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

[3] 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.

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

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

[16] The common iliac artery is classified as:[19] Aneurysm presentation may range from life-threatening complications of hypovolemic shock to being found incidentally on X-ray.

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.

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

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).

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.

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.

[29][30][31] Copper deficiency results in vessel wall thinning,[32] and thus has been noted as a cause of death in copper-deficient humans,[33] chickens, and turkeys.

[35] 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.

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.

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

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

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

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.

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

At least, in the case of abdominal aortic aneurysm (AAA), the decision does not come without 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.

[43] 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.

[44][45] 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[46][47][48] Less invasive endovascular techniques allow covered metallic stent grafts to be inserted through the arteries of the leg and deployed across the aneurysm.

[49][50] Conservative treatment with control of concomitant hypertension being the primary option with aneurysms smaller than 3 cm.

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

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

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

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

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

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