blood health

Thrombus: What is it? of I.Randi


The thrombus is a solid mass consisting of red blood cells, platelets, fibrin and white blood cells, the result of alterations affecting the vasal endothelium, blood flow and / or blood clotting mechanisms.

A thrombus can form inside the arterial or venous blood vessels, just as it can form at the heart level. Depending on the place where it develops, the thrombus takes on different characteristics and can lead to the onset of different pathologies and consequences.

The causes underlying the formation of a thrombus are generally related to the vasal endothelium, to the blood flow (turbulence and stasis) and to platelet aggregation. Therefore, all the factors capable of negatively influencing or altering one or more of these aspects of the cardiovascular system are potentially able to predispose to the risk of the formation of one or more thrombus.

What is that

Thrombus: what is it?

The thrombus is a solid mass that is formed at the intravascular or intracardiac level, usually made up of platelets aggregated together, trapped red blood cells and fibrin (or factor Ia, it is an insoluble protein present inside the clots but not in the blood circulating that is formed starting from fibrinogen - or factor I - following a complex chain reaction also known as "coagulation cascade"). In addition, in the composition of the thrombus, white blood cells may also be present.

In other words, a thrombus can be defined as a blood clot formed inside a blood vessel (venous or arterial), or inside the heart .

Normally, the formation of clots in response to a lesion is a positive phenomenon, since it slows down and stops the loss of blood. Just think, for example, of what happens when you injure your skin: coagulation sets a limit and stops bleeding, preventing unpleasant consequences. However, when the clot forms inside a blood vessel or at an intracardiac level, it represents a real danger for the individual, since it can create occlusion, hindering the blood flow, as it can detach from the area where it is formed by reaching other parts of the body and giving rise to serious consequences (for example, pulmonary thromboembolism).


What are the Causes of Thrombus Formation?

The main causes believed to be responsible for thrombus formation are well described by the so-called Virchow triad and consist of:

  • Endothelial damage (a factor of particular importance in the formation of thrombi at the arteriolar and cardiac levels);
  • Changes and abnormalities in blood flow (both turbulence and stasis);
  • Hypercoagulability (this factor appears to be particularly significant in the formation of thrombus at venous level).

For more detailed information regarding the aforementioned factors and the mechanisms of action through which they are able to favor the formation of a thrombus, we recommend reading the dedicated article: Virchow Triad.

Risk Factors for Thrombus Formation

If the triad of Virchow summarizes the main causes of thrombus formation, it is reasonable to think that any factor - of a pathological and non-pathological nature - which predisposes and / or causes endothelial damage, alterations in blood flow and / or hypercoagulability may favor, consequently, the development of clots at the intravasal and intracardiac level. These factors include:

  • Taking some types of drugs (for example, oral contraceptives);
  • Long period of immobilization (for example, after surgery, following injury, trauma, etc.);
  • Obesity;
  • Diabetes mellitus;
  • Some types of cancer;
  • High cholesterol levels;
  • Cigarette smoke.

Those listed above are just some of the possible risk factors for the formation of a thrombus. Also in this case, more detailed information is reported in the article dedicated to the Virchow triad.

Types and Classification

Types and Classification of Trumpets

There are different types of thrombus that can be subdivided and classified according to various characteristics, such as the composition, the area of ​​the cardiovascular system in which they are formed, the dimensions, etc.

One of the best known and used classifications is that based on the site where the thrombus develops. Below, therefore, the different types of thrombus will be described according to this specific type of subdivision.

Arterial thrombus

The arterial thrombus forms inside the arteries . Its composition is rich in platelets, since the factors that tend to favor its appearance (such as endothelial damage) favor platelet activation and aggregation. This type of thrombus is usually defined as " white thrombus " due to the prevalence of the platelet component with respect to erythrocytes. However, the arterial thrombus is also made up of fibrin, red blood cells and degenerated leukocytes .

Although arterial thrombus can form in any artery, they tend to develop more frequently in the coronaries, cerebral arteries and femoral arteries.

Venous thrombus

The venous thrombus, of course, is a clot that develops inside the venous blood vessels and tends to grow taking an elongated shape that propagates towards the heart. Venous thrombi are also called " red thrombi ", as they are characterized by a prevalence of red blood cells compared to other blood cells. This prevalence is due to the fact that the thrombus is formed precisely in the slow venous circulation which facilitates the entrapment of erythrocytes. Because of this characteristic of the blood flow and the way in which they are formed, venous or red thrombi are also called " stasis thrombi ". However, thrombus development in the veins appears to be particularly favored by the individual's predisposition to hypercoagulability .

The veins most affected by thrombus formation are those of the lower limbs, but this does not remove the fact that they can also develop in the veins of the upper limbs, in the periprostatic venous plexus, in the periuterine veins, in the ovarian veins and, sometimes, even in the vein hepatic, in the portal vein or in the dural veins.

Wall thrombus

Wall thrombi form within the cavities of the heart, or in the lumen of the aorta .

Intracardiac thrombus formation is favored by abnormalities of cardiac contraction (arrhythmias, myocardial infarction, cardiomyopathies) or myocardial lesions .

The formation of mural thrombi at the aortic level, on the other hand, is favored by the presence of atherosclerotic ulcerated plaques and aneurysms .

