Abdominal aortic aneurysm (AAA) is a localized enlargement of the

abdominal aorta In human anatomy, the abdominal aorta is the largest artery in the abdominal cavity. As part of the aorta, it is a direct continuation of the descending aorta (of the thorax). Structure The abdominal aorta begins at the level of the diaphragm ...

such that the diameter is greater than 3 cm or more than 50% larger than normal. An AAA usually causes no symptoms, except during rupture. Occasionally, abdominal, back, or leg pain may occur. Large aneurysms can sometimes be felt by pushing on the abdomen. Rupture may result in pain in the abdomen or back, low blood pressure, or

loss of consciousness Unconsciousness is a state in which a living individual exhibits a complete, or near-complete, inability to maintain an awareness of self and environment or to respond to any human or environmental stimulus. Unconsciousness may occur as the re ...

, and often results in death. AAAs occur most commonly in men, those over 50, and those with a family history of the disease. Additional risk factors include

smoking Smoking is a practice in which a substance is combusted, and the resulting smoke is typically inhaled to be tasted and absorbed into the bloodstream of a person. Most commonly, the substance used is the dried leaves of the tobacco plant, whi ...

high blood pressure Hypertension, also known as high blood pressure, is a long-term medical condition in which the blood pressure in the arteries is persistently elevated. High blood pressure usually does not cause symptoms itself. It is, however, a major ri ...

, and other heart or blood vessel diseases. Genetic conditions with an increased risk include

Marfan syndrome Marfan syndrome (MFS) is a multi-systemic genetic disorder that affects the connective tissue. Those with the condition tend to be tall and thin, with dolichostenomelia, long arms, legs, Arachnodactyly, fingers, and toes. They also typically ha ...

and

Ehlers–Danlos syndrome Ehlers–Danlos syndromes (EDS) is a group of 14 genetic connective-tissue disorders. Symptoms often include loose joints, joint pain, stretchy velvety skin, and abnormal scar formation. These may be noticed at birth or in early childhood. Co ...

. AAAs are the most common form of

aortic aneurysm An aortic aneurysm is an enlargement (dilatation) of the aorta to greater than 1.5 times normal size. Typically, there are no symptoms except when the aneurysm dissects or ruptures, which causes sudden, severe pain in the abdomen and lower back ...

. About 85% occur below the

kidney In humans, the kidneys are two reddish-brown bean-shaped blood-filtering organ (anatomy), organs that are a multilobar, multipapillary form of mammalian kidneys, usually without signs of external lobulation. They are located on the left and rig ...

s, with the rest either at the level of or above the kidneys. In the

United States The United States of America (USA), also known as the United States (U.S.) or America, is a country primarily located in North America. It is a federal republic of 50 U.S. state, states and a federal capital district, Washington, D.C. The 48 ...

, screening with

abdominal ultrasound Abdominal ultrasonography (also called abdominal ultrasound imaging or abdominal sonography) is a form of medical ultrasonography (medicine, medical application of ultrasound technology) to visualise abdomen, abdominal anatomy, anatomical structu ...

is recommended for males between 65 and 75 years of age with a history of smoking. In the

United Kingdom The United Kingdom of Great Britain and Northern Ireland, commonly known as the United Kingdom (UK) or Britain, is a country in Northwestern Europe, off the coast of European mainland, the continental mainland. It comprises England, Scotlan ...

and

Sweden Sweden, formally the Kingdom of Sweden, is a Nordic countries, Nordic country located on the Scandinavian Peninsula in Northern Europe. It borders Norway to the west and north, and Finland to the east. At , Sweden is the largest Nordic count ...

, screening all men over 65 is recommended. Once an aneurysm is found, further ultrasounds are typically done regularly until an aneurysm meets a threshold for repair. Abstinence from cigarette smoking is the single best way to prevent the disease. Other methods of prevention include treating high blood pressure, treating high blood cholesterol, and avoiding being

overweight Being overweight is having more body fat than is optimally healthy. Being overweight is especially common where food supplies are plentiful and lifestyles are sedentary. , excess weight reached epidemic proportions globally, with more than ...

. Surgery is usually recommended when the diameter of an AAA grows to >5.5 cm in males and >5.0 cm in females. Other reasons for repair include symptoms and a rapid increase in size, defined as more than one centimeter per year. Repair may be either by

open surgery Minimally invasive procedures (also known as minimally invasive surgeries) encompass surgical techniques that limit the size of incisions needed, thereby reducing wound healing time, associated pain, and risk of infection. Surgery by definitio ...

endovascular aneurysm repair Endovascular aneurysm repair (EVAR) is a type of minimally-invasive endovascular surgery used to treat pathology of the aorta, most commonly an abdominal aortic aneurysm (AAA). When used to treat thoracic aortic disease, the procedure is then s ...

