General pathology · Hemodynamic disorders
Arterial vs venous thrombi; mural thrombi and lines of Zahn !
- Lesion
Arterial thrombi are pale and platelet-rich; venous thrombi are red and rich in red cells. Lines of Zahn prove a thrombus formed in life.
Updated 2026-11-01
What it is
Where a thrombus forms decides what it is like. In arteries, with fast flow, it starts on an endothelial injury and is rich in platelets and fibrin (white thrombus). In veins, with slow flow, it is rich in red cells trapped in fibrin (red thrombus) and makes a long cast of the vein. In the heart chambers and the aorta it sticks to the wall (mural thrombus). Alternating layers of platelets and red cells, the lines of Zahn, tell a thrombus formed in life from a post-mortem clot.
Structure
- Ante-mortem thrombus: firm, dry, friable, attached to the wall, with a ridged surface.
- On H&E: pink sheets of platelets and fibrin alternating with layers of red cells (lines of Zahn).
- Vegetation: a thrombus on a valve; infected in endocarditis, sterile in advanced cancer (nonbacterial thrombotic endocarditis) and in lupus (Libman-Sacks).
Arterial vs venous thrombus
| Feature | Arterial | Venous |
|---|---|---|
| Main factor | Endothelial injury | Stasis |
| Composition | Platelets and fibrin (pale) | Red cells and fibrin (red) |
| Direction of growth | Against the flow, from the point of attachment | With the flow, toward the heart |
| Typical sites | Coronary, cerebral, femoral arteries | Deep leg veins, pelvic veins |
| Main consequence | Ischemia and infarction of the territory | Distal edema and pulmonary embolism |
Clinical notes
- In Colombia, Chagas cardiomyopathy produces apical aneurysms with mural thrombi and cerebral emboli.
- Calf vein thrombi seldom embolise; proximal ones (popliteal, femoral, iliac) are the dangerous ones.
Test yourself
Think of the answer, then tap the question to see it.
What are the lines of Zahn and what do they show?
Alternating layers of platelets and fibrin with red cells; they show the thrombus formed in circulating blood, that is, in life.
Why are arterial thrombi pale?
Because they form in fast flow on an endothelial injury and consist mostly of platelets and fibrin.
How is a post-mortem clot told from a thrombus?
A post-mortem clot is gelatinous, not attached to the wall, and has a red dependent part and a yellow upper part, with no lines of Zahn.
Where do mural thrombi form after a myocardial infarction?
On the endocardium of the infarcted left ventricle, especially if the wall becomes akinetic or aneurysmal.
Related
- Thrombosis and Virchow's triad
- What happens to a thrombus: propagation, embolism, dissolution, organization
- Systemic (arterial) thromboembolism
- The autopsy: clinical and medicolegal
Related conditions
- Deep vein thrombosis
- Atrial fibrillation
- Infective endocarditis
- Myocardial Infarction (Heart Attack)
- Abdominal aortic aneurysm
- Acute limb ischaemia
- Chagas cardiomyopathy
- Superficial thrombophlebitis (superficial vein thrombosis)
Elsewhere in DurgiPedia
- Thrombosis and bleeding: Virchow's triad and hemostatic defects
- Blood vessels: artery, vein and capillary layers
Educational content on the mechanisms of disease; not a diagnostic or treatment guide and no substitute for a health professional's advice. No doses are given.
Sources: Venous Thromboembolism - What Is Venous Thromboembolism? | NHLBI, NIH (National Heart, Lung, and Blood Institute (NHLBI), 2022); Arterial embolism: MedlinePlus Medical Encyclopedia (MedlinePlus, US National Library of Medicine, 2026); Heart attack: MedlinePlus Medical Encyclopedia (MedlinePlus, US National Library of Medicine, 2024).
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Representative model, for educational purposes only.