Abdominal aortic aneurysm
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2008-06-21T21:30:04Z
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{{Infobox_Disease |
Name = Abdominal aortic aneurysm |
Image = |
Caption = |
DiseasesDB = 792 |
ICD10 = {{ICD10|I|71|3|i|70}}, {{ICD10|I|71|4|i|70}} |
ICD9 = {{ICD9|441.3}}, {{ICD9|441.4}} |
ICDO = |
OMIM = 100070 |
MedlinePlus = 000162 |
eMedicineSubj = med |
eMedicineTopic = 3443 |
eMedicine_mult = {{eMedicine2|emerg|27}} {{eMedicine2|radio|1}} |
MeshID = D017544 |
}}
[[Image:Aortadiagramgray.png|frame|A plate from ''[[Gray's Anatomy]]'' with yellow lines depicting the most common infrarenal location of the AAA.]]
'''Abdominal aortic aneurysm''', also written as '''AAA''' and often pronounced 'triple-A', is a localized dilatation of the [[abdominal aorta]], that exceeds the normal diameter by more than 50%. The normal diameter of the infrarenal aorta is 2 cm. It is caused by a [[degenerative]] process of the aortic wall, however the exact etiology remains unknown. It is most commonly located below the kidneys ([[wiktionary:infrarenal|infrarenally]]; 90%), other possible locations are above or at the level of the kidneys ([[wiktionary:suprarenal|suprarenal]] and [[wiktionary:pararenal|pararenal]]). The aneurysm can extend to include one or both of the [[iliac arteries]]. An [[aortic aneurysm]] may also occur in the [[thorax]].
An abdominal aortic aneurysm occurs most commonly in [[elderly|older individuals]] (between 65 and 75), and more in men and smokers. There is moderate evidence to support [[screening]] in individuals with these risk factors. The majority of abdominal aortic aneurysms do not cause [[symptoms]]. Symptomatic and large aneurysms (>5 cm in diameter) are considered for repair.
The most important complication of an abdominal aortic aneurysm is rupture, which is most often a fatal event. An abdominal aortic aneurysm weakens the walls of the blood vessel, leaving it vulnerable to bursting open, or rupturing, and spilling large amounts of blood into the abdominal cavity.<ref name="AAFP">{{cite journal |author=Upchurch GR, Schaub TA |title=Abdominal aortic aneurysm |journal=Am Fam Physician |volume=73 |issue=7 |pages=1198–204 |year=2006 |pmid=16623206 |doi=}}</ref>
==History==
The first historical records about AAA are from [[Ancient Rome]], more precisely from the [[2nd century]] AD, when Greek surgeon [[Antyllus]] tried to treat the AAA with [[proximal]] and [[distal]] ligature, central incision and evacuation of thrombotic material from the [[aneurysm]].
However, attempts to treat the AAA surgically were unsuccessful until [[1923]]. In that year, [[Rudolph Matas]] (who also proposed the concept of endoaneurysmorrhaphy), performed the first successful aortic ligation on a human.<ref name="livesay">Livesay JJ ''et al''. Milestones in Treatment of Aortic Aneurysm. ''Tex Heart Inst J'' 2005; '''32''': 130–134. PMCID 1163455</ref> Other methods that were successful in treating the AAA included wrapping the aorta with polyethene [[cellophane]], which induced [[fibrosis]] and restricted the growth of the aneurysm. [[Albert Einstein]] was operated on by [[Nissen fundoplication|Rudolf Nissen]] with use of this technique in 1949, and survived five years after the operation.<ref>[http://www.medscape.com/viewarticle/436253 Famous Patients, Famous Operations, 2002 - Part 3: The Case of the Scientist with a Pulsating Mass] from Medscape Surgery</ref>
==Epidemiology==
