An aneurysm is an excessive localized enlargement of an artery caused by weakness in the arterial wall. Aneurysms may remain silent or rupture, causing serious problems and even death.
While most aneurysms go undetected and do not lead to serious events, the statistics show that:
- Aortic aneurysms cause or contribute to over 25,000 deaths in America each year, according to evidence reported to the Centers for Disease Control and Prevention (CDC)1,2
- Around 30,000 brain aneurysms rupture annually, resulting in death in around 40% of cases, according to estimates by the US National Institutes of Health (NIH).3
Here are some key points about aneurysms. More detail and supporting information is in the article.
- The etiology (causes) of aneurysms are not fully understood, although some modifiable risk factors have been identified.
- A variety of arteries can be affected by aneurysms, including peripheral arteries.
- The most significant aneurysms affect the arteries supplying the brain, and the aorta (the largest artery in the body, which originates in the heart).
- If an aortic aneurysm ruptures, this causes internal bleeding; if a cerebral aneurysm ruptures, this causes bleeding in the brain.
- The risk of an aneurysm varies between individuals, as does the risk of an aneurysm rupturing.
- Not all aneurysms need treatment - some can be monitored while risk factors are managed.
- High-risk aortic aneurysms may warrant surgical treatment to prevent rupture, but the risks of brain surgery mean that most brain aneurysms are not treated surgically until absolutely necessary.
- Many aneurysms are asymptomatic, but ruptured aneurysms do produce life-threatening bleeds that need emergency hospital care.
- Bleeding from the aorta is particularly dangerous in the chest, and abdominal bleeding is also dangerous; an aneurysm that ruptures and causes bleeding in the brain is called a stroke and is an medical emergency.
- The risk of developing an aneurysm in the first place, and of an aneurysm rupturing is increased by smoking, excessive alcohol intake and drug abuse, especially cocaine use.
- Aneurysms are more common in males and in older people, especially in people with high blood pressure and/or arteriosclerosis (hardening of the arteries).
What is an aneurysm?
An aneurysm is an arterial condition in which the wall of an artery weakens, creating a bulge, or distension of the artery.4,5
A comparison between an artery with an aneurysm and two different types of artery. Note the cross-section showing a thinner artery wall in the third diagram for aneurysm, compared with normal and narrowed arteries.
An aneurysm can occur in important arteries such as those supplying blood to the brain, and the aorta; the large artery that originates at the left ventricle of the heart and passes down through the chest and abdominal cavities.
The normal diameter of the aorta is around 0.8 inches. This width can bulge to beyond 2 inches with an aneurysm, a width that would typically necessitate surgical treatment.6
An aneurysm can also occur in peripheral arteries - usually behind the knee (popliteal aneurysms) - although rupture of these is relatively uncommon.4,7
The two most important common locations for aneurysms are:
- In the artery directly leaving the heart - an aortic aneurysm (including thoracic and, further down, abdominal aortic aneurysms)
- In an artery in the brain - a cerebral aneurysm.
Thoracic aortic aneurysm is often abbreviated to TAA, and abdominal aortic aneurysm to AAA. Brain aneurysms are often termed intracranial aneurysms, as well as "berry aneurysms" on account of their size and shape.
Two other examples of aneurysm are mesenteric artery aneurysm (affecting the artery supplying the intestines of the gut) and splenic artery aneurysm (occurring in the spleen, an abdominal organ).8
Causes of aneurysm
The pathophysiology of an aneurysm (how it develops) is straightforward, although the causes (etiology) are less well understood.
How an aneurysm develops
The bulge in an artery forms as a result of a weakening of the artery wall, which allows the blood pressure to distend the artery wall wider than usual.7
An aortic aneurysm can form a bulge that is either uniform all the way around the artery (a "fusiform" aneurysm) or that protrudes only from one side ("saccular" - forming a sac shape).
A cerebral aneurysm is usually saccular. This shape also accounts for most cases of ruptured brain aneurysms.8
Ruptured cerebral aneurysms are the most common cause of a type of stroke known as subarachnoid hemorrhage (SAH).5,8 This type of stroke is less common than ischemic strokes - strokes caused by a blocked artery rather than an internal bleed.2
Why do aneurysms develop?