(EVAR). As compared to open surgery, EVAR has a lower risk of death in the short term and a shorter hospital stay, but may not always be an option. There does not appear to be a difference in longer-term outcomes between the two. Repeat procedures are more common with EVAR. AAAs affect 2-8% of males over the age of 65. They are five times more common in men. In those with an aneurysm less than 5.5 cm, the risk of rupture in the next year is below 1%. Among those with an aneurysm between 5.5 and 7 cm, the risk is about 10%, while for those with an aneurysm greater than 7 cm the risk is about 33%. Mortality if ruptured is 85% to 90%. Globally, aortic aneurysms resulted in 168,200 deaths in 2013, up from 100,000 in 1990. In the United States AAAs resulted in between 10,000 and 18,000 deaths in 2009.

Signs and symptoms

The vast majority of aneurysms are asymptomatic. However, as the abdominal aorta expands and/or ruptures, the aneurysm may become painful and lead to pulsating sensations in the abdomen or pain in the chest, lower back, legs, or scrotum.

Complications

The complications include rupture, peripheral

embolization Embolization refers to the passage and lodging of an embolus within the bloodstream. It may be of natural origin ( pathological), in which sense it is also called embolism, for example a pulmonary embolism; or it may be artificially induced ...

, acute aortic occlusion, and aortocaval (between the aorta and

inferior vena cava The inferior vena cava is a large vein that carries the deoxygenated blood from the lower and middle body into the right atrium of the heart. It is formed by the joining of the right and the left common iliac veins, usually at the level of the ...

) or aortoduodenal (between the aorta and the

duodenum The duodenum is the first section of the small intestine in most vertebrates, including mammals, reptiles, and birds. In mammals, it may be the principal site for iron absorption. The duodenum precedes the jejunum and ileum and is the shortest p ...

) fistulae. On physical examination, a

palpable {{Short pages monitor

Pathophysiology

The most striking

histopathological Histopathology (compound of three Greek language, Greek words: 'tissue', 'suffering', and ''-logy, -logia'' 'study of') is the light microscope, microscopic examination of Tissue (biology), tissue in order to study the manifestations of dis ...

changes of the aneurysmatic aorta are seen in the

tunica media The tunica media (Neo-Latin "middle coat"), or media for short, is the middle tunica (layer) of an artery or vein. It lies between the internal elastic lamina of the tunica intima on the inside and the tunica externa on the outside. Artery The ...

and intima layers. These changes include the accumulation of lipids in foam cells, extracellular free

cholesterol Cholesterol is the principal sterol of all higher animals, distributed in body Tissue (biology), tissues, especially the brain and spinal cord, and in Animal fat, animal fats and oils. Cholesterol is biosynthesis, biosynthesized by all anima ...

crystals,

calcification Calcification is the accumulation of calcium salts in a body tissue. It normally occurs in the formation of bone, but calcium can be deposited abnormally in soft tissue,Miller, J. D. Cardiovascular calcification: Orbicular origins. ''Nature M ...

thrombosis Thrombosis () is the formation of a Thrombus, blood clot inside a blood vessel, obstructing the flow of blood through the circulatory system. When a blood vessel (a vein or an artery) is injured, the body uses platelets (thrombocytes) and fib ...

, and ulcerations and ruptures of the layers. Adventitial inflammatory infiltrate is present. However, the degradation of the tunica media by means of a

proteolytic Proteolysis is the breakdown of proteins into smaller polypeptides or amino acids. Protein degradation is a major regulatory mechanism of gene expression and contributes substantially to shaping mammalian proteomes. Uncatalysed, the hydrolysis o ...

process seems to be the basic pathophysiologic mechanism of AAA development. Some researchers report increased expression and activity of matrix

metalloproteinase A metalloproteinase, or metalloprotease, is any protease enzyme whose catalytic mechanism involves a metal. An example is ADAM12 which plays a significant role in the fusion of muscle cells during embryo development, in a process known as myoge ...

s in individuals with AAA. This leads to the elimination of

elastin Elastin is a protein encoded by the ''ELN'' gene in humans and several other animals. Elastin is a key component in the extracellular matrix of gnathostomes (jawed vertebrates). It is highly Elasticity (physics), elastic and present in connective ...

from the media, rendering the aortic wall more susceptible to the influence of

blood pressure Blood pressure (BP) is the pressure of Circulatory system, circulating blood against the walls of blood vessels. Most of this pressure results from the heart pumping blood through the circulatory system. When used without qualification, the term ...

