THROMBOSIS

| 1. Define Thrombosis

Thrombosis is the formation of a solid mass (thrombus) from blood constituents within the vascular system during life. It is distinct from postmortem clotting. |

| 2. Predisposing Factors (Virchow's Triad) | Virchow's Triad describes the three primary abnormalities leading to thrombosis:

1. Endothelial Injury: Dominant influence; leads to exposure of vWF/collagen and downregulation of anticoagulants

2. Abnormal Blood Flow: Turbulence (arterial) and Stasis (venous) disrupt laminar flow, bringing platelets into contact with endothelium.

3. Hypercoagulability: Genetic (e.g., Factor V Leiden) or Acquired (e.g., cancer, pregnancy) tendency to clot.

| 3. Arterial vs. Venous Thrombosis | Arterial Thrombi:

① blood flow ② sites ③ morphology ④ effect ⑤ thrombogeneis

| 4. Morphology of Thrombus |

1. Venous thrombosis

• at the site of stasis

• Rarely occlusive

• Common at lower limb

2. Arterial thrombosis

• at the site of endothelial injury or cardiac thrombosis

• Occlusive

3. Propagation

• arterial thrombosis—> retrograde

• Venous thrombosis —> in direction of blood flow

4. Line of Zahn

• Lamination line of pale of fibrin and platelet deposition with dark red RBC layer

5. Post Mortem thrombosis

• soft gelatinous and rubbery

• No lamination line

• Red RBC deposition dominate

| 5. Fate of Thrombus |

1. Dissolution: Recent thrombi may dissolve via fibrinolysis.

2. Organization & Recanalization: Ingrowth of endothelial cells and fibroblasts; capillaries form to restore blood flow.

3. Propagation: Thrombus accumulates more platelets/fibrin and enlarges

4. Embolism: Thrombus dislodges and travels to other sites (e.g., lungs).

| 6. Clinical Effects

• Superficial Venous Thrombosis: Causes local congestion, pain, and edema; rarely embolizes.

• deep venous thrombosis: usually in popliteal, femoral and iliac artery, lead to pulmonary embolism

General effects: • Vascular Obstruction—>Leads to ischemia and infarction of the supplied tissue.

Type of thrombosis

1. Mural thrombosis

• at heart chamber or aortic lumen

• Abdominal aortic aneurysm

2. Vegatation

• at heart valve

• Rheumatic heart disease

3. Arterial thrombosis

• At site of ndothelial or cardiac injury, turbulence

• Cerebral, coronary and aorta

4. Venous thrombosis

• at site of stasis

• Popliteal, femoral and iliac vein