What is atherosclerosis of the aorta?

Atherosclerosis of the Aorta

Atherosclerosis of the aorta is a chronic disease process characterized by intimal lesions called atheromas—fibrofatty plaques that protrude into the arterial lumen, weaken the underlying media, and are often associated with calcification. 1

Pathologic Definition and Characteristics

Atheromas are the fundamental lesions of atherosclerosis, developing within the innermost layer (intima) of the aortic wall. 2 The disease process involves:

• Massive intimal thickening with fibrosis, calcification, and accumulation of extracellular fatty acids 1
• Progressive degradation of the extracellular matrix by histiocytic cells, leading to compromised structural integrity 1
• Reduced cellularity and collagen fiber hyalinization within fibrous tissue, particularly at plaque edges where intimal rupture most commonly occurs 1

Disease Progression and Complications

With aging, cardiovascular risk factors, and genetic predisposition, simple atheromas progress to complicated lesions featuring surface defects, hemorrhage, and thrombosis. 1, 2 This progression creates two distinct embolic syndromes:

• Thromboemboli: Relatively large emboli that occlude medium-to-large arteries, causing strokes, transient ischemic attacks, and peripheral thromboembolism 3
• Atheroemboli (cholesterol crystal emboli): Minute emboli that occlude small arteries and arterioles, causing blue toe syndrome, renal insufficiency, and gut ischemia 3

Anatomic Distribution and Clinical Significance

Thoracic aortic atherosclerosis is less common than abdominal aortic atherosclerosis, but carries substantial clinical importance. 1, 2 The prevalence of severe aortic atherosclerosis is approximately 27% in patients with previous embolic events. 4

In patients with aortic aneurysms, severe atherosclerosis involves more than 70% of the aortic surface in over 90% of cases, particularly affecting the infrarenal abdominal aorta. 1, 5

Pathophysiologic Mechanisms Leading to Aneurysm Formation

Atherosclerosis is the main cause of aortic aneurysms through several interconnected mechanisms: 1

• Intimal thickening increases the distance between the endothelial layer and media, compromising nutrient and oxygen supply 1
• Adventitial fibrosis obstructs small intramural vasa vasorum, further reducing medial nutrition 1
• Medial thinning occurs secondary to necrosis, primarily affecting smooth muscle cells 1
• Fibrotic changes in elastic structures of the medial layer increase vessel stiffness and vulnerability to shear stress 1

The infrarenal abdominal aorta is particularly vulnerable because vasa vasorum are absent in this segment, making it especially susceptible to medial degeneration and aneurysm formation. 1, 5

Risk Factors and Associated Conditions

Hypertension is the single most important modifiable risk factor, present in 85% of patients with ruptured aneurysms and 52% of those with non-ruptured aneurysms. 1, 5 High systolic and pulse pressure (but not diastolic pressure) are independently associated with both aortic atherosclerosis and complex atherosclerosis (protruding plaques ≥4 mm thick, mobile debris, or ulceration). 6

Additional risk factors include:

• Smoking history is independently associated with atherosclerosis of any degree and complex atherosclerosis 6
• Hypercholesterolemia contributes to atherosclerotic changes, though 60% of patients have cholesterol levels below 240 mg/dL 1, 5
• Male sex confers significantly higher risk with male-to-female ratios of 2-4:1 5
• Age is independently associated with both simple and complex atherosclerosis 6

Embolic Risk Stratification

Plaque thickness ≥4 mm correlates strongly with embolic risk. 4 Patients with thoracic aortic atheromas face a 12% risk of recurrent stroke within approximately one year, and up to 33% experience stroke or peripheral embolus. 4

During cardiac surgery requiring cardiopulmonary bypass, aortic arch atheromas detected by transesophageal echocardiography are associated with stroke in approximately 12% of operations—six times the general intraoperative stroke rate. 4

Diagnostic Approach

Transesophageal echocardiography remains the gold standard for visualization of aortic plaques in the thoracic aorta. 3 Complementary modalities include computed tomography, magnetic resonance imaging, and intraoperative epiaortic ultrasound. 4

Grading systems classify severity based on plaque characteristics, with grades III-V (atheroma ≥3 mm, atheroma ≥4 mm, and protruding mobile plaques, respectively) considered clinically significant aortic atherosclerosis. 1, 7

Clinical Associations

Aortic atherosclerosis serves as a marker for significant coronary artery disease, with 75.9% of patients with CAD demonstrating aortic atherosclerosis compared to 32.3% without CAD. 7 The sensitivity and specificity of aortic atherosclerosis in detecting CAD are 75.9% and 67.7%, respectively. 7

Atherosclerotic aortic disease is the second most frequent aortic pathology after aortic dilatation, with an estimated incidence of 40-51.3% in general populations, complicated in 7.6% of cases. 1