AAA is uncommon in individuals of African, Asian, and Hispanic heritage. The frequency varies strongly between males and females. The peak [[incidence (epidemiology)|incidence]] is among males around 70 years of age, the [[prevalence]] among males over 60 years totals 2-6%. The frequency is much higher in smokers than in non-smokers (8:1), and the risk decreases slowly after smoking cessation.<ref name="smoking">Wilmink TBM, Quick CRG, Day NE. The association between cigarette smoking and abdominal aortic aneurysms. ''J Vasc Surg'' 1999;30:1099-1105. PMID 10587395</ref> Other risk factors include [[hypertension]] and male sex.<ref name="Treska">Treska V. ''et al''.:Aneuryzma břišní aorty, Prague, 1999, ISBN 80-7169-724-9</ref> In the U.S., the incidence of AAA is 2-4% in the adult population. <ref name="emedicine">{{eMedicine|med|3443}}</ref>. AAA is 4-6 times more common in male siblings of known patients, with a risk of 20-30%.<ref name="siblings">Baird PA, Sadovnick AD, Yee IM, Cole CW, Cole L. Sibling risks of abdominal aortic aneurysm. ''Lancet'' 1995;346:601-604. PMID 7651004</ref>
Rupture of the AAA occurs in 1-3% of men aged 65 or more, the mortality is 70-95%.<ref name="screening">Lindholt JS, Juul S, Fasting H, Henneberg EW. Screening for abdominal aortic aneurysms: single centre randomised controlled trial. ''BMJ'' 2005; '''330''': 750. PMCID: 555873</ref>
==Etiology==
The exact causes of the degenerative process remain unclear. There are, however, some theories and [[risk factors]] defined.
* '''Genetic influences''': The influence of genetic factors is highly probable. The high familial prevalence rate is most notable in male individuals.<ref>Clifton, MA: Familial abdominal aortic aneurysms. Br. J. Surg., 64, 1977, p. 765-766</ref> There are many theories about the exact genetic disorder that could cause higher incidence of AAA among male members of the affected families. Some presumed that the influence of [[alpha 1-antitrypsin]] deficiency could be crucial, some experimental works favored the theory of [[X-linked]] [[mutation]], which would explain the lower incidence in [[heterozygous]] females. Other theories of genetic etiology were also formulated.<ref name="emedicine"/>
* '''Hemodynamic influences''': Abdominal aortic aneurysm is a focal degenerative process with predilection for the subrenal aorta. The histological structure and mechanical characteristics of subrenal aorta differ from those of the [[thoracic aorta]]. The diameter decreases from the root to the bifurcation, and the wall of the abdominal aorta also contains a lesser proportion of [[elastin]]. The mechanical [[tension]] in abdominal aortic wall is therefore higher than in the thoracic aortic wall. The [[Elasticity (physics)|elasticity]] and distensibility also decline with age, which can result in gradual dilatation of the segment. Higher intraluminal pressure in patients with arterial hypertension markedly contributes to the progression of the pathological process.<ref name="Treska"/>
* '''Atherosclerosis''': The AAA was long considered to be caused by [[atherosclerosis]], because the walls of the AAA are frequently affected heavily. However, this theory cannot be used to explain the initial defect and the development of occlusion, which is observed in the process.<ref name="emedicine"/>
* '''Other causes''': Other causes of the development of AAA include: [[infection]], [[Physical trauma|trauma]], [[arteritis]], [[cystic medial necrosis]] (m. Erdheim) and [[connective tissue]] disorders (e.g. [[Marfan syndrome]], [[Ehlers-Danlos syndrome]]).<ref name="Treska"/>
==Pathophysiology==
The most striking histopathological changes of aneurysmatic aorta are seen in [[tunica media]] and [[intima]]. These include accumulation of lipids in [[foam cells]], extracellular free [[cholesterol]] crystals, [[calcification]]s, ulcerations and ruptures of the layers and thrombosis. There is an adventitial inflammatory infiltrate.<ref name="Treska"/>
However, the [[degradation]] of tunica media by means of proteolytic process seems to be the basic pathophysiologic mechanism of the AAA development. Some researchers report increased expression and activity of matrix metalloproteinases in individuals with AAA. This leads to elimination of elastine from the media, rendering the aortic wall more susceptible to the influence of the [[blood pressure]]. <ref name="emedicine"/> Other pathophysiological cause for development of the AAA is inflammation.
