Iliac artery aneurysm

INTRODUCTION — Aneurysmal degeneration of the iliac arteries (common, internal, external iliac) can occur in isolation or in association with other large vessel aneurysms (eg, abdominal aorta, femoral artery).

Iliac artery aneurysms (IAAs) are often diagnosed as a result of screening or other imaging studies. Symptoms do not typically occur unless the aneurysm is large and are primarily related to compression of surrounding structures. Like abdominal aortic aneurysms, IAAs have a propensity for life-threatening rupture as diameter increases. On occasion, aneurysm thrombosis may lead to peripheral thromboembolism or acute limb ischemia.

The management of asymptomatic IAAs depends upon the size of the aneurysm, the presence or absence of coexisting abdominal aortic aneurysm or other aneurysm (eg, femoral, popliteal), and patient comorbidities. Patients with symptomatic IAAs should be referred for prompt vascular evaluation and repair.

The diagnosis and management of IAAs will be reviewed here. The surgical and endovascular management of IAAs is reviewed elsewhere. (See "Surgical and endovascular repair of iliac artery aneurysm".)

ANATOMIC ISSUES — Seventy percent of iliac aneurysms occur in the common iliac artery, while 20 and 10 percent are found in the internal and external iliac arteries, respectively [1]. Approximately two thirds of patients with IAA have involvement of more than one segment of the iliac arterial tree; one third of IAAs are bilateral [2].

The common iliac arteries are the terminal branches of the abdominal aorta and arise at the level of the fourth lumbar vertebra (figure 1). The common iliac artery bifurcates into the external iliac and internal iliac arteries at the pelvic inlet. The internal iliac artery gives off branches to the pelvic viscera and also supplies the musculature of the pelvis. The external iliac artery passes beneath the inguinal ligament to become the common femoral artery [3].

Definition of iliac aneurysm — As with any vessel, a true IAA is defined as a focal dilation of the artery with a diameter that is increased more than 50 percent compared with the normal diameter of the artery [4]. In males, the common iliac artery normally averages 1.2±0.2 cm, whereas in females it is smaller, averaging 1±0.2 cm. The internal iliac artery averages 0.54±0.15 cm [5]. Based upon these values, for the common iliac artery, an aneurysm is generally present if the artery measures >1.85 cm in males and >1.5 cm in females [6]. An internal iliac artery with a diameter more than 0.8 cm is likely aneurysmal.

EPIDEMIOLOGY AND RISK FACTORS — Solitary iliac artery aneurysms (IAAs) are uncommon. The overall incidence of solitary IAA in the general population is estimated to be approximately 0.03 percent [7]. Solitary IAA represents approximately 0.4 to 1.9 percent of all cases of aneurysmal disease [8]. Isolated IAAs are very rare in the pediatric population and are usually related to connective tissue disorders or infection [9]. The incidence of IAA associated with abdominal aortic aneurysm (AAA) is higher. Given an incidence of AAA of approximately 5 percent based upon screening studies, and that approximately 25 percent of patients with AAA have an IAA, the incidence of IAA associated with AAA in the general population is approximately 1 percent.

Risk factors for degenerative IAA are the similar risk factors for other degenerative large vessel aneurysms (abdominal aortic aneurysm, popliteal aneurysm) and include male sex, being from a White population, advancing age, history of smoking, hypertension, and other risk factors for atherosclerotic disease. (See "Clinical features and diagnosis of abdominal aortic aneurysm", section on 'Risk factors'.)

In a retrospective study evaluating surgical treatment for isolated IAA in 56 patients, 96 percent of the patients were males, 60 percent had a significant smoking history, 79 percent had hypertension, 50 percent had coronary artery disease, and 27 percent had prior AAA repair [10]. In a systematic review that included 981 isolated common IAAs in 879 patients treated with endovascular repair, 91 percent were males, the weighted mean age was 72 years [11]. In an earlier series, hypertension predicted faster iliac artery expansion compared with normotensive patients (0.32 versus 0.14 cm/year) [12].

PATHOGENESIS AND NATURAL HISTORY — The majority of iliac artery aneurysms (IAAs) are true aneurysms that are the result of arterial wall degeneration. Less commonly, a pseudoaneurysm is the cause of iliac artery dilation and can be due to para-anastomotic graft failure following a prior aortic graft repair [6], vascular injury from penetrating mechanisms (gunshot, knife), or iatrogenic injury during hip replacement, lumbar disc surgery, or other pelvic surgery [13,14].

