Aneurysm

From Wikipedia for FEVERv2
Jump to navigation Jump to search

For other uses, see Aneurysm (disambiguation). Aneurysm_sentence_0

Not to be confused with ebullism or embolism. Aneurysm_sentence_1

Aneurysm_table_infobox_0

aneurysmAneurysm_header_cell_0_0_0
Other namesAneurysm_header_cell_0_1_0 AneurismAneurysm_cell_0_1_1
SpecialtyAneurysm_header_cell_0_2_0 Vascular surgeryAneurysm_cell_0_2_1

An aneurysm is an outward , likened to a bubble or balloon, caused by a localized, abnormal, weak spot on a blood vessel wall. Aneurysm_sentence_2

Aneurysms may be a result of a hereditary condition or an acquired disease. Aneurysm_sentence_3

Aneurysms can also be a (starting point) for clot formation (thrombosis) and embolization. Aneurysm_sentence_4

The word is from Greek: ἀνεύρυσμα, aneurysma, "dilation", from ἀνευρύνειν, aneurynein, "to dilate". Aneurysm_sentence_5

As an aneurysm increases in size, the risk of rupture increases, leading to uncontrolled bleeding. Aneurysm_sentence_6

Although they may occur in any blood vessel, particularly lethal examples include aneurysms of the Circle of Willis in the brain, aortic aneurysms affecting the thoracic aorta, and abdominal aortic aneurysms. Aneurysm_sentence_7

Aneurysms can arise in the heart itself following a heart attack, including both ventricular and atrial septal aneurysms. Aneurysm_sentence_8

There are congenital atrial septal aneurysms, a rare heart defect. Aneurysm_sentence_9

Classification Aneurysm_section_0

Aneurysms are classified by type, morphology, or location. Aneurysm_sentence_10

True and false aneurysms Aneurysm_section_1

A true aneurysm is one that involves all three layers of the wall of an artery (intima, media and adventitia). Aneurysm_sentence_11

True aneurysms include atherosclerotic, syphilitic, and congenital aneurysms, as well as ventricular aneurysms that follow transmural myocardial infarctions (aneurysms that involve all layers of the attenuated wall of the heart are also considered true aneurysms). Aneurysm_sentence_12

A false aneurysm, or pseudoaneurysm, is a collection of blood leaking completely out of an artery or vein, but confined next to the vessel by the surrounding tissue. Aneurysm_sentence_13

This blood-filled cavity will eventually either thrombose (clot) enough to seal the leak, or rupture out of the surrounding tissue. Aneurysm_sentence_14

Pseudoaneurysms can be caused by trauma that punctures the artery, such as knife and bullet wounds, as a result of surgical procedures such as coronary angiography or arterial grafting, or use of an artery for injection. Aneurysm_sentence_15

Morphology Aneurysm_section_2

Aneurysms can also be classified by their macroscopic shape and size and are described as either saccular or fusiform. Aneurysm_sentence_16

The shape of an aneurysm is not specific for a specific disease. Aneurysm_sentence_17

The size of the base or neck is useful in determining the chance of for example endovascular coiling. Aneurysm_sentence_18

Saccular aneurysms, or "berry" aneurysms, are spherical in shape and involve only a portion of the vessel wall; they usually range 5-20 centimeters5 to 20 cm (2.0 to 7.9 in) in diameter, and are often filled, either partially or fully, by a thrombus.Saccular aneurysms have a "neck” that connects the aneurysm to its main (“parent”) artery, a larger, rounded area called the dome. Aneurysm_sentence_19

Fusiform aneurysms ("spindle-shaped" aneurysms) are variable in both their diameter and length; their diameters can extend up to 20 cm (7.9 in). Aneurysm_sentence_20

They often involve large portions of the ascending and transverse aortic arch, the abdominal aorta, or less frequently the iliac arteries. Aneurysm_sentence_21

Location Aneurysm_section_3

Aneurysms can also be classified by their location: Aneurysm_sentence_22

Aneurysm_unordered_list_0

Cerebral aneurysms, also known as intracranial or brain aneurysms, occur most commonly in the anterior cerebral artery, which is part of the circle of Willis. Aneurysm_sentence_23

This can cause severe strokes leading to death. Aneurysm_sentence_24

The next most common sites of cerebral aneurysm occurrence are in the internal carotid artery. Aneurysm_sentence_25