. Other reports have suggested the

serine protease Serine proteases (or serine endopeptidases) are enzymes that cleave peptide bonds in proteins. Serine serves as the nucleophilic amino acid at the (enzyme's) active site. They are found ubiquitously in both eukaryotes and prokaryotes. Serin ...

granzyme B may contribute to aortic aneurysm rupture through the cleavage of

decorin Decorin is a protein that in humans is encoded by the ''DCN'' gene. Decorin is a proteoglycan that is on average 90 - 140 kilodaltons (kDa) in molecular weight. It belongs to the small leucine-rich proteoglycan (SLRP) family and consists of a ...

, leading to disrupted

collagen Collagen () is the main structural protein in the extracellular matrix of the connective tissues of many animals. It is the most abundant protein in mammals, making up 25% to 35% of protein content. Amino acids are bound together to form a trip ...

organization and reduced tensile strength of the adventitia. There is also a reduced amount of

vasa vasorum Vasa vasorum are networks of small blood vessels that supply the walls of large blood vessels, such as elastic arteries (e.g., the aorta) and large veins (e.g., the venae cavae). The name derives . Occasionally, two different singular forms ar ...

in the abdominal aorta (compared to the thoracic aorta); consequently, the tunica media must rely mostly on diffusion for nutrition, which makes it more susceptible to damage.

Hemodynamics Hemodynamics or haemodynamics are the dynamics of blood flow. The circulatory system is controlled by homeostatic mechanisms of autoregulation, just as hydraulic circuits are controlled by control systems. The hemodynamic response continuously ...

affect the development of AAA, which has a

predilection In psychology, economics and philosophy, preference is a technical term usually used in relation to choosing between alternatives. For example, someone prefers A over B if they would rather choose A than B. Preferences are central to decision theo ...

for the infrarenal aorta. The histological structure and mechanical characteristics of the infrarenal aorta differ from those of the

thoracic aorta The thoracic aorta is a part of the aorta located in the thorax. It is a continuation of the aortic arch. It is located within the posterior mediastinal cavity, but frequently bulges into the left pleural cavity. The descending thoracic aorta be ...

. The diameter decreases from the root to the

aortic bifurcation The aortic bifurcation is the point at which the abdominal aorta bifurcates (forks) into the left and right common iliac arteries. The aortic bifurcation is usually seen at the level of L4, just above the junction of the left and right common ...

, and the wall of the infrarenal aorta also contains a lesser proportion of

. The mechanical tension in the abdominal aortic wall is therefore higher than in the thoracic aortic wall. The elasticity and

distensibility Distensibility is a metric of the stiffness of blood vessels. It is defined as D = \frac, where d_ and d_ are the diameter of the vessel in systole and diastole, and p_and p_are the systolic and diastolic blood pressure Blood pressure (BP) is ...

also decline with age, which can result in gradual dilatation of the segment. Higher

intraluminal In biology, a lumen (: lumina) is the inside space of a tubular structure, such as an artery or intestine. It comes . It can refer to: *the interior of a vessel, such as the central space in an artery, vein or capillary through which blood flows ...

pressure in patients with arterial hypertension markedly contributes to the progression of the pathological process. Suitable hemodynamic conditions may be linked to specific intraluminal thrombus (ILT) patterns along the aortic lumen, which in turn may affect AAA's development.

Diagnosis

An abdominal aortic aneurysm is usually diagnosed by

physical exam In a physical examination, medical examination, clinical examination, or medical checkup, a medical practitioner examines a patient for any possible medical signs or symptoms of a medical condition. It generally consists of a series of questions ...

, or

CT scan A computed tomography scan (CT scan), formerly called computed axial tomography scan (CAT scan), is a medical imaging technique used to obtain detailed internal images of the body. The personnel that perform CT scans are called radiographers or ...

. Plain abdominal radiographs may show the outline of an aneurysm when its walls are calcified. However, the outline will be visible by X-ray in less than half of all aneurysms. Ultrasonography is used to screen for aneurysms and to determine their size if present. Additionally, free peritoneal fluid can be detected. It is non-invasive and sensitive, but the presence of bowel gas or obesity may limit its usefulness. CT scan has nearly 100% sensitivity for an aneurysm and is also useful in preoperative planning, detailing the anatomy and possibility for endovascular repair. In the case of suspected rupture, it can also reliably detect retroperitoneal fluid. Alternative less often used methods for visualization of an aneurysm include

MRI Magnetic resonance imaging (MRI) is a medical imaging technique used in radiology to generate pictures of the anatomy and the physiological processes inside the body. MRI scanners use strong magnetic fields, magnetic field gradients, and rad ...

and

angiography Angiography or arteriography is a medical imaging technique used to visualize the inside, or lumen, of blood vessels and organs of the body, with particular interest in the arteries, veins, and the heart chambers. Modern angiography is perfo ...

