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Abdominal Aortic Aneurysm

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Description: An abdominal aortic aneurysm is a bulging or weakening in the wall of the abdominal aorta, which can lead to life-threatening internal bleeding if it ruptures.
Type: Abdominal aortic aneurysm (AAA) does not have a specific mode of genetic transmission. While there is a genetic component that may predispose individuals to developing AAA, it is generally considered multifactorial with contributions from both genetic and environmental factors. There is no single pattern of inheritance.
Signs And Symptoms: The vast majority of aneurysms are asymptomatic. However, as the abdominal aorta expands and/or ruptures, the aneurysm may become painful and lead to pulsating sensations in the abdomen or pain in the chest, lower back, legs, or scrotum.
Prognosis: Although the current standard of determining rupture risk is based on maximum diameter, it is known that smaller AAAs that fall below this threshold (diameter<5.5 cm) may also rupture, and larger AAAs (diameter>5.5 cm) may remain stable. In one report, it was shown that 10–24% of ruptured AAAs were less than 5 cm in diameter. It has also been reported that of 473 non-repaired AAAs examined from autopsy reports, there were 118 cases of rupture, 13% of which were less than 5 cm in diameter. This study also showed that 60% of the AAAs greater than 5 cm (including 54% of those AAAs between 7.1 and 10 cm) never experienced rupture. Vorp et al. later deduced from the findings of Darling et al. that if the maximum diameter criterion were followed for the 473 subjects, only 7% (34/473) of cases would have died from rupture prior to surgical intervention as the diameter was less than 5 cm, with 25% (116/473) of cases possibly undergoing unnecessary surgery since these AAAs may never have ruptured.Alternative methods of rupture assessment have been recently reported. The majority of these approaches involve the numerical analysis of AAAs using the common engineering technique of the finite element method (FEM) to determine the wall stress distributions. Recent reports have shown that these stress distributions have been shown to correlate to the overall geometry of the AAA rather than solely to the maximum diameter. It is also known that wall stress alone does not completely govern failure as an AAA will usually rupture when the wall stress exceeds the wall strength. In light of this, rupture assessment may be more accurate if both the patient-specific wall stress is coupled together with patient-specific wall strength. A noninvasive method of determining patient-dependent wall strength was recently reported, with more traditional approaches to strength determination via tensile testing performed by other researchers in the field. Some of the more recently proposed AAA rupture-risk assessment methods include: AAA wall stress; AAA expansion rate; degree of asymmetry; presence of intraluminal thrombus (ILT); a rupture potential index (RPI); a finite element analysis rupture index (FEARI); biomechanical factors coupled with computer analysis; growth of ILT; geometrical parameters of the AAA; and also a method of determining AAA growth and rupture based on mathematical models.The postoperative mortality for an already ruptured AAA has slowly decreased over several decades but remains higher than 40%. However, if the AAA is surgically repaired before rupture, the postoperative mortality rate is substantially lower, approximately 1-6%.
Onset: Abdominal aortic aneurysm (AAA) typically has an insidious onset, often developing without any noticeable symptoms until it becomes quite large or ruptures. It is more common in older adults, particularly men over the age of 65. Risk factors include smoking, hypertension, atherosclerosis, and family history of aneurysms. Regular screening is recommended for high-risk populations to detect AAA before it causes complications.
Prevalence: Abdominal aortic aneurysm (AAA) is more common in older adults, predominantly affecting males over 65 years of age. The prevalence is estimated at about 1.3-8.9% in men aged 65 and older, and around 0.5-1.3% in women in the same age group.
Epidemiology: The occurrence of AAA varies by ethnicity. In the United Kingdom, the rate of AAA in Caucasian men older than 65 years is about 4.7%, while in Asian men it is 0.45%. It is also less common in individuals of African, and Hispanic heritage. They occur four times more often in men than in women.There are at least 13,000 deaths yearly in the U.S. secondary to AAA rupture. The peak number of new cases per year among males is around 70 years of age, and the percentage of males affected over 60 years is 2–6%. The frequency is much higher in smokers than in non-smokers (8:1), and the risk decreases slowly after smoking cessation. In the U.S., the incidence of AAA is 2–4% in the adult population.Rupture of the AAA occurs in 1–3% of men aged 65 or more, for whom the mortality rate is 70–95%.
Intractability: An abdominal aortic aneurysm (AAA) is not necessarily intractable. The management and treatment depend on the size and growth rate of the aneurysm, as well as the patient's overall health. Small AAAs (less than 5 cm in diameter) are often monitored with regular imaging and lifestyle modifications.