Size Aneurysm_section_4

Aneurysm_table_general_1

Abdominal aorta size classificationAneurysm_table_caption_1
Ectatic or

mild dilatationAneurysm_cell_1_0_0

>2.0 cm and <3.0 cmAneurysm_cell_1_0_1
ModerateAneurysm_cell_1_1_0 3.0 - 5.0 cmAneurysm_cell_1_1_1
Large or severeAneurysm_cell_1_2_0 >5.0 or 5.5 cmAneurysm_cell_1_2_1

Abdominal aortic aneurysms are commonly divided according to their size and symptomatology. Aneurysm_sentence_26

An aneurysm is usually defined as an outer aortic diameter over 3 cm (normal diameter of the aorta is around 2 cm), or more than 50% of normal diameter that of a healthy individual of the same sex and age. Aneurysm_sentence_27

If the outer diameter exceeds 5.5 cm, the aneurysm is considered to be large. Aneurysm_sentence_28

The common iliac artery is classified as: Aneurysm_sentence_29

Aneurysm_table_general_2

NormalAneurysm_cell_2_0_0 Diameter ≤12 mmAneurysm_cell_2_0_1
EctaticAneurysm_cell_2_1_0 Diameter 12 to 18 mmAneurysm_cell_2_1_1
AneurysmAneurysm_cell_2_2_0 Diameter ≥18 mmAneurysm_cell_2_2_1

Signs and symptoms Aneurysm_section_5

Aneurysm presentation may range from life-threatening complications of hypovolemic shock to being found incidentally on X-ray. Aneurysm_sentence_30

Symptoms will differ by the site of the aneurysm and can include: Aneurysm_sentence_31

Cerebral aneurysm Aneurysm_section_6

Main article: Cerebral aneurysm Aneurysm_sentence_32

Symptoms can occur when the aneurysm pushes on a structure in the brain. Aneurysm_sentence_33

Symptoms will depend on whether an aneurysm has ruptured or not. Aneurysm_sentence_34

There may be no symptoms present at all until the aneurysm ruptures. Aneurysm_sentence_35

For an aneurysm that has not ruptured the following symptoms can occur: Aneurysm_sentence_36

Aneurysm_unordered_list_1

  • FatigueAneurysm_item_1_7
  • Loss of perceptionAneurysm_item_1_8
  • Loss of balanceAneurysm_item_1_9
  • Speech problemsAneurysm_item_1_10
  • Double visionAneurysm_item_1_11

For a ruptured aneurysm, symptoms of a subarachnoid hemorrhage may present: Aneurysm_sentence_37

Aneurysm_unordered_list_2

  • Severe headachesAneurysm_item_2_12
  • Loss of visionAneurysm_item_2_13
  • Double visionAneurysm_item_2_14
  • Neck pain or stiffnessAneurysm_item_2_15
  • Pain above or behind the eyesAneurysm_item_2_16

Abdominal aneurysm Aneurysm_section_7

Main article: Abdominal aneurysm § Signs and symptoms Aneurysm_sentence_38

Abdominal aortic aneurysm involves a regional dilation of the aorta and is diagnosed using ultrasonography, computed tomography, or magnetic resonance imaging. Aneurysm_sentence_39

A segment of the aorta that is found to be greater than 50% larger than that of a healthy individual of the same sex and age is considered aneurysmal. Aneurysm_sentence_40

Abdominal aneurysms are usually asymptomatic but in rare cases can cause lower back pain or lower limb ischemia. Aneurysm_sentence_41

Renal (kidney) aneurysm Aneurysm_section_8

Aneurysm_unordered_list_3

  • Flank pain and tendernessAneurysm_item_3_17
  • HypertensionAneurysm_item_3_18
  • HaematuriaAneurysm_item_3_19
  • Signs of hypovolemic shockAneurysm_item_3_20

Risk factors Aneurysm_section_9

Risk factors for an aneurysm include diabetes, obesity, hypertension, tobacco use, alcoholism, high cholesterol, copper deficiency, increasing age, and tertiary syphilis infection. Aneurysm_sentence_42

Connective tissue disorders such as Loeys-Dietz Syndrome, Marfan Syndrome, and certain forms of Ehlers-Danlos Syndrome are also associated with aneurysms. Aneurysm_sentence_43

Aneurysms, dissections, and ruptures in individuals under 40 years of age are a major diagnostic criteria of the vascular form of Ehlers-Danlos Syndrome (vEDS). Aneurysm_sentence_44

Specific infective causes associated with aneurysm include: Aneurysm_sentence_45

Aneurysm_unordered_list_4

A minority of aneurysms are associated with genetic factors. Aneurysm_sentence_46

Examples include: Aneurysm_sentence_47

Aneurysm_unordered_list_5

Pathophysiology Aneurysm_section_10

Aneurysms form for a variety of interacting reasons. Aneurysm_sentence_48

Multiple factors, including factors affecting a blood vessel wall and the blood through the vessel, contribute. Aneurysm_sentence_49