. An aneurysm ruptures if the mechanical stress (tension per area) exceeds the local wall strength; consequently, peak wall stress (PWS), mean wall stress (MWS), and peak wall rupture risk (PWRR) are more reliable parameters than diameter to assess AAA rupture risk. Medical software allows computing these rupture risk indices from standard clinical CT data and provides a patient-specific AAA rupture risk diagnosis. This type of biomechanical approach has been shown to accurately predict the location of AAA rupture. File:Ultrasonographic measurement of aortic diameter at the navel.svg, Aortic measurement on

abdominal ultrasonography Abdominal ultrasonography (also called abdominal ultrasound imaging or abdominal sonography) is a form of medical ultrasonography (medical application of ultrasound technology) to visualise abdominal anatomical structures. It uses transmission a ...

in the

axial plane A transverse plane is a plane that is rotated 90° from two other planes. Anatomy The transverse plane is an anatomical plane that is perpendicular to the sagittal plane and the dorsal plane. It is also called the axial plane or horizontal ...

between the outer margins of the aortic wall File:Ultrasonography of abdominal aortic aneurysm in sagittal plane, annotated.jpg, Ultrasonography in the

sagittal plane The sagittal plane (; also known as the longitudinal plane) is an anatomical plane that divides the body into right and left sections. It is perpendicular to the transverse and coronal planes. The plane may be in the center of the body and divi ...

, showing axial plane measure (dashed red line), as well as maximal diameter (dotted yellow line), which is preferred File:RupturedAAA.png, A ruptured AAA with an open arrow marking the aneurysm and the closed arrow marking the free blood in the abdomen File:Sagital aaa.JPG, Sagittal CT image of an AAA File:AAA rupture risk.png, Biomechanical AAA rupture risk prediction File:Contrast-enhanced CT scan demonstrating abdominal aortic aneurysm.jpg, An axial contrast-enhanced CT scan demonstrating an abdominal aortic aneurysm of 4.8 by 3.8 cm File:RupturedAAAXray.png, The faint outline of the calcified wall of an AAA as seen on a plain X-ray File:Abdominal aortic aneurysm.JPG, Abdominal aortic aneurysms (3.4 cm) File:AneursymCTMark.png, An aortic aneurysm as seen on CT with a small area of remaining blood flow File:UOTW 35 - Ultrasound of the Week 1.webm, Ultrasound showing a previously repaired AAA that is leaking with flow around the graft File:Ultrasonography of abdominal aortic aneurysm with mural thrombus.jpg, Ultrasonography of an aneurysm with a mural thrombus

Classification

Abdominal aortic aneurysms are commonly divided according to their size and symptomatology. An aneurysm is usually defined as an outer aortic diameter over 3 cm (normal diameter of the

aorta The aorta ( ; : aortas or aortae) is the main and largest artery in the human body, originating from the Ventricle (heart), left ventricle of the heart, branching upwards immediately after, and extending down to the abdomen, where it splits at ...

is around 2 cm), or more than 50% of normal diameter. If the outer diameter exceeds 5.5 cm, the aneurysm is considered to be large. Ruptured AAA should be suspected in any person older than 60 who experiences collapse, unexplained low blood pressure, or sudden-onset back or abdominal pain. Abdominal pain, shock, and a pulsatile mass are only present in a minority of cases. Although an unstable person with a known aneurysm may undergo surgery without further imaging, the diagnosis will usually be confirmed using CT or ultrasound scanning. The suprarenal aorta normally measures about 0.5 cm larger than the infrarenal aorta.

Differential diagnosis

Aortic aneurysm rupture may be mistaken for the pain of kidney stones, or muscle related

back pain Back pain (Latin: ''dorsalgia'') is pain felt in the back. It may be classified as neck pain (cervical), middle back pain (thoracic), lower back pain (lumbar) or coccydynia (tailbone or sacral pain) based on the segment affected. The lumbar area ...

Prevention

In terms of prevention, the following are effective measures to reduce the risk of developing a AAA: *

Smoking cessation Smoking cessation, usually called quitting smoking or stopping smoking, is the process of discontinuing tobacco smoking. Tobacco smoke contains nicotine, which is Addiction, addictive and can cause Substance dependence, dependence. As a resu ...

* Treatment of

hypertension Hypertension, also known as high blood pressure, is a Chronic condition, long-term Disease, medical condition in which the blood pressure in the artery, arteries is persistently elevated. High blood pressure usually does not cause symptoms i ...

Screening

The

U.S. Preventive Services Task Force The United States Preventive Services Task Force (USPSTF) is "an independent panel of experts in primary care and prevention that systematically reviews the evidence of effectiveness and develops recommendations for clinical preventive services". ...

