Incidence rates of cranial aneurysms are estimated at between 0.4% and 3.6%. Those without risk factors have expected prevalence of 2–3%. In adults, females are more likely to have aneurysms. They are most prevalent in people ages 35 – 60, but can occur in children as well. Aneurysms are rare in children with a reported prevalence of .5% to 4.6%. The most common incidence are among 50-year-olds, and there are typically no warning signs. Most aneurysms develop after the age of 40.

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 whites, but four times less in certain Asian populations.

Most patients, particularly infants, present with subarachnoid hemorrhage and corresponding headaches or neurological deficits. The mortality rate for pediatric aneurysms is lower than in adults.

Vein of Galen malformations are devastating complications. Studies have shown that 77% of untreated cases result in mortality. Even after surgical treatment, the mortality rate remains as high as 39.4%. Most cases occur during infancy when the mortality rates are at their highest. Vein of Galen malformations are a relatively unknown affliction, attributed to the rareness of the malformations. Therefore, when a child is diagnosed with a faulty Great Cerebral Vein of Galen, most parents know little to nothing about what they are dealing with. To counteract this, support sites have been created which offer information, advice, and a community of support to the afflicted (, ).

An aortic aneurysm can occur as a result of trauma, infection, or, most commonly, from an intrinsic abnormality in the elastin and collagen components of the aortic wall. While definite genetic abnormalities were identified in true genetic syndromes (Marfan, Elher-Danlos and others) associated with aortic aneurysms, both thoracic and abdominal aortic aneurysms demonstrate a strong genetic component in their aetiology.

Hypertension and cigarette smoking are the most important risk factors, though the importance of genetic factors has been increasingly recognized. Approximately 10% of patients may have other family members who have aortic aneurysms. It is also important to note that individuals with a history of aneurysms in other parts of the body have a higher chance of developing a thoracic aortic aneurysm.

The risk of aneurysm enlargement may be diminished with attention to the patient's blood pressure, smoking and cholesterol levels. There have been proposals to introduce ultrasound scans as a screening tool for those most at risk: men over the age of 65. The tetracycline antibiotic doxycycline is currently being investigated for use as a potential drug in the prevention of aortic aneurysm due to its metalloproteinase inhibitor and collagen stabilizing properties. In contrast, fluoroquinolones antibiotics are being investigated as a potential contributor to aortic aneurysms, given their tendency to break down collagen fibrils.

Anacetrapib is a cholesteryl ester transfer protein inhibitor that raises high-density lipoprotein (HDL) cholesterol and reduces low-density lipoprotein (LDL) cholesterol.

Anacetrapib reduces progression of atherosclerosis, mainly by reducing non-HDL-cholesterol, improves lesion stability and adds to the beneficial effects of atorvastatin

Elevating the amount of HDL cholesterol in the abdominal area of the aortic artery in mice both reduced the size of aneurysms that had already grown and prevented abdominal aortic aneurysms from forming at all. In short, raising HDL cholesterol is beneficial because it induces programmed cell death. The walls of a failing aorta are replaced and strengthened. New lesions should not form at all when using this drug.

Intracranial aneurysms may result from diseases acquired during life, or from genetic conditions. Lifestyle diseases including hypertension, smoking, excessive alcoholism, and obesity are associated with the development of brain aneurysms. Cocaine use has also been associated with the development of intracranial aneurysms.

Other acquired associations with intracranial aneurysms include head trauma and infections.

Each year in the United States, some 45,000 people die from diseases of the aorta and its branches. Acute aortic dissection, a life-threatening event due to a tear in the aortic wall, affects 5 to 10 patients per million population each year, most often men between the ages of 50 and 70; of those that occur in women younger than 40, nearly half arise during pregnancy. The majority of these deaths occur as a result of complications of thoracic aneurysmal disease.

The complications that are usually associated with vein of Galen malformations are usually intracranial hemorrhages. Over half the patients with VGAM have a malformation that cannot be corrected. Patients frequently die in the neonatal period or in early infancy.

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 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, 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. 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, the mortality is 70–95%.

Can occur due to autosomal dominant diseases, such as hereditary hemorrhagic telangiectasia.

Coarctation of the aorta is also a known risk factor, as is arteriovenous malformation. Genetic conditions associated with connective tissue disease may also be associated with the development of aneurysms. This includes:

- autosomal dominant polycystic kidney disease,

- neurofibromatosis type I,

- Marfan syndrome,

- multiple endocrine neoplasia type I,

- pseudoxanthoma elasticum,

- hereditary hemorrhagic telangiectasia and

- Ehlers-Danlos syndrome types II and IV.

Specific genes have also had reported association with the development of intracranial aneurysms, including perlecan, elastin, collagen type 1 A2, endothelial nitric oxide synthase, endothelin receptor A and cyclin dependent kinase inhibitor. Mutations in interleukin 6 may be protective. . Recently, several genetic loci have been identified as relevant to the development of intracranial aneurysms. These include 1p34-36, 2p14-15, 7q11, 11q25, and 19q13.1-13.3.

