Abdominal Aortic Aneurysm: Symptoms, Types, Causes and Treatment

Abdominal aortic aneurysm (AAA) is a serious and often silent vascular condition characterized by the abnormal dilation of the abdominal aorta. While many cases remain undetected until a life-threatening rupture occurs, understanding the signs, types, underlying causes, and available treatments is crucial for improving patient outcomes. Below, we explore the key aspects of AAA, synthesizing the latest research to provide a comprehensive overview.

Symptoms of Abdominal Aortic Aneurysm

Most abdominal aortic aneurysms are asymptomatic in their early stages, which contributes to the insidious nature of this condition and the high risk associated with sudden rupture 2 7 14. Frequently, AAAs are discovered incidentally during imaging studies performed for unrelated reasons, such as abdominal ultrasound or computed tomography scans 2 4 7.

Common and Atypical Presentations

When symptoms do occur, they can vary and are often non-specific. The most frequently reported symptoms include:

• Abdominal or back pain: Patients may experience persistent or intermittent discomfort in the lower back or central abdomen. This pain often has a pulsatile quality, reflecting the underlying vascular pathology 2 4 7.
• Pulsatile abdominal mass: A physician may detect a pulsatile mass during a physical examination, particularly in thin individuals 3 4.
• Peripheral symptoms: In some cases, symptoms may result from complications such as thromboembolism, causing pain or ischemia in the legs or feet 2.

Less commonly, AAAs may manifest with unusual symptoms:

• Duodenal obstruction: Rarely, AAA can initially present as duodenal obstruction, leading to symptoms such as nausea, vomiting, and abdominal distension, especially in older adults with a pulsatile abdominal mass 3.
• Testicular pain: Isolated acute testicular pain has been described as an atypical warning sign, often leading to misdiagnosis as a urological condition. This symptom may precede rupture by days or weeks and warrants consideration of AAA in at-risk older adults 5.
• Weight loss and constitutional symptoms: Particularly in inflammatory AAA (a distinct subtype), patients may report chronic abdominal pain, weight loss, and systemic symptoms such as fever and elevated inflammatory markers 1.

Symptoms of Rupture

The most catastrophic presentation of AAA is rupture, which typically causes:

• Sudden, severe abdominal or back pain
• Signs of shock (hypotension, tachycardia, pallor)
• Collapse or loss of consciousness

Ruptured AAAs are associated with extremely high mortality rates, with estimates ranging from 65–85% 7 14. Rapid recognition and emergency intervention are critical for survival.

Types of Abdominal Aortic Aneurysm

Abdominal aortic aneurysms can be classified in several ways, primarily based on their anatomical characteristics, etiology, and underlying pathology.

Anatomical Subtypes

1. Fusiform aneurysms: The most common form, fusiform AAAs involve a circumferential, spindle-shaped dilation of the aorta 2. These tend to be associated with a higher risk of rupture as their diameter increases.
2. Saccular aneurysms: Less common, these involve a localized, pouch-like outpouching of the aortic wall 2. Saccular aneurysms may be more prone to rupture at smaller sizes due to their focal wall stress.

Pathological Variants

• Atherosclerotic (degenerative) AAA: The majority of AAAs are the result of chronic atherosclerotic changes leading to weakening of the aortic wall 2 7 10.
• Inflammatory AAA: Representing about 4.5% of cases, inflammatory AAAs are characterized by marked inflammation and fibrosis of the aortic wall and surrounding tissues 1. These patients are more likely to have constitutional symptoms (pain, weight loss, elevated erythrocyte sedimentation rate) and may also have associated iliac, femoral, or popliteal aneurysms 1.
• Mycotic (infected) AAA: A rare type resulting from infection of the aortic wall, often with bacteria such as Salmonella or Staphylococcus 2. These require different management strategies due to the infectious component.

Location-Based Classification

• Infrarenal AAA: The most common location, occurring below the renal arteries 7.
• Juxtarenal and suprarenal AAA: Less frequently, aneurysms may extend to or above the level of the renal arteries, impacting surgical repair options 7.

Causes of Abdominal Aortic Aneurysm

The development of AAA is multifactorial, involving a complex interplay of genetic, environmental, and biological factors.

Major Risk Factors

• Age and gender: AAAs are most prevalent in men over 65 years old, though women are at increased risk of rapid aneurysm growth and rupture 2 7.
• Smoking: Tobacco use is the single most important modifiable risk factor, implicated in both the initiation and acceleration of aneurysm growth 1 2 7. Studies indicate that upwards of 90% of patients with AAA are current or former smokers 1.
• Family history and genetics: A positive family history significantly increases the risk, suggesting a heritable component. Numerous genetic risk factors have been identified, and ongoing research is expanding our understanding of the underlying genetic architecture 7 14.
• Chronic diseases: Coexisting conditions such as hypertension, atherosclerosis, and heart disease increase susceptibility to AAA 4.