(USPSTF) recommends a single screening

for abdominal aortic aneurysm in males aged 65 to 75 years who have a history of smoking. Among this group who does not smoke, screening may be selective. It is unclear if screening is useful in women who have smoked and the USPSTF recommends against screening in women who have never smoked. In the United Kingdom, the NHS AAA Screening Programme invites men in England for screening during the year they turn 65. Men over 65 can contact the programme to arrange to be screened. In Sweden one time screening is recommended in all males over 65 years of age. This has been found to decrease the risk of death from AAA by 42% with a number needed to screen just over 200. In those with a close relative diagnosed with an aortic aneurysm, Swedish guidelines recommend an ultrasound at around 60 years of age. Australia has no guideline on screening. Repeat ultrasounds should be carried out in those who have an aortic size greater than 3.0 cm. In those whose aorta is between 3.0 and 3.9 cm this should be every three years, if between 4.0 and 4.4 cm every two years, and if between 4.5 and 5.4 cm every year.

Management

The treatment options for asymptomatic AAA are

conservative Conservatism is a cultural, social, and political philosophy and ideology that seeks to promote and preserve traditional institutions, customs, and values. The central tenets of conservatism may vary in relation to the culture and civiliza ...

management, surveillance with a view to eventual repair, and immediate repair. Two modes of repair are available for an AAA: open aneurysm repair, and endovascular aneurysm repair ( EVAR). An intervention is often recommended if the aneurysm grows more than 1 cm per year or it is bigger than 5.5 cm. Repair is also indicated for symptomatic aneurysms. Ten years after open AAA repair, the overall survival rate was 59%. Mycotic abdominal aorta aneurysm (MAAA) is a rare and life-threatening condition. Because of its rarity, there is a lack of adequately powered studies and consensus on its treatment and follow-up. A management protocol on the management of mycotic abdominal aortic aneurysm was recently published in the Annals of Vascular Surgery by Premnath et al.

Conservative

Conservative management is indicated in people where repair carries a high mortality risk and in patients where repair is unlikely to improve life expectancy. The mainstay of the conservative treatment is

cessation. Surveillance is indicated in small asymptomatic aneurysms (less than 5.5 cm) where the risk of repair exceeds the risk of rupture. As an AAA grows in diameter, the risk of rupture increases. Surveillance until an aneurysm has reached a diameter of 5.5 cm has not been shown to have a higher risk as compared to early intervention.

Medication

No medical therapy is effective at decreasing the growth rate or rupture rate of asymptomatic AAAs.

Blood pressure Blood pressure (BP) is the pressure of Circulatory system, circulating blood against the walls of blood vessels. Most of this pressure results from the heart pumping blood through the circulatory system. When used without qualification, the term ...

and

lipids Lipids are a broad group of organic compounds which include fats, waxes, sterols, fat-soluble vitamins (such as vitamins Vitamin A, A, Vitamin D, D, Vitamin E, E and Vitamin K, K), monoglycerides, diglycerides, phospholipids, and others. The fu ...

should, however, be treated per usual.

Surgery

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 comorbidities that increase operative risk or decrease life expectancy. Evidence, however, does not usually support repair if the size is less than 5.5 cm.

Open repair

Open repair is indicated in young patients as an elective procedure, or in growing or large, symptomatic or ruptured aneurysms. The aorta must be clamped during the repair, denying blood to the abdominal organs and sections of the

spinal cord The spinal cord is a long, thin, tubular structure made up of nervous tissue that extends from the medulla oblongata in the lower brainstem to the lumbar region of the vertebral column (backbone) of vertebrate animals. The center of the spinal c ...

; this can cause a range of complications. As it is essential to perform the critical part of the operation quickly, the incision is typically made large enough to facilitate the fastest repair. Recovery after open AAA surgery takes significant time. The minimums are a few days in intensive care, a week total in the hospital, and a few months before full recovery.

Endovascular repair

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 portion of AAAs, depending on the morphology of the aneurysm. The main advantages over open repair are that there is less peri-operative mortality, less time in

intensive care Intensive care medicine, usually called critical care medicine, is a medical specialty that deals with seriously or critically ill patients who have, are at risk of, or are recovering from conditions that may be life-threatening. It includes p ...

, less time in hospital overall, and an earlier return to normal activity. Disadvantages of endovascular repair include a requirement for more frequent ongoing hospital reviews and a higher chance of further required procedures. According to the latest studies, the EVAR procedure does not offer any benefit for overall survival or health-related

quality of life Quality of life (QOL) is defined by the World Health Organization as "an individual's perception of their position in life in the context of the culture and value systems in which they live and in relation to their goals, expectations, standards ...

compared to open surgery, although aneurysm-related mortality is lower. In patients unfit for open repair, EVAR plus conservative management was associated with no benefit, more complications, subsequent procedures and higher costs compared to conservative management alone. Endovascular treatment for paraanastomotic aneurysms after aortobiiliac reconstruction is also a possibility. A 2017

Cochrane review Cochrane is a British international charitable organisation formed to synthesize medical research findings to facilitate evidence-based choices about health interventions involving health professionals, patients and policy makers. It includes ...

found tentative evidence of no difference in outcomes between endovascular and open repair of ruptured AAA in the first month.

