How does arterial dissection cause stenosis?

Mechanism of Arterial Dissection Causing Stenosis

Arterial dissection causes stenosis primarily through subintimal dissection, where an intimal tear initiates an intramural hematoma that compresses the true lumen of the vessel. 1, 2

Pathophysiology of Arterial Dissection and Stenosis

Arterial dissection begins with an intimal tear in the arterial wall, which allows blood to enter between the layers of the vessel wall. This creates a false lumen and initiates an intramural hematoma. The pathophysiological process follows these steps:

1. Initial Tear and Hematoma Formation:

   • Blood enters the arterial wall through an intimal tear
   • Creates a false lumen within the vessel wall
   • Forms an intramural hematoma 2

2. Mechanisms of Stenosis:

   • Subintimal Dissection: When dissection occurs between the intima and media, the expanding hematoma pushes inward, compressing the true lumen and causing stenosis 1
   • Static Narrowing: Occurs when the dissection intersects a branch vessel origin and the hematoma propagates into the vessel wall, directly stenosing the lumen 1
   • Dynamic Narrowing: Occurs when the dissection flap positions across a vessel origin like a curtain, covering the branch vessel origin 1

3. Progression of Stenosis:

   • The intramural hematoma expands as blood continues to enter the false lumen
   • Increasing pressure within the false lumen further compresses the true lumen
   • This compression results in hemodynamically significant stenosis 2

Anatomical and Clinical Considerations

Different outcomes can occur depending on the location and extent of the dissection:

• Subintimal Dissection: Tends to cause stenosis of the vessel 1
• Subadventitial Dissection: More likely to result in aneurysmal degeneration rather than stenosis 1

The stenosis from arterial dissection can lead to significant clinical consequences:

• In carotid dissection: cerebral or retinal ischemia develops in 50-95% of cases 1
• Accounts for approximately 2% of all ischemic strokes and up to 15% of strokes in younger patients 2
• Can cause branch vessel compromise leading to end-organ ischemia 1

Diagnostic Imaging Findings

Several imaging modalities can visualize the dissection and resulting stenosis:

• MRI/MRA with fat-saturated T1 imaging: Preferred first-line imaging to visualize the intramural hematoma 2
• CT Angiography: Excellent for visualizing the dissection flap and vessel lumen 2
• Carotid Duplex Ultrasonography: May identify the dissection flap and differential flow in true and false lumens 1, 2
• Intravascular Ultrasound: Can reveal the intramural hematoma compressing the true lumen 1

Clinical Implications

Understanding the mechanism of stenosis in arterial dissection is crucial for appropriate management:

• Treatment typically begins with anticoagulation or antiplatelet therapy to prevent thromboembolic complications 2
• In cases of persistent symptoms despite medical therapy, intervention may be necessary 2
• Endovascular treatment with stenting can restore vessel lumen integrity in selected cases 3

Important Considerations

• Both static and dynamic mechanisms of stenosis may be present in the same patient at different levels 1
• Stenosis may resolve over time with appropriate treatment as the intramural hematoma resorbs 4
• Iatrogenic dissections can occur during endovascular procedures, particularly in vessels with pre-existing atherosclerotic disease 5, 6

Understanding these mechanisms is essential for proper diagnosis, management, and prevention of complications in patients with arterial dissection.