Iliac Artery Aneurysm Size Thresholds and Management

Guideline‑Recommended Repair Thresholds

• The 2022 ACC/AHA cardiovascular guidelines recommend elective repair of common iliac artery aneurysms when the maximal diameter reaches 3.5 cm, balancing procedural risk against rupture risk. 1, 2

Evidence on Rupture Risk and Surveillance Below 3.5 cm

• In a prospective case series of ≈440 patients followed for a mean of 3.7 years, no aneurysm ≤3.8 cm ruptured, supporting the safety of continued surveillance for lesions below the 3.5 cm repair threshold. 1, 2
• The median diameter of ruptured iliac aneurysms at presentation was ≈6.8 cm, indicating a substantial safety margin when intervening at 3.5 cm. 1, 2
• Real‑world practice data from the Dutch Surgical Aneurysm Audit show that elective repairs were commonly performed at a median size of 4.3 cm, although the guideline‑recommended threshold remains 3.5 cm to prevent progression to higher‑risk sizes. 1, 2
• A multinational review documented rare ruptures below 4 cm (1 case ≤3 cm and 4 cases ≤4 cm), providing empirical support for the 3.5 cm intervention threshold for internal iliac aneurysms as well. 1, 2

Screening for Concomitant Aortic Disease

• Among patients with iliac artery aneurysms, 20–40 % have a coexisting abdominal aortic aneurysm (AAA), and ≈86 % of those with common iliac aneurysms have a current or previously treated AAA, underscoring the need for routine AAA screening. 1, 2

Procedural Considerations: Internal Iliac Artery Preservation

• Preservation of at least one internal iliac artery during repair is essential to avoid pelvic ischemia complications. 1
• Unilateral internal iliac exclusion results in buttock claudication in about 27 % of patients, while bilateral exclusion raises this to ≈36 % and is associated with erectile dysfunction in ≈10 % of male patients. 1, 2
• Severe complications such as spinal cord, bowel, or gluteal ischemia occur in <1 % of cases but are devastating when they arise, necessitating individualized planning and shared decision‑making. 1, 2

Endovascular Landing Zone Implications

• Common iliac arteries with a diameter ≥18 mm exhibit a higher incidence of type Ib endoleaks after EVAR (7.2 % vs 3.2 %) and a greater rate of late reinterventions (19 % vs 11.8 %) compared with smaller diameters, influencing graft selection and landing‑zone strategy. 1, 2

Internal Iliac Artery Aneurysm Management

Size-Based Risk Stratification

• Internal iliac artery aneurysms ≥3.5 cm are considered high risk for rupture and warrant elective repair rather than continued surveillance, as established by the American College of Cardiology 3
• The 2022 ACC/AHA guidelines establish 3.5 cm as the repair threshold for internal iliac artery aneurysms, balancing procedural risks against rupture risk 3
• Rupture of internal iliac artery aneurysms at diameters <4 cm is rare, with only 1 patient presenting with a ruptured internal iliac artery aneurysm ≤3 cm, and 4 patients had ruptures at diameters ≤4 cm in a multinational retrospective review 3
• Ruptured iliac aneurysms have a median diameter of 6.8 cm at presentation, indicating a higher risk for larger aneurysms 3, 4

Critical Clinical Context

• The 3.5 cm threshold is based on large case series and registry data showing that rupture below 4 cm is uncommon, while procedural risks of repair are acceptable at this size, as demonstrated by the Dutch Surgical Aneurysm Audit 3
• Any symptomatic internal iliac artery aneurysm warrants immediate intervention regardless of size, according to the American College of Cardiology 4

Concomitant Disease Considerations

• 20-40% of patients with iliac artery aneurysms have coexisting abdominal aortic aneurysms, requiring comprehensive imaging of the entire aortoiliac system 5, 4
• When treating aortoiliac disease, the internal iliac artery aneurysm may reach repair threshold before the abdominal aortic aneurysm does, as noted by the American College of Cardiology 3

Surveillance Protocol for Sub-Threshold Aneurysms

• For 2.0-2.9 cm aneurysms, ultrasound surveillance is recommended every 12 months, while for 3.0-3.4 cm aneurysms, ultrasound surveillance is recommended every 6 months, with consideration of CT angiography as size approaches 3.5 cm for pre-intervention planning 5
• Documenting maximum diameter and growth rate at each visit is crucial, as accelerated growth may warrant earlier intervention even below 3.5 cm threshold 5

Intraoperative Considerations

• Preservation of at least one hypogastric artery is crucial to prevent pelvic ischemia during intervention, with unilateral internal iliac artery exclusion causing buttock claudication in 27% of patients, and bilateral exclusion in 36%, according to the American College of Cardiology 3, 5, 4

Iliac Artery Size Definitions and Clinical Management

Definition and Classification

• The European Society of Cardiology defines an iliac artery diameter of 18 mm as mild ectasia, not a true aneurysm, because aneurysms are defined as focal dilations ≥ 30 mm or ≥ 1.5 × the normal diameter. 6

Intervention Thresholds

• The ACC/AHA vascular guidelines state that repair of a common iliac artery aneurysm is indicated at a diameter of 35 mm (3.5 cm); therefore, an 18 mm vessel does not meet the threshold for surgical or endovascular intervention. 7

Surveillance Recommendations

• For patients with common iliac artery diameters of 20–29 mm, the ACC/AHA guidelines recommend annual duplex ultrasound surveillance to monitor for growth. 7

Association with Abdominal Aortic Aneurysm (AAA)

• The ACC/AHA guidance notes that 20–40 % of individuals with iliac artery ectasia also have a coexisting AAA, supporting comprehensive aorto‑iliac imaging in this population. 7
• Among patients identified with a common iliac artery aneurysm, 86 % have a current or previously treated AAA, emphasizing the importance of AAA screening even when the iliac lesion is only ectatic. 7