Iliac artery aneurysm

Iliac arterial aneurysms are focal dilatations of the iliac artery. 

Although the dimensions that define the aneurysm are dependent on the sex of the patient and the portion of the artery involved, a common iliac artery (CIA) with a diameter ≥1.7 cm in males or ≥1.5 cm in females is considered ectatic. A diameter >2.5 cm is considered aneurysmal ³.

 An internal iliac artery diameter ≥0.8 cm is ectatic. 

Terminology

The overarching term "iliac artery", and by extension aneurysms thereof, includes the common iliac artery (CIA), external iliac artery (EIA) and internal iliac artery (IIA).

Epidemiology

Iliac artery aneurysms are associated with abdominal aortic aneurysms (AAA); 10-20% of AAAs involve the iliac arteries.

Isolated iliac artery aneurysm are uncommon, accounting for <2% of abdominal aneurysms. The common iliac artery is most commonly involved (70%), whereas the internal iliac artery is involved in 25%. Iliac artery aneurysms are bilateral in approximately 30% cases. External iliac arterial involvement is very rare ^1-2. 

They are more common in men. The incidence rises with age. 

Clinical presentation

Enlarged iliac arteries <3.0 cm tend to be asymptomatic and discovered incidentally on imaging studies. Occasionally they present with mass effect and cause compression with gastrointestinal, genitourinary (hydronephrosis) and neurologic symptoms (sciatica). Ruptured aneurysms present with acute abdominal pain and shock. Patients may also present with leg cellulitis, edema or claudication. 

Pathology

Etiology

Causes of iliac artery aneurysms include ¹:

• atherosclerosis

• infection

• trauma

• dissection

• connective tissue disorders

• fibromuscular dysplasia

• cystic medial necrosis

Classification of isolated iliac arterial aneurysms

Isolated iliac artery aneurysms (IIAs) are classified according to their anatomy ¹. The proximal non-aneurysmal artery is defined as the proximal neck or landing zone and distal non-aneurysmal artery is defined as the distal landing zone. This classification allows selection of appropriate candidates for endovascular or surgical therapy. 

• type A

  • CIA aneurysm proximally involves or extends within 1.5 cm of the aortic bifurcation

  • distally, it extends to or beyond the internal iliac artery

• type B

  • CIA aneurysm has an adequate proximal neck (i.e. ≥1.5 cm of non-aneurysmal artery)

  • there is however, no distal landing zone

• type C: CIA has an adequate proximal neck as well as a distal landing zone

• type D: solitary internal iliac artery aneurysm which spares the internal iliac artery origin

• type E: CIA aneurysm extends into the internal iliac artery

Treatment and prognosis

Follow-up of asymptomatic incidentally-detected iliac artery aneurysms ³:

• <3.0 cm: rarely rupture, grow slowly, follow-up not generally needed

• 3.0-3.5 cm: followed up initially at 6 months

  • if stable, then annual imaging

• >3.5 cm: greater likelihood of rupture

  • <6 month follow up

  • consider intervention