Iliac Artery Aneurysm
An iliac artery aneurysm is a localized enlargement of one of the iliac arteries—the main blood vessels in the pelvis that continue from the abdominal aorta down into the legs. Iliac artery aneurysms most commonly involve the common iliac arteries and are often associated with atherosclerosis and abdominal aortic aneurysms. Many are discovered incidentally on imaging, since they typically cause no symptoms until they become large or complicated. Imaging—particularly CT angiography and MR angiography—plays a central role in identifying, monitoring, and planning treatment of these aneurysms.
What is it?
The iliac arteries are the major blood vessels in the pelvis. The abdominal aorta divides at approximately the level of the navel into the right and left common iliac arteries, each of which further branches into an internal iliac artery (which supplies the pelvic organs) and an external iliac artery (which continues into the leg as the femoral artery). An iliac artery aneurysm is a localized enlargement of one of these vessels, typically defined as a diameter that is at least 1.5 times the normal size of the vessel or that meets certain size thresholds. The common iliac arteries are most commonly affected, followed by the internal iliac arteries; aneurysms of the external iliac arteries are uncommon.
Most iliac artery aneurysms develop in the setting of atherosclerosis and share many of the same risk factors as abdominal aortic aneurysms. These include older age, male sex, smoking, high blood pressure, high cholesterol, a family history of aneurysmal disease, and known atherosclerosis elsewhere. Iliac artery aneurysms frequently occur together with abdominal aortic aneurysms, and aneurysmal disease often extends from the aorta down into the iliac vessels. Less common causes include connective tissue disorders such as Marfan syndrome, Loeys-Dietz syndrome, and vascular Ehlers-Danlos syndrome; vasculitis; infection (mycotic aneurysm); trauma; and prior surgery or radiation. Pseudoaneurysms (false aneurysms) can develop at sites of prior catheterization or injury, but these differ from true aneurysms and are managed separately.
Most iliac artery aneurysms cause no symptoms until they become large or develop complications. Because the iliac arteries lie deep within the pelvis, smaller aneurysms are often impossible to detect on physical examination. When symptoms do occur, they may include vague lower abdominal, flank, lower back, or groin pain; urinary symptoms such as frequency or hesitancy from pressure on the bladder or ureter; bowel symptoms from pressure on nearby segments of intestine; constipation; or, in some cases, leg pain or swelling if the aneurysm affects venous return or causes clot formation. Aneurysms may also be a source of small clots that travel into the leg arteries, causing pain or other signs of embolism.
The most serious complication is rupture, in which the wall of the aneurysm breaks open and causes severe internal bleeding. Iliac artery aneurysm rupture typically presents with sudden, severe abdominal, back, or groin pain and signs of shock and is a surgical emergency. Smaller aneurysms have a lower risk of rupture, while larger aneurysms (often defined as greater than approximately 3.0–3.5 centimeters for the common iliac arteries) carry a higher risk, and treatment thresholds are based on size, growth, symptoms, and patient factors.
CT angiography of the abdomen and pelvis is the primary imaging test for evaluating iliac artery aneurysms because it provides detailed three-dimensional information about size, location, shape, involvement of nearby structures, and any complications such as clot or rupture. MR angiography is an alternative when avoiding radiation or iodinated contrast is preferred. Ultrasound of the iliac arteries provides useful information in some patients but can be limited by body habitus and overlying bowel gas. Invasive catheter-based angiography is typically reserved for selected patients, often at the time of planned endovascular intervention.
Important to Know
Management of an iliac artery aneurysm depends on its size, growth rate, symptoms, and the patient’s overall health. For small, asymptomatic aneurysms, periodic imaging surveillance and aggressive cardiovascular risk reduction are typically recommended.
Important measures include smoking cessation, control of blood pressure, statins and other lipid-lowering therapies to reduce overall cardiovascular risk, treatment of diabetes when present, antiplatelet therapy in selected patients, healthy diet, regular physical activity, weight management, and limited alcohol. While these measures may not directly shrink an established aneurysm, they reduce overall cardiovascular risk and may help slow aneurysm growth and address coexisting disease.
Repair is typically considered when an iliac artery aneurysm reaches certain size thresholds (commonly around 3.0–3.5 cm for the common iliac arteries, although guidelines and individual circumstances vary), when it is growing rapidly, when it causes symptoms (such as pain or compression of nearby structures), when it has been a source of embolism, or, urgently, when it has ruptured. Patients with connective tissue disorders or other high-risk conditions may be considered for repair at smaller sizes because of higher rupture risk.
Endovascular aneurysm repair (EVAR) using stent grafts placed via catheter is now the most common approach for elective treatment of many iliac artery aneurysms. Specialized stent grafts and techniques (including iliac branch devices) allow preservation of important branches such as the internal iliac arteries when feasible. Open surgical repair, in which the aneurysm is excluded and replaced with a graft, remains an important option, particularly for complex anatomy or when endovascular repair is not feasible. Treatment decisions depend on anatomy, age, surgical risk, and patient preferences.
Patients with iliac artery aneurysms frequently have coexisting abdominal aortic aneurysms or aneurysmal disease elsewhere. Comprehensive imaging often evaluates the aorta, thoracic vessels, and other arterial territories. First-degree relatives of patients with aortic and iliac aneurysmal disease may benefit from screening, particularly when there is a strong family history or evidence of a connective tissue disorder.
Care is typically coordinated by primary care clinicians, vascular surgeons, vascular medicine specialists, interventional radiologists, and other relevant providers. Imaging findings are interpreted alongside the patient’s symptoms, examination, and overall health.
Patients with known iliac artery aneurysms should be aware of the warning signs of rupture or other complications and seek immediate care if these develop.
Red flag symptoms include sudden severe abdominal, flank, lower back, or groin pain; lightheadedness or fainting; rapid heart rate; cool, clammy skin or signs of shock; sudden severe leg pain, coolness, paleness, or numbness; or sudden loss of pulse in a leg. These warrant immediate emergency evaluation, as they may indicate rupture, dissection, or embolism related to the aneurysm.