A number of risk factors are known to be associated with the development of aneurysms, and the same factors also affect the chances of a developed aneurysm then rupturing - see the section on prevention for more about these risk factors.
However, it is not fully understood why the artery wall weakens in the way that it does to cause an aneurysm. Some aneurysms, though less common, are present as an artery defect at birth (congenital).9
Aortic dissection - a tear in the inner arterial wall can lead to a bulge as blood pushes through to "dissect" the layers of the aorta. If the blood-filled channel tears through the outer layer of the artery, this can be fatal. See more about aortic dissection under complications, including how it killed King George II of Great Britain in 1760.
Symptoms of aneurysm
Most aneurysms do not themselves cause any symptoms.4,5
Even if an aneurysm does not rupture, however, a large aneurysm may obstruct circulation to other tissues. An aneurysm can also contribute to the formation of blood clots that then obstruct smaller blood vessels, potentially causing ischemic stroke or other serious problems; this is known as thromboembolism.
Back pain can be a symptom of an aneurysm although most aneurysms are asymptomatic.
Abdominal aneurysms are sometimes associated with symptoms if they grow rapidly. Some people report abdominal or lower back pain, or a pulsating sensation in the abdomen.
Similarly, thoracic aneurysms can cause symptoms by affecting nearby tissues, including nerves and other blood vessels.
If an aneurysm compresses the laryngeal or vagus nerve, it can cause chest or back pain and symptoms such as coughing, wheezing and difficulty swallowing. Compression of the coronary artery can also cause chest pain.4
Otherwise, aneurysms tend to produce symptoms only when there are complications such as rupture.
Symptoms can also be related to the cause of the aneurysm rather than the aneurysm itself. In the case of infection or vasculitis (blood vessel inflammation), for example, there may be fever, malaise or weight loss.4
Complications of aneurysm
If an aneurysm has remained undetected, the first sign of it could be when there is a complication - in particular, a rupture - with symptoms resulting from this rather than the aneurysm itself.4
The majority of people living with an aneurysm do not suffer any of the complications in the following list. Managing the risk factors is important, however, because all of these possibilities are serious.
Complications of aneurysm include:4,5,8,9
Brain aneurysm can lead to subarachnoid hemorrhage; a symptom of this stroke bleed is a sudden extreme headache.
- Thromboembolism - depending on where the clot has traveled to, thromboembolism can cause pain in the extremities or the abdomen. If a clot travels to the brain, it can cause a stroke
- Dissection of the aorta - see below for more detail
- Severe chest and/or back pain - if a silent or diagnosed aortic aneurysm in the chest ruptures, severe chest or back pain may arise. Such symptoms may help hospital medical staff diagnose an aneurysm.
- Angina - certain types of aneurysm can lead to angina, another type of chest pain; the pain is related to narrowed arteries supplying the heart itself (causing myocardial ischemia and possibly heart attack).
- Sudden extreme headache - if a brain aneurysm leads to subarachnoid hemorrhage (a kind of stroke), the main symptom is sudden extreme headache; often so severe that it is unlike any previous experience of head pain.
- Other symptoms - with any aneurysm rupture there may be pain, low blood pressure, a rapid heart rate, and light-headedness.
Again, most people with an aneurysm will not suffer any of these complications, and the risk can be reduced by taking preventive steps.
Aortic dissection can be caused by aneurysm but, conversely, aortic dissection itself can lead to a type of aneurysm.
People who have an aortic dissection often describe a tearing or ripping pain in the chest that is abrupt and excruciating, and the pain can travel as the dissection progresses along the aorta. The pain can radiate toward the back, for example.
Dissections sometimes rupture and kill - King George II of Great Britain died in 1760 following a partial tear in his thoracic aorta (his ascending aorta, nearest the heart).
King George II's death was the first recorded fatality resulting from a rupture of the aorta following part of the artery wall tearing in this way.
The blood bursting out of the king's aorta filled the cavity surrounding his heart (the pericardial sac), leading to compression that prevented blood from returning to his heart. This is now referred to as "pericardial tamponade."
The term "aortic dissection" was coined later for the newly described bulge that had led to this rupture.
Aortic dissection can occur when the artery bulges because blood has pushed through a tear in the inner wall of the artery, "dissecting" or splitting the layers of the arterial wall.
