The aorta is the largest artery in the human body, acting as the main pipeline that carries oxygen-rich blood from the heart to the rest of the body. An aortic aneurysm represents a localized ballooning or swelling in the wall of this vessel, which can weaken the structure over time. The infrarenal location, meaning the segment situated below the arteries that branch off to the kidneys, is the most common site for this weakening to occur. While an infrarenal aortic aneurysm may remain silent for many years, its rupture constitutes a life-threatening medical emergency.
Defining the Infrarenal Aortic Aneurysm
The infrarenal aorta is the section of the major artery in the abdomen that extends downward from the renal arteries toward the pelvis. An artery is officially considered aneurysmal when its diameter increases by at least 50% compared to its normal size, or when it reaches a diameter of 3 centimeters or greater.
The normal diameter of the infrarenal aorta is around 1.7 cm in men and 1.5 cm in women. A dilation to 3 cm or more meets the formal definition of an aneurysm. Pathologically, the condition involves the degeneration of the arterial wall’s middle layer, the media, leading to a loss of structural proteins like elastin and collagen.
Most infrarenal aneurysms are fusiform, describing a symmetrical, spindle-shaped swelling involving the entire circumference of the vessel wall. They are classified as true aneurysms, meaning they involve all three layers of the aortic wall.
Key Risk Factors and Etiology
Advanced age is a primary non-modifiable risk factor for infrarenal aortic aneurysms, particularly in individuals over 65 years old. Male gender is another significant non-modifiable factor, with men being four times more likely to develop an aneurysm than women.
Smoking stands out as the single greatest modifiable risk factor. A history of smoking is strongly associated with the condition, as it appears to accelerate the destruction of the aortic wall’s structural matrix through inflammatory processes.
Other contributing factors include high blood pressure (hypertension) and high cholesterol. Although often attributed to atherosclerosis, the degenerative process leading to aneurysm formation is distinct. A family history of AAA, especially having a first-degree relative with the condition, also increases genetic predisposition and lifetime risk.
Detection, Screening, and Clinical Presentation
Most aneurysms are discovered incidentally when a person undergoes imaging, such as an ultrasound or CT scan, for an unrelated medical complaint. Occasionally, a clinician may detect a pulsatile mass during a physical examination of the abdomen.
Screening guidelines recommend a one-time abdominal ultrasonography for men aged 65 to 75 who have any history of smoking. For men in that age bracket who have never smoked, screening may be offered based on other individual risk factors, such as a strong family history.
The danger of an infrarenal aortic aneurysm lies in its potential to rupture, which is a catastrophic event with a very high mortality rate. Acute rupture involves a sudden onset of severe, tearing pain, often localized in the abdomen or radiating to the back. This pain is accompanied by signs of internal bleeding, such as a rapid drop in blood pressure and shock.
Management and Treatment Pathways
Small aneurysms, typically measuring less than 5.5 cm in diameter in men, are managed through watchful waiting or surveillance. This approach involves regular imaging, usually with ultrasound or CT scans, to monitor the aneurysm’s growth rate and size.
During surveillance, aggressive control of cardiovascular risk factors, including blood pressure and cholesterol levels, is implemented. Elective intervention for men is recommended when the aneurysm reaches 5.5 cm, as the risk of rupture outweighs the risk of surgical repair. A lower threshold (5.0 to 5.4 cm) is applied to women due to their higher relative risk of rupture at smaller diameters.
There are two primary surgical options for repair. Endovascular Aneurysm Repair (EVAR) is a minimally invasive technique preferred for many patients. EVAR involves accessing the artery through small groin incisions to deploy a stent-graft inside the aorta, which relines the weakened section and diverts blood flow away from the aneurysm wall. This technique offers advantages such as a shorter hospital stay, less blood loss, and a lower short-term mortality rate compared to the alternative.
The traditional approach is Open Surgical Repair (OSR), which requires a large abdominal incision to access the aorta. The surgeon removes the diseased segment and replaces it with a synthetic graft sewn into place. OSR remains necessary for patients whose aortic anatomy is unsuitable for EVAR or those requiring a more durable, long-term fix. Although OSR has a higher initial risk, it provides a durable repair and may be favored for younger patients with a long life expectancy.