study (MASS), there were no differences in anxiety or depression between those who screened negative and those who screened positive when assessed six weeks after screening. Among those who screened positive, however, there were slightly lower scores on the physical and mental subscales of the SF-36, and lower self-rated health as measured by the EQ-5D. Twelve months after screening or surgery, there were no differences between the groups in mood, physical or mental subscale of SF-36, or EQ-5D-weighted health index [8,66].

Increased number of procedures — Pooled analysis of screening studies have shown a greater number of procedures in patients undergoing screening than in control groups, as would be expected [39]. One study, however, found that almost 40 percent of AAA repaired in men in the United States between 2005 and 2012 were less than 5.5 cm [62].

Complications of treatment — Complications of AAA repair are common and can be severe [67]. (See "Complications of endovascular abdominal aortic repair".)

Patients who undergo screening and are managed with endovascular or surgical repair are at risk for immediate harms (procedural complications, hospitalization, death), while harm from an AAA rupture would occur at some future point in time. The perioperative (30-day) mortality rate with elective AAA endovascular repair in major randomized trials varied from 0.5 to 2.0 percent, and with elective surgical repair from 2.4 to, in some instances, as high as 5.8 percent, depending upon comorbidity factors and the type of procedure [68-74].

The relative mortality in patients undergoing elective open surgery compared with endovascular repair is discussed in more detail elsewhere. (See "Management of asymptomatic abdominal aortic aneurysm", section on 'Open versus endovascular aneurysm repair' and "Endovascular repair of abdominal aortic aneurysm".)

OUR APPROACH TO SCREENING — Careful consideration of risk factors is warranted when determining whether to screen for abdominal aortic aneurysm (AAA).

Risk stratification — The main risk factors for development of AAA are age, sex, smoking, and family history. The combination of male sex and age ≥65 years, and either smoking >100 cigarettes in a lifetime or having a family history of AAA repair or rupture, places a patient at high risk of AAA. Among women, the combination of age >65 years and a family history of AAA elevates risk somewhat above the average range.

Shared decision-making — It is important to explore patient preferences and to explain the potential benefits and harms of screening. An abdominal ultrasound is a simple test that does not itself carry risks to the patient. However, the test may detect a small aneurysm for which regular follow-up will be recommended, which may result in anxiety for the patient. Many small aneurysms will never grow sufficiently to warrant repair, and, for those patients, knowing of an AAA may cause worry and may or may not have been of benefit, depending in part on whether the patient makes medication or lifestyle changes (eg, smoking cessation) that could affect morbidity or mortality from other diseases. However, some AAAs will grow, and the patient may then choose to have elective repair and thus avoid an AAA rupture with its significant risk of mortality.

Screening high-risk patients — We recommend one-time screening for AAA with abdominal ultrasonography in men ages 65 to 75 who have ever smoked. We also suggest one-time screening with abdominal ultrasonography in men ages 65 to 75 who have a first-degree relative who required AAA repair or died from AAA rupture. We offer screening to women who have a strong family history of either AAA repair or death due to AAA rupture, basing the decision to screen upon their values and preferences. Screening generally is not indicated for other women, although data are limited.

SOCIETY GUIDELINE LINKS — Links to society and government-sponsored guidelines from selected countries and regions around the world are provided separately. (See "Society guideline links: Aortic and other peripheral aneurysms".)

FUNDING

Medicare coverage in the United States — Among the eligibility criteria for coverage by the Centers for Medicare and Medicaid services (CMS) in the United States for a one-time ultrasound study looking for abdominal aortic aneurysm (AAA), the following clinical criteria may be included [41,42]:

●Males between 65 and 75 years of age who smoked at least 100 cigarettes

●Males or females with a family history of AAA

United Kingdom National Health Service — In the United Kingdom, a National Health Service AAA Screening Program (NAAASP) has been funded to screen 65-year-old men for AAAs in England, with full implementation involving 40 local programs offering screening [75]. It is estimated that 300,000 new men will be invited for screening annually.

INFORMATION FOR PATIENTS — UpToDate offers two types of patient education materials, "The Basics" and "Beyond the Basics." The Basics patient education pieces are written in plain language, at the 5^th to 6^th grade reading level, and they answer the four or five key questions a patient might have about a given condition. These articles are best for patients who want a general overview and who prefer short, easy-to-read materials. Beyond the Basics patient education pieces are longer, more sophisticated, and more detailed. These articles are written at the 10^th to 12^th grade reading level and are best for patients who want in-depth information and are comfortable with some medical jargon.

Here are the patient education articles that are relevant to this topic. We encourage you to print or e-mail these topics to your patients. (You can also locate patient education articles on a variety of subjects by searching on "patient info" and the keyword(s) of interest.)

●Basics topic (see "Patient education: Abdominal aortic aneurysm (The Basics)")

●Beyond the Basics topic (see "Patient education: Abdominal aortic aneurysm (Beyond the Basics)")

SUMMARY AND RECOMMENDATIONS

●Undetected abdominal aortic aneurysm (AAA) commonly presents catastrophically with fatal rupture. (See "Management of asymptomatic abdominal aortic aneurysm".)

●Abdominal ultrasonography is a highly sensitive and specific screening test for AAA. (See 'Abdominal ultrasonography' above.)

●Screening for AAA in men over age 65 is associated with a decreased risk of AAA-related mortality; however, any absolute benefit on overall mortality is likely to be small in people at no increased risk for AAA. (See 'Effectiveness of screening' above.)

●Screening for AAA may lead to psychological distress, particularly in those found to have small AAAs that will be managed conservatively. (See 'Psychological distress' above.)

●When a clinician discusses with a patient whether to screen for AAA with ultrasound, it is important to explore patient preferences and to include both the potential benefits and the harms of screening. (See 'Effectiveness of screening' above and 'Harms from screening' above.)

●We recommend one-time screening for AAA with abdominal ultrasonography in men ages 65 to 75 who have ever smoked (Grade 1A).

●We also suggest one-time screening for AAA with abdominal ultrasonography in men ages 65 to 75 who have a first-degree relative who required AAA repair or died from AAA rupture (Grade 2C). (See 'Screening high-risk populations' above.)

●We offer screening to women who have a strong family history of either AAA repair or death due to AAA rupture, basing the decision to screen upon their values and preferences. Screening is otherwise generally not indicated for women. (See 'Our approach to screening' above and 'Screening high-risk patients' above.)

ACKNOWLEDGMENT — The UpToDate editorial staff acknowledges Emile R Mohler, III, MD (deceased), who contributed to an earlier version of this topic review.