Most aneurysms cause no symptoms at all. An estimated 3% to 5% of people have a brain aneurysm they don’t know about, and abdominal aortic aneurysms are similarly silent. The signs you’d notice depend entirely on where the aneurysm is and whether it’s still intact or has started to leak or rupture. Here’s what to watch for with each type.
Brain Aneurysms Are Usually Silent Until They Aren’t
An unruptured brain aneurysm can sit quietly for years or even a lifetime without producing a single symptom. Small ones, under 10 millimeters, are especially unlikely to cause trouble. A meta-analysis of thousands of patients found that among small aneurysms managed without surgery, roughly 1 in 100 ruptured over a nearly four-year period. That’s reassuring, but it also means most people with a brain aneurysm have no way of knowing it’s there based on how they feel.
Larger unruptured aneurysms sometimes press on nearby nerves or brain tissue, which can produce warning signs. These include pain behind or above one eye, a dilated pupil, double vision, or numbness on one side of the face. These symptoms develop gradually, not all at once, and they’re easy to chalk up to something less serious.
The “Worst Headache of Your Life” Is the Red Flag
When a brain aneurysm ruptures, it bleeds into the space surrounding the brain. The hallmark symptom is a sudden, explosive headache that people consistently describe as the worst headache they’ve ever experienced. It reaches full intensity within seconds, not minutes or hours. This is fundamentally different from a migraine, which builds gradually and often comes with familiar warning signs like aura.
Along with that headache, a ruptured brain aneurysm can cause nausea and vomiting, a stiff neck, blurred or double vision, sensitivity to light, seizures, confusion, and loss of consciousness. Not everyone gets all of these, but the headache alone is reason enough to call emergency services immediately.
Sometimes an aneurysm leaks before it fully ruptures. A “sentinel leak” produces a severe headache that can persist for days to two weeks. This is essentially a warning that a larger rupture may follow. Anyone who experiences a sudden, unusually intense headache that feels different from any headache they’ve had before should treat it as an emergency.
Abdominal Aortic Aneurysms Feel Like a Pulse in Your Belly
An abdominal aortic aneurysm (AAA) forms in the large blood vessel that runs through your abdomen. Like brain aneurysms, most cause no symptoms until they’re dangerously large. When symptoms do appear, they tend to include a steady, deep pain in the lower back or belly, pain radiating into the leg, groin, or pelvic area, and a pulsing sensation in the abdomen that feels like a heartbeat.
That pulsing feeling is the most distinctive clue. You might notice it when lying down, particularly if you’re thin. But plenty of people can feel their normal aortic pulse without having an aneurysm, so the sensation alone isn’t diagnostic. It becomes more concerning when paired with persistent back or abdominal pain that doesn’t have an obvious cause. A ruptured AAA causes sudden, severe pain in the abdomen, lower back, or legs and is a life-threatening emergency.
Chest Aneurysms Can Mimic Other Conditions
Thoracic aortic aneurysms form in the section of the aorta that passes through your chest. These are sometimes called “silent killers” because they typically grow without symptoms until they rupture. Research suggests the prevalence in the general population is low, around 0.16%, though autopsy studies indicate many go undetected during life.
When a thoracic aneurysm does cause symptoms, they often mimic other chest or throat conditions. An aneurysm pressing on the esophagus can make swallowing difficult or painful. Pressure on the windpipe can trigger a persistent cough or shortness of breath. If it compresses the nerves near the voice box, you may develop unexplained hoarseness. These symptoms tend to be subtle and easy to attribute to something else, which is part of what makes thoracic aneurysms so dangerous.
Who Is at Higher Risk
Smoking is one of the strongest risk factors across all aneurysm types. Smokers face a rupture risk for brain aneurysms roughly three times higher than nonsmokers. Tobacco smoke triggers inflammation and damages blood vessel walls, producing weaker, more fragile tissue that’s more prone to ballooning and tearing. Even the definition of “ever smoker” used in screening guidelines is surprisingly low: 100 or more cigarettes over a lifetime.
High blood pressure is the other major contributor. Sustained pressure against artery walls accelerates the weakening that allows aneurysms to form and grow. Family history matters too, especially for brain aneurysms, where having a first-degree relative with one significantly raises your own risk. Connective tissue disorders, being over 50, and being female (for brain aneurysms) or male (for abdominal aortic aneurysms) also shift the odds.
Screening Catches What Symptoms Miss
Because most aneurysms are silent, screening is the most reliable way to find them before they become dangerous. The U.S. Preventive Services Task Force recommends a one-time abdominal ultrasound for men aged 65 to 75 who have ever smoked. For men in that age range who have never smoked, screening is offered selectively based on other risk factors. The task force currently recommends against routine screening for women who have never smoked and have no family history, though the evidence for women who have smoked remains inconclusive.
Brain aneurysm screening isn’t routine for the general population. It’s typically offered when you have a strong family history (two or more first-degree relatives with brain aneurysms) or a connective tissue disorder. The screening itself is painless: an MR angiography scan captures detailed images of the blood vessels in the brain and can reveal the size, shape, and location of any aneurysm present.
How Aneurysms Are Diagnosed
If you show up at a hospital with symptoms suggesting a possible aneurysm, imaging is the first step. For a suspected brain aneurysm, a CT scan with injected dye can reveal bleeding or the aneurysm itself. An MRI or MR angiography provides more detailed images and can measure the aneurysm precisely. For cases where those scans aren’t definitive, a cerebral angiogram offers the highest resolution. In this procedure, a thin catheter is threaded through an artery (usually from the wrist or groin) to the brain, and dye is injected to map the blood vessels in detail.
If a rupture is suspected but the CT scan looks normal, a spinal tap can check for blood in the cerebrospinal fluid, which would confirm bleeding around the brain. For abdominal and thoracic aneurysms, an abdominal ultrasound or CT scan is the standard approach, and these are quick, widely available tests.
What a Small Aneurysm Means for You
Finding out you have a small, unruptured aneurysm can feel alarming, but the numbers are often reassuring. For brain aneurysms 5 millimeters or smaller, the rupture rate is around 1% over nearly four years when managed conservatively. For aneurysms 3 millimeters or smaller, it drops to about 0.8% over the same period. That translates to roughly 8 to 15 ruptures per 1,000 small aneurysms over several years.
Conservative management typically means regular imaging to monitor for growth, blood pressure control, and quitting smoking if you smoke. Surgery carries its own risks, so for many small aneurysms the math favors watchful waiting. Your size, location, shape, and personal risk factors all factor into whether monitoring or intervention makes more sense. If an aneurysm grows or changes shape on follow-up imaging, the calculus shifts toward treatment.