==Screening==
A [[clinical practice guideline]] by the [[U.S. Preventive Services Task Force]] "recommends one-time screening for abdominal aortic aneurysm (AAA) by ultrasonography in men age 65 to 75 years who have ever smoked".<ref name="pmid15684208">{{cite journal |author=U.S. Preventive Services Task Force |title=Screening for abdominal aortic aneurysm: recommendation statement |journal=Ann. Intern. Med. |volume=142 |issue=3 |pages=198–202 |year=2005 |pmid=15684208 |doi=|url=http://www.annals.org/cgi/content/full/142/3/198}}</ref><ref name="pmid15684209">{{cite journal |author=Fleming C, Whitlock EP, Beil TL, Lederle FA |title=Screening for abdominal aortic aneurysm: a best-evidence systematic review for the U.S. Preventive Services Task Force |journal=Ann. Intern. Med. |volume=142 |issue=3 |pages=203–11 |year=2005 |pmid=15684209 |doi=|url=http://www.annals.org/cgi/content/full/142/3/203}}[http://www.acpjc.org/Content/143/1/issue/ACPJC-2005-143-1-011.htm ACP Journal Club]</ref> This is a grade B recommendation<ref>[http://www.ahrq.gov/clinic/3rduspstf/ratings.htm Recommendation ratings]</ref>. A re-analysis of the meta-analysis estimated a [[number needed to treat| number needed to screen]] of approximately 850 patients.<ref name="pmid15989299">{{cite journal |author=Cinà CS, Devereaux PJ |title=Review: population-based screening for abdominal aortic aneurysm reduces cause-specific mortality in older men |journal=ACP J. Club |volume=143 |issue=1 |pages=11 |year=2005 |pmid=15989299 |doi= |url=http://www.acpjc.org/Content/143/1/issue/ACPJC-2005-143-1-011.htm}}</ref>
The largest of the [[randomized controlled trial]]s on which this guideline was based studied a screening program that consisted of<ref name="pmid12443589">{{cite journal |author=Ashton HA, Buxton MJ, Day NE, ''et al'' |title=The Multicentre Aneurysm Screening Study (MASS) into the effect of abdominal aortic aneurysm screening on mortality in men: a randomised controlled trial |journal=Lancet |volume=360 |issue=9345 |pages=1531–9 |year=2002 |pmid=12443589 |doi=}} [http://www.acpjc.org/Content/138/3/issue/ACPJC-2003-138-3-066.htm ACP Journal Club]</ref>:
:Screening men ages 65-74 years (not restricted to ever smokers). 'Men in whom abdominal aortic aneurysms (> or =3 cm in diameter) were detected were followed-up... Patients with an aortic diameter of 3·0–4·4 cm were rescanned at yearly intervals, whereas those with an aortic diameter of 4·5–5·4 cm were rescanned at 3-monthly intervals ... Surgery was considered on specific criteria (diameter > or =5.5 cm, expansion > or =1 cm per year, symptoms)'.