IAAs have also been associated with Behçet syndrome [15], fibromuscular dysplasia [16], Takayasu's arteritis, and other connective tissue disorders [17]. In rare cases, infected aneurysm can develop in the iliac arteries, and organisms including Salmonella, Staphylococcus aureus, Klebsiella, and Candida have been isolated [6,18]. (See "Overview of infected (mycotic) arterial aneurysm".)

Aneurysm formation — True aneurysm formation is due to a loss of the mechanical integrity of the vessel wall due to an altered balance between the production and degradation of the vascular wall constituents [19]. The etiology of this imbalance is multifactorial and likely a complex interplay of inflammatory, immunologic, and potentially mechanical and genetic factors. A common systemic etiology for large vessel aneurysm formation is supported by the occurrence of multiple large vessel aneurysms in the same patient. The pathogenesis of abdominal aortic aneurysm is discussed in detail elsewhere. (See "Management of asymptomatic abdominal aortic aneurysm", section on 'Aneurysm diameter and rupture risk'.)

Aneurysm expansion — The natural history of IAAs (isolated IAA or in association with abdominal aortic aneurysm [AAA]) is continued expansion over time with the observed rate of expansion related to iliac artery diameter on initial diagnosis. Data for the expansion of IAA come mostly from studies evaluating the much more prevalent common IAA. There are few studies relating to the natural history of other IAAs to help guide their management.

Iliac artery aneurysm associated with abdominal aortic aneurysm — IAA is frequently associated with AAA (image 1). Between 15 to 40 percent of patients who present with AAA have at least one IAA [12,20-25]. In a retrospective review of 439 patients with 715 common IAAs, 86 percent had an AAA [12]. Iliac aneurysm was bilateral in 70 percent of those who had an associated AAA.

In a review of 190 patients with AAA, 41 percent of the patients had a concomitant common IAA defined by a diameter >16 mm [25]. In this study, a regression model was developed to determine iliac artery expansion rates. Iliac artery expansion depended upon baseline iliac diameter. A common iliac artery measuring 16 mm could be expected to expand to 25 mm within 10 years, and a 23 mm common iliac artery would reach 35 mm. Expansion of an IAA was more likely in patients who had AAA that also expanded. No correlation was found between AAA expansion rate and common iliac artery (CIA) expansion rate, or AAA diameter and CIA expansion rate. The authors concluded the following:

●A common iliac artery measuring <16 mm when diagnosed and associated with AAA <4 cm could reasonably be reevaluated when intervention for the AAA is planned because of the slower expansion rates.

●A common iliac artery measuring >16 mm should be followed independent of the AAA.

Although this model is helpful in guiding surveillance of small IAAs, it does not predict expansion for common IAA >26 mm. It also does not reflect the impact of smoking and hypertension on common IAA expansion rates.

Other clinical studies have found increased expansion rates for larger versus smaller iliac artery diameters.

●A retrospective review of 201 patients found that after elective open infrarenal abdominal aortic aneurysm repair with a tube graft, aneurysmal common IAAs measuring 19 to 25 mm in diameter expanded more compared with normal caliber common iliac arteries over an average follow-up of 7.1 years (mean expansion 2.4 versus 1.1 mm) [26].

●Expansion of IAAs following endovascular repair of abdominal aortic aneurysm was 1.5 mm for larger (>16 mm) and 1.1 mm with smaller (≤16 mm) iliac arteries over a mean follow-up of 44 months [27].

●Lastly, in a review of 438 patients with 715 common IAAs, 377 patients with 633 common IAAs had current or previously repaired AAA. Expansion rates were measured in 15 percent of the treated iliac aneurysms (n = 104). Of the common IAAs that were monitored for expansion, 51 percent were >3 cm. The median expansion rate for common IAAs >3 cm was 3.2 mm/year [12]

Isolated iliac artery aneurysms — In a retrospective review evaluating aneurysm expansion rates, isolated IAAs <3 cm in diameter expanded at an average rate of 1.1 mm per year, whereas those >3 cm expanded by 2.6 mm per year [28].

Site of aneurysm and association with other aneurysms — Patients with an IAA also have a high incidence of aneurysms in the contralateral iliac artery and femoral arteries. The presence of these other aneurysms, particularly abdominal aortic aneurysm, impacts the management of the IAA. (See 'Indications for repair' below.)

