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



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



In individuals without risk factors have expected prevalence of 2–3%.



They can also be a nidus for clot thrombosis and embolization. 



The increase in aneurysms’ size increases the risk of rupture.



Aneurysms can occur in any blood vessel.



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



Aneurysm associated with mortality include: aneurysms of the Circle of Willis in the brain, aortic aneurysms affecting the thoracic aorta, and abdominal aortic aneurysms. 



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



Following a heart attack aneurysm can occur in both ventricular and atrial septal chambers.



Rarely congenital atrial septal aneurysms can exist.



Risk factors: diabetes, obesity, hypertension, tobacco use, alcoholism, high cholesterol, copper deficiency, increasing age, and tertiary syphilis infection, connective tissue disorders such as Marfan Syndrome, and certain forms of Ehlers-Danlos Syndrome are also associated with aneurysms. 



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



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



True aneurysms include atherosclerotic, syphilitic, congenital, and ventricular aneurysms that follow transmural myocardial infarctions.



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



This extraarterial blood-filled cavity will eventually clot enough to seal the leak, or rupture out of the surrounding tissue.



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



Aneurysms can also be classified by their shape and size: saccular or fusiform. 



Saccular aneurysms are spherical in shape and involve only a portion of the blood vessel wall.



Saccular aneurysms vary in size from 5 to 20 cm in diameter.



Saccular aneurysms are often filled by a blood clot.


Saccular aneurysms are almost always the result of hereditary weakness in blood vessels.


Saccular aneurysms typically occur within the arteries of the Circle of Willis.


Saccular aneurysms tend to have a lack of tunica media and elastic lamina around its dilated location.


The wall of sac made up of thickened hyalinized intima and adventitia.


Fusiform aneurysms are spindle-shaped, and are variable in both their diameter and length.



Fusiform aneurysm diameters can extend up to 20 cm.



Fusiform aneurysms often involve the ascending and transverse aortic arch, the abdominal aorta, or less frequently the iliac arteries.



Aneurysms are also be classified by their location:



The heart-coronary artery aneurysms, ventricular aneurysms, aneurysm of sinus of Valsalva, and aneurysms following cardiac surgery.



The aorta-aortic aneurysms including thoracic aortic aneurysms and abdominal aortic aneurysms.



The brain-cerebral aneurysms, berry aneurysms, and Chariot–Bouchard aneurysms.



The legs-popliteal arteries.



The kidney-renal artery aneurysm and intraparechymal aneurysms.



Capillary aneurysms.



Cerebral aneurysms occur most commonly in the anterior cerebral artery, which is part of the circle of Willis. 



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



Abdominal aorta size classification: 



Ectatic or mild dilatation >2.0 cm and <3.0 cm



Moderate 3.0 – 5.0 cm



Large or severe >5.0 or 5.5 cm



Aortic aneurysms are commonly divided according to their size and symptomatology. 



The definition of an aortic aneurysm is usually an outer aortic diameter over 3 cm , (while the normal diameter of the aorta is around 2 cm), which is more greater than 50% of normal diameter that of a healthy individual of the same sex and age.



If the diameter of an aortic aneurysm exceeds 5.5 cm, the aneurysm is considered to be large.



The common iliac artery is classified as:



Normal Diameter ≤12 mm



Ectatic Diameter 12 to 18 mm



Aneurysm Diameter ≥18 mm



Aneurysms may present in a range from incidental finding to life-threatening with hypovolemic shock.



Symptoms differ by its site.



Symptoms can occur when the aneurysm pushes on an adjacent structure, or whether it has ruptured or not. 



There may be no symptoms  unless the aneurysm ruptures.



Ruptured aneurysm symptoms:  






Loss of perception



Loss of balance



Speech problems



Double vision



Symptoms of a subarachnoid hemorrhage may present:



Severe headaches



Loss of vision



Double vision



Neck pain or stiffness



Pain above or behind the eyes



Abdominal aneurysms are usually asymptomatic.



