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formation, development, or presence of a thrombus; this can happen whenever the flow of blood in arteries or veins is impeded. Many factors can interfere with normal blood flow: heart failure or physical inactivity may retard circulation generally; a change in the shape or inner surface of a vessel wall may impede blood flow, as in atherosclerosis; a mass may grow inside the body and exert pressure on a vessel; the vessel wall may be injured and roughened by an accident, surgery, a burn, cold, inflammation, or infection; or the blood may thicken in reaction to the presence of a foreign serum or snake venom. adj., adj thrombot´ic.

Sometimes a thrombus detaches itself from the wall and is carried along by the bloodstream. Such a clot is called an embolus, and the condition is known as embolism. A thrombus may form in the heart chambers, such as after coronary thrombosis (see below) at the place where the wall of the heart is weakened, or in the dilated atria in a case of mitral stenosis. Because blood normally flows more slowly through the veins than through the arteries, thrombosis is more common in veins than in arteries.
Venous Thrombosis. This occurs most often in the legs or pelvis; it may be a complication of phlebitis, result from injury to a vein, or occur with prolonged bed rest. The symptoms—a feeling of heaviness, pain, warmth, or swelling in the affected part, and sometimes chills and fever—do not necessarily indicate its severity. Immediate medical attention is necessary in any case. Under no circumstances should the affected limb be massaged.

In thrombosis of superficial veins, bed rest with legs elevated and application of heat to the affected area may be all that is necessary. In thrombosis of deep veins, the affected part must be immobilized to prevent the clot from spreading or turning into an embolus, and anticoagulant drugs may be given. With proper treatment, recovery occurs within a short time unless an embolism develops. Practice management guidelines for venous thromboembolism in trauma patients note that a vena cava filter should be considered in patients at high risk who are not candidates for anticoagulants.
Prevention of Venous Thrombosis. Immobility is a prime factor in the development of thrombosis; hence, all patients should be mobilized as soon as possible after surgery or an illness that requires bed rest or produces paralysis. Those who cannot get out of bed should follow an exercise routine involving either active or passive motion of the extremities.  dehydration also plays a role in the development of thrombosis, and the patient should be kept well hydrated. The use of sequential compression devices, such as graded elastic stockings or automated devices providing intermittent compression to the legs, are widely used and accepted, but there are few clinical studies related to their use. They probably play a role in the prevention of stasis and should be combined with other methods to prevent thromboembolism. Clinical guidelines also support the use of low molecular weight heparin for patients at high risk when the bleeding risk is not considered a problem.
Arterial Thrombosis. The main types of arterial thrombosis are related to arteriosclerosis, although thrombosis can also result from infection or from injury to an artery. Arteriosclerosis may be hereditary or may be brought on by diabetes mellitus. Coronary thrombosis, arterial thrombosis in a coronary artery, is a complication of coronary atherosclerosis. A thrombus in one of these arteries will block part of the blood supply to the heart muscle and cause severe myocardial infarction, which is a medical emergency. Cerebral thrombosis is arterial thrombosis in one of the cerebral arteries; the thrombus obstructs the supply of blood to the brain and results in stroke syndrome. Causes include hardening of the cerebral arteries, hypertension, complications of syphilis or other infections, dehydration, diabetes mellitus, or a violent injury.

In advanced cases of arteriosclerosis, a thrombus may fill up whatever channel remains through a vessel, completely blocking off circulation and causing gangrene. This occurs most frequently in arteries of the legs and is called peripheral thrombosis. The onset, often sudden, is characterized by either a tingling feeling or numbness and coldness in the limb. Pain is not always present. Immediate treatment with anticoagulants is necessary to discourage clotting. If this is not effective, surgery may be required. This condition is most common in the elderly and in diabetics. There are now methods of treatment that may save the limb, such as surgical removal of a thrombus or embolus, or surgery of blood vessels to remove old, narrowed, or deteriorated vessels and replace them with grafts.
cerebral thrombosis arterial thrombosis of a cerebral vessel, which may cause stroke syndrome; see also thrombosis.
coronary thrombosis arterial thrombosis in a coronary artery, which may cause myocardial infarction. See also thrombosis.
deep venous thrombosis (DVT) venous thrombosis of one or more of the deep veins of the lower limb, characterized by swelling, warmth, and erythema; it is frequently a precursor of a pulmonary embolism. See also thrombosis.
venous thrombosis phlebothrombosis.


, pl.


(throm-bō'sis, -sēz),
1. Formation or presence of a thrombus.
2. Clotting within a blood vessel that may cause infarction of tissues supplied by the vessel.
[G. thrombōsis, a clotting, fr. thrombos, clot]


/throm·bo·sis/ (throm-bo´sis) the formation or presence of a thrombus.thrombot´ic
cerebral thrombosis  thrombosis of a cerebral vessel, which may result in cerebral infarction.
coronary thrombosis  thrombosis of a coronary artery, usually associated with atherosclerosis and often causing sudden death or myocardial infarction.
deep venous thrombosis  thrombosis of one or more deep veins, usually of the lower limb, with swelling, warmth, and erythema, frequently a precursor of pulmonary embolism.


n. pl. thrombo·ses (-sēz)
The formation, presence, or development of a thrombus.


[thrombō′sis] pl. thromboses,
an abnormal condition in which a clot (thrombus) develops within a blood vessel. See also blood clotting. thrombotic, adj.


The formation of one or more blood clots or thrombi. See Coronary thrombosis, Deep vein thrombosis, Effort thrombosis, Late-stent thrombosis, Protein C deficiency, Pulmonary thromboembolism.


