The formation of a thrombus (blood clot) is an undamaged blood vessel. Clotting is a normal response when a blood vessel wall is injured, but abnormal when a vessel has not been punctured. A thrombus that forms within an artery supplying the heart muscle (coronary thrombosis) is the usual cause of myocardial infarction (heart attack). A thrombus in an artery of the brain (cerebral thrombosis) is a common cause of stroke.

Thrombi may block arteries supplying blood to the legs, kidneys, retinas, intestines, and other organs, sometimes causing severe damage and symptoms such as pain and loss of function. Another danger is that an embolus (fragment of a thrombus) may break off and be carried by the blood to block an important blood vessel in another area (embolism).

Thrombi can also form in veins, either just beneath the skin or in deeper veins.

THROMBOSIS CAUSES

In the blood there is a fine balance between the mechanisms that encourage and discourage clotting, so there is neither a tendency to bleed nor to form clots too readily (blood clotting). Thrombosis can occur if this mechanism is disturbed in favour of clotting (thrombophilia).

In arteries, thrombus formation is encouraged by atherosclerosis (a build-up of fatty deposits on the walls of arteries), smoking, hypertension (high blood pressure), and damage to blood vessel walls from inflammation in arteritis and phlebitis. An increased clotting tendency may occur in pregnancy, with the use of oral contraceptives or hormone replacement therapy (HRT), or through prolonged immobility.

THROMBOSIS SYMPTOMS

An arterial thrombosis may cause no symptoms until the blood flow is impaired. When this occurs, it leads to reduced function in the tissue supplied by the affected artery, and sometimes severe pain. Venous thrombosis may cause pain and swelling.

THROMBOSIS DIAGNOSIS AND TREATMENT

Diagnosis of thrombosis is by Doppler ultrasound. In some cases, angiography or venography may also be used. Treatment may include anticoagulant drugs or thrombolytic drugs, non-steroidal anti-inflammatory drugs, and, in some cases, antibiotic drugs. In life-threatening cases, thrombectomy (surgical removal of the blood clot) may be needed.

Source: A-Z Family medical encyclopedia by BMA

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