"Microscopically all types of thrombi arterial & venous show lines of Zahn formed by alternate layers of light-staining aggregated platelets & dark staining red cells"- Harshmohan 7th/105 Arterial thrombi tend to be white & mural while the venous thrombi) are red & occlusive"- Harshmohan 7th/103 "Postmortem clot: The surface is chicken fat yellow covering the underlying red currant jelly"- Harshmohan 7th/104 MORPHOLOGY Robbins 9th/125 Arterial or cardiac thrombi usually begin at a site of endothelial injury (e.g., atherosclerotic plaque) or turbulence (vessel bifurcation): venous thrombi characteristically occur in sites of stasis. An area of attachment to the underlying vessel or heart wall, frequently firmest at the point of origin, is characteristic of all thromboses. Arterial thrombi tend to grow in a retrograde direction from the point of attachment, whereas venous thrombi extend in the direction of blood flow (i.e., toward the heart). The propagating tail may not be well attached and, particularly in veins, is prone to fragmentation, creating an embolus. When formed in the heart or aorta, thrombi may have grossly (and microscopically) apparent laminations, called lines of Zahn; these are produced by alternating pale layers of platelets admixed with some fibrin and darker layers containing more red cells. Lines of Zahn are significant only in that they imply thrombosis at a site of blood flow; in veins or in smaller arteries, the laminations are typically not as apparent When arterial thrombi arise in heart chambers or in the aortic lumen, they usually adhere to the wall of the underlying structure and are termed mural thrombi. Arterial thrombi are usually occlusive; the most common sites, in descending order, are coronary, cerebral, and femoral arteries. Venous thrombosis, or phlebothrombosis, is almost invariably occlusive; the thrombus often creates a long cast of the vein lumen. Because these thrombi form in a relatively static environment, they tend to contain more enmeshed erythrocytes and are therefore known as red, or stasis, thrombi