Rupture

In those with

aortic rupture Aortic rupture is the breakage of all walls of the aorta, the largest artery in the body. Aortic rupture is a rare, extremely dangerous condition that is considered a medical emergency. The most common cause is an abdominal aortic aneurysm that ...

of the AAA, treatment is immediate surgical repair. There appear to be benefits to allowing permissive hypotension and limiting the use of intravenous fluids during transport to the operating room.

Prognosis

Although the current standard of determining rupture risk is based on maximum diameter, it is known that smaller AAAs that fall below this threshold (diameter<5.5 cm) may also rupture, and larger AAAs (diameter>5.5 cm) may remain stable. In one report, it was shown that 10–24% of ruptured AAAs were less than 5 cm in diameter. It has also been reported that of 473 non-repaired AAAs examined from autopsy reports, there were 118 cases of rupture, 13% of which were less than 5 cm in diameter. This study also showed that 60% of the AAAs greater than 5 cm (including 54% of those AAAs between 7.1 and 10 cm) never experienced rupture. Vorp ''et al.'' later deduced from the findings of Darling ''et al.'' that if the maximum diameter criterion were followed for the 473 subjects, only 7% (34/473) of cases would have died from rupture before surgical intervention as the diameter was less than 5 cm, with 25% (116/473) of cases possibly undergoing unnecessary surgery since these AAAs may never have ruptured. Alternative methods of rupture assessment have been recently reported. The majority of these approaches involve the numerical analysis of AAAs using the common engineering technique of the finite element method (FEM) to determine the wall stress distributions. Recent reports have shown that these stress distributions have been shown to correlate to the overall geometry of the AAA rather than solely to the maximum diameter. It is also known that wall stress alone does not completely govern failure as an AAA will usually rupture when the wall stress exceeds the wall strength. In light of this, rupture assessment may be more accurate if the patient-specific wall stress is coupled together with patient-specific wall strength. A noninvasive method of determining patient-dependent wall strength was recently reported, with more traditional approaches to strength determination via tensile testing performed by other researchers in the field. Some of the more recently proposed AAA rupture-risk assessment methods include: AAA wall stress; AAA expansion rate; degree of asymmetry; presence of intraluminal thrombus (ILT); a rupture potential index (RPI); a finite element analysis rupture index (FEARI); biomechanical factors coupled with computer analysis; growth of ILT; geometrical parameters of the AAA; and also a method of determining AAA growth and rupture based on mathematical models. The postoperative mortality for an already ruptured AAA has slowly decreased over several decades but remains higher than 40%. However, if the AAA is surgically repaired before rupture, the postoperative mortality rate is substantially lower, approximately 1-6%.

Epidemiology

The occurrence of AAA varies by ethnicity. In the United Kingdom, the rate of AAA in Caucasian men older than 65 years is about 4.7%, while in Asian men it is 0.45%. It is also less common in individuals of African, and Hispanic heritage. They occur four times more often in men than in women. There are at least 13,000 deaths yearly in the U.S. secondary to AAA rupture. The peak number of new cases per year among males is around 70 years of age, and the percentage of males affected over 60 years is 2–6%. The frequency is much higher in smokers than in non-smokers (8:1), and the risk decreases slowly after

smoking cessation Smoking cessation, usually called quitting smoking or stopping smoking, is the process of discontinuing tobacco smoking. Tobacco smoke contains nicotine, which is Addiction, addictive and can cause Substance dependence, dependence. As a resu ...

. In the U.S., the incidence of AAA is 2–4% in the adult population. Rupture of the AAA occurs in 1–3% of men aged 65 or more, for whom the mortality rate is 70–95%.

History

The first historical records about AAA are from

Ancient Rome In modern historiography, ancient Rome is the Roman people, Roman civilisation from the founding of Rome, founding of the Italian city of Rome in the 8th century BC to the Fall of the Western Roman Empire, collapse of the Western Roman Em ...

in the 2nd century AD, when Greek surgeon Antyllus tried to treat the AAA with

proximal Standard anatomical terms of location are used to describe unambiguously the anatomy of humans and other animals. The terms, typically derived from Latin or Greek roots, describe something in its standard anatomical position. This position prov ...

and

distal Standard anatomical terms of location are used to describe unambiguously the anatomy of humans and other animals. The terms, typically derived from Latin or Greek roots, describe something in its standard anatomical position. This position provi ...

ligature Ligature may refer to: Language * Ligature (writing), a combination of two or more letters into a single symbol (typography and calligraphy) * Ligature (grammar), a morpheme that links two words Medicine * Ligature (medicine), a piece of suture us ...

