Iliac artery aneurysm is a focal dilatation exceeding >1.5 cm for the common iliac artery (CIA) or >0.8 cm for the internal iliac artery (IIA). Isolated iliac aneurysms comprise 2-7% of all abdominal aneurysms; however, association with abdominal aortic aneurysm (AAA) is far more common (present in 10-20% of AAA patients). They are 5-10 times more prevalent in men and typically found in atherosclerotic patients over 65 years. Most are asymptomatic and discovered incidentally; however, they may become symptomatic through rupture, thromboembolic events, or compression of adjacent structures (ureteral obstruction, venous compression, neuropathy). Rupture mortality ranges from 50-70% and requires emergency surgery. CT angiography is the gold standard for diagnosis and treatment planning.
Age Range
55-85
Peak Age
70
Gender
Male predominant
Prevalence
Uncommon
The pathogenesis of iliac artery aneurysm is based on degenerative weakening of the vessel wall, similar to aortic aneurysms. Atherosclerosis causes progressive degradation of elastin and collagen fibers in the medial layer — matrix metalloproteinases (MMP-2, MMP-9) released by adventitial inflammatory infiltrate break down structural proteins. As the media thins, wall stress increases according to Laplace's law (wall stress = pressure × radius / 2 × wall thickness): as the artery dilates, wall stress increases, causing further dilatation in a positive feedback loop. Mural thrombus forming within the lumen paradoxically does not protect the wall — a hypoxic environment develops beneath the thrombus that increases proteolytic activity and accelerates medial degeneration. On CT angiography, the contrast-opacified patent lumen is typically smaller than the true aneurysm diameter because the periphery filled with mural thrombus does not enhance — therefore assessing aneurysm size by lumen alone is misleading and outer wall-to-outer wall measurement is essential.
Focal dilatation of the common iliac artery exceeding 1.5 cm or internal iliac artery exceeding 0.8 cm on CTA, patent lumen surrounded by mural thrombus and calcified atherosclerotic wall — fundamental finding for iliac aneurysm diagnosis.
Focal fusiform or saccular dilatation of the iliac artery is seen in the arterial phase. Aneurysm is diagnosed when the common iliac artery diameter exceeds >1.5 cm or internal iliac artery >0.8 cm. The contrast-filled patent lumen appears brightly hyperdense while surrounding mural thrombus remains iso- to hypodense. Measurement should be made from outer wall to outer wall — cross-referenced in axial and sagittal reformations.
Report Sentence
Fusiform aneurysmal dilatation of the right/left common iliac artery measuring ___ cm from outer wall to outer wall is noted, with intraluminal mural thrombus.
On non-contrast CT, iliac artery aneurysm characteristically appears as hypodense mural thrombus surrounded by calcified wall with central isodense patent lumen. Wall calcifications may be crescent or complete ring-shaped and define the aneurysm boundaries. Mural thrombus may show concentric or eccentric distribution. Acute thrombus appears hyperdense at ~60-70 HU while chronic thrombus remains hypodense at ~30-40 HU.
Report Sentence
Non-contrast CT demonstrates aneurysmal dilatation of the right/left iliac artery with calcified wall and mural thrombus.
In ruptured iliac aneurysm, active contrast extravasation is seen in the arterial phase — contrast leakage outside the aneurysm wall appears as a hyperdense focus or jet in the retroperitoneal space. Sentinel clot sign (most dense clot area adjacent to the aneurysm) indicates rupture location. Retroperitoneal hematoma, hemorrhage into the psoas muscle, and ipsilateral hematoma are indirect signs of rupture.
Report Sentence
Active contrast extravasation from the right/left iliac aneurysm with surrounding retroperitoneal hematoma is noted, findings consistent with acute rupture; emergent surgical/endovascular intervention is recommended.
In large iliac aneurysms, compression findings of adjacent structures are evaluated in the portal venous phase. Ureteral compression leads to ipsilateral hydronephrosis and proximal ureteral dilatation. Iliac vein compression may cause ipsilateral lower extremity edema and deep vein thrombosis. Lumbosacral nerve root compression can cause neuropathic pain.