The pressure of blood within the expanding aneurysm may also injure the blood vessels supplying the artery itself, further weakening the vessel wall. Aneurysm_sentence_50

Without treatment, these aneurysms will ultimately progress and rupture. Aneurysm_sentence_51

Infection. Aneurysm_sentence_52

A mycotic aneurysm is an aneurysm that results from an infectious process that involves the arterial wall. Aneurysm_sentence_53

A person with a mycotic aneurysm has a bacterial infection in the wall of an artery, resulting in the formation of an aneurysm. Aneurysm_sentence_54

The most common locations include arteries in the abdomen, thigh, neck, and arm. Aneurysm_sentence_55

A mycotic aneurysm can result in sepsis, or life-threatening bleeding if the aneurysm ruptures. Aneurysm_sentence_56

Less than 3% of abdominal aortic aneurysms are mycotic aneurysms. Aneurysm_sentence_57

Syphilis. Aneurysm_sentence_58

The third stage of syphilis also manifests as aneurysm of the aorta, which is due to loss of the vasa vasorum in the tunica adventitia. Aneurysm_sentence_59

Copper deficiency. Aneurysm_sentence_60

A minority of aneurysms are caused by copper deficiency, which results in a decreased activity of the lysyl oxidase enzyme, affecting elastin, a key component in vessel walls. Aneurysm_sentence_61

Copper deficiency results in vessel wall thinning, and thus has been noted as a cause of death in copper-deficient humans, chickens and turkeys Aneurysm_sentence_62

Mechanics Aneurysm_section_11

Aneurysmal blood vessels are prone to rupture under normal blood pressure and flow due to their special mechanical properties that make them weaker. Aneurysm_sentence_63

To better understand this phenomenon, we can first look at healthy arterial vessels which exhibit a J-shaped stress-strain curve with high strength and high toughness (for a biomaterial in vivo). Aneurysm_sentence_64

Unlike crystalline materials whose linear elastic region follows Hooke's Law under uniaxial loading, many biomaterials exhibit a J-shaped stress-strain curve which is non-linear and concave up. Aneurysm_sentence_65

The blood vessel can be under large strain, or the amount of stretch the blood vessel can undergo, for a range of low applied stress before fracture, as shown by the lower part of the curve. Aneurysm_sentence_66

The area under the curve up to a given strain is much lower than that for the equivalent Hookean curve, which is correlated to toughness. Aneurysm_sentence_67

Toughness is defined as the amount of energy per unit volume a material can absorb before rupturing. Aneurysm_sentence_68

Because the amount of energy release is proportional to the amount of crack propagation, the blood vessel wall can withstand pressure and is “tough.” Thus, healthy blood vessels with the mechanical properties of the J-shaped stress-strain curve have greater stability against aneurysms than materials with linear elasticity. Aneurysm_sentence_69

Blood vessels with aneurysms, on the other hand, are under the influence of an S-shaped stress-strain curve. Aneurysm_sentence_70

As a visual aid, aneurysms can be understood as a long, cylindrical balloon. Aneurysm_sentence_71

Because it's a tight balloon under pressure, it can pop at any time a stress beyond a certain force threshold is applied. Aneurysm_sentence_72

In the same vein, an unhealthy blood vessel has elastic instabilities that lead to rupture. Aneurysm_sentence_73

Initially, for a given radius and pressure, stiffness of the material increases linearly. Aneurysm_sentence_74

At a certain point, the stiffness of the arterial wall starts to decrease with increasing load. Aneurysm_sentence_75

At higher strain values, the area under the curve increases, thus increasing the impact on the material that would promote crack propagation. Aneurysm_sentence_76

The differences in the mechanical properties of the aneurysmal blood vessels and the healthy blood vessels stem from the compositional differences of the vessels. Aneurysm_sentence_77

Compared to normal aortas, aneurysmal aortas have a much higher volume fraction of collagen and ground substance (54.8% vs. 95.6%) and a much lower volume fraction of elastin (22.7% vs. 2.4%) and smooth muscles (22.6% vs. 2.2%), which contribute to higher initial stiffness. Aneurysm_sentence_78

It was also found that the ultimate tensile strength, or the strength to withstand rupture, of aneurysmal vessel wall is 50% lower than that of normal aortas. Aneurysm_sentence_79

The wall strength of ruptured aneurysmal aortic wall was also found to be 54.2 N/cm, which is much lower than that of a repaired aorta wall, 82.3 N/cm. Aneurysm_sentence_80

