February 15, 2022
Pale thrombus occurs in the site of fast blood flow (such as arteries and ventricles) or in the period of fast blood flow during thrombus formation (such as the initial part of venous mixed thrombus, i.e., the head of persistent thrombus). Microscopically, the white thrombus is mainly composed of many aggregated coral-like platelet trabeculae, on which many neutrophils adhere to form a leukocyte boundary layer, presumably attracted by chemotaxis of cellulose disintegration products. A network of cellulose between platelet trabeculae containing a small number of red blood cells is formed by activated clotting factors. Naked eye is gray, rough surface corrugated, hard, closely connected with the vascular wall.
The main part (body part) of the continuous thrombus in the vein shows layers of red and white stripes, that is, mixed thrombus. The formation process is that the platelet trabecula-dominated thrombus continues to grow so that its downstream blood flow forms whirlpools and regenerates into another platelet dominated thrombus. The blood between the two is coagulated and becomes a red blood cell dominated thrombus. If it alternates, it becomes mixed thrombus. In mitral stenosis and atrial fibrillation, spherical thrombus can form in the left atrium. Both this type of thrombus and the thrombus within the aneurysm have alternating grayish-white and reddish-brown layered structures called layered thrombus and also mixed thrombus.
Red thrombus occurs after extremely slow or even stopped blood flow, and the formation process is the same as that of extravascular coagulation. Thus, the red thrombus is seen at the tail of a continuing thrombus after the mixed thrombus gradually increases to block the lumen and local blood flow stops. Microscopically, the cellulose mesh is filled with blood cells that resemble normal blood distribution. Dark red to the naked eye. Fresh red thrombus is moist and has some elasticity, while old red thrombus becomes dry, fragile, loses elasticity and tends to fall off and cause embolism due to absorption of water.
Hyaline Thrombus occurs in small blood vessels of microcirculation and can only be seen under a microscope, so it is also called microthrombus. It is mainly composed of cellulose and can be seen in disseminated intravascular coagulation.