Report Sentence
Ipsilateral ureteral compression and pelvicalyceal dilatation consistent with mild/moderate/severe hydronephrosis related to the iliac aneurysm is noted.
On delayed phase after endovascular stent-graft (EVAR) for iliac aneurysm, contrast accumulation within the aneurysm sac indicates endoleak. Type II endoleak (most common) occurs through retrograde filling from lumbar arteries or internal iliac artery branches. Delayed phase is more sensitive than arterial phase for endoleak detection because low-flow endoleaks become visible only in the late phase due to slow contrast accumulation.
Report Sentence
Contrast accumulation within the iliac aneurysm sac on delayed phase post-EVAR consistent with Type ___ endoleak.
On B-mode ultrasound, focal fusiform or saccular dilatation of the iliac artery is seen. Patent lumen appears anechoic while mural thrombus shows variable echogenicity. Calcified wall appears as a hyperechoic linear structure with posterior acoustic shadowing. US can be used as a screening test but evaluation of the iliac region may be limited by bowel gas and obesity.
Report Sentence
B-mode ultrasound demonstrates aneurysmal dilatation of the right/left iliac artery measuring ___ cm with mural thrombus; further evaluation with CT angiography is recommended.
On MR angiography, signal characteristics of mural thrombus vary with age. Acute thrombus is iso- to slightly hyperintense on T1, subacute thrombus appears markedly T1 hyperintense due to methemoglobin. Chronic organized thrombus appears hypointense on T1. Gadolinium-enhanced MR angiography shows the patent lumen as brightly hyperintense while thrombus does not enhance.
Report Sentence
MR angiography demonstrates aneurysmal dilatation of the right/left iliac artery with T1 hyperintense/hypointense mural thrombus.
Criteria
Common iliac artery diameter >1.5 cm. Most common type (70-90%). Often seen as AAA extension. Bilateral in 33-50%.
Distinct Features
Usually fusiform, extending from aortic bifurcation to iliac bifurcation. EVAR must plan for IIA preservation or embolization.
Criteria
IIA diameter >0.8 cm. ~10-30% of all iliac aneurysms. Isolated IIA aneurysms are rare but carry high rupture risk.
Distinct Features
Late symptoms due to pelvic location. Rupture usually into pelvic cavity. May compress rectum, bladder, ureter. Treated with endovascular embolization; buttock claudication risk.
Criteria
Very rare — less than 5% of all iliac aneurysms. Usually associated with connective tissue disorders or vasculitis.
Distinct Features
Risk of lower extremity ischemia. Investigate Ehlers-Danlos, Marfan. Usually requires open surgery.
Criteria
AAA extension to iliacs or concomitant isolated iliac aneurysm. Present in 10-20% of AAA patients.
Distinct Features
Distal sealing zone may be inadequate in EVAR — branched/flared endograft may be needed. In bilateral cases, at least one IIA should be preserved.
Distinguishing Feature
AAA involves infrarenal aorta proximal to bifurcation, iliac aneurysm is distal. They frequently coexist.
Distinguishing Feature
Iliac artery dissection shows intimal flap and dual lumen; aneurysm shows dilated single lumen + mural thrombus without intimal flap.
Distinguishing Feature
Pseudoaneurysm does not involve all wall layers — typically post-trauma/surgery. True aneurysm preserves all wall layers.
Distinguishing Feature
Iliac vein thrombosis involves venous structures with filling defect on portal venous phase. Iliac aneurysm involves arterial structures enhancing on arterial phase.
Urgency
urgentManagement
surgicalBiopsy
Not NeededFollow-up
6-monthIliac aneurysms require active surveillance or treatment due to rupture risk. Surgical/endovascular repair is indicated when CIA >3.5 cm or IIA >3 cm. For smaller aneurysms, 6-12 month CTA surveillance is recommended. Symptomatic aneurysms require treatment regardless of size. Rupture is an emergency surgical indication.
Common iliac artery aneurysm >3.5-4 cm or internal iliac artery >3 cm is an indication for surgical/endovascular repair. Rupture risk is lower compared to AAA but increases with size. Iliac involvement must be assessed when planning AAA treatment, and EVAR landing zone planning is essential.