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Abdominal aortic aneurysm

Abdominal aortic aneurysm ( AAA ) are dilatation of the aorta measuring > 3 cm in diameter commonly involving the infra-renal portion. Other criteria mentioned in the literature include focal dilatation of the aorta exceeding 1.5 times its normal diameter aortic diameter of atleast one and one-half times the normal diameter at the level of renal arteries , which is approximately 2 cm

 

Seen in up to 8 % of men aged > 65 Can be seen in 4 % to 8 % of men and 0.5 % to 1 % of women above 50 Risk increases with age – particularly after 60 They are more common in men ( 4-6 times ) Seen more commonly in whites in comparison to blacks AAA is quite rare in Asian populations AAA is responsible for 8000 deaths annually in the UK

 

advancing age atherosclerosis smoking ( major risk factor associated with development , expansion & rupture of AAAs ) male sex Caucasian race family history of AAA ○ a h/o surgical intervention in 1st degree relative increases the risk by 2 fold hypertension hypercholesterolaemia respiratory disease cerebrovascular disease claudication renal insufficiency prior h/o aortic dissection

 

severe , silent ,potentially life threatening condition significant risk mortality if remains undetected major complications are ○ rupture ( most serious complication ) & likelihood of rupture is influenced by factors as size , expansion rate and sex ( risk of rupture increases markedly if diameter > 5.5 cm for males and 5.2 cm for females ) ○ thrombi formation in the lumen ○ compression of adjacent organs ○ pseudoaneurysm ○ aortic fistulas estimated mortality between 50 % and 80 % ( rupture )

 

AAA screening is secondary prevention Screening is for men only ( during the year they turn 65 ) and is not offered to women , men under 65 or those who have already been treated for AAA Screening reduces AAA-related mortality by reducing AAA -ruptures Maximum diameter criterion is widely used as the predictor of rupture risk It is known that about 50 % of AAA screening detected will reach a size in about 5 yrs for which surgery will be indicated It is common practice to repair larger aneurysms ( ie > 5.5 cm ) and to monitor smaller aneurysms Repair can also be offered for smaller aneurysms if they are growing rapidly or are symptomatic Mortality has declined in developed countries

 

usually asymptomatic often detected on imaging for some other reason on US , abdominal CT or MRI in thin patients they can be palpated ○ non-tender pulsatile abdominal mass at or above umbilicus enlarging aneurysms can cause abdominal pain , flank or back pain rupture ( vascular emergency ) can present as ○ shock ○ diffuse abdominal pain / distension ○ pulsatile mass most patients would die before reaching hospital AAA presentation can also be with other complications as ○ thrombosis ○ embolization ○ over DIC causing haemorrhage and thrombotic complications

 

Clinical examination is unreliable in diagnosis of AAA Laboratory tests can not be used in diagnosis Imaging tests are reliable

 

Ultrasound -Cheap and free of ionising radiation Method of choice in AAA screening High sensitivity ( 95 % ) and specificity ( nearly 100 % ) US can also detect thrombus or echodense calcifications in or adjacent to the aortic wall In 1-3 % of the patients the visualisation can be poor due to patient habitus or overlying bowel gas

 

Plain XR-calcification in the wall of the aneurysm not reliable calcification can happen without aneurysm

 

CT-provides additional information as exact location , size and involvement of other vessels CT is not limited by bowel gas or body habitus CT angiography ( CTA ) is considered gold standard but requires use of intravenous contrast ( employed less now as superior images are obtained with CT scans ) Spiral CT ( helical ) renders 3D superior images of abdominal contents

MRI-free of ionizing radiation can be more accurate than CT but costlier and not widely available

 

all men > 66 about AAA screening programme if not enrolled already they can self-refer

Risk factors -men over 66 ( if not already screened ) to self refer if they have any risk factors as ○ chronic obstructive lung disease ( COPD ) ○ coronary , cerebrovascular or peripheral arterial disease ○ family h/o AAA ○ hyperlipidaemia ○ hypertension ○ they smoke or used to smoke

 

Consider an aortic US in women –Women aged 70 and over if AAA has not been excluded on abdominal imaging if they have any of the risk factors as mentioned above in bold red

 

Offer aortic US – identifying asymptomatic AAAs In whom a diagnosis of asymptomatic AAA is being considered and if they are not already in the NHS screening programme refer people with AAA of 5.5 cm or larger -to be seen within 2 weeks of diagnosis refer with AAA of 3.0 cm to 5.4 cm to be seen within 12 weeks of diagnosis Offer an US if AAA is suspected on abdominal palpation

 

Identifying symptomatic or ruptured AAA’s Consider AAA in people with new abdominal and / or back pain, cardiovascular collapse or loss of consciousness. Ruptured AAA is more likely if they have any of the following risk factors ○ an existing AAA ○ 60 or over ○ current or previous smoker ○ h/o hypertension AAAs are more likely to rupture in women.

 

Patient education inform about the diagnosis that most AAA’s do not cause any problems what is AAA rupture that AAA’s can become larger and larger AAA’s are at greater risk of rupture AAA’s may run in families ( to tell close relatives that they may be at increased risk and that they should consider assessment ) address CV disease and discuss risk reduction

 

If the patient has not been offered AAA repair – discuss small AAA’s-low risk of rupture and repair itself is associated with risks hence repair does not offer benefit current criteria on repair and that AAA growth is unpredictable ○ if it is symptomatic ○ asymptomatic , larger than 4.0 cm and has grown by > 1 cm in 1 year ○ asymptomatic and 5.5 cm or larger 

 

Repair options Open or Endovascular-this would be the field of specialized vascular centres dealing with AAAs who would discuss the pros / cons /benefits / risks

 

Risk reduction-Smoking is the biggest modifiable risk factor and NICE recommends a referral to stop smoking services (in one study it has been shown that continued smoking increases the rate of aneurysm growth by 20-25 % ) Address hypertension in keeping with NICE guideline 

REFERENCES

  1. Shaw PM, Loree J, Gibbons RC. Abdominal Aortic Aneurysm. [Updated 2021 Jan 3]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2021 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK470237/
  2. Aggarwal, Sourabh et al. “Abdominal aortic aneurysm: A comprehensive review.” Experimental and clinical cardiology vol. 16,1 (2011): 11-5.
  3. Nordon IM, Hinchliffe RJ, Loftus IM, Thompson MM. Pathophysiology and epidemiology of abdominal aortic aneurysms. Nat Rev Cardiol. 2011 Feb;8(2):92-102. doi: 10.1038/nrcardio.2010.180. Epub 2010 Nov 16. PMID: 21079638. (Abstract )
  4. Abdominal Aortic Aneurysm: Practice Essentials, Background, Anatomy (medscape.com)
  5. Prevalence and Trends of the Abdominal Aortic Aneurysms Epidemic in General Population – A Meta-Analysis (plos.org)
  6. Overview | Abdominal aortic aneurysm: diagnosis and management | Guidance | NICE
  7. Abdominal aortic aneurysm | Radiology Reference Article | Radiopaedia.org
  8. Metcalfe DHolt P J EThompson M MThe management of abdominal aortic aneurysms doi:10.1136/bmj.d1384 ( Abstract )

 

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