Venous thrombosis, the most common disorder of the veins, involves the formation of a thrombus or blood clot associated with vein inflammation. It can be classified as either superficial vein thrombosis or deep vein thrombosis.
Superficial Vein Thrombosis: This involves the formation of a thrombus in a superficial vein, usually the greater or lesser saphenous vein. Though less severe than deep vein thrombosis (DVT), SVT can lead to complications if untreated.
Deep Vein Thrombosis (DVT): This involves a thrombus in a deep vein, most often the iliac or femoral veins.
The three key factors, known as Virchow's triad that contribute to venous thrombosis are:
Venous Stasis: Normal venous blood flow relies on muscle action in the extremities and functional venous valves that ensure unidirectional flow. Venous stasis occurs when these valves are dysfunctional or the extremity muscles are inactive. This condition is common in individuals who are obese or pregnant, have chronic heart failure or atrial fibrillation, travel on long trips (over four hours) without exercise, undergo prolonged surgical procedures, or are immobile for extended periods, such as those with spinal cord injuries or hip fractures.
Endothelial Damage: Damage to the endothelium, the vein's inner lining, can be direct or indirect. Direct injuries may result from surgery, intravascular catheterization, trauma, burns, or prior VTE. Indirect injuries include chemotherapy, diabetes, or sepsis. Damaged endothelium stimulates platelet activation and initiates the coagulation cascade, increasing the risk of thrombus development.
Hypercoagulability: Blood hypercoagulability can result from conditions such as severe anemia, polycythemia, various cancers (e.g., breast, gastrointestinal tract), nephrotic syndrome, high homocysteine levels, and deficiencies in protein C, protein S, or antithrombin. Sepsis also predisposes patients to hypercoagulability due to endotoxins released from bacteria. Certain medications, such as corticosteroids and estrogens, and lifestyle factors, such as smoking
combined with estrogen-based oral contraceptives or hormone therapy in postmenopausal women, significantly increase the risk of VTE.
The pathophysiology of venous thrombosis begins with thrombus formation, triggered by venous stasis, hypercoagulability, and endothelial damage—collectively known as Virchow's Triad. Platelet aggregation and fibrin trap red and white blood cells, forming a thrombus. As the thrombus enlarges, it accumulates more blood cells and fibrin, forming a larger clot with a "tail" that can block the vein's lumen.
If a thrombus partially blocks the vein, endothelial cells may cover it, halting the thrombotic process. If the thrombus does not detach, it can undergo lysis or become firmly organized and adherent within days to weeks. However, an organized thrombus may detach, resulting in an embolus. Turbulent blood flow significantly contributes to embolization. The embolus can travel through the venous circulation to the heart and lodge in the pulmonary circulation, causing a pulmonary embolism (PE).
Venous thrombosis occurs when a blood clot, or thrombus, forms within a vein, partially or completely blocking blood flow.
A thrombus is an aggregate of platelets attached to the vein wall with a tail-like appendage containing white and red blood cells and fibrin. As the thrombus enlarges, it can block the vein's lumen.
Venous thrombosis can occur in any vein. Superficial vein thrombosis occurs in a superficial vein, such as a saphenous vein.
Conversely, deep vein thrombosis occurs in a deep vein, often in the femoral veins.
Venous thrombosis develops due to three key factors, known as Virchow’s triad.
First, venous stasis occurs when venous valves are dysfunctional or extremity muscles are inactive. It disrupts normal venous blood flow in conditions like obesity and atrial fibrillation.
Second, blood hypercoagulability in conditions like polycythemia and antithrombin deficiency raises the risk of thrombus development.
Third, endothelial damage from direct injuries like catheterization or trauma and indirect causes such as chemotherapy or sepsis stimulates platelet activation and initiates the coagulation cascade, leading to thrombus formation.
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