Thrombosis is a medical disease which occurs when there is a blood clot in a blood vessel, obstructing the flow of blood within the circulatory system. Thrombosis can occur both in veins as well as in arteries. For thrombosis that occurs within the vein, it leads to congestion to the affected part of the body, usually visible by the blackening of the skin around the region. In case of arterial thrombosis, the blood clot restricts the flow of blood, thereby damaging tissue around the region. In special cases, the blood clot can break free from the region and travel within the circulatory system. The broken blood clot is known as an embolus.