This trial reported significant short<ref name="pmid12443589"/> ([[number needed to treat| number needed to screen]] after 4 years of approximately 590 to prevent nonfatal ruptured AAA plus AAA-related deaths<ref name="pmid12725621">{{cite journal |author=Cina CS |title=Screening for abdominal aortic aneurysm reduced death from AAA in older men |journal=ACP J. Club |volume=138 |issue=3 |pages=66 |year=2003 |pmid=12725621 |doi=}}</ref>) and long term<ref name="pmid17502630">{{cite journal |author=Kim LG, P Scott RA, Ashton HA, Thompson SG |title=A sustained mortality benefit from screening for abdominal aortic aneurysm |journal=Ann. Intern. Med. |volume=146 |issue=10 |pages=699–706 |year=2007 |pmid=17502630 |doi=}}</ref> ([[number needed to treat| number needed to screen]] after 7 years of approximately 280 to prevent nonfatal ruptured AAA plus AAA-related deaths) benefit and cost effectiveness.<ref name="pmid12433761">{{cite journal |author=Multicentre Aneurysm Screening Study Group |title=Multicentre aneurysm screening study (MASS): cost effectiveness analysis of screening for abdominal aortic aneurysms based on four year results from [[randomized controlled trial]] |journal=BMJ |volume=325 |issue=7373 |pages=1135 |year=2002 |pmid=12433761 |doi=10.1136/bmj.325.7373.1135}} [http://www.acpjc.org/Content/139/1/issue/ACPJC-2003-139-1-024.htm ACP Journal Club]</ref> Subsequent [[randomized controlled trial]]s also found benefit:
* [[number needed to treat| number needed to screen]] after 4 years of 300<ref name="pmid15757960">{{cite journal |author=Lindholt JS, Juul S, Fasting H, Henneberg EW |title=Screening for abdominal aortic aneurysms: single centre randomised controlled trial |journal=BMJ |volume=330 |issue=7494 |pages=750 |year=2005 |pmid=15757960 |doi=10.1136/bmj.38369.620162.82}} [http://www.acpjc.org/Content/143/2/issue/ACPJC-2005-143-2-039.htm ACP Journal Club]</ref>
* [[number needed to treat| number needed to screen]] after and after 7 years of 563 ([http://medinformatics.uthscsa.edu/calculator/calc.shtml?calc_rx_2x2.shtml?a=47.0&b=2898&c=54.0&d=2991&row1total=2945&row2total=3045 calculation]).<ref name="pmid17514666">{{cite journal |author=Ashton HA, Gao L, Kim LG, Druce PS, Thompson SG, Scott RA |title=Fifteen-year follow-up of a randomized clinical trial of ultrasonographic screening for abdominal aortic aneurysms |journal=The British journal of surgery |volume=94 |issue=6 |pages=696–701 |year=2007 |pmid=17514666 |doi=10.1002/bjs.5780}}</ref>
In the U.S., effective January 1, 2007, provisions of the SAAAVE Act (Screening Abdominal Aortic Aneurysm Very Efficiently) now provide a free, one-time, ultrasound AAA screening benefit for those qualified seniors. Men who have smoked at least 100 cigarettes during their life, and men and women with a family history of AAA qualify for the one-time ultrasound screening. Enrollees must visit their healthcare professional for their Welcome to Medicare physical within six months of enrolment in order to qualify for the free screening. The Welcome to Medicare Physical Exam must be completed within the first six months of Medicare eligibility, but there is no published time limit thereafter for completion of the AAA screening. Providers who perform the physical and order the AAA screening need to document the AAA risk factors.<ref>Society for Vascular Surgery</ref>
==Manifestations and Diagnosis==
AAAs are commonly divided according to their size and symptomatology. An aneurysm is usually considered to be present if the measured outer aortic diameter is over 3 cm (normal diameter of [[aorta]] is around 2 cm). The natural history is of increasing diameter over time, followed eventually by the development of symptoms (usually rupture). If the outer diameter exceeds 5 cm, the aneurysm is considered to be large. For aneurysms under 5 cm, the risk of rupture is low, so that the risks of surgery usually outweigh the risk of rupture. Aneurysms less than 5cm are therefore usually kept under surveillance until such time as they become large enough to warrant repair, or develop symptoms.<ref name="Treska"/><ref name="screening"/>
The vast majority of aneurysms are asymptomatic. The risk of rupture is high in a symptomatic aneurysm, which is therefore considered an indication for surgery. Possible symptoms include low back pain, flank pain, abdominal pain, groin pain or pulsating abdominal mass.<ref name="emed2">[http://www.emedicine.com/emerg/topic27.htm O'Connor RE: Aneurysm, Abdominal], on [http://www.emedicine.com emedicine], accessed June 23, 2006.</ref> The complications include rupture, peripheral [[embolisation]], acute aortic occlusion, aortocaval or aortoduodenal [[fistulae]]. On physical examination, a palpable abdominal mass can be noted. Bruits can be present in case of renal or visceral arterial stenosis.<ref name="emedicine"/>
[[Image:AAA-101.jpg|right|thumb|CT image showing an abdominal aortic aneurysm.]]