Thus, it is important to perform a full arterial assessment when iliac aneurysm is detected because of the high rate of coexistent aneurysm. (See "Clinical features and diagnosis of abdominal aortic aneurysm" and "Popliteal artery aneurysm".)

CLINICAL PRESENTATION — The clinical manifestations of IAA depend upon its diameter and location [29]. Larger aneurysms (diameter >6 cm) are more likely to be associated with the development of symptoms (compression, thrombosis, thromboembolism) or iliac artery rupture [2,30,31]. In a study of internal IAAs, the mean size at diagnosis was 7.7 cm [2].

Approximately one-half of patients are asymptomatic and the IAA discovered incidentally at the time of abdominal/pelvic imaging for a different indication. Plain abdominal and pelvic radiography may show the calcified wall of an aneurysm in the lower pelvis [6].

IAAs behave more like abdominal aortic aneurysm with symptoms more commonly due to expansion, compression, erosion of surrounding structures, or rupture compared with symptoms related to thrombosis or thromboembolism as is seen with popliteal artery aneurysm.

Most available studies have evaluated symptoms related to common or internal IAA. The clinical presentation of external IAA may be similar. A retrospective review found 11 cases of isolated true external IAAs. Of these, three patients were asymptomatic, three had a painful pulsatile mass, four presented with rupture, and one with peripheral embolization [32]. The diameter of each of the ruptured aneurysms was >4 cm, and there were no cases of acute arterial thrombosis.

Compression of surrounding structures — Symptoms related to compression may lead to one or more of the following clinical manifestations (figure 2) [8,33-36]:

●Compression of the ureter can lead to urinary retention, ureteric colic, pyelonephritis, and renal failure due to ureteral obstruction. (See "Clinical manifestations and diagnosis of urinary tract obstruction (UTO) and hydronephrosis".)

●Compression of the colon can cause pain with defecation, tenesmus, and constipation secondary to rectal compression.

●Compression of the lumbar plexus can result in paresthesia, paresis, sciatic neuralgia, or lumbosacral pain.

Rupture — Reported five-year rupture rates for IAA range from 14 to 70 percent [2], and as many as 33 percent of patients with isolated iliac aneurysms present with rupture [2,8,37]. The average size of ruptured isolated iliac aneurysms is between 5 and 7 cm [2,11,12,30]. The size of ruptured external IAA may be slightly smaller at 4 cm [32].

Iliac aneurysm rupture causes acute abdominal and thigh or groin pain, often accompanied by hemodynamic instability. Retroperitoneal rupture may be contained, but intraperitoneal rupture can lead to rapid exsanguination. Rupture into the rectum, ureter, bladder, iliac veins, and rectus sheath have all been described [38-42]. Rupture into adjacent veins can cause high-output heart failure. (See "Causes and pathophysiology of high-output heart failure".)

Mortality from iliac aneurysm rupture is high with a mortality rate of approximately 30 percent following open repair, with reports ranging from 0 to 60 percent [1,3,43-45]. Worse outcomes are related to a delay in diagnosis [33,46,47]. Endovascular stent grafting for emergency repair has lowered perioperative mortality rates [48]. (See "Surgical and endovascular repair of iliac artery aneurysm".)

Aneurysm thrombosis and thromboembolism — Symptoms related to aneurysm thrombosis or thromboembolism are less common, occurring in 5 to 13 percent of patients.

●In a study that identified 16 aneurysms in 11 patients, only 1 patient presented with distal embolization and there were no cases of thrombosis [49].

●In a review of the literature that identified 94 internal IAAs, thrombosis of the internal iliac artery did not occur [50].

●In a retrospective review of 53 patients with isolated IAA (common and internal), seven patients presented with lower extremity peripheral ischemia. Four patients had iliac aneurysm thrombosis causing symptoms of intermittent claudication, and three patients had peripheral embolization as the cause of ischemia [36].

DIAGNOSIS — The diagnosis of IAA may be suggested in a patient with risk factors or based upon clinical presentation. Although abdominal palpation may demonstrate a pulsatile mass that confirms the diagnosis, a negative examination does not exclude IAA. Imaging is required to definitively exclude IAA and, if an aneurysm is found, accurately determine the extent and dimensions of the aneurysm to guide further management. (See 'Management' below.)