Other types of aneurysm are more common, but King George's death from aortic dissection marked the start of the history of cardiology that today has seen innovations such as stent-grafting.
Screening for aneurysms
Aneurysms often remain undetected. Screening aims to detect cases that could otherwise progress unnoticed, in order to identify patients who need to be monitored or treated for their aneurysm.
The US Preventive Services Task Force recommends screening for abdominal aortic aneurysms (AAA) - by ultrasound scan - in all men aged 65-75 who have smoked 100 cigarettes or more in their lives.
The task force's recommendation is based on evidence strong enough to suggest screening and surgical repair of large aneurysms (5.5 cm or greater) in men 65-75 years of age who have ever smoked leads to decreased AAA-related deaths.
The task force also notes that while men over the age of 75 have a higher risk of AAAs, the increased presence of comorbidities and limited life expectancy decreases the likely benefits of screening.
Because women are at lower risk of AAA, the taskforce does not recommend routine screening; the taskforce actively recommends against screening being offered to women if they have never smoked, regardless of their age.
Even for women who do have some history of smoking, it says there is not enough evidence to know either way whether there would be any benefit screening those between 65 and 75 years of age.
The UK's National Health Service (NHS) has a similar approach to the US, inviting all male citizens to be screened for abdominal aortic aneurysm - also using ultrasonography - when they reach the age of 65 years.5
As part of its campaign against "too much medicine," The BMJ has published reviews that question the value of screening for breast cancer in women and aneurysm in men - asking whether the harm of "over-diagnosis" outweighs the benefit of detecting and treating real cases of disease.
Research published in the journal Stroke in 2014 identified new characteristics about the natural progression of cerebral aneurysms.
Researchers at Brigham and Women's Hospital have recently found an association between asthma and abdominal aortic aneurysm rupture.24,25
While the association does not show that asthma causes aneurysms, the latest study did find that patients aged 50 and older with recent asthma activity were significantly more likely than non-asthmatics to experience abdominal aortic aneurysm rupture and sudden death.25 This may be due to increased levels of inflammation, as mediated by immunoglobulin E (IgE), a substance produced by the body in response to allergens.
IgE has been seen to activate inflammatory cells and contribute to the development and rupture of aneurysms.24,25
Treatments for aneurysm
Not all cases of unruptured aneurysm need active treatment, but when an aneurysm ruptures, emergency surgery is needed.
More details follow for the treatment options against the two main types of aneurysm.
Aortic aneurysm treatment options
An aortic aneurysm, whether abdominal or thoracic, may not need any active treatment and instead may just be monitored regularly. Medications and preventive measures may form part of conservative management or they may accompany active surgical treatment - through open or endovascular surgery.
Aortic aneurysm surgery can be performed as open surgery or as endovascular surgery.
Aneurysms that rupture require emergency surgery. Without immediate repair, a ruptured aneurysm is always fatal in the thoracic aorta, and almost always fatal in the abdominal aorta.4
The decision to operate on an unruptured aneurysm in the aorta depends on a number of factors related to the individual patient, as well as to features of the aneurysm itself:4,5,7
- Individual factors - age, general health, coexisting conditions and personal choice
- The aneurysm's characteristics - size relative to location in the thorax or abdomen and the rate of growth
- Other factors - chronic abdominal pain or risk of thromboembolism may make surgery a good option.
An aortic aneurysm that has a larger diameter (about 2 inches or 5 cm) is more likely to prompt a recommendation of surgery, as is an aneurysm which is growing more quickly (a little less than 1/4 inch over the last 6-12 months).23
For both elective unruptured and emergency ruptured cases, surgery can take one of two forms:4
- Open surgery to fit a synthetic or stent graft
- Endovascular stent-graft surgery.
Endovascular surgery involves accessing the blood vessels through a small incision near the hip. In stent-graft surgery, an endovascular graft is inserted through this incision using a catheter and is positioned in the aorta to seal off the aneurysm.21
In the emergency of a ruptured abdominal aortic aneurysm, the decision over which procedure to perform will be urgent. For elective operations to repair unruptured aneurysms, a review published in 2014 sought to determine the relative risks and benefits of open vs. endovascular surgery.4,15
The review found that while there was a lack of robust studies comparing the two options directly, similar rates of complication were reported for both types of surgery.
