Abdominal Aortic Aneurysm 腹主動脈瘤
1.1 About abdominal aortic aneurysm
An aneurysm is a degenerative condition where the blood vessel wall of an artery weakens due to degeneration, causing the artery’s lumen to expand and the vessel wall to become thinner, resulting in an aneurysm.
One common type of aneurysm occurs in the abdominal aorta and is known as an abdominal aortic aneurysm (AAA). AAA is more prevalent among older individuals, with a higher incidence in male smokers, who are three to four times more likely to develop the condition compared to females. The normal diameter of the abdominal aorta is approximately 1.8 to 2.2 centimeters. If the localized portion of the abdominal aorta expands to more than 3 centimeters, it is considered an abdominal aortic aneurysm. Due to the thinning of the aneurysm’s blood vessel wall, it becomes prone to rupture or even burst, leading to acute bleeding and potentially life-threatening consequences. Therefore, patients must be vigilant and consider surgical intervention. Additionally, the growth rate of an aneurysm is correlated with its diameter. Larger aneurysms tend to grow faster and have a higher risk of rupture.
1.2 Causes of abdominal aortic aneurysm
Abdominal aortic aneurysm is a degenerative disease, and the continuous expansion of the blood vessel wall is actually caused by multiple factors interacting with each other:
- Aging and weakening of the arterial wall’s connective tissue, leading to a decrease in elasticity.
- Accumulation of atherosclerotic plaques on the inner wall, hindering the nutrient supply to the vessel wall.
- Long-term mild inflammation of the vessel wall due to stimulation by atherosclerotic plaques.
- Structural defects.
- Increased activity of elastin-degrading enzymes in the blood vessel wall, causing a gradual reduction of elastic tissue within the vessel wall over time.
◼ 1.3 Symptoms of abdominal aortic aneurysm
Early-stage aneurysms usually have no symptoms, and most cases are discovered when a doctor palpates a pulsating abdominal mass during an examination or incidentally through abdominal ultrasound or computer scans.
Significantly enlarged aneurysms can compress the intestines, urinary system, or nerves, leading to abdominal and back pain.
It is important to note that if a patient experiences severe abdominal pain, dizziness, low blood pressure, or even shock, it may be due to the rupture of an aortic aneurysm causing acute bleeding. This is a critical situation, and the patient may be in life-threatening danger. Immediate medical attention should be sought.
Furthermore, atherosclerotic plaques accumulated on the inner walls of arterial blood vessels have the potential to dislodge and travel downstream with the bloodstream, causing blockages in the arteries of the lower limbs. This can result in ischemic necrosis of the lower limb tissues, leading to gangrene at the toes.
◼ 1.4 Risk factors of abdominal aortic aneurysm
- Men over 40 years old have a higher risk, and the older they are, the higher the risk.
- Population with hypertension, high cholesterol or diabetes
- Individuals with unhealthy lifestyle habits: long-term smoking, alcohol consumption, and irregular sleep patterns.
- Individuals with a family history of the condition.
- Specific genetic disorders (such as Marfan syndrome and others).
◼ 1.5 Diagnosis of abdominal aortic aneurysm
If a doctor suspects an abdominal aortic aneurysm during a clinical examination, they will arrange for imaging scans to gain a clear understanding of the characteristics of the aneurysm:
Abdominal Ultrasound Examination
Abdominal ultrasound is the simplest and initial examination method. The doctor uses an ultrasound probe to obtain real-time images of the aorta. Ultrasound examination can help the doctor determine the size, location, adjacent vascular relationships, and blood flow of the abdominal aortic aneurysm. Doctors generally use abdominal ultrasound for clinical screening or annual follow-up of abdominal aortic aneurysms.
Abdominal CT Scan
Abdominal CT scan is a type of computed tomography imaging that provides clear information to assist the doctor in formulating a surgical plan. The CT scan allows the doctor to obtain important information about the size, location, shape, calcification, relationship with surrounding vessels, and the presence of intraluminal blood clots in the abdominal aortic aneurysm. Additionally, CT scans can be reconstructed into multiple different planes and 3D images using computer software, helping the doctor understand the structure of the aneurysm and develop a surgical plan.
◼ 1.6 Treatment of abdominal aortic aneurysm
Treatment methods for abdominal aortic aneurysm depend on the size, location, risk of rupture, and the patient’s overall health condition, and require a comprehensive evaluation.
Conservative Therapy
For small abdominal aortic aneurysms without significant symptoms, regular (every six months to one year) ultrasound monitoring is generally recommended to track any continuous enlargement of the aneurysm. If the abdominal aortic aneurysm continues to grow in size, the doctor may discuss the necessity of surgical treatment with the patient.
Surgical Treatment
In general, the size of the abdominal aortic aneurysm directly correlates with the risk of rupture and bleeding. To prevent rupture, doctors may recommend surgical intervention for patients with certain conditions:
- Abdominal aortic aneurysm with a diameter greater than 5 centimeters or showing a gradual increase of 0.5-1 centimeter every six months to one year.
- Abdominal aortic aneurysm that has already ruptured and is causing bleeding. This situation is considered an emergency, and surgical intervention is immediately required to control the bleeding.
- Patients with significant abdominal pain symptoms, which may indicate an imminent rupture or a high risk of rupture and bleeding.
- Patients experiencing continuous blood clot embolism affecting the lower limbs.
Traditional Open Abdominal Aortic Surgery
Traditional open surgical repair of the abdominal aorta involves an abdominal incision. The surgery is performed under general anesthesia. The surgeon opens the abdomen, locates the abdominal aortic aneurysm, controls the aorta on both sides using surgical clamps, removes the aneurysm, and then sutures an artificial blood vessel to both ends of the aorta. Finally, the blood vessel wall is re-sutured. After releasing the surgical clamps controlling the aorta, allowing blood circulation to resume in the lower limbs, the surgery is generally completed.
During the procedure, as the surgeon needs to control the main arterial vessel with surgical clamps, the increased stress on the heart can potentially lead to complications such as cardiac attack. Therefore, if the patient’s overall health condition is not ideal, this type of surgery may not be suitable. Additionally, traditional open surgery is also suitable for cases of abdominal aortic aneurysm rupture leading to acute bleeding. During the surgery, the surgeon needs to quickly control both ends of the abdominal aortic aneurysm with surgical clamps to temporarily stop the bleeding, and then suture the artificial blood vessel to restore blood flow in the lower limbs.
Endovascular Aortic Stenting
Endovascular aortic stenting, also known as minimally invasive surgery, involves making an incision near the groin in the patient’s thigh. A guidewire is inserted into the femoral artery, and the surgeon uses X-ray guidance to navigate the guidewire into the abdominal aortic aneurysm. Contrast material is then injected to perform angiography, allowing the surgeon to understand the structure of the abdominal aortic aneurysm. Subsequently, the surgeon places an artificial stent across the abdominal aortic aneurysm using a specialized catheter and secures it to the aortic wall using a vascular balloon. The artificial stent redirects blood flow in the aorta into the artificial vessel, reducing blood pressure within the abdominal aorta and thereby avoiding complications such as rupture.
Finally, the surgeon performs another aortic angiography to ensure the proper positioning of the artificial stent, and the surgery is considered complete.