Introduction:
An abdominal aortic aneurysm (AAA) is a weakening of the lower part of the main blood vessel that supplies the lower part of the body, such as the abdomen, legs, and pelvis. When the weakened walls of the aorta bulge, they might rupture and result in an abdominal aortic aneurysm rupture. AAA rupture is more common in intraperitoneal space, retroperitoneum, aortocaval fistula, aortoenteric fistula and aorto-left renal vein fistula. AAA is classified into two types based on their size.
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Small - Slow-growing or small AAAs are less than 5.5 centimeters, have a lower risk for rupture, and need to be regularly monitored with an abdomen ultrasound.
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Large - Fast-growing or large AAAs are more significant than 5.5 centimeters in size and have higher chances for rupture than small AAAs, which results in heavy internal bleeding.
What Are the Symptoms of Abdominal Aortic Aneurysm Rupture?
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Acute severe pain in the abdomen or back.
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Pain radiating from the abdomen or back to the pelvis, legs, or buttocks.
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Increased heart rate.
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Clammy (sweaty) skin.
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Loss of consciousness.
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Pulsatile abdominal mass (retroperitoneal rupture).
What Are the Risk Factors for Abdominal Aortic Aneurysm Rupture?
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Smoking.
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Hypertension (abnormally increased blood pressure).
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Vasculitis (swelling of the blood vessels).
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Women aged above 70 years.
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High cholesterol.
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Obesity.
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Family history of abdominal aortic aneurysm.
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History of an aneurysm in any other body parts.
What Are the Screening Recommendations for Abdominal Aortic Aneurysm (AAA)?
According to the American College of Cardiology (ACC) or American Heart Association (AHA), the screening recommendations are classified into:
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Class l, Level A - Patients with infrarenal or juxtarenal AAAs, which measure about 4 to 5.4 centimeters in diameter, can be monitored by imaging techniques such as ultrasonography or computed tomography scans every six to 12 months to detect the lumen expansion.
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Class ll, Level B - Patients with infrarenal or juxtarenal AAAs, which measure about 5.5 centimeters or larger, should undergo repair to avoid the risk of rupture.
According to the United States preventive services task force (USPSTF), the screening recommendations are:
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One-time screening with ultrasonography is recommended in smoking men between the age of 65 to 75 years.
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Selective offers screening with ultrasonography in non-smoking men between the age of 65 to 75 years.
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The recommendation against routine screening for abdominal aortic aneurysms (AAA) is for women.
What Are the Imaging Techniques Used in the Diagnosis of Abdominal Aortic Aneurysm Rupture?
Plain Abdominal Radiograph:
- A plain abdominal radiograph is not commonly used to diagnose abdominal aortic aneurysm rupture. An abdominal aortic aneurysm may be seen as a calcified rim located left to the midline in patients present with unexplained abdominal pain. In lateral view, calcification in the aortic wall is seen in more than fifty percent of patients. A calcified aortic aneurysm with the blurring of the psoas outline is seen in retroperitoneal hemorrhage.
Ultrasonography:
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Ultrasonography visualizes AAA as the focal enlargement of the aorta and focal abnormality at the interface between the blood vessel lumen and the thrombus within the lumen. In ultrasound, partially encapsulated hematomas appear as hypoechoic or anechoic space. Color Doppler ultrasound helps detect the area of leakage or extravasation.
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Contrast-enhanced ultrasound helps detect leakage after aneurysm repair and is more accurate (89.3 percent) than unenhanced ultrasound (63.1 percent). Contrast-enhanced study of AAA rupture usually requires 2.4 mL (milliliter) of contrast medium. Though duplex ultrasound is 95 percent highly sensitive in the diagnosis of abdominal aortic aneurysms, they cannot visualize the surrounding structures properly.
Computed Tomography (CT):
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A CT scan can visualize the aortic wall's details and the thrombus's presence. They can provide excellent information on the surrounding structures and their relationship with the abdominal aortic aneurysm. Perianeurysmal fibrosis, horseshoe kidney, and venous anomalies can be seen in CT scans.
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CT scan may show a crescent sign (dissecting blood through the wall of the aneurysm), the draped aorta sign (posterior wall of aorta molds into the front surface of the vertebrae), para-aortic hemorrhage (loss of blood from the damaged blood vessel), and intraluminal expansion, which indicates the aortic aneurysm instability.
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Helical or spiral computed tomography angiography (CTA) can visualize the aortic branches. Multidetector computed tomography (MDCT) scans can visualize the rapid increase in the size of the AAA that may result in rupture.
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Postoperative follow-up imaging after endovascular aneurysm repair (EVAR) can be done with a CT scan. Endoleak (persistent blood flow within the sac) is the most common complication after EVAR, occurring in about twenty-five percent of patients. Endoleak is classified into five types based on the source of blood flow into the aneurysm sac.
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Type 1 - The ineffective sealing of the graft site (an early complication of endoleaks).
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Type 2- Retrograde blood flow from collateral vessels.
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Type 3- Disruption of graft.
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Type 4 - Porosity of the graft.
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Type 5 - Expansion of the aneurysm.
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Angiography:
- In angiography, the leaking aneurysm presents as extravasation of the contrast material. This is rarely seen as the patients are most unstable in such conditions and will be taken to the operating room. Extensive collections of blood may displace the kidneys, uterus, or visceral arteries. Sometimes when the AAA ruptures, the contrast materials may pass into structures such as the gastrointestinal tract or inferior vena cava (IVC).
Magnetic Resonance Imaging (MRI) :
- MRI is an excellent alternative to CT scans for patients who cannot tolerate contrast material due to kidney disorders, as they might cause contrast material-induced kidney failure. MRI can visualize the aorta when the retroperitoneal collection hides the adjacent structures and clots in the aneurysm wall. Patients with ferromagnetic implants or claustrophobia (fear of enclosed spaces) are not eligible for MRI scans.
Conclusion:
Abdominal aortic aneurysm rupture is a life-threatening condition and is managed by a prompt diagnosis. Computed tomography (CT) scan and ultrasonography are the most commonly used diagnostic tools in abdominal aortic aneurysm rupture. CT scans are highly sensitive, and ultrasonography is highly specific for diagnosing AAA. But ultrasonography is less specific in the diagnosis of AAA rupture. Magnetic resonance angiography (MRA) can prevent the need for nephrotoxic contrast materials and ionizing radiation. Still, the speed and imaging quality is a limiting factors in the diagnosis of AAA rupture.