Trumpet characteristics: Zahn's Strie

Zahn's striae are striations found inside the thrombus. They may be visible, depending on the case, macroscopically or microscopically. These striae are due to the alternation of light layers - characterized by an accumulation of platelets and fibrin - and of darker, richer layers of red blood cells .

Other Types of Classification

Another method of classification of the thrombi is that which is based on their composition and on the aspect it gives it. In this case, we can distinguish the aforementioned white thrombus (composed mainly of platelets) and red thrombus (characterized by a greater quantity of red blood cells); to these are added the mixed thrombi (or variegates), having intermediate characteristics to the two types of thrombus mentioned above.

Another type of classification can be made on the basis of the dimensions and according to the portion of vasal lumen that occlude or occupy.

In this regard, it is possible to distinguish:

  • Obstructive thrombus: these are thrombi that occupy the entire lumen of the vessel, occluding it completely. In this way, therefore, the blood flow is completely hindered. Obstructive thrombi tend to form more frequently in the arteries.
  • Parietal thrombi: these are thrombi that occlude the blood vessel only partially. However, their evolution towards an obstructive form cannot be excluded if they are not identified and promptly treated.
  • Cavalier thrombi: these are thrombi that develop at the level of the vascular bifurcations.

Did you know that ...

There is also another type of thrombus called post-mortem clots . As one can easily guess from their own name, they are formed after the death of the individual and, during autopsy, could potentially be confused with ante-mortem venous thrombus . However, they differ from the latter in that they have a more gelatinous consistency and have a dark red lower part due to the deposition of red blood cells which - due to death occurring - occurs by gravity; the upper portion, on the other hand, is yellow and is often described as similar to chicken fat. In addition to this, it is reported that the thrombi that form when the individual is alive have the above described Zahn streaks which, instead, are absent in the post-mortem clots.


Destiny of the Thrombus

Once the thrombus has formed - regardless of the place of development - it can face different destinies. More in detail, it may undergo one or more of the processes described below.


In this case the thrombus continues to increase its size leading to an increased risk of vasal occlusion.


The thrombus can - in whole or in part - break away from the wall of the vessel in which it is formed and enter the bloodstream, becoming - in all respects - an embolus and thus giving rise to embolism .


In some cases - and, in particular, if the thrombus is of recent formation - thanks to the activation of fibrinolytic systems, it is possible that the thrombus goes into dissolution . The old formation thrombus, on the other hand, are more resistant to fibrinolysis.

Organization and Recanalization

In the presence of old formation thrombus, the so - called organization process can begin. This organization involves the intervention of localized endothelial cells on the vessel wall around the thrombus which - stimulated by factors released by macrophages - invade it growing inside and outside giving rise to nourishing capillaries . Fibroblasts that transform the thrombus into a sort of fibrous mass rich in collagen also take part in the organization process. In this way, internally and around the thrombus new vessels are formed that are very similar to the capillaries typically found in granulation tissues. The organization process stops here, leading - at least in part - to a re-establishment of the continuity of the vessel lamp and giving rise to what is called an " organized thrombus ".

In some cases, however, it is possible for recombination of the organized thrombus to occur, thanks to which the latter is reduced to a vascularized mass of connective tissue which can subsequently be incorporated into the remodeled blood vessel wall.


Consequences and pathologies related to the formation of the Thrombus

The consequences of the formation of a thrombus can be more or less serious depending on the size of the thrombus and the place where it is formed.

In any case, the formation of a thrombus always represents a clinically significant event that cannot and should not be underestimated in any way.

Consequences of the formation of venous thrombus

The formation of thrombi in the veins can give rise to superficial venous thrombosis, as it can lead to the onset of deep venous thrombosis, depending on the vessel in which the clot develops.

Deep vein thrombosis presents a more serious clinical picture than superficial thrombosis and, above all, exposes the patient to the risk of pulmonary embolism due to detachment of the thrombus, as well as exposing him to an increased risk of experiencing chronic venous insufficiency .

Consequences of Arterial Thrombus Formation

The thrombi that form in the arteries lead to arterial thrombosis which - depending on the place where the clot forms and depending on the extent of the obstruction caused - can give rise to serious pathologies, such as, for example, ischemia ( peripheral, intestinal, cerebral, cardiac or myocardial, etc.), stroke and infarction .

Consequences of Intracardiac Thrombus Formation

The thrombi that form at the intracardiac level give rise to cardiac thrombosis whose consequences include myocardial dyskinesia, myocardial damage and embolism in the event of thrombus detachment.


In the presence of bacterial endocarditis, the microorganisms responsible for the pathology can organize themselves forming particular masses called " vegetations ". These masses can behave similarly to intracardiac thrombi, leading to serious and sometimes dramatic consequences similar to those induced by the thrombus proper.

Care and Treatment

Treatments and Treatments to Eliminate and Prevent Thrombus Formation

The treatments that can be put into practice to prevent the formation of thrombus or to eliminate those already formed can be either pharmacological or surgical.

The anticoagulant drugs and the antiplatelet agents are mainly used in the preventive sphere .

Fibrinolytic drugs (or thrombolytics, if you prefer), instead, act on the already formed thrombus.

When drug therapy cannot be undertaken or does not give the desired results, just as in particularly severe cases it is instead possible to intervene by means of thrombectomy, that is through surgical removal of the thrombus.