What is the etiology and pathophysiology of arterial dissection?

Arterial Dissection: Etiology and Pathophysiology

Arterial dissection is fundamentally characterized by a tear in the arterial wall that creates a false lumen, with blood entering the media through an intimal-medial tear, separating lamellar layers, and potentially propagating in antegrade or retrograde directions. 1

Pathophysiological Mechanism

Arterial dissection occurs through two primary mechanisms:

1. Intimal Tear Mechanism:

   • An initial tear in the intimal layer creates an entry point for blood
   • Blood enters the arterial wall, creating an intramural hematoma
   • The dissection plane propagates within the medial layer
   • Subintimal dissection tends to cause stenosis (luminal narrowing)
   • Subadventitial dissection can result in aneurysmal degeneration 1

2. Vasa Vasorum Dysfunction:

   • Hemorrhage from the vasa vasorum (small vessels that supply the arterial wall)
   • Creates an intramural hematoma without an intimal tear
   • Can lead to compression of the true lumen and downstream ischemia 1

Anatomical Consequences

The pathological outcomes of arterial dissection include:

• Luminal Compression: The intramural hematoma compresses the true lumen
• False Lumen Formation: Blood flows through an abnormal channel within the arterial wall
• Propagation: The dissection can extend proximally or distally from the initial site
• Stenosis: Narrowing of the true lumen, particularly with subintimal dissection
• Aneurysmal Degeneration: Outward bulging of the vessel wall, more common with subadventitial dissection
• Thrombosis: Formation of thrombi within the false lumen 1, 2

Etiological Factors

Genetic and Structural Factors

• Connective Tissue Disorders:

  • Marfan syndrome
  • Ehlers-Danlos syndrome
  • Loeys-Dietz syndrome
  • Bicuspid aortic valve (associated with 1-5% of carotid dissections) 1

• Genetic Pathway Disruptions:

  • TGF-β signaling pathway abnormalities
  • Extracellular matrix disruptions
  • Cytoskeletal abnormalities
  • Mutations in genes including LRP1, collagen genes, fibrillin, and TGF-β receptors 2

Vascular Conditions

• Fibromuscular Dysplasia (FMD):

  • Non-atherosclerotic, non-inflammatory vascular disease
  • Associated with approximately 15% of carotid dissections
  • Characterized by stenosis due to arterial wall thickening
  • More common in middle-aged women 1

• Hypertension:

  • Present in 65-75% of aortic dissection cases
  • Creates increased wall stress that can predispose to dissection 3

Traumatic and Environmental Factors

• Trauma:

  • Direct trauma to the neck or chest
  • Penetrating injuries
  • Sudden or excessive neck movements (particularly for vertebral artery dissection) 1

• Substance Use:

  • Amphetamine abuse
  • Other sympathomimetic drugs 1

Clinical Manifestations by Anatomical Location

Coronary Artery Dissection (SCAD)

• Accounts for up to 4% of all acute coronary syndromes
• Much higher incidence (22-35%) in women <60 years
• Presents with chest discomfort and elevated cardiac biomarkers
• Three angiographic types:
  1. Type 1: Contrast dye staining of arterial wall with multiple radiolucent lumen
  2. Type 2: Long diffuse and smooth narrowing
  3. Type 3: Focal or tubular stenosis mimicking atherosclerosis 1

Cervical (Carotid and Vertebral) Artery Dissection

• Accounts for approximately 2% of all ischemic strokes
• Up to 15% of ischemic strokes in younger patients
• Carotid dissection typically presents with:
  • Pain on one side of head or neck
  • Horner syndrome
  • Cerebral or retinal ischemia (in 50-95% of cases)
• Vertebral artery dissection typically presents with:
  • Headache
  • Neck pain
  • Vertigo
  • Nausea
  • Visual disturbances
  • Syncope 1, 4

Aortic Dissection

• Characterized by sudden onset, maximal intensity pain
• Sharp, tearing, ripping quality
• Type A (proximal) typically presents with retrosternal chest pain
• Type B (distal) typically presents with interscapular or back pain
• May present with syncope (up to 20% of cases)
• Can cause end-organ ischemia including paraplegia, renal failure, limb ischemia
• Approximately 6.4% are painless, more common in older patients 3

Cellular and Molecular Mechanisms

• Phenotype Switching: Endothelial and vascular smooth muscle cells switch from quiescent to proliferative activated phenotypes
• Extracellular Matrix Degradation: Breakdown of structural components of the vessel wall
• Inflammatory Processes: Contribute to weakening of the arterial wall
• Metabolic Disruptions: Affect cellular function and integrity of the vessel wall 2

Diagnostic Considerations

• Imaging Modalities:
  • Carotid duplex ultrasonography may identify dissection flap and differential flow
  • CTA or MRA increasingly used and largely supplanting catheter-based angiography
  • Intracoronary imaging (OCT and IVUS) for coronary dissections
  • For SCAD: OCT shows intimal dissection and intramural hematoma; IVUS shows intramural hematoma compressing true lumen 1

Clinical Implications and Management

• Treatment Approach:

  • Conservative management is typically preferred for SCAD
  • Anticoagulation or antiplatelet therapy is the mainstay for cervical artery dissections
  • Surgical or endovascular intervention reserved for persistent symptoms or high-risk anatomy
  • Beta-blockers should be considered for SCAD as they are associated with reduced risk of recurrence 1

• Prognosis:

  • Generally favorable for cervical artery dissections
  • SCAD has risk of recurrence (reported in 10-30% of cases)
  • Aortic dissection carries significant mortality risk, especially Type A 1, 4

Understanding the complex pathophysiology and etiology of arterial dissection is crucial for proper diagnosis, risk stratification, and management of this potentially life-threatening condition.