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

Although the exact cause is unknown, some risk factors associated with individuals with IAA are:

Tobacco Use: Cigarette smoking and other forms of tobacco use appear to increase your risk of aortic aneurysms. In addition to the damaging effects that smoking causes directly to the arteries, smoking contributes to the buildup of fatty plaques in your arteries (atherosclerosis) and high blood pressure. Smoking can also cause your aneurysm to grow faster by further damaging your aorta.

Hardening of the arteries (atherosclerosis). Atherosclerosis occurs when fat and other substances build up on the lining of a blood vessel, increasing your risk of an aneurysm.

Infection in the aorta (vasculitis). In rare cases, abdominal aortic aneurysm may be caused by an infection or inflammation that weakens a section of the aortic wall.

The estimated detection rate of AVM in the US general population is 1.4/100,000 per year. This is approximately one fifth to one seventh the incidence of intracranial aneurysms. An estimated 300,000 Americans have AVMs, of whom 12% (approximately 36,000) will exhibit symptoms of greatly varying severity.

IIAs are uncommon, accounting for 2.6% to 6% of all intracranial aneurysms in autopsy studies.

It is unclear whether stenting or open surgery is a better for those with aneurysms that are not causing symptoms.

Preexisting diabetes mellitus of a pregnant mother is a risk factor that has been described for the fetus having TGV.

10-15% of intracranial AV malformations are DAVFs. There is a higher preponderance in females (61-66%), and typically patients are in their fourth or fifth generation of life. DAVFs are rarer in children.

Mortality of IIA is high, unruptured IIA are associated with a mortality reaching 30%, while ruptured IIA has a mortality of up to 80%. IIAs caused by fungal infections have a worse prognosis than those caused by bacterial infection.

The main risk is intracranial hemorrhage. This risk is difficult to quantify since many patients with asymptomatic AVMs will never come to medical attention. Small AVMs tend to bleed more often than do larger ones, the opposite of cerebral aneurysms. If a rupture or bleeding incident occurs, the blood may penetrate either into the brain tissue (cerebral hemorrhage) or into the subarachnoid space, which is located between the sheaths (meninges) surrounding the brain (subarachnoid hemorrhage). Bleeding may also extend into the ventricular system (intraventricular hemorrhage). Cerebral hemorrhage appears to be most common.

One long-term study (mean follow up greater than 20 years) of over 150 symptomatic AVMs (either presenting with bleeding or seizures) found the risk of cerebral hemorrhage to be approximately 4% per year, slightly higher than the 2-3% seen in other studies. A simple, rough approximation of a patient's lifetime bleeding risk is 105 - (patient age in years), assuming a 3% bleed risk annually. For example, a healthy 30-year-old patient would have approximately a 75% lifetime risk of at least one bleeding event. Ruptured AVMs are a significant source or morbidity and mortality; post rupture, as many as 29% of patients will die, and only 55% will be able to live independently.

A dural arteriovenous fistula (DAVF), is an abnormal direct connection (fistula) between a meningeal artery and a meningeal vein or dural venous sinus. In cases where there are multiple fistulas, the related term dural arteriovenous malformation (DAVF) is used.

In general, an aneurysm is bulge that can occur in blood vessels or sometimes in the heart itself. In the case of IAA, this type of aneurysm is localized in the aortic artery, which is the artery that carries oxygenated blood from the heart to the rest of the body. . This location is ideal for aneurysms to develop based upon the high stress and pressure from blood circulation. Fibrosis, a stiffening of the muscle, may occur due to the exposure to stress and blood pressure. In the development of the fibrosis an autoimmune response may occur which in the area causing the "inflammation." This inflammation is what gives IAA the characteristic thickened walls of the aneurysm.

All types of abdominal aortic aneurysms occur in the part of the aorta that passes through the middle to low abdomen. Thoracic aortic aneurysms occur on the aorta as it passes through the chest cavity. These are less common than abdominal aneurysms. Small aneurysms generally pose no threat. However, aneurysms increase the risk for:

- Atherosclerotic plaques to form at the site of the aneurysm, which causes further weakening of the artery wall.

- blood clots may form at the site and dislodge, increasing the chance of stroke

- Increase in the size of the aneurysm, causing it to press on other organs, which may cause pain.

- Aneurysm may also rupture. It is fragile and may burst under stress. The rupture of an aortic aneurysm is a catastrophic, life-threatening event.

A popliteal aneurysm is a bulging (aneurysm) of the popliteal artery. People with popliteal aneurysms rarely have symptoms, and they are typically discovered during a routine physical examination. The cause of these aneurysms is unknown, but they are more common in older people and men and occur in both legs about 50% of the time.

Bicuspid aortic valves are the most common cardiac valvular anomaly, occurring in 1–2% of the general population. It is twice as common in males as in females.

Bicuspid aortic valve is a heritable condition, with a demonstrated association with mutations in the NOTCH1 gene. Its heritability (formula_1) is as high as 89%. Both familial clustering and isolated valve defects have been documented. The incidence of bicuspid aortic valve can be as high as 10% in families affected with the valve problem..Recent studies suggest that BAV is an autosomal dominant condition with incomplete penetrance. Other congenital heart defects are associated with bicuspid aortic valve at various frequencies, including coarctation of the aorta.