Size Criteria for Internal Iliac Artery Aneurysm Repair
Elective repair of internal iliac artery aneurysms is recommended at ≥3.5 cm diameter, based on the 2022 ACC/AHA guidelines which establish this as the threshold where rupture risk justifies procedural risk. 1, 2
Evidence-Based Size Threshold
The 3.5 cm repair threshold is a Class 1, Level C-LD recommendation from the 2022 ACC/AHA guidelines for patients with asymptomatic internal iliac artery aneurysms, particularly when occurring with concomitant abdominal aortic aneurysms. 1
This threshold balances procedural risks against rupture risk, as rupture of internal iliac artery aneurysms at diameters <4 cm is rare but does occur. 1, 2
In a multinational retrospective review, only 1 patient presented with a ruptured internal iliac artery aneurysm ≤3 cm, and 4 patients had ruptures at diameters ≤4 cm out of 63 patients studied. 1, 2
The median diameter of ruptured iliac aneurysms at presentation is 6.8 cm, indicating substantially higher risk with larger aneurysms. 1, 2
Critical Clinical Context
Any symptomatic internal iliac artery aneurysm warrants immediate intervention regardless of size, as symptoms indicate impending rupture or compression of adjacent structures. 2, 3
The 3.5 cm threshold applies specifically to asymptomatic aneurysms discovered incidentally or during surveillance. 1
In the largest single-center series of 438 patients with common iliac artery aneurysms, no iliac aneurysm ≤3.8 cm ruptured during an average follow-up of 3.7 years. 1
Surveillance Protocol for Sub-Threshold Aneurysms
For internal iliac artery aneurysms measuring 2.0-2.9 cm: ultrasound surveillance every 12 months is recommended. 2
For aneurysms measuring 3.0-3.4 cm: ultrasound surveillance every 6 months is recommended, with consideration of CT angiography as size approaches 3.5 cm for pre-intervention planning. 2
Document maximum diameter and growth rate at each visit, as accelerated growth (≥0.5 cm in 6 months) may warrant earlier intervention even below the 3.5 cm threshold. 2
Common iliac artery aneurysms grow at an average rate of 2.9 mm/year, though internal iliac artery aneurysms may have different growth patterns. 1
Important Anatomic and Technical Considerations
Preservation of at least one hypogastric (internal iliac) artery is a Class 1, Level B-NR recommendation when treating iliac aneurysms to prevent pelvic ischemia. 1, 3
Unilateral internal iliac artery exclusion causes buttock claudication in 27% of patients, bilateral exclusion in 36%, and erectile dysfunction in 10% of men. 1, 2, 3
Other ischemic complications including spinal cord ischemia, bowel ischemia, and gluteal necrosis occur at rates <1% but are devastating when they occur. 1
Concomitant Disease Screening
20-40% of patients with internal iliac artery aneurysms have coexisting abdominal aortic aneurysms, requiring comprehensive imaging of the entire aortoiliac system with CT angiography. 2, 3
In patients with both aortic and iliac aneurysms, the internal iliac artery aneurysm commonly reaches repair threshold before the abdominal aortic aneurysm does. 1, 2
41.7% of patients with internal iliac artery aneurysms have concomitant abdominal aortic aneurysms in registry data. 1
Common Pitfalls to Avoid
Do not delay repair of symptomatic aneurysms based on size criteria—symptoms override size thresholds and mandate immediate intervention. 2, 3
Do not sacrifice both internal iliac arteries unless absolutely unavoidable, as bilateral exclusion carries unacceptably high rates of pelvic ischemia complications. 1, 3
Do not use ultrasound alone for pre-operative planning—CT angiography with 3D reconstruction is required to assess anatomy and plan endovascular or open repair. 3
Do not assume isolated internal iliac artery aneurysms—always image the entire aortoiliac system to identify concomitant aneurysms that may require simultaneous treatment. 2, 3