Abdominal Aortic Aneurysm (AAA) are abnormal dilatation or bulging of the abdominal aorta resulting from chronic weakening of the arterial wall, measuring greater than 30mm or exceeding 50% of the normal aortic diameter. Majority of AAAs occur at a focal area within the infrarenal segment of the abdominal aorta.
AAAs develop over time and have few noticeable symptoms. The larger the aneurysm, the higher the risk of rupture, with high mortality. Ruptured AAA is a surgical emergency, invariably leading to death without urgent intervention. Therefore, AAAs must be identified early, followed up and then treated with elective repair.
Clinical Presentation:
Majority of AAAs are asymptomatic and often incidentally detected. Patient presentation can be variable, non-specific, and often misleading. Symptoms suggesting AAA can mimic other conditions such as appendicitis, cholelithiasis, diverticular disease, bowel obstruction, ischemic bowel, perforated ulcer, and urinary tract infection.
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If an aneurysm expands rapidly, tears and leaks, the following symptoms may develop suddenly:
- Severe abdominal or back pain radiating to the buttocks and legs
- Sweating and clamminess
- Dizziness
- Nausea and vomiting
- Rapid heart rate
- Shortness of breath
- Low blood pressure
Risk Factors:
- Age older than 60 years
- Gender – more common in males
- Ethnicity - Caucasian race
- Family history of aortic aneurysm
- History of smoking
- Hypertension
- Coronary artery disease
- Hyperlipidemia
Risk of Rupture:
Aneurysm size is one of the strongest predictors of the risk of rupture
- Less than 4.0 cm in diameter – 0%
- 4.0 cm to 4.9 cm in diameter – 0.5% to 5%
- 5.0 cm to 5.9 cm in diameter – 3% to 15%
- 6.0 cm to 6.9 cm in diameter – 10% to 20%
- 7.0 cm to 7.9 cm in diameter – 20% to 40%
- 8.0 cm in diameter or greater – 30% to 50%
Expansion rate may also be a predictor of the risk of rupture
- Considered to be at high risk of rupture if AAA expands 0.5cm or more over size months of follow-up
*Other factors that contribute to the increasing risk of rupture include continued smoking, uncontrolled hypertension, and aortic increased wall stress
Role of Imaging in AAA management and treatment
Management and treatment are dependent on whether the patient is symptomatic, the size of the aneurysm, and associated risk factors.
- Asymptomatic AAA < 5.5 cm in diameter - for surveillance via ultrasound, CT or MRI
- Symptomatic AAA >5.5 cm in diameter – recommended for surgical repair via open or endovascular aneurysm repair
Plain Radiography
- not adequate for AAA detection or follow-up
- may be sufficient for initial detection and diagnosis as may be visible as an area of curvilinear calcification in the paravertebral region on either abdominal or lumbar spine radiographs
Ultrasound
- Method of choice for screening and surveillance of AAA
- Non-invasive, non-ionizing, non-expensive
- High sensitivity and specificity
- Quantifies the maximal anterior-posterior transverse diameter and estimates orthogonal diameter of the aorta
- However, does not provide sufficient information for procedural planning
Magnetic Resonance Imaging - MRA
- Minimally invasive, non-ionizing and no iodinated contrast medium exposure
- Accurate anatomical delineation of AAA, successfully identifies the proximal and distal extent of the aneurysms, the number and origins of renal arteries and presence of inflammation
- Disadvantages includes increased cost, longer scanning time, difficulty with patient compliance in lying still to avoid motion artifact
Computed Tomography - CTA
- CT angiogram of the abdominal aorta provides more accurate assessment of the morphology of the AAA
- Excellent for pre-operative planning as it accurately delineates the size and shape of the AAA and its relationship to branch arteries and aortic bifurcation
- Signs of frank rupture:
- Retroperitoneal hematoma
- Para-aortic fat stranding
- Contrast extravasation from the aorta into the retroperitoneum
- Signs of impending rupture or contained leakage:
- Draped aorta sign
- Hyperattenuating crescent sign
- Thrombus fissuration
- Focal discontinuity of intimal calcification
- Tangential calcium sign
Angiography - Endovascular aneurysm repair (EVAR):
- Less invasive surgical alternative – less blood loss, decreased intensive care, more rapid recovery, and earlier return to function
- Consists of placing a stent-graft within the aorta to exclude the aneurysm from arterial circulation, reducing the risk of rupture
- Complications after EVAR can be life threatening therefore life-long imaging surveillance is necessary to detect complications, which are often asymptomatic
References:
Aggarwal, S, Qama, A, Sharma, V & Sharma, A, 2011, ‘Abdominal aortic aneurysm: A comprehensive review’, Experimental & Clinical Cardiology, vol. 16, no. 1, pp. 11-15
Hong, H, Yang, Y, Liu, Bo & Cai, Weibo, 2011, ‘Imaging of abdominal aortic aneurysm: the present and the future’, Current Vascular Pharmacology, vol. 8, no. 6, pp. 808-819
Lattanzi, S, 2020, ‘Abdominal aortic aneurysms: pathophysiology and clinical issues’, Journal of Internal Medicine, vol. 388 no. 3
Vu, K, Kaitoukov, Y, Morin-Roy, F, Kauffmann, C, Giroux, M, Therasse, Eric, Soulez, G & Tang, A, 2014, ‘Rupture signs on computed tomography treatment, and outcome of abdominal aortic aneurysm’, Insights Imaging, vol. 5, no. 1, pp. 281-293. DOI: 10.1007/s13244-014-0327-3
Presented by: Lucia P
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