Iliac Artery Aneurysm

An iliac artery aneurysm is a dilatation of the iliac artery to 18 mm or more in the common iliac artery (or 1.5 times the normal diameter). Normal common iliac diameter is 10 to 12 mm.

Isolated disease is rare. Most iliac aneurysms accompany an abdominal aortic aneurysm, and about 10 to 20% of aortic aneurysms have iliac involvement.

The common iliac artery is involved in 70 to 90%, the internal iliac artery in 10 to 30%, and the external iliac artery rarely. Men are affected about seven times as often as women, usually over 65 years.

Most are degenerative. Others follow infection, trauma, vasculitis, connective tissue disease and previous graft surgery.

The risk of rupture rises sharply at over 30 mm. Rupture carries a mortality of about 40 to 60%.

Pathophysiology. Medial degeneration with loss of elastin weakens the wall, and wall stress increases with diameter. The aneurysm lies deep in the pelvis, so it can reach a large size before it is felt.

Growth is often slow, about 1 to 3 mm each year, but is faster in large aneurysms.

• Usually asymptomatic. Found on imaging for another reason.
• Lower abdominal, pelvic, groin or buttock pain. Sciatica like pain from compression of the lumbosacral plexus.
• Hydronephrosis from ureteric compression, constipation or urinary symptoms, and leg swelling or deep vein thrombosis from iliac vein compression.
• Rectal or pelvic examination may find a pulsatile mass. The abdomen and femoral pulses should be examined.
• Distal embolisation (blue toe), and arteriovenous fistula with high output heart failure.
• Rupture: sudden severe pain, hypotension, shock, or haematuria and rectal bleeding with erosion into the bowel or bladder.

Red flags.

• Sudden pain, hypotension or syncope
• Diameter of 30 mm or more, or growth of 5 mm or more in 6 months (10 mm or more in 1 year)
• Fever or raised inflammatory markers
• Hydronephrosis with rising creatinine
• Distal embolisation

• Ultrasound. Screening and surveillance, but pelvic bowel gas limits views.
• CT angiography. The main test for diameter (perpendicular to the flow axis), extent, neck and landing zones, internal iliac involvement, relation to the ureter and veins, and infection. MR angiography is an alternative.
• Whole aorta imaging. Abdominal aortic aneurysm and femoral and popliteal aneurysms are looked for.
• Laboratory. Creatinine, full blood count, CRP and ESR, blood cultures with fever or gas on imaging.

Differential diagnosis.

• Abdominal aortic aneurysm extending into the iliac arteries
• Ectatic or tortuous iliac arteries
• Pseudoaneurysm after catheterisation or surgery
• Pelvic or ovarian mass, lymphadenopathy and psoas abscess
• Mycotic aneurysm
• Spinal causes of sciatica
• Arteriovenous malformation

Medical therapy. Aspirin 75 to 100 mg orally once daily (usual maximum 325 mg daily), atorvastatin 40 to 80 mg once daily (liver enzymes at baseline and 3 months, avoid in pregnancy), blood pressure under 130/80 mm Hg and smoking cessation. No drug reliably slows growth.

Surveillance. Diameter 18 to 29 mm: ultrasound or CT every 12 months, every 6 months from 25 mm. Repair at 30 mm or more, with symptoms, rapid growth, infection or rupture.

Elective repair.

• Endovascular repair is preferred when anatomy suits. Preserve flow to at least one internal iliac artery with an iliac branch device. Coil embolisation of the internal iliac artery with a covered stent in the common iliac artery is the alternative.
• Occluding both internal iliac arteries causes buttock claudication (up to 30 to 50%), erectile dysfunction, colonic ischaemia and spinal cord ischaemia, so avoid it.
• Open repair with tube or bifurcated graft when anatomy does not suit stenting. Early mortality is about 2 to 5%, and ureteric and venous injury are risks.
• Prophylaxis: cefazolin 2 g intravenously as a single dose 30 to 60 minutes before incision (3 g if over 120 kg), with vancomycin 15 mg/kg intravenously for severe penicillin allergy or MRSA.
• After endovascular repair: aspirin 75 to 100 mg once daily long term.

Rupture. Emergency. Resuscitation with permissive hypotension (systolic pressure 70 to 90 mm Hg) until control, crossmatched blood, emergency endovascular or open repair. Watch for abdominal compartment syndrome after repair. Mortality is about 30 to 50% with treatment.

Infected aneurysm. Prolonged intravenous antibiotics by culture for at least 6 weeks with surgical debridement and reconstruction.

Special groups. Pregnancy is rare, but rupture carries a high maternal and foetal mortality, so plan with a vascular and obstetric team. Region: tuberculosis and Salmonella are causes of infected aneurysm in sub-Saharan Africa.

Monitoring. After endovascular repair, CT at 1 month and 12 months, then yearly (duplex in between for endoleak and sac size). Annual aortic imaging.

Referral and escalation. Refer to vascular surgery with endovascular capability. Emergency for rupture, sepsis, or rapid growth.