What is an Aortic Aneurysm?
An aortic aneurysm is a balloon-like bulge in the aorta—the large artery that carries oxygen-rich blood from your heart—caused by weakening of the artery wall. 1
Basic Definition
An aortic aneurysm occurs when the aortic wall becomes weak, allowing blood pressure to push the wall outward like an inflating balloon. 1 More precisely, it's defined as permanent dilation of the aorta by more than 50% (at least 1.5 times) larger than the normal expected diameter for someone of the same age and sex. 1
Where Aneurysms Occur
The aorta runs from your heart through your chest (thoracic aorta) and down into your abdomen (abdominal aorta). 1 Aneurysms can develop in either location:
Thoracic aortic aneurysms (TAA): Most commonly affect the ascending aorta near the heart (about 60% of cases), with the descending thoracic aorta affected less often (30%), and the aortic arch least commonly (10%). 1
Abdominal aortic aneurysms (AAA): Occur in the part of the aorta that passes through the belly, typically below the kidneys. 1
Why Aneurysms Are Dangerous
The critical danger is rupture (bursting), which causes life-threatening internal bleeding and often leads to death. 1, 2 Most people with an aortic aneurysm have no symptoms until it ruptures. 1 The mortality rate for ruptured AAA is 65-85%. 2
The risk of rupture increases as the aneurysm grows larger:
- Aneurysms 6.0-6.5 cm carry a 7% annual risk of rupture 1
- The risk roughly doubles with every 1 cm of growth over 5 cm 1
Who Gets Aortic Aneurysms
Older male smokers have the highest risk of developing aortic aneurysms. 1 Key risk factors include:
- Smoking (the most important modifiable risk factor) 1, 3
- Male sex (men are affected 3 times more often than women for some types) 1, 2
- Age over 65 years 1, 2
- Hypertension (present in 80% of cases) 1
- Family history (genetics may be involved in 20% of cases) 1, 4
- Genetic conditions like Marfan syndrome, Loeys-Dietz syndrome, bicuspid aortic valve, and Turner syndrome 1, 4
The incidence is approximately 10.4-13.8 cases per 100,000 person-years for thoracic aneurysms. 1
How Aneurysms Develop
The underlying mechanism involves weakening and breakdown of the aortic wall structure. 5 Specifically, there is thinning of the wall layers due to loss of smooth muscle cells and degradation of the elastic fibers and connective tissue that normally give the aorta its strength. 1, 2 This process is called medial degeneration. 1