The evidence suggested that endovascular aneurysm repair (EVAR) was "less invasive," but the procedure did "not always significantly alter the postoperative course or length of hospital stay for patients."
The authors concluded that open surgery still had a role for those patients who were not suitable for endovascular surgery.
Endovascular surgery has become the generally preferred method of aortic aneurysm surgery because of:15
- Shorter operative times
- Often shorter hospital stays
- Better levels of surgical experience
- A perceived lower risk of disease or death surrounding surgery compared with laparoscopic surgery (although the review found this could be more perception than reality).
Endovascular surgery for the repair of aortic aneurysms does carry the following risks however, in addition to the usual risks of surgery:23
- Bleeding around the graft (which requires additional surgery)
- Bleeding before or after the procedure
- Blockage of the stent
- Nerve damage, resulting in weakness, pain or numbness in the leg
- Kidney failure
- Reduced blood supply to the legs, kidneys or other organs
- Erectile dysfunction
- Unsuccessful surgery that then requires open surgery
- Slippage of the stent.
Cerebral aneurysm treatment options
Surgical treatment of an aneurysm in the brain is reserved for cases that present a high risk of rupture.5
Aneurysms that are less likely to burst are not treated surgically because of the potential risk of brain-damage resulting from possible surgical complications.
In lieu of surgery, patients are given guidance on how to monitor and modify, where possible, the risk factors for rupture of a brain aneurysm. This will likely involve monitoring blood pressure - see prevention below.17
Where a ruptured brain aneurysm has led to a subarachnoid hemorrhage (a medical emergency), a patient may be admitted to hospital and undergo brain surgery.
Such a procedure would aim to close off the artery that ruptured due to the aneurysm, in the hope of preventing another bleed.4
Prevention of aneurysm
The single most important way a person can reduce their risk of developing an aneurysm is to not smoke or to quit if already smoking. Smoking is not only the strongest risk factor for the development of an aortic aneurysm, it is also one of the greatest risk factors for an aneurysm growing and rupturing.
Smoking is the strongest risk factor for both the development and rupture of aneurysms.
Smoking is a greater risk factor for aneurysm than it is for atherosclerosis, the cardiovascular disease where fatty deposits accumulate on the arterial wall and which can weaken artery walls.18
The fact that smoking is also a big risk factor for atherosclerosis is directly relevant, however, because most aneurysms are caused by weakening of the artery wall brought on by atherosclerosis:4
Studies have shown that continued smoking induces a significantly faster expansion of aortic aneurysms - by about 0.4 millimeters a year).11,18
Brain aneurysms are not always possible to avoid to the same extent as aortic aneurysms because ruptured brain aneurysms causing subarachnoid hemorrhage stroke can be congenital - present at birth.4
Brain aneurysm has both genetic and environmental risk factors, and a history of brain aneurysms in the family is an established risk factor, as is increasing age. However, known risk factors also include, alongside hypertension (high blood pressure), smoking.19
Cigarette smoke is also a major source of free radicals which cause oxidative stress. Oxidative stress and resulting tissue damage can occur due to higher production or reduced removal of free radicals. Oxidative stress can also increase inflammation, which contributes to the formation and rupture of cerebral aneurysms.20
Almost 80% of patients who sustain a hemorrhagic stroke because of a ruptured brain aneurysm have a significant history of smoking.20
In addition to quitting smoking, there are other modifiable risk factors for damage to blood vessels. Changing the following factors through lifestyle and other measures reduces the risk of aneurysm:5,17,21,22
- Hypertension - using diet, exercise and, where appropriate, medications to reduce high blood pressure can help to decrease pressure and stress on artery walls
- Poor diet - an unhealthy diet with a lack of energy balance is a risk factor for cardiovascular disease and can lead to obesity. Adhering to a healthy diet can reduce cholesterol and decrease the risk of atherosclerosis
- Lack of exercise - being more active helps to reduce blood pressure
- Overweight and obesity - requires the heart to pump hard and so raises blood pressure. Excess adipose (fatty) tissue can also increase levels of inflammation.
Anyone diagnosed with an aneurysm and whose treatment plan is conservative can work with a health care practitioner to help them address any modifiable risk factors.