For larger or rapidly growing AAAs, surgical intervention may be required. The two main surgical treatments are open surgical repair and endovascular aneurysm repair (EVAR). With timely diagnosis and appropriate treatment, many patients have favorable outcomes. However, if an AAA ruptures, it can become a life-threatening emergency, highlighting the importance of early detection and management.
Disease Severity: An abdominal aortic aneurysm (AAA) is a serious condition where the lower part of the aorta becomes enlarged. The severity of an AAA can vary depending on its size and rate of growth. Small, slow-growing aneurysms might never rupture, but larger and faster-growing ones carry a high risk of rupturing, which can cause life-threatening internal bleeding.
Healthcare Professionals: Disease Ontology ID - DOID:7693
Pathophysiology: The most striking histopathological changes of the aneurysmatic aorta are seen in the tunica media and intima layers. These changes include the accumulation of lipids in foam cells, extracellular free cholesterol crystals, calcifications, thrombosis, and ulcerations and ruptures of the layers. Adventitial inflammatory infiltrate is present.
However, the degradation of the tunica media by means of a proteolytic process seems to be the basic pathophysiologic mechanism of AAA development. Some researchers report increased expression and activity of matrix metalloproteinases in individuals with AAA. This leads to elimination of elastin from the media, rendering the aortic wall more susceptible to the influence of blood pressure. Other reports have suggested the serine protease granzyme B may contribute to aortic aneurysm rupture through the cleavage of decorin, leading to disrupted collagen organization and reduced tensile strength of the adventitia. There is also a reduced amount of vasa vasorum in the abdominal aorta (compared to the thoracic aorta); consequently, the tunica media must rely mostly on diffusion for nutrition, which makes it more susceptible to damage.Hemodynamics affect the development of AAA, which has a predilection for the infrarenal aorta. The histological structure and mechanical characteristics of the infrarenal aorta differ from those of the thoracic aorta. The diameter decreases from the root to the aortic bifurcation, and the wall of the infrarenal aorta also contains a lesser proportion of elastin. The mechanical tension in the abdominal aortic wall is therefore higher than in the thoracic aortic wall. The elasticity and distensibility also decline with age, which can result in gradual dilatation of the segment. Higher intraluminal pressure in patients with arterial hypertension markedly contributes to the progression of the pathological process. Suitable hemodynamic conditions may be linked to specific intraluminal thrombus (ILT) patterns along the aortic lumen, which in turn may affect AAA's development.
Carrier Status: An abdominal aortic aneurysm (AAA) is not typically associated with a concept of "carrier status" as it is not a hereditary or infectious disease in the usual sense. It involves the enlargement of the abdominal aorta, often due to factors like aging, hypertension, smoking, and atherosclerosis. Genetic predisposition can play a role, but "carrier status" does not apply to AAA.
Mechanism: An abdominal aortic aneurysm (AAA) is an enlargement of the abdominal aorta that exceeds the normal diameter by more than 50%.

**Mechanism:**
The primary mechanism involves the weakening and subsequent dilation of the aortic wall, which is influenced by several factors including genetics, inflammation, and hemodynamic stresses.

**Molecular Mechanisms:**
1. **Matrix Metalloproteinases (MMPs):** These enzymes degrade extracellular matrix components like collagen and elastin, weakening the structural integrity of the aortic wall.
2. **Inflammation:** Inflammatory cells such as macrophages infiltrate the aortic wall, releasing cytokines and proteolytic enzymes that contribute to tissue degradation.
3. **Genetic Factors:** Variations in genes that regulate the structure and repair of the aortic wall, such as FBN1 (fibrillin-1) and COL3A1 (collagen type III), can predispose individuals to AAA.
4. **Oxidative Stress:** The excessive production of reactive oxygen species (ROS) can damage cellular components and enhance inflammatory responses, promoting aneurysm formation.
5. **Smooth Muscle Cell Apoptosis:** Loss of vascular smooth muscle cells via programmed cell death can reduce the aorta's ability to maintain its structural integrity.

Collectively, these molecular mechanisms contribute to the weakening and eventual expansion of the abdominal aortic wall, leading to an aneurysm.
Treatment: For abdominal aortic aneurysm (AAA), treatment options generally depend on the size and growth rate of the aneurysm, as well as the presence of symptoms.

1. **Monitoring:** Small aneurysms (less than 5 centimeters in diameter) that are not causing symptoms may be monitored with regular ultrasound or CT scans every 6 to 12 months to ensure they are not growing quickly.

2. **Medications:** While medications cannot repair an aneurysm, they may be used to control risk factors such as high blood pressure and high cholesterol, which can slow the growth of the aneurysm. Beta-blockers, ACE inhibitors, and statins are commonly prescribed.

