Rudolf Virchow, a German pathologist in the 1800s, is considered by many to be “the father of pathology.” His famous Omnis cellula e cellula (“every cell originates from another existing cell like it”) theory, published in1858,rejected the then-prevalent belief that organisms could spontaneously arise from non-living matter (e.g., that maggots could spontaneously appear in decaying meat).
Another of Virchow’s accomplishments was the elucidation of mechanisms of pulmonary thromboembolism. He developed the concept of embolism, defining it as: “The detachment of larger or smaller fragments from the end of the softening thrombus which are carried along by the current of blood and driven into remote vessels. This gives rise to the very frequent process on which I have bestowed the name of Embolia.” He defined the types of conditions that could predispose patients to abnormal thrombus formation. These categories of risk factors, called “Virchow’s triad,” are: 1) endothelial damage, 2) abnormal blood flow, and 3) hypercoagulability.
Endothelial damage increases the risk of thrombus formation through many mechanisms. One thing that happens when endothelium gets ripped up is that tissue factor is exposed (which initiates the coagulation cascade). Conditions falling under this category of risk include atherosclerosis and bacterial sepsis. The next category, abnormal blood flow, applies to patients who undergo prolonged immobilization, or those who have varicose veins or atrial fibrillation. In these conditions, blood is allowed to pool or stagnate, increasing the chance that platelets and coagulation factors will meet up and start doing their thing. The final arm of the triad, hypercoagulability, includes a lot of different disorders such as oral contraceptive use, obesity, pregnancy, and smoking; the mechanisms underlying this category of risk are numerous and often poorly-understood.
So if you have a patient with a thrombus, don’t automatically jump to the conclusion that he or she has a hereditary thrombotic disorder, such as factor V Leiden! Many times, thrombi are caused by the presence of too many risk factors (e.g, a patient who smokes, takes oral contraceptives, and is obese). However, if there are not many risk factors present, you may want to consider the possiblility of a hereditary thrombotic disorder. You should start worrying if other family members have venous thrombi, if the thrombus is anywhere other than the leg veins or lungs, if the patient is young, or if there have been multiple thrombotic episodes.
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