A solid mass or plug formed intravascularly (in the living heart or vessels) from constituents of the blood (Welch, 1899). Hemodynamic factors influence the composition of a thrombus. Arterial thrombi (white thrombi) are formed under conditions of high flow (sites of rupture of an atherosclerotic plaque) and are composed mainly of platelet aggregates bound together by thin fibrin strands. Venous thrombi (red thrombi) form in areas of stasis and are composed of red cells and with a large amount of interspersed fibrin and relatively few platelets. Though commonly used as interchangeable terms, blood clot and thrombus are not synonymous.