3. **Surgical Repair:**
- **Open Surgical Repair:** This involves open abdominal surgery to replace the weakened section of the aorta with a synthetic graft.
- **Endovascular Aneurysm Repair (EVAR):** A less invasive procedure where a graft is placed inside the aorta using a catheter inserted through the groin.

These treatment options are typically recommended for an AAA larger than 5.5 centimeters, rapidly growing aneurysms, or those causing symptoms. The choice of treatment depends on various factors including the patient's overall health and suitability for surgery.
Compassionate Use Treatment: Abdominal aortic aneurysm (AAA) does not typically have a specific "compassionate use" treatment, as this term is often applied to very rare or life-threatening conditions without established therapies. However, experimental and off-label treatments in clinical trials may be considered for certain patients, especially those who are not candidates for standard surgical or endovascular repair.

Off-label or experimental treatments for AAA might include:
1. **Pharmacological Approaches**: Some studies have looked at the use of medications like statins, antibiotics (doxycycline), and anti-inflammatory drugs to limit aneurysm growth and reduce the risk of rupture, although results have been mixed and these are not standard treatments.

2. **Stem Cell Therapy**: Investigational research has explored the use of stem cell therapy for repairing aneurysm-damaged tissues or promoting tissue regeneration, but this remains at the experimental stage.

3. **Elastin Stabilization**: Experimental treatments aimed at stabilizing the elastic fibers in the aortic wall to prevent further expansion of the aneurysm are being explored in some preclinical studies.

4. **Gene Therapy**: Although still in experimental stages, gene therapy research is looking into ways to genetically modify cells to stabilize or reverse the pathology of AAA.

Patients interested in these novel therapies should talk to their healthcare providers about ongoing clinical trials and whether they might be eligible to participate.
Lifestyle Recommendations: ### Lifestyle Recommendations for Abdominal Aortic Aneurysm:

1. **Quit Smoking**: Smoking is a major risk factor for aneurysms. Quitting can significantly reduce complications.
2. **Healthy Diet**: Focus on a diet rich in fruits, vegetables, whole grains, and lean proteins. Limit saturated fats, cholesterol, and sodium.
3. **Regular Exercise**: Engage in moderate exercise such as walking, swimming, or cycling. However, avoid heavy lifting and high-intensity workouts which can strain the aorta.
4. **Manage Blood Pressure**: High blood pressure can worsen an aneurysm. Regular monitoring and management through medication and lifestyle changes are essential.
5. **Control Cholesterol Levels**: Keeping cholesterol levels in check can help prevent the worsening of the aneurysm. Medication and dietary changes can assist in this.
6. **Weight Management**: Maintain a healthy weight to reduce the strain on the aorta.
7. **Limit Alcohol Intake**: Excessive alcohol consumption can contribute to high blood pressure; moderate or eliminate alcohol intake.
8. **Routine Monitoring**: Regular medical check-ups including imaging tests to monitor the size and rate of growth of the aneurysm.

Consult with healthcare providers to tailor these recommendations to individual health needs.
Medication: No medical therapy has been found to be effective at decreasing the growth rate or rupture rate of asymptomatic AAAs. Blood pressure and lipids should, however, be treated per usual.
Repurposable Drugs: No specific repurposable drugs have been conclusively established for the treatment of abdominal aortic aneurysm (AAA) as of current medical guidelines. Research is ongoing to identify potential pharmacological treatments that can be repurposed for this condition. The primary therapeutic management of AAA typically involves monitoring and surgical intervention when necessary.
Metabolites: For abdominal aortic aneurysm (AAA), specific metabolites directly linked to the condition are not well-characterized. AAA is primarily a structural vascular disease, and while metabolic changes can contribute to vascular wall weakening, there are no definitive metabolites universally recognized as biomarkers for AAA. Research into metabolic profiling and biomarkers is ongoing to better understand the pathophysiology and potential diagnostic indicators related to AAA. If you have a specific aspect of metabolites in mind or require details on associated metabolic changes, providing more context would be helpful.
Nutraceuticals: There is no direct evidence to support the effectiveness of nutraceuticals in preventing or treating abdominal aortic aneurysm (AAA). However, maintaining a healthy lifestyle, including a balanced diet rich in antioxidants, omega-3 fatty acids, and vitamins, may support overall vascular health. Always consult a healthcare professional before taking any supplements.
Peptides: Peptides have been studied for their potential role in diagnosing and treating abdominal aortic aneurysm (AAA). They can serve as biomarkers for early detection or as therapeutic agents to target specific pathways involved in the degeneration of the aortic wall. Research is ongoing to fully understand their efficacy and application in clinical settings.