An aortic aneurysm is a bulge or ballooning in the wall of the aorta, the largest blood vessel in your body. The aorta runs from your heart down through your chest and abdomen, delivering blood to every major organ. When a section of this vessel weakens and stretches outward, that’s an aneurysm. Most aortic aneurysms produce no symptoms at all, which is what makes them dangerous: they can grow silently for years and, in rare cases, rupture with life-threatening consequences.
Where Aortic Aneurysms Form
Aortic aneurysms fall into two main types based on location. An abdominal aortic aneurysm (AAA) forms below the diaphragm, in the section of the aorta that runs through the belly. A thoracic aortic aneurysm (TAA) forms above the diaphragm, in the chest portion of the vessel. Of the two, abdominal aneurysms are far more common, affecting 4% to 7% of men over 65 and 1% to 2% of women in the same age group. Thoracic aneurysms are estimated to occur in roughly 1% of the general population.
The two types also differ in their underlying causes. Abdominal aneurysms are strongly tied to lifestyle factors like smoking, high blood pressure, and high cholesterol. Thoracic aneurysms have a stronger genetic component: about 20% to 25% of people with a thoracic aneurysm have a family history of the condition, and roughly a quarter of those familial cases follow a clear pattern of inheritance linked to a single gene mutation.
What Causes the Aortic Wall to Weaken
The aortic wall is made of layered tissue that includes muscle, elastic fibers, and a structural scaffolding called the extracellular matrix. An aneurysm develops when this scaffolding breaks down. Inflammation, the death of smooth muscle cells in the vessel wall, and the gradual destruction of elastic tissue all contribute. Over time, the weakened section stretches under the constant pressure of blood flow, forming a bulge that slowly expands.
Smoking is the single most important avoidable risk factor for abdominal aortic aneurysms, and the level of exposure matters more than how many years a person has smoked. Men are nearly six times more likely to develop an AAA than women. After age 65, the risk increases by about 40% every five years. High blood pressure raises the likelihood by 30% to 40%, and a long history of blood pressure medication use (which signals years of elevated pressure) is associated with an even higher risk.
Certain connective tissue disorders dramatically increase the chance of developing an aneurysm at a younger age. In Marfan syndrome, a genetic mutation produces abnormal fibrillin, a protein that gives the aortic wall its elasticity. People with Marfan syndrome carry a lifetime aortic dissection risk of 5% to 30%, with the highest danger in their 30s and 40s. Vascular Ehlers-Danlos syndrome, caused by a different mutation that weakens collagen, is even more aggressive: nearly 80% of affected individuals experience vascular complications, including aortic dissection, by age 40.
Why Most People Have No Symptoms
The aorta is deep inside the body, and a slowly expanding bulge rarely presses on anything that would cause noticeable discomfort. Most aortic aneurysms are discovered incidentally during imaging for an unrelated problem, or through a screening ultrasound. This silent growth is the defining feature of the condition.
When an aneurysm does start to produce symptoms, it usually means the bulge has grown large enough to press on surrounding structures, or that rupture is imminent. Warning signs of a large, intact abdominal aneurysm include steady, deep pain in the lower back or belly, pain radiating to the leg, groin, or pelvis, and a pulsing sensation in the abdomen that feels like a heartbeat.
A ruptured aortic aneurysm is a medical emergency. Symptoms come on suddenly: severe pain in the abdomen, lower back, or legs, along with shortness of breath, a rapid heartbeat, dizziness or fainting, nausea, and clammy skin. Internal bleeding from a ruptured aorta can be fatal within minutes. If you or someone near you develops sudden, severe abdominal or back pain with any of these other signs, call 911 immediately.
How Aneurysms Are Found
Because aortic aneurysms rarely announce themselves, screening plays a critical role. The U.S. Preventive Services Task Force recommends a one-time abdominal ultrasound for men aged 65 to 75 who have ever smoked (defined as at least 100 cigarettes in a lifetime). Men in that age range who have never smoked may or may not benefit from screening, depending on other risk factors. The Task Force does not recommend routine screening for women, though individual cases with strong risk factors may warrant it.
