An aneurysm is a bulge in the wall of an artery where the vessel has weakened and ballooned outward, like a thin spot on a tire. Many aneurysms cause no symptoms at all and are discovered by accident during imaging for something else. But when an aneurysm grows large enough to press on surrounding tissue, or when it ruptures and bleeds, the consequences range from manageable to life-threatening depending on where it is and how quickly it’s treated.
How an Aneurysm Forms
Arteries have layered walls designed to handle the constant pressure of blood flow. An aneurysm develops when those layers weaken. The muscle cells in the artery wall lose their normal structure, and enzymes begin breaking down the supportive scaffolding that holds the wall together. As this scaffolding degrades, the wall can no longer resist the outward push of blood pressure, so it stretches and bulges. Once that bulge forms, the abnormal shape creates turbulent blood flow that puts even more stress on the weakened area, which can cause the aneurysm to grow over time.
Where Aneurysms Occur
Aneurysms can form in any artery, but two locations account for most of the serious cases. Brain aneurysms tend to develop at branching points along the ring of arteries at the base of the skull, with roughly 85% forming in the front portion of this network. The aorta, the body’s largest artery running from the chest through the abdomen, is the other common site. Abdominal aortic aneurysms are particularly common in older men and often grow silently for years.
Less commonly, aneurysms can form in the arteries behind the knees, in the spleen, or in other peripheral vessels. The location matters enormously because it determines what symptoms you experience, what’s at risk if it ruptures, and how it’s treated.
What an Unruptured Aneurysm Feels Like
Most unruptured aneurysms produce no symptoms whatsoever. Small brain aneurysms are frequently found incidentally when someone gets an MRI or CT scan for an unrelated reason. When an unruptured brain aneurysm does cause symptoms, it’s usually because the bulge has grown large enough to compress nearby nerves or brain tissue. The signs depend on the location but can include pain above and behind one eye, a dilated pupil, double vision or other vision changes, numbness on one side of the face, or seizures.
Abdominal aortic aneurysms are similarly quiet in most cases. When they do produce symptoms, you might feel a deep, steady pain in your abdomen or lower back, or a pulsing sensation near your navel.
What Happens During a Rupture
A rupture is the event most people are thinking about when they search this question, and it is a medical emergency. The experience differs depending on where the aneurysm is located.
Brain Aneurysm Rupture
When a brain aneurysm bursts, blood spills into the space surrounding the brain. The hallmark symptom is a sudden, explosive headache, often described as the worst headache of your life, reaching maximum intensity within seconds. This isn’t a headache that builds gradually. It hits like a thunderclap. Other symptoms that typically come with it include nausea and vomiting, a stiff neck, sensitivity to light, blurred or double vision, confusion, loss of consciousness, and sometimes seizures.
Inside the skull, the escaping blood raises pressure rapidly. The brain has no room to accommodate extra fluid, so the rising pressure compresses brain tissue and reduces blood flow. This pressure and the direct contact of blood with brain tissue causes cell death. About 15% of people with a ruptured brain aneurysm die before they reach a hospital. Overall, ruptured brain aneurysms are fatal in about 50% of cases, and roughly two-thirds of survivors are left with some permanent neurological deficit, according to the Brain Aneurysm Foundation.
Aortic Aneurysm Rupture
A ruptured aortic aneurysm causes sudden, severe pain in the abdomen, back, or chest depending on whether the rupture is in the abdominal or thoracic section. Because the aorta carries such a large volume of blood, a rupture can lead to massive internal bleeding and dangerously low blood pressure within minutes. Lightheadedness, a racing heartbeat, clammy skin, and loss of consciousness can follow quickly.
Complications After a Brain Aneurysm Rupture
Surviving the initial bleed is only the first hurdle. In the days and weeks that follow, several serious complications can develop. One of the most dangerous is a condition where the arteries in the brain narrow and constrict, reducing blood flow to areas that were not directly damaged by the bleed. This narrowing typically begins around day 3 to 4 after the rupture, peaks around day 7 to 10, and usually resolves by day 14. The reduced blood flow from this narrowing can cause strokes, with the highest risk falling around day 5 and again around day 9 to 10.
Other complications include a buildup of fluid in the brain’s internal chambers, rebleeding from the original site, seizures, and heart-related problems. This is why patients who survive the initial rupture are closely monitored in intensive care, often for two weeks or more.
Risk Factors for Developing an Aneurysm
Several factors make aneurysms more likely, and they fall into two categories: things you can’t change and things you can.
- High blood pressure is one of the most significant contributors, placing chronic extra force on arterial walls.
- Smoking is the single biggest lifestyle risk factor. It directly damages artery walls and accelerates both plaque buildup and high blood pressure.
- Atherosclerosis (plaque buildup in the arteries) narrows and stiffens vessels, creating additional stress on the walls.
- Age increases risk because blood vessels naturally lose elasticity over time.
- Genetic conditions like Ehlers-Danlos syndrome, Marfan syndrome, and polycystic kidney disease affect connective tissue throughout the body, including in blood vessel walls.
- Family history of aneurysms raises your own risk even without a known genetic condition.
Quitting smoking, keeping blood pressure well controlled, and managing cholesterol are the most effective steps for reducing your risk.
How Aneurysms Are Treated
Treatment depends on whether the aneurysm has ruptured and on its size, location, and shape.
Monitoring Small Aneurysms
Many small, unruptured aneurysms are simply watched with periodic imaging. For abdominal aortic aneurysms, the traditional threshold for recommending repair is 5.5 cm in diameter for men and 5.0 cm for women, though recent research suggests the optimal threshold may actually be higher for many patients, particularly when factoring in age and overall health. Below these sizes, the risk of the aneurysm rupturing is generally lower than the risk of surgery itself.
Surgical Clipping
For brain aneurysms that need treatment, one option is surgical clipping. A surgeon opens a section of the skull, locates the aneurysm, and places a small metal clip across its base to seal it off from normal blood flow. This is an open surgery, so recovery is longer. Hospital stays for unruptured aneurysms average around 7 to 9 days, and many patients are discharged to a rehabilitation facility before going home.
Endovascular Coiling
The less invasive alternative is coiling. A thin catheter is threaded through an artery in the leg up into the brain, and tiny metal coils are packed into the aneurysm. The coils trigger clotting inside the bulge, effectively sealing it off. Because there’s no need to open the skull, recovery is faster. Hospital stays for unruptured aneurysms treated with coiling average around 1 to 4.5 days, and patients generally return to normal activities sooner.
For ruptured aneurysms, both procedures are performed on an emergency basis. Patients treated with coiling tend to have shorter hospital stays (by about 2 to 3 days on average) and somewhat better early recovery scores compared to those who undergo clipping. The choice between the two depends on the aneurysm’s size, shape, and location, and some aneurysms are only suitable for one approach.
Living With an Unruptured Aneurysm
Being told you have an unruptured aneurysm can be deeply unsettling, but the reality is that many people live their entire lives with one that never causes a problem. The key is regular monitoring. Your imaging schedule will depend on the aneurysm’s size and whether it’s growing. Between scans, the most impactful things you can do are keep your blood pressure in a healthy range, avoid smoking, limit heavy straining or lifting that spikes blood pressure, and moderate alcohol intake. These steps won’t shrink an existing aneurysm, but they reduce the forces that could cause it to grow or rupture.