Physical examination — Physical exam including abdominal examination, rectal examination, and a complete peripheral arterial examination is performed to identify suspected IAA based upon the presence of risk factors, or the diagnosis of another large vessel aneurysm.

Physical exam detects a pulsatile mass in up to 70 percent of patients with IAA [2]; however, undetected IAAs with diameters up to 11 cm have been reported [30]. As with the diagnosis of abdominal aortic aneurysm, the sensitivity of abdominal and rectal palpation in detecting IAA is probably dependent upon the size of the aneurysm. In a retrospective review that identified 71 IAAs, a mass was detected on physical examination with abdominal palpation and rectal exam in 70 percent of patients; the mean diameter of IAA was 5.5 cm [2]. In another study in which the mean diameter of IAA was 3.7 cm, physical exam identified the presence of IAA in 55 percent of the patients [49].

An audible bruit can also indicate the presence of IAA. In a review of 53 isolated IAAs, a bruit was present in 18 patients [36]. Only 17 percent of patients in this study had a palpable mass (by abdominal exam in seven patients and rectal exam in two).

Imaging — Imaging provides the diagnosis of IAA in patients with risk factors or physical examination findings suggestive of IAA. Abdominal and pelvic ultrasound is the screening test of choice for asymptomatic patients, whereas for patients with symptoms, abdominal and pelvic computed tomography provides a more accurate diagnosis. The diagnostic accuracy of vascular imaging for iliac aneurysm is based upon sensitivities and specificities measured using these modalities to diagnose other vascular diseases, most notably abdominal aortic aneurysm, which is often coexistent with IAA. Specific considerations for imaging the iliac artery are discussed below. (See "Clinical features and diagnosis of abdominal aortic aneurysm", section on 'Diagnosis'.)

●Ultrasound of the abdomen and pelvis is a good noninvasive technique to demonstrate iliac artery disease, but imaging may be limited if the iliac vessels are tortuous or deep, and overlying bowel gas may obscure the examination [34,51,52]. The precise location of the aneurysm (common, external, internal iliac artery) may be difficult to determine on ultrasound. If the IAA can be adequately imaged with ultrasound, then ultrasound is generally used to follow the aneurysm over time for expansion. (See 'Surveillance ultrasound' below.)

●Computed tomography (CT) angiography (image 2A-B) is very accurate for diagnosing IAAs and provides extensive detail of aorto-iliac anatomy [36]. It also allows characterization of coexistent abdominal aortic aneurysm or other peripheral artery aneurysm. If ultrasound cannot make the diagnosis, we prefer to obtain CT imaging to diagnose suspected IAA [36]. Disadvantages of CT angiography include the need for intravenous contrast and radiation exposure.

●Magnetic resonance (MR) imaging and MR angiography are equal to CT in providing an accurate diagnosis and anatomic detail; however, given its expense and other issues (metal implants, gadolinium-related nephrogenic systemic fibrosis), MR is not typically used as the study to diagnose or follow up IAA.

●Arteriography (image 1) is invasive and inaccurate for determining the true diameter of IAA because thrombus often lines the aneurysm sac, obscuring the true iliac artery diameter.

MANAGEMENT — The management of IAA is based on published outcomes of retrospective reviews and expert consensus (algorithm 1). Ruptured and symptomatic aneurysms are repaired to reduce mortality associated with rupture, relieve symptoms, and reduce the risk of future rupture. Early diagnosis, careful surveillance of small iliac aneurysms, and repair of symptomatic and larger iliac aneurysms reduce the morbidity and mortality associated with IAA. Multiple studies have reported that mortality ranges from 20 to 55 percent for emergency repair of IAA compared with approximately 1 percent for elective repair [12,30,36,43,53].

Asymptomatic IAA is managed conservatively with serial imaging studies or repaired. A conservative approach is appropriate for small asymptomatic IAAs and a subset of patients with symptomatic aneurysm who have a low life expectancy or limited functional status [54]. The decision for elective repair is based on rupture risk, which depends upon aneurysm size and the expected expansion rate of the aneurysm relative to the patient's life expectancy. The presence of other aneurysms and the risk of rupture associated with them, particularly abdominal aortic aneurysm (AAA), also impacts decision making.