The ultrasound itself is painless, takes about 15 minutes, and can measure the diameter of the aorta with precision. A normal abdominal aorta is roughly 2 centimeters across. An aneurysm is generally defined as a dilation of 3 centimeters or more. For thoracic aneurysms, imaging is typically done with a CT scan or MRI, since ultrasound doesn’t penetrate the chest wall as effectively.
Monitoring Based on Size
Not every aneurysm needs surgery. Small aneurysms grow slowly in most people, and the risk of an operation can outweigh the risk of rupture at smaller sizes. Instead, doctors use a “watchful waiting” approach with scheduled imaging to track growth over time. The American College of Cardiology and American Heart Association guidelines lay out specific intervals based on the aneurysm’s diameter.
For abdominal aneurysms between 3.0 and 3.9 cm, imaging every three years is typical. At 4.0 to 4.9 cm in men (or 4.0 to 4.4 cm in women), that tightens to once a year. Once an AAA reaches 5.0 cm in men or 4.5 cm in women, monitoring increases to every six months, and the conversation about surgical repair becomes more urgent.
For thoracic aneurysms, initial follow-up imaging is usually recommended 6 to 12 months after discovery. If the size is stable, subsequent imaging shifts to every 6 to 24 months depending on the diameter and how quickly it appears to be growing.
When Surgery Is Recommended
Surgery is generally recommended when an abdominal aortic aneurysm reaches about 5.5 cm in men or 5.0 cm in women. For thoracic aneurysms, current guidelines support repair at a 5.5 cm threshold in people without a connective tissue disorder. People with Marfan syndrome or vascular Ehlers-Danlos syndrome typically qualify for repair at smaller diameters because their aneurysms are more prone to rupture.
Rapid growth also triggers surgical discussion regardless of current size. If an aneurysm expands by more than 0.5 cm in six months, that pace suggests the wall is deteriorating faster than average.
Open Repair vs. Endovascular Repair
There are two main surgical approaches. Open repair involves a large incision in the abdomen or chest, removing the weakened section of aorta, and replacing it with a synthetic graft. It’s a major operation with a longer recovery, but it works for almost any anatomy.
Endovascular aneurysm repair (EVAR) is less invasive. A surgeon threads a stent graft through a small incision in the groin, guides it up into the aorta using X-ray imaging, and deploys it inside the aneurysm. The graft lines the weakened wall from the inside, redirecting blood flow away from the bulge. In a meta-analysis of over 37,000 patients, people who had endovascular repair spent roughly five to six fewer days in the hospital compared to those who had open surgery. For planned (non-emergency) repairs, the difference was still significant at about five days shorter.
Endovascular repair isn’t an option for everyone. It requires specific anatomy: the aneurysm needs to be in the right location, with a suitable “neck” of healthy aorta above it for the graft to anchor. Patients with complex anatomy or aneurysms that extend into branch arteries may need open repair. Interestingly, patients referred for endovascular repair often have more serious underlying health conditions that make open surgery too risky, which complicates direct comparisons between the two approaches.
Living With an Aortic Aneurysm
If you’ve been told you have a small aortic aneurysm that doesn’t yet need repair, the focus shifts to slowing its growth. Quitting smoking is the most impactful step you can take. Managing blood pressure reduces the mechanical stress on the weakened wall. Staying physically active is encouraged, though heavy weightlifting and intense straining that spike blood pressure are typically discouraged.
Aortic aneurysms are the 15th leading cause of death in people 55 and older, but mortality rates have dropped sharply over the past two decades. Between 1999 and 2020, the age-adjusted death rate from ruptured aortic aneurysms in the U.S. fell from 4.87 to 1.15 per 100,000 people, a decline of more than 75%. Better screening, improved surgical techniques, and wider use of blood pressure and cholesterol medications all contributed to that trend. The condition is serious, but for most people, early detection transforms it from a hidden threat into a manageable one.