Thrombosis (patient information)

Associate Editor(s)-in-Chief: Vahid Eidkhani, M.D.

Thrombosis is the formation of a thrombus (medical term for a clot) inside a blood vessel. This can dislodge from the site it was formed and can move along the flow of blood to distant places in the body. A piece of thrombus that is transported in this way is called an embolus (plural emboli). This process of formation an emboli, from a thrombus is called thromboembolism. The term was coined in 1848 by Rudolph Carl Virchow.

The most important sites of thrombosis formation, based on their frequency and clinical effect are coronary arteries and deep veins of the legs. Former, the most important site of arterial thrombosis and latter the most important site of venous thrombosis.

Causes

Rudolf Virchow noted several factors affecting the clot formation, which are as follows:

1) Alterations in blood flow (stasis): Blood flows throughout the circulatory system, without significantly stopping or slowing any where. In certain pathological conditions where the blood flow slows down or stops, it causes:

• Increase in platelet to endothelium contact
• Decrease the dilution of clotting factors

This increases the risk of clot formation and form microthrombi, which further grow and propagate.

2) Injury to the vascular endothelium: Intrinsic or secondary to external trauma (eg, catheterization) can cause intimal damage and stimulates clot formation. See Coagulation.

3) Alterations in the constitution of blood (hypercoagulability): It is the propensity to develop thrombosis due to an abnormality in the system of coagulation.

These three conditions are collectively known as Virchow's triad and lead to intravascular coagulation, forming a mass of red blood cells, leukocytes, and fibrin.

Risk factors

The Thrombosis formation is a phenomenon that can be elicited by various conditions, all of which take effect by means of mechanisms of Virchow's triad.

• General
  • Older age
  • Female gender
  • Smoking
  • Obesity
  • Pregnancy
  • Immobilization

• Medical
  • Surgery
  • Heart failure
  • Trauma
  • Oral contraceptive use
  • Varicose veins
  • Malignancy
  • Kidney disorders
  • Lupus anticoagulant
  • Paroxysmal nocturnal hemoglobinuria
  • Inflammatory bowel disease
  • Thromboangiitis obliterans
  • Disseminated intravascular coagulation

• Familial
  • Antithrombin III deficiency
  • Protein C deficiency/Protein S deficiency
  • APC resistance (Factor V Leiden)
  • Dysfibrogenemia
  • Hypoplasminogenemia
  • Familial homocysteinemia

Diagnosis

With the occlusion of the tissue artery in each organ, organ specefic symptoms, clinical and para-clinical signs and laboratory findings my be used to confirm the diagnosis.

In arterial thrombosis, the organ tissue encounters ischemia and usually visceral pain is the main symptom, the diagnosis is confirmed by imaging modalities like color doppler sonography, CT angiography, MRI and arteriography.

In venous thrombosis, which most commonly occurs in lower extremities, the diagnosis can be ruled out by negetive blood sample (D-dimer check) and confirmed by positive imaging modality mainly color doppler sonography.

Prognosis

After a thrombosis/clot is developed in any part of the body, many times it dissolves simultaneously, sometimes it becomes dislodged and create an emboli which is transferred by the blood stream and will deposit in another organ. In the cases of deep vein thrombosis of lower extremities, the emboli usually deposits in the lungs tissue.