At 4 centimeters (cm), an aortic aneurysm is either safe to monitor with imaging or at risk of rupturing, which may require surgery to prevent serious complications.

The aorta is the body’s largest artery. It runs from the heart to the pelvis and supplies most of your organs with oxygen-rich blood.

When a portion of the aorta bulges or balloons outward, it’s called an aortic aneurysm. If an aortic aneurysm ruptures, it can be a life threatening medical emergency.

One way doctors assess the risk of an aortic aneurysm is by measuring it with imaging, such as a CT scan.

An aneurysm under 4 cm may be monitored yearly. It may not require any intervention.

An aneurysm greater than 4 cm is more concerning. It may require more frequent imaging or surgery if it appears likely to rupture.

Learn more about what causes aortic aneurysms and how doctors monitor and treat them depending on their size and location.

There are two main types of aortic aneurysms. They are classified by their location.

A thoracic aortic aneurysm (TAA) is located in the chest. An abdominal aortic aneurysm (AAA) develops somewhere between the chest and the pelvis.

AAAs are more common than TAAs. A 2020 report suggests AAAs occur in about 0.5%–7.2% of males and 1.0–1.3% of females. TAAs occur in about 6–10 out of every 100,000 people.

A 4-cm aortic aneurysm is a little larger than the average diameter of the aorta. The average diameter of the abdominal aorta is about 2 cm, according to the American Heart Association.

A 2021 study suggests that the average diameter of the thoracic aorta is about 2.9–3.7 cm in females and about 3.1–3.9 cm in males.

Most aortic aneurysms are smaller than 4 cm and should be monitored annually for growth and a change in rupture risk.

Larger aortic aneurysms, though less common, must be monitored more frequently. Surgery may be needed to treat the bulging artery and prevent serious health risks.

The biggest risk of aortic aneurysms is rupture and massive internal bleeding. These events are often fatal.

However, an aortic aneurysm of 4 cm is considered low risk for rupture.

A 2016 study suggests that the rupture risk for an AAA between 4 and 4.9 cm is 1% per year, though the risk increases significantly with every additional centimeter of growth.

That same study suggests the rate of rupture for a TAA under 5 cm is 2% per year, with the risk increasing substantially if the aneurysm continues to grow.

The main risk factor for an aortic aneurysm is a history of smoking. Other risk factors include:

Injury to the aorta from blunt trauma or another cause can also lead to an aortic aneurysm.

For small aneurysms that do not appear to have a rupture risk, a doctor may prescribe medications to:

  • support better blood flow
  • lower high blood pressure
  • keep cholesterol levels in a healthy range

If a doctor determines your aortic aneurysm could rupture soon, surgery may be needed to secure the aneurysm and prevent a rupture.

The two main surgical procedures include open surgery and endovascular surgery, which is less invasive. The aim of both procedures is to repair the aneurysm with a special graft or tube that wraps around the affected portion of the aorta to keep it stable.

The 2022 American Heart Association and American College of Cardiology guidelines for aortic aneurysm management suggest that surgery may be appropriate for aneurysms starting at 5 cm.

Previously, interventions were recommended starting at 5.5 cm.

An aortic aneurysm will not disappear on its own or shrink once it has been formed.

Some aneurysms may reach a certain size and remain that way, but they won’t grow smaller.

The outlook, or prognosis, for someone with a 4-cm aortic aneurysm varies. A person’s outlook primarily depends on whether the aneurysm grows and ruptures or is treated before any problems occur.

A 2020 study found that elective surgery to replace the ascending aorta (the portion of the aorta nearest the heart) because of an aneurysm was associated with a 5-year survival rate of nearly 90%.

In cases of aortic aneurysm rupture, the survival odds are low. A 2016 study suggests that about 85% of people who experience a ruptured AAA will not survive, and most die before reaching the hospital.

If you receive a diagnosis of a 4-cm aortic aneurysm, work with your healthcare team closely to prevent serious complications. Your care team can help you find a cardiologist who specializes in vascular disorders and aortic aneurysm management.

Getting regular imaging can help you and your care team monitor your condition and prepare for surgery if needed.