Thrombosis

Frequently asked questions

What factors are included in the classic Virchow's triad?

The classic Virchow's triad includes three main pathogenetic factors promoting the activation of thrombus formation.

• Endothelial injury — disruption of the structure and function of the endothelium (due to trauma, infections, or atherosclerosis).
• Abnormal blood flow — stasis or venous congestion (e.g., in heart failure or immobilization).
• Hypercoagulability — increased blood coagulability and suppression of fibrinolysis.

What biologically active substances do platelets release upon degranulation during thrombus formation?

During degranulation and the release reaction, platelets secrete biologically active substances involved in thrombosis. These include:

• ADP — released upon platelet activation, stimulating adjacent platelets via purinergic receptors.
• Thromboxane A2 — exerts a vasoconstrictive effect, slows blood flow, and enhances platelet aggregation.
• Serotonin.
• Histamine.
• Platelet-derived growth factor.
• Platelet clotting factors, including thromboplastin, which initiates coagulation.

What types of thrombi are distinguished based on macroscopic structure and composition?

Depending on their macroscopic structure and composition, four main types of thrombi are distinguished.

Thrombus Type	Composition	Features
White thrombus	Platelets, fibrin, leukocytes	Forms slowly under rapid blood flow, more common in arteries
Red thrombus	Erythrocytes, fibrin, platelets	Forms rapidly under slow blood flow, more common in veins
Mixed thrombus	Platelets, fibrin, erythrocytes, leukocytes	Has a layered structure, the most common type
Hyaline thrombus	Disrupted erythrocytes, platelets, denatured fibrin	Forms in microvasculature, homogenous mass

What are the favorable and unfavorable outcomes of thrombosis?

Thrombosis outcomes are divided into two main groups.

Favorable outcomes:

• Organization of the thrombus — replacement by connective tissue.
• Canalization — formation of channels within the thrombotic masses.
• Vascularization — ingrowth of blood vessels into the thrombus.
• Calcification — deposition of calcium salts (forming phleboliths in veins).
• Ossification — formation of bone tissue.
• Aseptic autolysis — dissolution of the thrombus by the fibrinolytic system.

Unfavorable outcomes:

• Thromboembolism — detachment of the thrombus or its fragment.
• Septic softening — occurs when pyogenic bacteria invade the thrombus.

In which vessels do red thrombi predominantly form?

Red thrombi predominantly form in veins. Their formation occurs rapidly and under conditions of slow blood flow. Structurally, such a thrombus includes erythrocytes, fibrin, and platelets. Examples of venous thrombosis include marantic thrombi, which form during venous stasis against a backdrop of dehydration and hemoconcentration, as well as thrombi seen in polycythemia vera.

What macroscopic parts (sections) make up a mixed thrombus?

A mixed thrombus consists of three macroscopic sections.

• Head — structurally represents a white thrombus, tightly adhered to the vessel wall.
• Body — the mixed thrombus proper, possessing a layered structure.
• Tail — structurally corresponds to a red thrombus, loosely attached to the intima. This part is most prone to detachment, becoming a thromboembolus.

What is the difference between a thrombus and a postmortem clot?

Thrombosis is strictly an intravital process. A thrombus is firmly adherent to the vessel wall, whereas postmortem clots are easily detached and lack the structured architecture characteristic of true thrombi.

What role does aspirin play in thrombosis?

Aspirin blocks the synthesis of thromboxane A2. This substance is necessary for platelet aggregation, so its inhibition prevents thrombus growth.

What is von Willebrand factor?

It is a protein produced by the endothelium that ensures platelet attachment to the damaged vascular site, initiating the aggregation process.