, pl. thromboses (throm-bō'sis, -sēz)
Formation or presence of a thrombus; clotting within a blood vessel that may cause infarction of tissues supplied by the vessel.
[G. thrombōsis, a clotting, fr. thrombos, clot]


Clotting of blood within an artery or vein so that the blood flow is reduced or impeded. If the vessel is supplying a vital part, such as the heart muscle or the brain, and the thrombosis cuts off the flow, the result may be fatal. Thrombosis of arteries supplying limbs or organs may lead to GANGRENE. See also CORONARY THROMBOSIS and CEREBRAL THROMBOSIS.


the formation of a clot of blood in a blood vessel.


Formation of a clot in the blood that either blocks, or partially blocks a blood vessel. The thrombus may lead to infarction, or death of tissue, due to a blocked blood supply.


intravascular clot formation; may cause infarction of subserved tissues
  • coronary thrombosis thrombus occlusion of coronary arteries, usually in association with intimal atheroma, leading to a myocardial infarction/heart attack

  • mural thrombosis intimal thrombus formation within a large artery, without local arterial occlusion; clot may detach to cause distal arterial thrombosis and ischaemic gangrene

  • venous thrombosis intimal thrombus formation of a deep vein, e.g. of leg; thrombus can detach, passing through venous system and heart to block the pulmonary vein (causing sudden death) or a cerebral artery (causing stroke/cerebrovascular accident)

thrombosis (thräm·bōˑ·sis),

n an atypical condition wherein a blood clot or thrombus forms inside a blood vessel.


, pl. thromboses (throm-bō'sis, -sēz)
1. Formation or presence of a thrombus.
2. Clotting within a blood vessel that may cause infarction of tissues supplied by vessel.
[G. thrombōsis, a clotting, fr. thrombos, clot]

thrombosis (thrombō´sis),

n presence of a clot or deposit in a blood vessel, formed in situ and remaining in place. An abnormal vascular condition in which a thrombus (blood clot) develops within a blood vessel of the body.
thrombosis, cavernous sinus,
n a blood clot in the cavernous sinus occasionally arising from maxillary periapical infection. The prognosis is poor but not so grave as before antibiotic therapy.
thrombosis, coronary,
n thrombosis of the coronary artery; also called
heart attack and
coronary occlusion.


formation, development, or presence of a thrombus.
A thrombus may form whenever the flow of blood in the arteries or the veins is impeded. If the thrombus detaches itself from the wall and is carried along by the bloodstream, the clot is called an embolus. The condition is known as embolism. Because blood normally flows more slowly through the veins than through the arteries, thrombosis is more common in the veins than in the arteries.
The effect of a thrombosis is engorgement of the obstructed vein, usually further aggravation of the thrombus formation, and edema of the local area drained by the vein. The clinical signs will depend on the location of the vessel, e.g. cerebrovascular, pulmonary.

caudal vena cava thrombosis
see caudal vena caval thrombosis.
iliac thrombosis
see iliac artery thrombosis.

Patient discussion about thrombosis

Q. How can I prevent blood clots? I am 45 years old and am supposed to go on a business trip overseas. The flight itself is 12 hours long and then I have to continue traveling by bus. Could this cause me to have blood clots? If so, how can I prevent it?

A. Always walk as much as you can on the plane. Also, rotate your ankels in circles. Sometimes try to use your ankels and make the alphabet with them. Have fun..

Q. Are long flights dangerous? I'm flying next week to my vacation, and the flight is going to be rather long (almost 16 hours non-stop). Several years ago, my 75 years-old aunt had blood clot in her lung after a flight of similar length. I also heard that during flight the blood in the legs clots and that it can cause after that problems with the lungs and breathing. Does this mean it's dangerous for me to fly? Should I change my ticket to shorter connection flights?

A. Do other relatives of yours have blood clotting problems too, like your aunt? You should tell a doctor about the problem your aunt had and ask if it's genetic.

More discussions about thrombosis
References in periodicals archive ?
The prevalence of factor V (G1691A), MTHFR (C677T) and PT (G20210A) gene mutations in arterial thrombosis.
In contrast to the association between risk of arterial thrombosis and C-reactive protein elevation, C-reactive protein is not very useful in predicting future venous thrombosis or pulmonary embolism.
The report reviews key players involved Arterial Thrombosis therapeutics and enlists all their major and minor projects
Arterial thrombosis in patients without atherosclerosis and known CVD risk factors should always raise the suspicion of occult malignancy.
Another hereditary risk factor in terms of arterial thrombosis is MTHFR C677T mutation.
There are numerous predisposing factors to arterial thrombosis within this clinical picture.
We report the case of a male patient with Crohn disease developing arterial thrombosis after infliximab administration.
Smoking and use of oral contraceptives drove the risk of these arterial thrombosis events yet higher in the survivors who tested positive for lupus anticoagulant, according to a report posted online in the Lancet Neurology.
Infection with the human immunodeficiency virus (HIV) is a type of hypercoagulable state that predisposes to the development of serious and potentially life-threatening thromboembolic disorders such as deep venous thrombosis, pulmonary embolism, and arterial thrombosis.
The management of patients with arterial thrombosis has yielded poor results.
The expert opined that if the arterial occlusion had been discovered earlier, more likely than not, the leg could have been saved, and that the failure of the nurses to appropriately monitor the decedent resulted in their failure to detect the arterial thrombosis at or near the time it occurred.
The combination protocol dissolved the clots in all of the patients with arterial thrombosis and in 10 of the 16 patients with DVT.