- An AAA is an increase in aortic diameter by greater than 50% of normal
- Usually regarded as aortic diameter of greater than 3 cm diameter
- More prevalent in elderly men
- Male : female ratio is 4:1
Picture provided by Peter Lin, Baylor College of Medicine, Houston, Texas, USA
- Risk factors – hypertension, peripheral vascular disease, family history
- Accounts for 2% male deaths above the age of 55 years
- 3000 elective and 1,500 emergency operations in UK each year
- Mortality of emergency operation is greater than 50%
- Mortality of elective surgery is less than 5%
- Selection of patients for operation depends on risk of operation vs. risk of rupture
Natural history
- AAA diameter expands exponentially at approximately10% / year
- Risk of rupture increases as aneurysm expands
- 5 year risk of rupture:
- 5.0 – 5.9 cm = 25%
- 6.0 – 6.9 cm = 35%
- More than 7 cm = 75%
- Overall only 15% aneurysms ever rupture
- 85% of patients with a AAA die from an unrelated cause
Screening
- AAA are suitable for screening as elective operation of asymptomatic aneurysms can reduce mortality
associated with rupture
- Who should be screened?
- Probably males over 65 years - especially hypertensives
- Single US at 65 years reduces death from ruptured AAA by 70% in screened population
- Patients with small aneurysms should undergo regular surveillance
- Repeated ultrasound every 6 months
Clinical features
- 75% are asymptomatic
- Possible symptoms include
- Epigastric pain
- Back pain
- Malaise and weight loss (with inflammatory aneurysms)
- Rupture presents with
- Sudden onset abdominal pain
- Hypovolaemic shock
- Pulsatile epigastric mass
- Rare presentations include
- Distal embolic features
- Aorto-caval fistula
- Primary aorto-intestinal fistula
Indication for operation
- Rupture
- Symptomatic aneurysm
- Rapid expansion
- Asymptomatic > 6 cm – exact lower limit controversial
UK Small Aneurysm Trial
- Randomised 1090 small aneurysms (4.0-5.5 cm) to operation or surveillance
- Showed no improvement in overall mortality for those offered early surgery
- Similar results obtained in US Aneurysm Detection and Management Study
Pre-operative investigation
- Need to determine
- Extent of aneurysm
- Fitness for operation
- Ultrasound, conventional CT and more recently spiral CT
- Determines – aneurysm size, relation to renal arteries, involvement of iliac vessels
- Most significant post op morbidity and mortality related to cardiac disease
- If pre-operative symptoms of cardiac disease need cardiological opinion
- May need thallium scan or cardiac catheterisation
- Cardiac revascularisation required in up to 10% patients
Picture provided by Andrew McIrvine, Darwent Valley Hospital, Dartford, United Kingdom
Endovascular aneurysm repair
- Introduced into clinical practice with few clinical trials over the past 10 years
- Exact role unclear and medium and late-complications only recently recognised
- Morbidity of conventional open aneurysm surgery related to:
- Exposure of infra-renal aorta
- Cross clamping of aorta
- Endovascular repair may be associated with:
- Reduced physiological stress
- Reduced morbidity
- Reduced mortality
Technique
- Endovascular repair achieved by transfemoral or transiliac placement of prosthetic graft
- Proximal and distal cuffs / stents anchor graft
- Exclude aneurysm from circulation
- Three main types of graft
- Aorto-aortic
- Bifurcated aorto-iliac
- Aorto-uniiliac graft with femoro-femoral crossover and contralateral iliac occlusion
- Use of technique depends on aneurysm morphology
- Aneurysm morphology is best assessed with spiral CT
- Only about 40% of aneurysms suitable for this type of repair
- Aorto-aortic grafts less frequently used due to high complication rate
- Successful stenting associated with reduced aneurysm expansion
- Still has 1% per year risk of aneurysm rupture
Complications
- Graft migration
- Endovascular leak
- Graft kinking
- Graft occlusion
Popliteal artery aneurysms
- Defined as a popliteal artery diameter greater than 2 cm
- Account for 80% of all peripheral aneurysms
- 50% are bilateral
- 50% are associated with an abdominal aortic aneurysm
- 50% are asymptomatic
- Symptomatic aneurysms present with features of:
- Compression of adjacent structures (veins or nerves)
- Rupture
- Limb ischaemia due to emboli or acute thrombosis
- Treatment is by proximal and distal ligation
- Revascularisation of the leg with a femoropopliteal bypass
- With a symptomatic popliteal aneurysm 20% patients will undergo an amputation
Picture provided by Luke Evans, Norfolk and Norwich Hospital, United Kingdom
Bibliography
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