Due to the change in composition of the arterial wall, aneurysms overall have much lower strength to resist rupture. Aneurysm_sentence_81

Predicting the risk of rupture is difficult due to the regional anisotropy the hardened blood vessels exhibit, meaning that the stress and strength values vary depending on the region and the direction of the vessel they are measured along. Aneurysm_sentence_82

Diagnosis Aneurysm_section_12

Diagnosis of a ruptured cerebral aneurysm is commonly made by finding signs of subarachnoid hemorrhage on a computed tomography (CT) scan. Aneurysm_sentence_83

If the CT scan is negative but a ruptured aneurysm is still suspected based on clinical findings, a lumbar puncture can be performed to detect blood in the cerebrospinal fluid. Aneurysm_sentence_84

Computed tomography angiography (CTA) is an alternative to traditional angiography and can be performed without the need for arterial catheterization. Aneurysm_sentence_85

This test combines a regular CT scan with a contrast dye injected into a vein. Aneurysm_sentence_86

Once the dye is injected into a vein, it travels to the cerebral arteries, and images are created using a CT scan. Aneurysm_sentence_87

These images show exactly how blood flows into the brain arteries. Aneurysm_sentence_88

Treatment Aneurysm_section_13

Historically, the treatment of arterial aneurysms has been limited to either surgical intervention, or watchful waiting in combination with control of blood pressure. Aneurysm_sentence_89

At least, in case of Abdominal Aortic Aneurysm (AAA) the decision does not come without a significant risk and cost, hence, there is a great interest in identifying more advanced decision making approaches that are not solely based on the AAA diameter, but involve other geometrical and mechanical nuances such as local thickness and wall stress. Aneurysm_sentence_90

In recent years, endovascular or minimally invasive techniques have been developed for many types of aneurysms. Aneurysm_sentence_91

Aneurysm clips are used for surgical procedure i.e. clipping of aneurysms. Aneurysm_sentence_92

Intracranial aneurysms Aneurysm_section_14

Main article: Cerebral aneurysm treatment Aneurysm_sentence_93

There are currently two treatment options for brain aneurysms: surgical clipping or endovascular coiling. Aneurysm_sentence_94

There is currently debate in the medical literature about which treatment is most appropriate given particular situations. Aneurysm_sentence_95

Surgical clipping was introduced by Walter Dandy of the Johns Hopkins Hospital in 1937. Aneurysm_sentence_96

It consists of a craniotomy to expose the aneurysm and closing the base or neck of the aneurysm with a clip. Aneurysm_sentence_97

The surgical technique has been modified and improved over the years. Aneurysm_sentence_98

Endovascular coiling was introduced by Italian neurosurgeon Guido Guglielmi at UCLA in 1989. Aneurysm_sentence_99

It consists of passing a catheter into the femoral artery in the groin, through the aorta, into the brain arteries, and finally into the aneurysm itself. Aneurysm_sentence_100

Platinum coils initiate a clotting reaction within the aneurysm that, if successful, fills the aneurysm dome and prevents its rupture. Aneurysm_sentence_101

A flow diverter can be used, but risks complications. Aneurysm_sentence_102

Aortic and peripheral aneurysms Aneurysm_section_15

For aneurysms in the aorta, arms, legs, or head, the weakened section of the vessel may be replaced by a bypass graft that is sutured at the vascular stumps. Aneurysm_sentence_103

Instead of sewing, the graft tube ends, made rigid and expandable by nitinol wireframe, can be easily inserted in its reduced diameter into the vascular stumps and then expanded up to the most appropriate diameter and permanently fixed there by external ligature. Aneurysm_sentence_104

New devices were recently developed to substitute the external ligature by expandable ring allowing use in acute ascending aorta dissection, providing airtight (i.e. not dependent on the coagulation integrity), easy and quick anastomosis extended to the arch concavity Less invasive endovascular techniques allow covered metallic stent grafts to be inserted through the arteries of the leg and deployed across the aneurysm. Aneurysm_sentence_105

Renal aneurysms Aneurysm_section_16

Renal aneurysms are very rare consisting of only 0.1–0.09% while rupture is even more rare. Aneurysm_sentence_106

Conservative treatment with control of concomitant hypertension being the primary option with aneurysms smaller than 3 cm. Aneurysm_sentence_107

If symptoms occur, or enlargement of the aneurysm, then endovascular or open repair should be considered. Aneurysm_sentence_108

Pregnant women (due to high rupture risk of up to 80%) should be treated surgically. Aneurysm_sentence_109

