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
Fast facts on aneurysms
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
On the next page, we look at the complications, treatment and prevention of aneurysm.