, central incision and removal of thrombotic material from the

aneurysm An aneurysm is an outward :wikt:bulge, bulging, likened to a bubble or balloon, caused by a localized, abnormal, weak spot on a blood vessel wall. Aneurysms may be a result of a hereditary condition or an acquired disease. Aneurysms can also b ...

. However, attempts to treat the AAA surgically were unsuccessful until 1923. In that year,

Rudolph Matas Rudolph Matas (September 12, 1860 – September 23, 1957) was an American surgeon. He was born outside New Orleans in St. Charles Parish, Louisiana, and spent much of his childhood in his parents' native land of Spain. Matas returned to New Orl ...

(who also proposed the concept of endoaneurysmorrhaphy), performed the first successful aortic ligation on a human. Other methods that were successful in treating the AAA included wrapping the aorta with polyethene

cellophane Cellophane is a thin, transparent sheet made of regenerated cellulose. Its low permeability to air, oils, greases, bacteria, and liquid water makes it useful for food packaging. Cellophane is highly permeable to water vapour, but may be coate ...

, which induced

fibrosis Fibrosis, also known as fibrotic scarring, is the development of fibrous connective tissue in response to an injury. Fibrosis can be a normal connective tissue deposition or excessive tissue deposition caused by a disease. Repeated injuries, ch ...

and restricted the growth of the aneurysm. Endovascular aneurysm repair was first performed in the late 1980s and has been widely adopted in the subsequent decades. Endovascular repair was first used for treating a ruptured aneurysm in Nottingham in 1994.

Society and culture

Theoretical physicist

Albert Einstein Albert Einstein (14 March 187918 April 1955) was a German-born theoretical physicist who is best known for developing the theory of relativity. Einstein also made important contributions to quantum mechanics. His mass–energy equivalence f ...

underwent an operation for an abdominal aortic aneurysm in 1949 that was performed by Rudolph Nissen, who wrapped the aorta with polyethylene

. Einstein's aneurysm ruptured on April 13, 1955. He declined surgery, saying, "I want to go when I want. It is tasteless to prolong life artificially. I have done my share, it is time to go. I will do it elegantly." He died five days later at age 76. Actress

Lucille Ball Lucille Désirée Ball (August 6, 1911 – April 26, 1989) was an American actress, comedian, producer, and studio executive. She was recognized by ''Time (magazine), Time'' in 2020 as one of the most influential women of the 20th century for h ...

died on April 26, 1989, from an abdominal aortic aneurysm. At the time of her death, she was in

Cedars-Sinai Medical Center Cedars-Sinai Medical Center is a non-profit, Tertiary referral hospital, tertiary, 915-bed teaching hospital and multi-specialty academic health science centre, academic health science center located in Los Angeles, California. Part of the Cedars ...

recovering from emergency surgery performed just six days earlier because of a dissecting aortic aneurysm near her heart. Ball was at increased risk as she had been a heavy smoker for decades. Musician

Conway Twitty Harold Lloyd Jenkins (September 1, 1933 – June 5, 1993), better known by his stage name Conway Twitty, was an American singer and songwriter. Initially a part of the 1950s rockabilly scene, Twitty was best known as a country music performer. ...

died in June 1993 from an abdominal aortic aneurysm at the age of 59, two months before the release of what would be his final studio album, ''Final Touches''. Actor George C. Scott died in 1999, aged 71, from a ruptured abdominal aortic aneurysm. In 2001, former presidential candidate

Bob Dole Robert Joseph Dole (July 22, 1923 – December 5, 2021) was an American politician and attorney who represented Kansas in the United States Senate from 1969 to 1996. He was the Party leaders of the United States Senate, Republican Leader of th ...

underwent surgery for an abdominal aortic aneurysm in which a team led by

vascular surgeon Vascular surgery is a surgical subspecialty in which vascular diseases involving the arteries, veins, or lymphatic vessels, are managed by medical therapy, minimally-invasive catheter procedures and surgical reconstruction. The specialty evolve ...

Kenneth Ouriel Kenneth Ouriel (born October 21, 1956) is a vascular surgeon and medical researcher. In 2007, Ouriel was appointed the chief executive officer of Sheikh Khalifa Medical City in Abu Dhabi. In 2009, he was senior vice president and chief of intern ...

inserted a stent graft: — ''

Associated Press The Associated Press (AP) is an American not-for-profit organization, not-for-profit news agency headquartered in New York City. Founded in 1846, it operates as a cooperative, unincorporated association, and produces news reports that are dist ...

'' Actor Robert Jacks, who played

Leatherface Leatherface is a character from The Texas Chainsaw Massacre (franchise), ''The Texas Chainsaw Massacre'' series. He first appeared in ''The Texas Chain Saw Massacre'' (1974) as the mentally disabled member of a family of deranged Human cannibalis ...

in '' Texas Chainsaw Massacre: The Next Generation'', died from an abdominal aneurysm on August 8, 2001, one day shy of his 42nd birthday. When Jacks was a child, his father died from the same cause. Actor Tommy Ford died of abdominal aneurysm in October 2016 at 52 years old.

