What Are the Types of Aneurysms?

An aneurysm occurs when part of an artery’s wall weakens, causing it to bulge or widen. Aneurysms can occur due to poor diet, high blood pressure, high cholesterol, atherosclerosis, obesity, smoking, and using drugs that spike blood pressure, like cocaine.

Aneurysms are most commonly found in the arteries of the brain or in the aorta — the largest artery in the body, which runs from the heart to the lower abdomen — but they can also form in other parts of the body. Although some people are born with diseases and health conditions that predispose them to aneurysms, and they can run in families, others develop them later on in life with no warning, says George P. Teitelbaum, MD, an interventional neuroradiologist at the Pacific Neuroscience Institute in Santa Monica, California.

Here’s a look at the various types of brain aneurysms and what you need to know about them.

What Is a Brain Aneurysm, and What Causes Them?

A brain aneurysm, also referred to as a cerebral or intracranial aneurysm, is a weak or thin spot in an artery in the brain. Over time, pressure from blood pressure creates wear and tear on the artery and causes an “outpouching,” or bulge, to form.

In the United States, an estimated 1 out of every 50 people have an unruptured brain aneurysm, but most will never have any symptoms or problems. Each year, about 30,000 people in the country have a brain aneurysm rupture. Brain aneurysms occur most commonly in people between ages 35 and 60, and they’re more frequently seen in women than in men. (1)

An aneurysm can press on a nerve or surrounding tissue, becoming progressively weaker and eventually bursting. Either an intracerebral hemorrhage, when blood leaks into the brain itself, or a subarachnoid hemorrhage, bleeding into the space between the skull and the brain, can occur.

Aneurysms located on the posterior circulation or vestibular system of the brain are less common than those located on the anterior (front) circulation of the brain, but they have a higher risk for rupture.

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Brain aneurysms located on the basilar artery, near the brainstem at the base of the skull, are extremely difficult to operate on and carry a high rate of mortality.

Aneurysms that carry the greatest risk of rupture are those that are larger than 7 milliliters in diameter, are located in the posterior or anterior arteries, and have a “daughter sac.” These “daughter aneurysms,” have a complex shape and an additional bulge on the top or dome, Dr. Teitelbaum says.

Some symptoms of a brain aneurysm include a severe headache, described as the worst headache you’ve ever had, dilated pupils, blurred or double vision, pain above and behind an eye, weakness, numbness, and difficulty speaking.

There are two types of brain aneurysms: saccular and fusiform.

Saccular Aneurysm

Saccular aneurysms are the most common type of brain aneurysms. They are also referred to as “berry” aneurysms because a small sac forms at the point where an artery divides into two branches, and fills with blood.

Saccular aneurysms are also the most common cause of subarachnoid hemorrhages, which can lead to stroke, brain damage, or death.

About 30,000 people who have a brain aneurysm will also suffer a rupture, and an estimated 40 percent of those who do won’t survive 24 hours. (2)

Of those who survive, 66 percent will have some type of permanent neurological problems. (1)

Fusiform Aneurysm

A less common type of brain aneurysm, and one that’s less likely to rupture, is the fusiform aneurysm. A fusiform aneurysm has an equal outpouching on all sides of the arterial wall and no stem.

What Is an Aortic Aneurysm, and What Causes This Type of Aneurysm?

The aorta, the largest artery in the body, carries oxygen-rich blood throughout the body. Blood leaves the heart through the aortic valve, travels through the aorta and into other major arteries, and brings blood to the brain, muscles, and cells.

In an adult, the aorta normally measures about 2 to 3 centimeters in diameter, depending on the size and sex of the person. The aorta also has three layers:

  • Intima, the inner layer
  • Media, the middle layer
  • Adventitia, the outer layer

An aortic aneurysm occurs when a section of the aorta is permanently dilated, or expanded, to at least 50 percent its normal size. (3)

An aortic aneurysm can occur in the chest, called a thoracic aortic aneurysm, or in the abdomen, called an abdominal aortic aneurysm. Abdominal aortic aneurysms are much more common than thoracic aortic aneurysms and more common in men and people over age 65. (4)

What’s more, a study published in the journal Annals of Surgery found 28 percent of people who had an abdominal aortic aneurysm also had a thoracic aortic aneurysm. Women were also more likely than men to have both conditions. (5)

When an aortic aneurysm leaks or ruptures, severe bleeding or hemorrhage can occur.