As most of the AAAs are asymptomatic, their presence is usually revealed during an abdominal examination for another reason - the most common being abdominal ultrasonography. A physician may also detect the presence of an AAA by abdominal palpation. Ultrasonography provides the initial assessment of the size and extent of the aneurysm, and is the usual modality for surveillance. Preoperative examinations include [[Computed tomography|CT]], [[MRI]] and special modes thereof, like CT/MR angiography. Angiography may be useful also, as an additional method of measurement for the planning of endoluminal repair. Note that an aneurysmal aorta may appear normal on angiogram, due to thrombus within the sac.
==Rupture==
The clinical manifestation of ruptured AAA can include low back, flank, abdominal or groin pain, but the bleeding usually leads to a [[hypovolemic shock]] with [[hypotension]], [[tachycardia]], [[cyanosis]], and altered mental status. The mortality of AAA rupture is up to 90%. 65-75% of patients die before they arrive at hospital and up to 90% die before they reach the operating room.<ref name="SmallAneurysmTrial">Brown LC, Powell JT, UK Small Aneurysm Trial Participants. Risk factors for aneurysm rupture in patients kept under ultrasound surveillance. ''Ann Surg'' 1999;230:289-297. PMID 10493476</ref> The bleeding can be retroperitoneal or intraperitoneal, or the rupture can create an aortocaval or aortointestinal fistula.<ref name="Treska"/>. Flank [[ecchymosis]] (appearance of a bruise) is a sign of retroperitoneal hemorrhage, and is also called the Grey-Turner sign.<ref name="emedicine"/>
Ruptured AAA is a clinical diagnosis: the presence of the triad of abdominal pain, shock and pulsatile abdominal mass makes the diagnosis; no further investigations are required for diagnostic purposes, and imaging should not delay surgery. The operative mortality has slowly decreased over several decades but remains higher than 40%.<ref name="repair">Bown MJ, Sutton AJ, Bell PR, Sayers RD. A meta-analysis of 50 years of ruptured abdominal aortic aneurysm repair. ''Br J Surg'' 2002;89:714-730. PMID 12027981</ref>
==Treatment==
The treatment options for asymptomatic AAA are immediate repair, surveillance with a view to eventual repair, and [[wiktionary:conservative treatment|conservative]] management.
There are currently two modes of repair available for an AAA: open aneurysm repair (OR), and endovascular aneurysm repair ([[EVAR]]).
* ''Conservative treatment'' is indicated in patients where repair carries a high risk of mortality and also in patients where repair is unlikely to improve life expectancy. The two mainstays of the conservative treatment are [[tobacco smoking|smoking]] cessation and [[blood pressure]] control. Recent studies have suggested possible protective effects of therapy with [[angiotensin converting enzyme inhibitor]]s or [[statin]]s.<ref name="ACE">Hackam DG, Thiruchelvam D, Redelmeier DA. Angiotensin-converting enzyme inhibitors and aortic rupture: a population-based case-control study. ''Lancet'' 2006;368:659-665. PMID 16920471</ref><ref name="EVAR2-posthoc">Powell JT, Brown LC, Greenhalgh RM, Thompson SG. The rupture rate of large abdominal aortic aneurysms: is this modified by anatomical suitability for endovascular repair? ''Ann Surg'' 2008;247:173-179. PMID 18156938</ref>
* ''Surveillance'' is indicated in small aneurysms, where the risk of repair exceeds the risk of rupture. As an AAA grows in diameter the risk of rupture increases. Surveillance until the aneurysm has reached a diameter of 5cm has not been shown to have a higher risk as compared to early intervention.<ref name="SmallAneurysm">Powell JT, Brown LC, Forbes JF, et al. Final 12-year follow-up of patients enrolled in the UK Small Aneurysm Trial. Br J Surg 2007;94:702-708. PMID 17514693</ref><ref name="ADAM">Lederle FA, Wilson SE, Johnson GR, et al. Immediate repair compared with surveillance of small abdominal aortic aneurysms. ''N Engl J Med'' 2002;346:1437-1444. PMID 12000813 [http://content.nejm.org/cgi/content/full/346/19/1437 Free full text]</ref> The threshold for repair varies slightly from individual to individual, depending on the balance of risks and benefits when considering repair versus ongoing surveillance. The size of an individual's native aorta may influence this, along with the presence of comorbitities that increase operative risk or decrease life expectancy.