All patients with IAA should be treated to manage their risk factors for cardiovascular disease. The management of risk factors associated with IAA is similar to that used to limit the expansion of abdominal aortic aneurysm and is discussed in detail elsewhere. (See "Management of asymptomatic abdominal aortic aneurysm", section on 'Conservative management'.)

Aneurysm diameter — Based on the results of retrospective reviews of ruptured IAA and expert consensus opinion, an IAA diameter of 3 cm is the traditional threshold above which asymptomatic iliac aneurysm repair is recommended [1,2,28,30,55]. However, given the natural history of IAA with relatively slow expansion rates and low rupture rates for iliac aneurysms <3.5 cm, aneurysms up to 3.5 cm can likely be safely observed, but higher quality data are needed before confirming a higher threshold [12,30,36,43,53]. In a systematic review that included 981 isolated common IAA in 879 patients treated with endovascular repair, the weighted mean diameter prior to repair was 4.1 cm and 5.8 for unruptured and ruptured aneurysms, respectively [11]. In an earlier retrospective review of 715 common iliac aneurysms reported a median diameter of 6 cm (438 patients) for ruptured iliac aneurysms and no aneurysm <3.8 cm in diameter ruptured [12]. (See 'Surveillance ultrasound' below.)

Coexistent AAA — If a coexisting AAA is present that meets criteria for repair, an IAA that is smaller than 3 cm may be considered for treatment. In a multicenter study, 147 patients who previously underwent open repair of AAA with a tube graft were included and divided into three groups based upon common iliac artery diameter [56]:

●Group A (n = 59): Normal common iliac artery diameter ≤12 mm

●Group B (n = 53): Ectatic iliac arteries with a diameter that was 12 to 18 mm

●Group C (n = 35): Aneurysmal iliac arteries with a diameter ≥18 mm

After 5.5 years, common iliac arteries in group A or B remained ≤25 mm and no patient experienced significant iliac artery expansion. In group C, 10 of 35 patients had a common iliac artery diameter ≥25 mm; three patients required surgery to treat the IAA during follow-up. If the preoperative iliac artery diameter is ≥25 mm, a bifurcated graft should be used when treating AAA and IAA simultaneously. For patients with a life expectancy of more than eight years, taking into account iliac artery expansion rates (discussed above), repair of AAA with a bifurcated graft is justified for an IAA with a diameter ≥18 mm.

For patients with AAA undergoing endovascular repair, it is essential to provide adequate distal fixation of the iliac limb into the iliac artery. If appropriate apposition of the iliac endograft limb to the common iliac artery cannot be achieved due to aneurysmal dilatation, then the iliac aneurysm should be treated simultaneously. This is usually accomplished by extending the iliac limb of the AAA endograft into the external iliac artery [57]. (See "Surgical and endovascular repair of iliac artery aneurysm".)

Indications for repair — Taking into account expansion rates (which are approximately 1 mm/year for a 1 cm aneurysm and 3 mm/year for a 3 cm aneurysm), risk of rupture and the high mortality rate associated with emergency (20 to 55 versus 1 percent) compared with elective repair, indications for IAA repair include the following [12,30,36,43,53]. (See 'Aneurysm expansion' above and 'Rupture' above.)

●Ruptured IAA – Ruptured IAA is a surgical emergency, and repair should be performed without delay. (See 'Rupture' above.)

●Symptomatic IAA – Patients who present with symptoms generally have larger aneurysms that are at a high risk for rupture, and IAA should be repaired urgently. (See 'Clinical presentation' above.)

●Rapidly expanding IAA – Rapidly expanding IAA (≥7 mm in six months or >1 cm in one year) [12,55]. (See 'Aneurysm expansion' above.)

●Asymptomatic IAA ≥3 cm. (See 'Aneurysm diameter' above.)

●Coexistent AAA repair – Patients with AAA associated with common iliac arteries ≥2.5 cm are treated by using a bifurcated graft rather than a tube graft. In association with endovascular aneurysm repair of AAA, common iliac aneurysms of any size are treated to obtain an adequate distal seal zone. (See 'Coexistent AAA' above.)

Surveillance ultrasound — There are no studies to help guide the follow-up of IAA. Patients who do not have an indication for iliac aneurysm repair should be followed with serial physical examination and computed tomography or B-mode ultrasound at six-month intervals [28]. If a patient has a coexistent AAA, both aneurysms should be followed by the same modality. If the IAA remains stable over several exams, it may be reasonable to undergo follow-up annually.