An aortic dissection, or tear, can cause blood to lift up the intima and cause an aneurysm. Not only can a dissecting aneurysm rupture and bleed, but the layers can cut off blood flow to other small blood vessels and lead to stroke or damage to the kidneys and other organs, Teitelbaum says.

In 2019, aortic aneurysms were the primary cause of 9,904 deaths. A history of smoking accounts for about 75% of all abdominal aortic aneurysms. (4)

Abdominal Aortic Aneurysms

Most people with abdominal aortic aneurysms will not have symptoms, and these are often identified during a routine diagnostic imaging screen for something else. (6) But once it’s identified, it should be monitored by a doctor.

An abdominal aortic aneurysm that’s between 3 and 3.5 centimeters in diameter — about the size of a garden hose — is considered small. Although those that are larger than 3.5 centimeters are more likely to rupture, the risk of rupture for those under 5.5 centimeters is about 1 percent per year. Aneurysms larger than 5.5 are treated with endovascular aneurysm repair (EVAR)/stent grafting or surgery. Those larger than 7 centimeters carry the highest risk of rupture, between 20 and 40 percent. (7)

Abdominal aortic aneurysms can vary greatly in size, shape, and degree. Although they can take a fusiform or saccular shape, they can have features of both.

Thoracic Aortic Aneurysms

A thoracic aortic aneurysm occurs in the portion of the aorta located in the chest above the diaphragm, the dome-shaped muscle that helps you breathe. Like abdominal aortic aneurysms, thoracic aortic aneurysms do not cause symptoms in about 50 percent of people. (8)

There are several types of thoracic aortic aneurysms, depending on where they are located. (9) These include:

  • Ascending aortic aneurysms
  • Aortic arch aneurysms
  • Descending thoracic aneurysms, or thoracoabdominal aneurysms

A common type of thoracic aortic aneurysm occurs when the aorta walls weaken and a portion near the heart enlarges, preventing the valve between the heart and the aorta from closing properly and allowing blood to leak into the heart. Another, less common type of thoracic aortic aneurysm develops in the upper back and happens as a result of trauma to the chest. (8)

What Are Mycotic Aneurysms, and Why Do They Occur?

Aneurysms that are caused by a bacterial infection are called mycotic aneurysms. These aneurysms usually occur from an infection that originates in the heart, such as endocarditis, and causes the arterial wall to become infected and dilate.

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Nearly all untreated mycotic aneurysms lead to rupture and can be fatal, which is why timely diagnosis and treatment are key. (10)

Aneurysms are categorized as either true, or those that involve all the three layers of the arterial wall, or false (pseudoaneurysms), which is marked by a collection of blood that leaks out of the artery but is confined by the surrounding tissue.

What Are Peripheral Aneurysms, and What Are the Different Types of This Aneurysm?

A peripheral aneurysm occurs when the wall of a blood vessel in an organ or another part of the body weakens and dilates. The dilation can cause blood clots and interrupt blood flow, and can rupture and cause serious bleeding and compression of adjacent tissues. Peripheral aneurysms are usually genetic and are rare. (11)

A popliteal aneurysm is one that develops in an artery behind the knee. It is the most common type of peripheral aneurysm, accounting for 85 percent of all peripheral aneurysms and is associated with abdominal aortic aneurysms 40 to 50 percent of the time. (12)

Other types of peripheral aneurysms include: (13)

  • Splenic Artery Aneurysm An aneurysm that develops near the spleen
  • Mesenteric Artery Aneurysm An aneurysm in the artery that transports blood to the intestines
  • Femoral Artery Aneurysm An aneurysm that forms in the femoral artery in the groin
  • Carotid Artery Aneurysm An aneurysm that occurs in the carotid artery in the neck
  • Visceral Aneurysm A bulge of the arteries that supply blood to the bowel or kidneys

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