An aneurysm is a bulge or ballooning in the wall of a blood vessel. While it can occur in any artery, it is most commonly found in the brain or the aorta, the body’s largest artery. Aneurysm growth is not uniform, varying significantly among individuals and types, which influences medical management and risk assessment.
The Nature of Aneurysm Growth
Aneurysm growth patterns vary; some remain stable for years, while others grow slowly or rapidly. Medical professionals track this growth using serial imaging techniques like computed tomography (CT) scans, CT angiography (CTA), magnetic resonance imaging (MRI), or magnetic resonance angiography (MRA). These methods allow for precise measurement of the aneurysm’s maximum diameter.
Aortic aneurysms typically grow about one millimeter per year, though rates vary. Small abdominal aortic aneurysms (AAAs) have a median growth rate of 1.7 to 1.9 millimeters annually, with overall rates ranging from -1.0 to 6.1 millimeters. Thoracic aortic aneurysms (TAAs) can grow between 0.2 and 4.2 millimeters per year, with descending aorta aneurysms often growing faster than those in the ascending aorta or arch. Brain aneurysms also show variable growth, sometimes increasing by 1 to 3 millimeters, but their growth is not always predictable based on initial size.
Key Factors Influencing Growth
Aneurysm growth rates are influenced by intrinsic characteristics of the aneurysm and extrinsic factors related to an individual’s health and lifestyle. Larger aneurysms tend to expand more rapidly than smaller ones. The specific location of an aneurysm also plays a role; for example, brain aneurysms at arterial branching points may be more prone to growth due to blood flow dynamics, and descending thoracic aortic aneurysms can grow faster than those in the ascending aorta. Furthermore, an irregular or non-saccular shape is associated with faster enlargement.
Modifiable and non-modifiable factors contribute to vessel wall weakening and expansion. Uncontrolled high blood pressure (hypertension) damages arterial walls, accelerating growth by increasing pressure. Smoking is a significant risk factor, as it weakens vessel walls and hastens expansion. High levels of LDL (“bad”) cholesterol have been linked to the development of small abdominal aortic aneurysms, potentially by promoting inflammation that degrades the vessel’s matrix. Conversely, elevating HDL (“good”) cholesterol might help block aneurysm development or reduce their size.
Genetic predispositions also contribute to aneurysm growth. A family history of aneurysms or certain inherited conditions, such as Marfan syndrome, Ehlers-Danlos syndrome, or Loeys-Dietz syndrome, can increase both the risk of developing an aneurysm and the rate at which it grows. Inflammation within the vessel wall is another important factor. Chronic inflammatory cell infiltration, including macrophages and T cells, is observed in aneurysms and can contribute to the breakdown of elastin and smooth muscle cells, which weakens the arterial wall. Midlife body inflammation, indicated by elevated white blood cell levels, has been associated with a higher risk of abdominal aortic aneurysm development.
Monitoring and Risk Assessment
Monitoring aneurysm growth is a fundamental aspect of patient care, as it directly informs the assessment of rupture risk. Regular non-invasive imaging, such as CT scans, CT angiography, or magnetic resonance imaging, is routinely used to track changes in aneurysm size over time. The frequency of these studies can vary depending on the aneurysm’s size, location, and the patient’s overall health status.
The rate of growth, current aneurysm size, and other individual risk factors guide clinical decisions regarding watchful waiting or intervention. Aneurysm rupture risk increases exponentially with its diameter. For instance, abdominal aortic aneurysms smaller than 4 centimeters have a very low annual rupture risk (typically less than 1%), but this risk increases significantly for larger aneurysms: 1-2% for 4-5 cm, 3-5% for 5-6 cm, and over 20% for those larger than 7 cm. Rapid growth is a significant indicator of increased rupture risk; for aortic aneurysms, growth exceeding 5 millimeters per year is often classified as high-risk, potentially prompting more aggressive management. For brain aneurysms, observable growth can signify a 12-fold increased risk of rupture.