Gary Gygax Ernest Gary Gygax ( ; July 27, 1938 – March 4, 2008) was an American game designer and author best known for co-creating the pioneering tabletop role-playing game ''Dungeons & Dragons'' (''D&D'') with Dave Arneson. In the 1960s, Gygax creat ...

, co-creator of ''

Dungeons & Dragons ''Dungeons & Dragons'' (commonly abbreviated as ''D&D'' or ''DnD'') is a fantasy tabletop role-playing game (TTRPG) originally created and designed by Gary Gygax and Dave Arneson. The game was first published in 1974 by TSR (company)#Tactical ...

'', died from an abdominal aortic aneurysm in 2008, at the age of 69.

Harvey Korman Harvey Herschel Korman (February 15, 1927May 29, 2008) was an American actor and comedian who performed in television and film productions. He is best remembered as a main cast member alongside Carol Burnett, Tim Conway and Vicki Lawrence on the ...

died on May 29, 2008, aged 81, at UCLA Medical Center as the result of complications from a ruptured abdominal aortic aneurysm he had suffered four months earlier. He is interred at Santa Monica's Woodlawn Cemetery.

Research

Risk assessment

There have been many calls for alternative approaches to rupture risk assessment over the past number of years, with many believing that a biomechanics-based approach may be more suitable than the current diameter approach. Numerical modeling is a valuable tool to researchers allowing approximate wall stresses to be calculated, thus revealing the rupture potential of a particular aneurysm. Experimental models are required to validate these numerical results and provide further insight into the biomechanical behavior of the AAA. ''In vivo'', AAAs exhibit a varying range of material strengths from localised weak hypoxic regions to much stronger regions and areas of calcifications. Finding ways to predict future AAA growth is seen as a research priority. Another related line of research is utilizing mathematical decision modeling (e.g., Markov decision processes) to determine improved treatment policies. Initial results suggest that a more dynamic policy could provide benefits, although such claims have not been clinically verified. A study recently showed that aneurysms can be accurately predicted as to whether they are stable (lacking repair or intervention), requiring repair, or at risk of rupture from scans years prior to any event based on a machine-learning based classification tool.

Experimental models

Experimental models can now be manufactured using a novel technique involving the injection-moulding lost-wax manufacturing process to create patient-specific anatomically correct AAA replicas. Work has also focused on developing more realistic material analogues to those ''in vivo'', and recently a novel range of silicone-rubbers was created allowing the varying material properties of the AAA to be more accurately represented. These rubber models can also be used in a variety of experimental situations, from stress analysis using the photoelastic method New endovascular devices are being developed that are able to treat more complex and tortuous anatomies.

Prevention and treatment

An animal study showed that removing a single protein prevents early damage in blood vessels from triggering a later-stage, frequently lethal complication. By eliminating the gene for a signaling protein called cyclophilin A (CypA) from a strain of mice, researchers were able to provide complete protection against abdominal aortic aneurysm. Other recent research identified Granzyme B ( GZMB) (a protein-degrading enzyme) to be a potential target in the treatment of abdominal aortic aneurysms. Elimination of this enzyme in mice models both slowed the progression of aneurysms and improved survival.

Preclinical Research

The mechanisms that lead to AAA development are still not completely understood at a cellular and molecular level. To better understand the pathophysiology of AAA, it is often necessary to use experimental animal models. It is often questioned how well these models translate to human disease. Even though no animal model exactly represents the human condition, all the existing ones focus on one different pathophysiological aspect of the disease. Combining the results from different animal models with clinical research can provide a better overview of the AAA pathophysiology. The most common animal models are rodents (mice and rats), although, for certain studies, such as testing preclinical devices or surgical procedures, large animal models (pig, sheep) are more frequently used. The rodent models of AAA can be classified according to different aspects. There are dissecting models vs non-dissecting models and genetically determined models vs chemically induced models. The most commonly used models are the angiotensin-II infusion into ApoE knockout mice (dissecting model, chemically induced), the calcium chloride model (non-dissecting, chemically induced), and the elastase model (non-dissecting, chemically induced model). A recent study has shown that β-Aminopropionitrile plus elastase application to abdominal aorta causes more severe aneurysm in mice as compared to elastase alone.

References

External links

Cochrane Peripheral Vascular Diseases Review Group
{{Vascular diseases Diseases of the aorta Vascular surgery Deaths from abdominal aortic aneurysm Wikipedia medicine articles ready to translate Men's health Medical triads Wikipedia emergency medicine articles ready to translate de:Aortenaneurysma#Bauchaortenaneurysma