Mechanism of Stroke with Extracranial Artery Dissection
The most common mechanism of stroke with extracranial artery dissection is artery-to-artery embolism from an intraluminal thrombus that forms at the site of the dissected vessel. 1
Primary Pathophysiological Mechanism
Artery-to-artery embolism is the dominant mechanism, accounting for the majority of ischemic events in extracranial dissection. 1 The American Heart Association/American Stroke Association explicitly states this is the rationale for using antithrombotic agents to decrease stroke risk. 1
How the Mechanism Works:
Intimal tear and thrombus formation: The dissection creates a hemorrhagic process within the arterial wall, which disrupts the intimal surface and exposes thrombogenic material. 1
Thrombus accumulation: Blood clots form on the damaged intimal surface at the dissection site. 2
Distal embolization: These thrombi break off and travel distally to occlude cerebral arteries, most commonly the middle cerebral artery territory. 2, 3
Research confirms that artery-to-artery embolism accounts for approximately 55.5% of stroke mechanisms in dissection cases, with extracranial dissections showing this mechanism in 97.6% of cases. 3
Secondary Mechanisms (Less Common)
While artery-to-artery embolism predominates, other mechanisms can contribute:
Hemodynamic insufficiency: Severe stenosis or complete occlusion from the dissection can reduce cerebral perfusion, though this is far less common than embolic mechanisms. 2, 3
Local branch occlusion: The dissection itself can directly occlude perforating arteries, accounting for approximately 31.7% of cases in research series. 3
In situ thrombotic occlusion: Complete thrombotic occlusion at the dissection site accounts for only 6.3% of cases. 3
Clinical Implications
The embolic mechanism explains why antithrombotic therapy is the cornerstone of treatment. 1 Despite arterial dissection being a hemorrhagic process within the vessel wall, the primary threat to the brain comes from thromboembolic material rather than the dissection itself. 1
Important Caveats:
Intracranial extension increases embolic risk: When extracranial vertebral dissection extends intracranially, the risk of ischemic events increases significantly (86% versus 48%, odds ratio 6.43). 4
Timing matters: The risk of stroke is greatest in the first few days after the initial vascular injury, which is why early antithrombotic therapy is recommended. 1
Dissecting aneurysms: A subset of dissections develop pseudoaneurysms that can serve as an additional source of thrombus formation and embolization. 1, 2