Epidemiology Aneurysm_section_17

Incidence rates of cranial aneurysms are estimated at between 0.4% and 3.6%. Aneurysm_sentence_110

Those without risk factors have expected prevalence of 2–3%. Aneurysm_sentence_111

In adults, females are more likely to have aneurysms. Aneurysm_sentence_112

They are most prevalent in people ages 35 – 60, but can occur in children as well. Aneurysm_sentence_113

Aneurysms are rare in children with a reported prevalence of .5% to 4.6%. Aneurysm_sentence_114

The most common incidence are among 50-year-olds, and there are typically no warning signs. Aneurysm_sentence_115

Most aneurysms develop after the age of 40. Aneurysm_sentence_116

Pediatric aneurysms Aneurysm_section_18

Pediatric aneurysms have different incidences and features than adult aneurysms. Aneurysm_sentence_117

Intracranial aneurysms are rare in childhood, with over 95% of all aneurysms occurring in adults. Aneurysm_sentence_118

Risk factors Aneurysm_section_19

Incidence rates are two to three times higher in males, while there are more large and giant aneurysms and fewer multiple aneurysms. Aneurysm_sentence_119

Intracranial hemorrhages are 1.6 times more likely to be due to aneurysms than cerebral arteriovenous malformations in whites, but four times less in certain Asian populations. Aneurysm_sentence_120

Most patients, particularly infants, present with subarachnoid hemorrhage and corresponding headaches or neurological deficits. Aneurysm_sentence_121

The mortality rate for pediatric aneurysms is lower than in adults. Aneurysm_sentence_122

Modeling Aneurysm_section_20

Modeling of aneurysms consists of creating a 3D model that mimics a particular aneurysm. Aneurysm_sentence_123

Using patient data for the blood velocity, and blood pressure, along with the geometry of the aneurysm, researchers can apply computational fluid dynamics (CFD) to predict whether an aneurysm is benign or if it is at risk of complication. Aneurysm_sentence_124

One risk is rupture. Aneurysm_sentence_125

Analyzing the velocity and pressure profiles of the blood flow leads to obtaining the resulting wall shear stress on the vessel and aneurysm wall. Aneurysm_sentence_126

The neck of the aneurysm is the most at risk due to the combination of a small wall thickness and high wall shear stress. Aneurysm_sentence_127

When the wall shear stress reaches its limit, the aneurysm ruptures, leading to intracranial hemorrhage. Aneurysm_sentence_128

Conversely, another risk of aneurysms is the creation of clots. Aneurysm_sentence_129

Aneurysms create a pocket which diverts blood flow. Aneurysm_sentence_130

This diverted blood flow creates a vortex inside of the aneurysm. Aneurysm_sentence_131

This vortex can lead to areas inside of the aneurysm where the blood flow is stagnant, which promotes formations of clots. Aneurysm_sentence_132

Blood clots can dislodge from the aneurysm, which can then lead to an embolism when the clot gets stuck and disrupts blood flow. Aneurysm_sentence_133

Model analysis allows these risky aneurysms to be identified and treated. Aneurysm_sentence_134

In the past, aneurysms were modeled as rigid spheres with linear inlets and outlets. Aneurysm_sentence_135

As technology advances, the ability to detect and analyze aneurysms becomes easier. Aneurysm_sentence_136

Researchers are able to CT scan a patient's body to create a 3D computer model that possesses the correct geometry. Aneurysm_sentence_137

Aneurysms can now be modeled with their distinctive "balloon" shape. Aneurysm_sentence_138

Nowadays researchers are optimizing the parameters required to accurately model a patient's aneurysm that will lead to a successful intervention. Aneurysm_sentence_139

Current modeling is not able to take into account all variables though. Aneurysm_sentence_140

For example, blood is considered to be a non-Newtonian fluid. Aneurysm_sentence_141

Some researchers treat blood as a Newtonian fluid instead, as it sometimes has negligible effects to the analysis in large vessels. Aneurysm_sentence_142

When analyzing small vessels though, such as those present in intracranial aneurysms. Aneurysm_sentence_143

Similarly, sometimes it is difficult to model the varying wall thickness in small vessels, so researchers treat wall thickness as constant. Aneurysm_sentence_144

Researchers make these assumptions to reduce computational time. Aneurysm_sentence_145

Nonetheless, making erroneous assumptions could lead to a misdiagnosis that could put a patient's life at risk. Aneurysm_sentence_146

Notable cases Aneurysm_section_21

Aneurysm_unordered_list_6


Credits to the contents of this page go to the authors of the corresponding Wikipedia page: en.wikipedia.org/wiki/Aneurysm.