Computed tomography (CT) is the standard diagnostic technique used to follow IAA but has the disadvantages of exposing the patient to radiation and intravenous contrast. B-mode ultrasonography is a good alternative to CT if the aneurysm can be adequately imaged. Studies comparing the sensitivities of CT and ultrasound specifically for IAA are few. One study found that IAA size may be slightly underestimated using B-mode ultrasound compared with CT scan, but the difference between the modalities was not found to be significant [28]. (See 'Imaging' above.)

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".)

SUMMARY AND RECOMMENDATIONS

●The iliac artery is defined as aneurysmal when a localized diameter is 1.5 times normal artery diameter. True aneurysms involve all layers of the vessel wall, whereas false aneurysms do not. The majority of aneurysms of the iliac arteries are true aneurysms. The common iliac artery is likely to be aneurysmal when it measures >1.85 cm in adult males and >1.5 cm in adult females. An internal iliac artery with a diameter more than 0.8 cm is consistent with aneurysm in most individuals. (See 'Introduction' above and 'Anatomic issues' above and 'Site of aneurysm and association with other aneurysms' above.)

●Iliac artery aneurysms (IAAs) are most closely associated with abdominal aortic aneurysm. Up to 40 percent of patients who present with abdominal aortic aneurysm have at least one IAA. The common iliac artery is affected in 70 percent of patients who have IAA. (See 'Site of aneurysm and association with other aneurysms' above.)

●The risk factors for true aneurysm of the iliac artery are similar to other degenerative large vessel aneurysms and include smoking, hypertension, male sex, advancing age, and other large vessel aneurysm. Other causes are generally due to trauma or iatrogenic instrumentation. (See 'Epidemiology and risk factors' above and 'Pathogenesis and natural history' above.)

●The natural history of IAAs, either isolated or in association with an abdominal aortic aneurysm (AAA), is continued expansion over time. Similar to AAA, expansion rates for IAAs depend upon diameter, with larger aneurysms having greater rates of expansion. (See 'Pathogenesis and natural history' above.)

●Nonruptured IAAs do not usually cause symptoms unless the aneurysm is large enough to compress surrounding structures. Less commonly, patients can present with symptoms of lower extremity ischemia due to arterial obstruction from iliac aneurysm thrombosis or distal embolization of intraluminal thrombus. (See "Popliteal artery aneurysm", section on 'Clinical presentation' and 'Pathogenesis and natural history' above.)

●IAA rupture can be the initial presentation with acute abdominal, thigh, or groin pain, accompanied by hemodynamic instability. Rupture into adjacent structures (eg, rectum, ureter, bladder, iliac vein) can also occur. The average size of ruptured isolated iliac aneurysms is 5.5 cm. Mortality with rupture ranges from 50 to 100 percent with poor outcomes often related to a delay in diagnosis. (See 'Rupture' above and "Surgical and endovascular repair of iliac artery aneurysm".)

●IAAs are often diagnosed incidentally as a result of imaging tests performed in patients being evaluated for other problems such as abdominal or pelvic pain, other aneurysm, or peripheral artery disease. IAA is reliably diagnosed using ultrasonography, computed tomography, or magnetic resonance imaging. (See 'Physical examination' above.)

●Patients with ruptured IAA undergo emergency repair of the aneurysm to reduce mortality. Symptomatic IAA is repaired to relieve symptoms. Patients who have symptoms typically have larger aneurysms and are also at high risk for rupture. (See 'Management' above.)

●For IAA ≥3 cm in diameter, we suggest elective repair over conservative management in patients with a good operative risk and life expectancy (Grade 2C). Patients with IAA <3 cm are typically observed; however, repair of asymptomatic IAA below this threshold may be prudent or required during the course of managing other aneurysmal disease in the aorta or femoropopliteal segments. Rapid aneurysmal expansion (ie, ≥7 mm in six months or >10 mm in one year) increases the risk of IAA rupture and also indicates the need for repair. (See 'Management' above.)

●There are no studies to help guide the follow-up of IAA. For patients who do not have an indication for iliac aneurysm repair, we perform serial physical examination and imaging at six-month intervals. If the size of the aneurysm is stable over several examinations, annual follow-up is reasonable. (See 'Surveillance ultrasound' above.)