The four types of aneurysms are classified by where they form in the body: cerebral (brain) aneurysms, abdominal aortic aneurysms, thoracic aortic aneurysms, and peripheral aneurysms. Each develops in a different artery, carries distinct risks, and produces different warning signs. An aneurysm is a weakened, ballooning section of an artery wall, and its location determines both how dangerous it is and how it gets treated.
Cerebral (Brain) Aneurysms
Cerebral aneurysms form in the arteries inside the skull, most commonly in or near a ring of arteries at the base of the brain called the circle of Willis. The internal carotid artery and middle cerebral artery are the most frequent sites, followed by the posterior and anterior communicating arteries. These aneurysms are typically small, balloon-like pouches that bulge from one side of the artery wall.
Most brain aneurysms cause no symptoms at all and are discovered incidentally during imaging for something else. The danger comes if one ruptures, which causes bleeding into the space surrounding the brain. A ruptured brain aneurysm produces a sudden, severe headache often described as the worst headache of a person’s life. Other symptoms include nausea, vomiting, a stiff neck, blurred or double vision, sensitivity to light, seizures, confusion, and loss of consciousness.
Rupture is a medical emergency with grim statistics. Among patients with ruptured brain aneurysms who don’t receive treatment, roughly 59% die within the first month, and 68% within two years, according to a multicenter study published in the AHA journal Stroke. Outcomes are worse for people over 70, those who lose consciousness at the time of rupture, and those with aneurysms 5 mm or larger. Among survivors who do recover, the majority regain reasonable function, though about 13% live with significant disability two years later.
Sometimes a brain aneurysm leaks slightly before a full rupture, causing a sudden, extremely severe headache that can persist for days to two weeks. This “sentinel headache” is a critical warning sign that a larger rupture may follow.
Abdominal Aortic Aneurysms
Abdominal aortic aneurysms (AAAs) develop in the section of the aorta that runs through the abdomen. The aorta is the body’s largest artery, carrying blood directly from the heart, and aortic aneurysms are by far the most common type overall. An AAA is generally defined as a bulge that widens the abdominal aorta beyond 3.0 cm in diameter.
AAAs affect men far more often than women, and the risk climbs sharply after age 60. Screening studies have found a prevalence of 3 to 8 percent in older populations, though rates have been declining in recent decades as fewer people smoke. In one large study of over 81,000 men, the prevalence of screen-detected AAA dropped from 5.0% in 1991 to 1.3% in 2015, a trend closely linked to falling smoking rates. Smoking is the single most important modifiable risk factor, and having a first-degree relative with an AAA doubles your own risk.
Like most aneurysms, AAAs are usually silent until they become large or rupture. Because of this, the U.S. Preventive Services Task Force recommends a one-time ultrasound screening for men aged 65 to 75 who have ever smoked (defined as 100 or more cigarettes in a lifetime). Men in that age range who have never smoked may still benefit from screening on a case-by-case basis. For women who have never smoked and have no family history, routine screening is not recommended.
Thoracic Aortic Aneurysms
Thoracic aortic aneurysms (TAAs) form in the portion of the aorta that passes through the chest. They’re further divided into three groups based on the exact segment involved: ascending aortic aneurysms (closest to the heart), aortic arch aneurysms (where the aorta curves and branches to supply the head and arms), and descending thoracic aneurysms, which are sometimes called thoracoabdominal aneurysms when they extend into the belly.
Most TAAs produce no symptoms until they rupture or grow large enough to press on nearby structures, which can cause chest or back pain, difficulty swallowing, or hoarseness. This silent nature makes them particularly dangerous. Some people carry genetic conditions that weaken connective tissue and predispose them to thoracic aneurysms at younger ages.
Surgery is generally considered when the aneurysm reaches a certain size. Updated guidelines from the American College of Cardiology have lowered the threshold for ascending aortic and aortic root aneurysms from 5.5 cm to 5.0 cm at experienced surgical centers, and even lower for patients with inherited connective tissue disorders. The decision depends on the aneurysm’s growth rate, your overall health, and whether you have risk factors that make rupture more likely.
Peripheral Aneurysms
Peripheral aneurysms develop in arteries outside the aorta and brain, most commonly in the legs. The popliteal artery (behind the knee) and the femoral artery (in the upper thigh) are the two most frequent sites. These are far less common than aortic aneurysms but carry real risks, particularly for the affected limb.
Unlike aortic aneurysms, where the primary danger is catastrophic rupture and internal bleeding, peripheral aneurysms threaten the limb mainly through blood clots. A clot can form inside the bulging artery and either block blood flow at that spot or break off and travel downstream, cutting off circulation to the lower leg or foot. Popliteal aneurysms are considered more hazardous than femoral ones. About 10% of men who already have an abdominal aortic aneurysm also have a popliteal aneurysm, a rate nearly four times higher than previously recognized. Femoral aneurysms tend to follow a somewhat less dangerous course.
Symptoms of a peripheral aneurysm can include a pulsing lump you can feel, pain or cramping in the affected leg, numbness or coolness in the foot, or sores that won’t heal due to poor circulation. If a clot suddenly blocks the artery, you may experience acute leg pain, pale or bluish skin, and loss of pulse in the foot, all of which require emergency care.
Shape Matters Too: Saccular vs. Fusiform
Beyond location, aneurysms are also classified by their shape. A saccular aneurysm (sometimes called a berry aneurysm in the brain) bulges outward on only one side of the artery, like a small pouch or balloon attached to the wall. A fusiform aneurysm bulges outward in all directions, causing an entire section of the artery to widen symmetrically. Fusiform aneurysms are relatively more common in the aorta, while saccular aneurysms are the typical form found in brain arteries. Shape can influence rupture risk and the approach used for repair, so it’s one of the details doctors assess on imaging.
Risk Factors Across All Types
Certain risk factors are shared across aneurysm types. High blood pressure places constant outward force on artery walls, gradually weakening them. Smoking damages the structural proteins that keep arteries elastic and strong, and it is the most well-established controllable risk factor for aortic aneurysms specifically. Age plays a major role: the incidence of AAA in men jumps from about 55 per 100,000 person-years at ages 65 to 74, to nearly 300 per 100,000 person-years after age 85.
Family history matters for every type. A first-degree relative with an aortic aneurysm doubles your own risk. Genetic connective tissue conditions can predispose people to aneurysms at multiple sites and at younger ages. Atherosclerosis, the buildup of plaque inside artery walls, weakens vessel structure over time and contributes to both aortic and peripheral aneurysms. Because most aneurysms grow silently for years, managing blood pressure, not smoking, and following screening recommendations when they apply to you are the most practical steps for catching one before it becomes an emergency.