Thrombus vs Embolus - Difference, Formation, Definition

Thrombus vs Embolus

Thrombus and embolus both are the blood clots but thrombus is stationary while embolus is floating. Blot clot is a clump that forms when blood changes its state from liquid to solid and gets hardened.

Blot clot formed inside veins or arteries are referred to as thrombus. Thrombus can also be formed inside the heart. A thrombus when broken and its pieces travel from one place to other, it is called embolus. Both thrombus and embolus can block the blood flow into the blood vessel which results in certain serious medical conditions. It can be a popliteal thrombus in the knee or deep vein thrombus in a thigh but embolus is a thrombus that moves from one place to the other.

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When the artery is blocked, it prevents oxygen from getting to the tissues in that particular area. These results in a medical condition called ischemia which if left untreated may become as serious as tissue damage or even death. When a vein is blocked, it causes fluid to build up and results in swelling. Sometimes thrombus and embolus are joined together and then they are called thromboembolic events.

Thrombus is a blood clot formed in the blood vessel or heart and remains in one area of the body. It forms within vascular system and mostly causes vascular obstruction. However if the clot moves from one part of the body to another it is termed as embolus. Complications arise when these blood clots attach to the walls of blood vessels and do not allow blood to pass in and out of the vessel. Thus surrounding tissues do not receive sufficient amount of blood and oxygen resulting in tissue killing or the permanent damage of that area.

Blood clots usually form during or after pregnancy, dehydration, long-term bed rest, sitting for long time period, taking birth control pills, taking estrogen hormones and using intravenous catheter for long time. Blood clot mostly occurs among people with cancer, obesity, kidney disease, liver disease or who have had surgery or an injury in the past.


Thrombus is a fibrous blood clot that is formed in blood vessel. It is an abnormal clot present in one of the four heart chambers and obstructs the blood flow.

Embolus is a mass or floating clot much like a detached blood clot, air bubble or some foreign mass that floats from one place to other and lodges somewhere. Usually embolus isa part of thrombus that has broken and has drifted towards the brain in bloodstream.

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Because of the fact that emboli usually forms from thrombi, the term thromboembolus is also commonly used. But other mass such as fat, plague, iodine, cotton, amniotic fluid, tumor, air bubbles etc. are also used for emboli. Typically embolus is anything that travels across the blood vessels until its flow is restricted by something too small to allow it to pass through it. As a result the blood flow is stopped due to the obstruction by this vessel which didn’t allow the embolus to pass through.

The embolus flows with the blood until it encounters the artery through which it cannot flow. Consequently the artery gets blocked and blood flow is restricted. Since adequate amount of blood does not reach to the tissues, they get ischemic.


The thrombus is formed from the blood constituents such as fibrin, cellular elements, platelets etc.

Embolus is formed from thrombus and so it represents a portion of removed thrombus. In fact almost 90 to 95% of the embolus arises from thrombus.


As discussed earlier, thrombus is a stationary solid mass that blocks the flow of blood. It is generally located at the vessel wall of its originating site. Embolus on the other hand is a floating mass, may be solid, liquid or gas, which moves from one place to the other and is not attached to any site. When thrombus is disrupted, embolus is formed.

Types of thrombus and embolus

Thrombus is broadly divided into two types: Anatomical and Morphological. Anatomical thrombus is further divided into cardiac arterial, capillary and venous forms. Morphological thrombus is of pale, red and mixed type each pertaining to platelet thrombus, Red blood cells thrombus and intermittent layers respectively.

Embolus is broadly classified into two forms: systematic thromboembolus and amniotic fluid embolus. Systematic thrombembolus is of two types’ namely fat embolus and air embolus whereas amniotic fluid embolus has no further division.

Effects of thrombus and embolus

The effect of thrombus depends upon the location and extent of vascular obstruction. It is also dependent upon the availability of guaranteed blood supply and how vulnerable is the area to have restricted blood supply.

The effect of embolus depends upon the degree of disorder caused to the local circulation and vulnerability of the tissue to such disorders.

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