Rarely  abdominal aneurysms in can cause lower back pain or lower limb ischemia.



Renal aneurysm may be associated with 


flank pain and tenderness, hypertension, 


and hematuria.



Infective causes associated with aneurysms include:



Advanced syphilis 






Brain infections



Aneurysms are associated with genetic factors: 



Berry aneurysms of the anterior communicating artery of the circle of Willis



Association with autosomal dominant polycystic kidney disease



Familial thoracic aortic aneurysms



Congenital arteriovenous malformations



Without treatment aneurysms will ultimately progress and rupture.



Mycotic aneurysms result from an infectious in the wall of an artery, and can result in sepsis, or life-threatening bleeding if the aneurysm ruptures. 



Fewer  than 3% of abdominal aortic aneurysms are mycotic aneurysms.



The third stage of syphilis may manifest as aneurysm of the aorta, due to loss of the vasa vasorum.



Rarely 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.



Aneurysmal blood vessels are prone to rupture under normal blood pressure and flow due to their weakened properties.



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


It is theorized low shear stress causes growth and rupture of large aneurysms through inflammatory response while high shear stress causes growth and rupture of small aneurysm through response from the blood vessel wall.


Arterial wall damage to its structural integrity  that results from shear stress causes an inflammatory response that occurs with the recruitment of T cells, macrophages, mast cells, and release of 

inflammatory mediators

The inflammatory mediators released include: Interleukin 1 beta, Interleukin 6, Tumor necrosis factor alpha, MMP1, MMP2, MMP9, prostaglandin E2, complement system, reactive oxygen species (ROS), and angiotensin II. 

With aneurysms smooth muscle cells from the media layer of the artery move into the intima, where the function of the smooth muscle cells changed from contractile function into pro-inflammatory function. 


This causes fibrosis of the arterial wall, with reduction of number of smooth muscle cells, abnormal collagen synthesis, resulting in thinning of arterial wall and formation of aneurysm and rupture. 



The differences in the mechanical properties of the aneurysmal blood vessel and the healthy blood vessel is  their compositional differences: 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.



The strength to withstand rupture, of aneurysmal vessel wall is 50% lower than that of normal aortas.



The treatment of arterial aneurysms has been either surgical intervention, or watchful waiting in combination with control of blood pressure. 



Endovascular or minimally invasive techniques have been developed for many types of aneurysms. 



Aneurysm clips are used for the surgical procedure.



The  two treatment options for brain aneurysms: surgical clipping or endovascular coiling. 



Over 95% of all intracranial aneurysms occur in adults.



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



Endovascular coiling consists of passing a catheter into the femoral artery, 


through the aorta, into the brain arteries, and finally into the aneurysm itself. 



The platinum coils initiates a clotting reaction within the aneurysm that fills it and prevents its rupture.



In aorta, arms, legs, or head aneurysms section of the vessel may be replaced by a bypass graft that is sutured in place.



Where the rigid yet expandable wireframe graft tube ends, it is 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.



Substituted for the external ligature are expandable rings that  allow use in acute ascending aorta dissection.



Endovascular techniques allow covered metallic stent grafts to be inserted through the arteries of the leg and deployed across an aneurysm.



Renal aneurysms are very rare consisting of only 0.1–0.09% of cases, and rupture is even more rare.



Pregnant women have a high rupture risk of up to 80% and renal aneurysms should be treated surgically.



In adults, females are more likely to have aneurysms. 



Aneurysms are most prevalent in people ages 35 – 60.



Typically there are no warning signs. 



Aneurysms can occur in children, but are rare with a reported prevalence of .5% to 4.6%. 



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



Intracranial hemorrhages are 1.6 times more likely to be due to aneurysms than cerebral arteriovenous malformations in Caucasians.



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



Aside from rupture aneurysms, they can  create clots. 



Pockets created by an aneurysm 


diverts blood flow, creating a vortex inside of the aneurysm. 



An aneurysm vortex can lead to areas of stagnant blood flow which promotes clot formation and thromboembolism..








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