* ''Open repair'' (operation) is indicated in young patients as an elective procedure, or in growing or large, symptomatic or ruptured aneurysms. Open repair has been the mainstay of intervention from the 1950s until recently.
* ''Endovascular repair'' first became practical in the 1990s and although it is now an established alternative to open repair, its role is yet to be clearly defined. It is generally indicated in older, high-risk patients or patients unfit for open repair. However, endovascular repair is feasible for only a proportion of AAA's, depending on the morphology of the aneurysm. The main advantage over open repair is that there is less peri-operative mortality, less time in [[intensive care]], less time in hospital overall and earlier return to normal activity. Disadvantages of endovascular repair include a requirement for more frequent ongoing hospital reviews, and a higher chance of further procedures being required. According to the latest studies, the EVAR procedure doesn't offer any benefit for overall survival or health-related [[quality of life]] compared to open surgery, although aneurysm-related mortality is lower.<ref name="pmid16782510">Rutherford RB. Randomized EVAR Trials and Advent of Level I Evidence: A Paradigm Shift in Management of Large Abdominal Aortic Aneurysms? ''Semin Vasc Surg'' 2006; '''19''':69-74. PMID 16782510</ref><ref name="pmid17502634">{{cite journal |author=Lederle FA, Kane RL, MacDonald R, Wilt TJ |title=Systematic review: repair of unruptured abdominal aortic aneurysm |journal=Ann. Intern. Med. |volume=146 |issue=10 |pages=735–41 |year=2007 |pmid=17502634 |doi=}}</ref><ref name="EVAR1">EVAR Trial Participants. Endovascular aneurysm repair versus open repair in patients with abdominal aortic aneurysm (EVAR trial 1): randomised controlled trial. ''Lancet'' 2005;365:2179-2186. PMID 15978925</ref><ref name="DREAM">Blankensteijn JD, de Jong SECA, Prinssen M, et al. Two-year outcomes after conventional or endovascular repair of abdominal aortic aneurysms. ''N Engl J Med'' 2005;352:2398-2405. PMID 15944424 [http://content.nejm.org/cgi/content/full/352/23/2398 Free full text]</ref> In patients unfit for open repair, EVAR plus conservative management was associated with no benefit and more complications and subsequent procedures and higher costs compared to conservative management alone.<ref name="EVAR2">EVAR Trial Participants. Endovascular aneurysm repair and outcome in patients unfit for open repair of abdominal aortic aneurysm (EVAR trial 2): randomised controlled trial. ''Lancet'' 2005;365:2187-2192. PMID 15978926</ref>
New endovascular devices are being developed that are able to treat more complex and tortuous anatomies.<ref>Albertini JN, Perdikides T, Soong CV, Hinchliffe RJ, Trojanowska M, Yusuf SW, Endovascular repair of abdominal aortic aneurysms in patients with severe angulation of the proximal neck using a flexible stent-graft: European Multicenter Experience. ''J Cardiovasc Surg (Torino)''. 2006;47(3):245-50.
PMID 16760860</ref>
==References==
{{Reflist|2}}
==External links==
* [http://videos.med.wisc.edu/videoInfo.php?videoid=1111 VIDEO: Factors that Influence Decision Making for Abdominal Aortic Aneurysm Repair] Margaret L. Schwarze, MD, speaks at the University of Wisconsin School of Medicine and Public Health, 2007.
{{Vascular diseases}}
[[Category:Vascular surgery]]
[[Category:Surgery]]
[[Category:Cardiovascular diseases]]