Occlusion in medicine refers to vascular occlusion that is the rapid obstruction of a blood vessel, normally by a clot. It varies from thrombosis in that it might be used to define any type of blockage, not just one made by a clot. If it occurs in a vein that is major, it can in certain cases, cause what is known as “deep vein thrombosis”. This situation is also fairly common in the retina of an eye which can cause total or partial loss of vision. Occlusions may often be diagnosed by the use of Doppler sonography which is a form of ultrasound.

Several procedures medically comprise the occluding of a blood vessel to manage a certain situation. This may be to lessen pressure on blood vessels that are weakened or to confine a hemorrhage. It also can be done to decrease blood to growths or tumors located in the body and thus restrict development. Occlusions can be done by using a ligature; by embedding coils that are small and which triggers the development of clots; or especially in cases of cerebral aneurysm by clipping.