THROMBOSIS | MORPHOLOGY & CLINICAL EFFECTS
April 29, 2020
Thrombosis is basically the process of formation of solid mass in blood circulation from the constituents of flowing blood. The mass is also known as a thrombus. In contrast, a blood clot is the mass of blood coagulated in vitro like in a test tube.
Haematoma is the extravascular collection of blood clots for e.g. into the tissues. Haemostatic plugs are therefore the clots of blood form in healthy individuals at the site of bleeding like, in injury to the blood vessel.
Haemostatic plugs are useful as it stops the escape of blood and plasma. Whereas thrombi in the unruptured cardiovascular system may be fatal.
It causes following harmful effects:-
1. Ischaemic injury. Thrombus can decrease or stop the blood supply to part of an organ or tissue. It can cause ischaemia which can result in infarction.
2. Thromboembolism. The thrombus or its part can get dislodged. It may be carry along in the blood flow as embolus to lodge in another vessel.
PATHOPHYSIOLOGY OF THROMBOSIS:-
Virchow described 3 primary events that predispose to thrombus formation (Virchow’s triad):
- ENDOTHELIAL INJURY.
- ROLE OF PLATELETS
- ROLE OF COAGULATION SYSTEM
Also there are the processes that follow these primary events:
- ALTERATION OF BLOOD FLOW
- HYPERCOAGULABILITY OF BLOOD
The general morphological features of thrombi are as under:
Grossly, thrombi can have different shapes, sizes, and composition depending upon the site of origin. Arterial thrombi seems as white and mural. While the venous thrombi are red and occlusive. Mixed or laminated thrombi are also common. It consists of alternate white & red layers called lines of Zahn. Red thrombi are soft, red, and gelatinous. White thrombi are pale and firm.
Microscopically, the composition of thrombus determines by the rate of bloodstream i.e. either it forms in the rapid arterial and cardiac circulation, or in the slow-moving flow in veins. Thus lines of Zahn formed by alternate layers of light-staining aggregated platelets. These platelets are admixed with fibrin meshwork and dark-staining layer of red cells. Venous thrombi have more abundant red cells, leucocytes, and platelets entrapped in fibrin meshwork.
1. Cardiac thrombi. Large thrombi in the heart can so cause sudden death of a person. It is due to mechanical obstruction of blood flow. Also through thromboembolism to vital organs.
2. Arterial thrombi. These cause basically ischaemic necrosis of the infarct part. So it may lead to gangrene. Sudden death may occur due to thrombosis of the coronary artery.
3. Venous thrombi ( i.e. Phlebothrombosis). These may cause following effects:
- Edema of drained area
- Poor wound healing
- Skin ulcer
- Painful thrombosed veins (i.e. thrombophlebitis)
- Painful white leg ( i.e. phlegmasia alba dolens). Due to iliofemoral venous thrombosis in postpartum cases.
- Thrombophlebitis migrans, in cancer.