Abdominal aortic aneurysm
Abdominal aortic aneurysms (AAA) are focal dilatations of the abdominal aorta that are 50% greater than the proximal normal segment or that are >3 cm in maximum diameter.
Its prevalence increases with age. Males are much more commonly affected than females (with a male:female ratio of 4:1).
It is the tenth most common cause death in the Western world. Approximately 10% of persons older than 65 years have an AAA.
Most AAAs are asymptomatic unless they leak or rupture. Unruptured aneurysms may uncommonly cause abdominal or back pain, or a pulsatile mass, if large.
Ruptured aneurysms present with severe abdominal or back pain, hypotension and shock. The mortality rate from a ruptured AAA is high (59-83% of patients succumb to death before they make it to a hospital or undergo surgery). The operative mortality rate for those who make it to surgery tends to be around 40%. Elective surgery mortality is much lower (4-6%).
- atherosclerosis (most common)
- inflammatory abdominal aortic aneurysm
- chronic aortic dissection
- vasculitis, e.g. Takayasu arteritis
- connective tissue disorders, e.g.
- mycotic aneurysm
- traumatic pseudoaneurysm
- anastomotic pseudoaneurysm
common iliac artery (CIA) aneurysm
- AAA commonly extends into common iliac arteries
- vast majority of patients with CIA aneurysms have an AAA
- isolated CIA aneurysms are rare
popliteal artery aneurysm
- 10-14% of patients with AAA have popliteal artery aneurysm
- 30-50% of patients with popliteal artery aneurysm have an AAA
Role of imaging
- detection of AAA
- monitoring of the rate of growth
- pre-operative planning
- post-operative follow-up
An aneurysm may be visible as an area of curvilinear calcification in the paravertebral region on either abdominal or lumbar spine films performed for alternative indications. Radiographs are not optimal for detection or follow-up.
Ultrasound assessment is simple, safe and inexpensive. It has a reported sensitivity of 95% and specificity close to 100%. It is usually the preferred choice for monitoring of small aneurysms. The measurement of error of ultrasound evaluation of AAAs is 4 mm 12, but remember that it will never decrease in size.
This is considered the imaging gold standard but has a high radiation dose. Excellent for pre-operative planning as it accurately delineates the size and shape of the AAA and its relationship to branch arteries and the aortic bifurcation. It is also superior to ultrasound in detecting and sizing common iliac artery aneurysms.
Signs of of frank rupture include:
- retroperitoneal haematoma
- para-aortic stranding
- contrast extravasation from the aorta into the retroperitoneum
Signs of impending rupture or contained leakage:
- draped aorta sign (contained rupture)
- high-attenuation crescent sign (intramural haematoma)
- focal discontinuity of intimal calcification
- tangential calcium sign
Increasing diameter of the aneurysm sac of 10 mm over 12 months and a diameter of 7 cm are also taken to be at high risk for rupture and can warrant urgent repair.
Same as for CTA but can be more costly and less widely available.
Does not show true aneurysm size if there is mural thrombus but good at delineating branch vessels. Usually performed intraoperatively during treatment.
Reported complications include:
- pseudoaneurysm from chronic contained leak/rupture
- distal thromboembolism
- thrombotic occlusion of a branch vessel
- compression of adjacent structures if large (rare)
- vertebral erosion
Treatment and prognosis
The natural history of abdominal aortic aneurysms is that of slow expansion and rupture with devastating consequences.
The risk of rupture is proportional to the size of the aneurysm and the rate of growth. Differing rates of rupture for a given aneurysm size have been reported in the literature but the general consensus is that aneurysms greater than 5.0 cm in women and 5.5 to 6.0 cm in men carry a significantly increased risk of rupture and should be treated. Furthermore, aneurysms that expand greater than 10 mm per year are also at significant risk of rupture and are considered for treatment even when less than 5.0 cm.
Follow up intervals for imaging an enlarged infrarenal abdominal aorta (when initially detected) 11:
- <2.5 cm: follow up not needed
- 2.5-2.9 cm: 5 year interval
- 3.0-3.4 cm: 3 year interval
- 3.5-3.9 cm: 2 year interval
- 4.0-4.4 cm: 1 year interval
- 4.5-4.9 cm: 6 month interval
- 5.0-5.5 cm: 3-6 month interval
- >5.5 cm: treatment
Management options include:
- endovascular aneurysm repair (EVAR)
- open surgical repair
Treatment is recommended in surgically fit patients if the aneurysm is greater than 5.0 cm diameter in women and 5.5 cm diameter in men. Treatment is also considered if aneurysm growth rate exceeds 10 mm per year in smaller aneurysms.
- acute aortic syndrome
- thoracic aortic aneurysm
- abdominal aortic aneurysm
- endovascular aneurysm repair (EVAR)
- reporting tips for aortic aneurysms
- traumatic aortic injuries
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