First, here’s a look at the different types of aneurysms and their associated risk factors. In the United States, an estimated 1 out of every 50 people will have a brain aneurysm, but most people will never notice symptoms or have problems. Between 10 and 15 percent of those individuals have more than one brain aneurysm. (1) About 30,000 people each year will have a ruptured cerebral aneurysm, which causes bleeding in the brain. About 40 percent of those people — nearly 11,000 — die within 24 hours of the rupture, and an estimated additional 25 percent die from complications within six months. (1) Brain aneurysms occur most commonly in people between ages 35 and 60, but most aneurysms develop after age 40. Brain aneurysms also develop more commonly in women than men at a ratio of 3:2. (1) People who are born with an abnormality in an artery wall and those with certain genetic conditions are also more likely to develop cerebral aneurysms. These conditions include Ehlers-Danlos syndrome, Marfan syndrome, osteogenesis imperfecta, Moyamoya disease, fibromuscular dysplasia, and neurofibromatosis. Those with polycystic kidney disease and certain circulatory disorders, such as arteriovenous malformations, as well as those with cancerous tumors in the head and neck, are also at a higher risk of developing a brain aneurysm. The median age that an aneurysmal hemorrhagic stroke, or a stroke caused by an aneurysm, occurs at is 50. African-Americans are twice as likely as Caucasians to have a brain aneurysm rupture. Hispanics are also nearly twice as likely as Caucasians. (1) Thoracic aortic aneurysms, which form in the portion of the aorta located in the chest, occur equally in men and women, but occur at a higher rate with age. Abdominal aneurysms, which form in the portion of the aorta located in the abdomen, are more common in men and those 65 and older, and are more common in Caucasians than in African-Americans. Physical trauma or an injury, such as from a car accident, can damage the walls of the aorta and lead to thoracic aortic aneurysms.
Smoking
Smoking is the most significant risk factor for aneurysms, especially for abdominal aortic aneurysms. (3) Smoking destroys the walls of the arteries and breaks down the lining. Over time, plaque and clots form in an effort to repair the wall, but it actually makes the wall weaker, says Kimberly Brown, MD, MPH, an emergency physician in Memphis. Current smokers and those who have a history of smoking are at risk for aneurysms and rupture. There is also a direct relationship between frequency or time spent smoking and aneurysm risk.
Hypertension
Hypertension, or high blood pressure, is a disease in which blood flows through the arteries at an elevated rate. Under the new American Heart Association guidelines released in 2017, which changed the definition of high blood pressure from 140/90 millimeters of mercury (mmHg) to 130/80 mmHg, 46 percent of adults in the United States are now estimated to have the condition. Hypertension is the leading cause of subarachnoid hemorrhage, or bleeding between the brain and the surrounding membrane, which occurs when a brain aneurysm ruptures. The bleeding can also damage the brain and lead to a hemorrhagic stroke, which can cause weakness or paralysis of an arm or a leg, vision problems, seizures, and trouble speaking or understanding language.
Atherosclerosis
Atherosclerosis is a condition that develops due to the build up of a waxy substance called plaque in the arteries. As plaque continues to build up, it hardens and narrows the arteries, and restricts the flow of oxygen to organs and other parts of the body. Coronary artery disease (or atherosclerosis that affects the arteries that supply blood to the heart) and stroke (a consequence of atherosclerosis within the brain) are the leading causes of death in the United States. In 2015, 366,000 died from coronary artery disease. (4) Stroke is responsible for 1 out of every 20 deaths in the United States each year. (5)
Illicit Drug Use or Drug Abuse
Certain illicit drugs, like cocaine and methamphetamine, can spike a person’s blood pressure and inflame the blood vessels, which increases the risk for brain aneurysms.
Family History
People with a family history of aortic aneurysms have an elevated risk and may develop aneurysms before age 65. People with two or more relatives who have had an abdominal aortic aneurysm have a 12 to 15 percent higher chance of developing one themselves, says George P. Teitelbaum, MD, an interventional neuroradiologist at the Pacific Neuroscience Institute in Santa Monica, California. Those with two or more relatives who had subarachnoid hemorrhage have between a 6 and 20 percent risk for developing an aneurysm. (6)
Bicuspid Aortic Valve
The aortic valve allows blood to flow from the heart to the aorta, and prevents blood from flowing back from the aorta to the heart. Unlike a normal aortic valve, which has three leaflets to allow for this flow, a bicuspid aortic valve has only two. People with a bicuspid aortic valve are believed to have a higher risk for thoracic aneurysm due to weakness in the aorta.
Poor Diet
A diet high in saturated fat and cholesterol can increase the risk for atherosclerosis and hypertension.
A History of Aneurysms
Those who have a history of aneurysms or subarachnoid hemorrhages may be prone to recurrence. According to a meta-analysis published in the journal Radiology, among those who had a brain aneurysm treated with endovascular treatment, a procedure in which a catheter is inserted through the artery and a stent graft or platinum coils (endovascular embolization) are placed in the aneurysm, more than 12 percent experienced a return of blood flow to the original aneurysm ten years later. Aneurysms can recur after endovascular aneurysm repair (EVAR) due to an endoleak, or leakage of blood flow into the aneurysm, Dr. Teitelbaum says. (7) Brain aneurysms treated with endovascular embolization may be associated with up to 20 percent risk of regrowth, which is treated by adding more coils to the aneurysm, Teitelbaum says.
Dissection
A dissection in the aorta or in the brain occurs when blood travels underneath a tear in the innermost layer (the intima), lifts it up, and causes a separation of the layers of the artery. A dissection can also restrict blood flow to the artery. Up to 3 percent of people are affected by an aortic dissection, and African-Americans, men, and the elderly have the highest risk. Aortic dissection occurs most commonly in those between ages 50 to 65, and between ages 20 and 40 for people with congenital connective tissue disorders, such as Marfan syndrome and Ehlers-Danlos syndrome. (8)
Size, Shape, and Pattern of the Aneurysm
The size of an aneurysm is a risk factor for rupture. In the brain, aneurysms considered small are those less than 10 millimeters (mm) in diameter, while those that are considered large are between 10 and 25 mm in diameter. Meanwhile, “giant” aneurysms are larger than 25 mm in diameter. The larger the aneurysm, the higher the risk for rupture and the poorest outcome for treatment. “Even though an aneurysm is small, if it is less than 10 mm [in diameter], that doesn’t mean it’s safe,” Teitelbaum says. An abdominal aortic aneurysm between 3 and 3.5 centimeters (cm) in diameter is considered small. Some enlarge at a rate of 10 percent each year, while about 20 percent stay the same. (8) Those smaller than 4 cm have a risk for enlargement of 1 percent each year. Those between 5 and 5.9 cm have a 5 to 10 percent risk for enlargement and should be treated. (8) In addition to its size, both the shape and pattern of blood flow in the aneurysm are considered risk factors for rupture. “It seems to increase the risk of rupture if over the past year the aneurysm increased in size,” Teitelbaum says. Also, those that have a complex shape and an additional bulge, known as a “daughter aneurysm,” have a higher risk for rupture, Teitelbaum says.
Location of the Aneurysm
The location of an aneurysm, particularly in the brain, is important to consider when evaluating risk of rupture. “Those aneurysms that are in the front part of the brain, or the anterior circulation, have a lower risk of rupture than those located in the back, or posterior circulation, of the brain,” Teitelbaum says. Although those aneurysms located in the posterior circulation are less likely to occur than those in the anterior circulation, they have a higher risk for rupture. Also, aneurysms located on the basilar artery, near the brainstem at the base of the skull, are extremely difficult to operate on and have a high rate of mortality.