Pathophysiological Mechanisms

Research into the pathogenesis of AAA reveals several key processes:

1. Extracellular matrix degradation: Destruction of elastin and collagen in the aortic wall leads to loss of structural integrity 8 10 14. Matrix metalloproteinases (MMPs) are enzymes that play a pivotal role in this degradation 10 16.
2. Inflammation: Chronic inflammation is a hallmark of AAA, involving infiltration of lymphocytes and macrophages, increased cytokine production, and neovascularization within the aortic wall 8 10 13 14.
3. Vascular smooth muscle cell (VSMC) loss: Apoptosis and phenotypic switching of VSMCs weaken the vessel wall, further predisposing it to dilation and rupture 8 14.
4. Oxidative stress: Increased oxidative stress contributes to cellular damage and exacerbates inflammatory and degradative processes 14.
5. Biomechanical wall stress: Hemodynamic forces act on the weakened wall, promoting progressive dilation 10 12.
6. Gut microbiome dysbiosis: Emerging evidence links alterations in the gut microbiota to AAA development, with certain bacterial species (e.g., R. intestinalis) and their metabolites (butyrate) shown to reduce inflammation and aneurysm progression in experimental models 11.

Other Contributing Factors

• Atherosclerosis: While not always present, atherosclerotic changes may contribute to aneurysm formation in some cases 13.
• Immune responses and genetic susceptibility: Inherited factors and immune-mediated processes are increasingly recognized as important contributors 7 13 14.

The interplay between these mechanisms underscores the complexity of AAA pathogenesis and highlights the need for further research to identify precise therapeutic targets.

Treatment of Abdominal Aortic Aneurysm

The primary goal in managing AAA is to prevent rupture, which carries a dire prognosis. Treatment strategies depend on aneurysm size, symptomatology, and risk of progression.

Surveillance and Risk Factor Modification

• Small, asymptomatic AAAs (<5 cm): For aneurysms below the threshold for intervention, careful monitoring with periodic imaging is recommended. The focus is on controlling modifiable risk factors—particularly smoking cessation and blood pressure management—to slow aneurysm growth 2 4 13.
• Screening: In many countries, screening programs target men over 65, especially those with a history of smoking or a family history of AAA, to enable early detection 2 7 14.

Indications for Intervention

Intervention is generally advised for:

• Aneurysms ≥5.5 cm in diameter (in men), or ≥5.0 cm (in women, due to higher rupture risk)
• Rapid aneurysm growth: >0.5 cm increase in 6 months
• Symptomatic aneurysms: Regardless of size, symptoms such as pain or distal embolization warrant intervention
• Rupture or contained leak: Immediate emergency surgery is required 2 7.

Surgical and Endovascular Repair

• Open surgical repair: The traditional gold standard, involving direct replacement of the affected aortic segment with a synthetic graft. While effective, it carries significant perioperative risks, particularly in older or frail patients 2 7 13.
• Endovascular aneurysm repair (EVAR): A minimally invasive alternative, EVAR involves placement of a stent graft within the aneurysm via the femoral arteries, excluding the aneurysmal sac from circulation. EVAR is associated with lower immediate morbidity and mortality, though long-term surveillance is required to monitor for endoleaks and graft complications 2 7 8 13.

Medical and Pharmacological Therapies

Despite decades of research, no medical therapy has yet been conclusively proven to halt or reverse AAA growth in humans. However, several avenues are under investigation:

• Matrix metalloproteinase inhibitors: Drugs like doxycycline may slow expansion by inhibiting matrix degradation, with ongoing clinical trials assessing their efficacy 16 17.
• Statins, ACE inhibitors, and angiotensin receptor blockers: These agents have theoretical and experimental support for reducing aneurysm progression, though definitive clinical benefit remains unproven 15 16 17.
• Anti-inflammatory agents and antibiotics: Some studies suggest potential benefit, but larger trials are needed 15 17.
• Antithrombotic therapies: The role of anticoagulants and antiplatelet agents is controversial, as intraluminal thrombus may stabilize the aneurysm wall but also contributes to local inflammation. The impact of these therapies on AAA progression and rupture risk remains unresolved 18.
• Microbiome-targeted therapies: Emerging evidence suggests that modulating gut flora or supplementing beneficial metabolites like butyrate could become future strategies to slow AAA progression 11.

Future Directions

With the expanding understanding of the molecular and cellular mechanisms underlying AAA, novel pharmacological and cell-based therapies are anticipated within the next decade 13 17. Ongoing international collaborations and clinical trials aim to identify safe and effective medical treatments to reduce the need for surgical intervention and improve patient outcomes 13 14 16.

Conclusion

Abdominal aortic aneurysm is a multifaceted disease that remains a significant cause of morbidity and mortality, particularly among older adults. Its often silent progression underscores the importance of routine screening and risk factor modification. While open and endovascular surgical repair are effective for large or symptomatic aneurysms, there is a pressing need for validated medical therapies to prevent aneurysm growth and rupture. Advances in our understanding of the genetic, inflammatory, and biomechanical factors driving AAA, as well as novel insights from microbiome research, hold promise for the development of targeted interventions. Early detection, individualized management, and ongoing research are key to improving outcomes for patients with this potentially lethal condition.