Vascular occlusion is a sudden blockage of a blood vessel, usually with a clot. It differs from thrombosis

Thrombosis

Thrombosis is the formation of a blood clot inside a blood vessel, obstructing the flow of blood through the circulatory system. When a blood vessel is injured, the body uses platelets and fibrin to form a blood clot to prevent blood loss...

 in that it can be used to describe any form of blockage, not just one formed by a clot. When it occurs in a major vein

Vein

In the circulatory system, veins are blood vessels that carry blood towards the heart. Most veins carry deoxygenated blood from the tissues back to the heart; exceptions are the pulmonary and umbilical veins, both of which carry oxygenated blood to the heart...

, it can, in some cases, cause deep vein thrombosis

Deep vein thrombosis

Deep vein thrombosis is the formation of a blood clot in a deep vein. Deep vein thrombosis commonly affects the leg veins or the deep veins of the pelvis. Occasionally the veins of the arm are affected...

. The condition is also relatively common in the retina

Retina

The vertebrate retina is a light-sensitive tissue lining the inner surface of the eye. The optics of the eye create an image of the visual world on the retina, which serves much the same function as the film in a camera. Light striking the retina initiates a cascade of chemical and electrical...

, and can cause partial or total loss of vision. An occlusion can often be diagnosed using Doppler sonography (a form of ultrasound

Medical ultrasonography

Diagnostic sonography is an ultrasound-based diagnostic imaging technique used for visualizing subcutaneous body structures including tendons, muscles, joints, vessels and internal organs for possible pathology or lesions...

).

Some medical procedures involve occluding a blood vessel to treat a particular condition. This can be to reduce pressure on aneurysm

Aneurysm

An aneurysm or aneurism is a localized, blood-filled balloon-like bulge in the wall of a blood vessel. Aneurysms can commonly occur in arteries at the base of the brain and an aortic aneurysm occurs in the main artery carrying blood from the left ventricle of the heart...

s (weakened blood vessels) or to restrict a haemorrhage. It can also be used to reduce blood supply to tumours or growths in the body, and therefore restrict their development. Occlusion can be carried out using a ligature

Ligature (medicine)

In surgery or medical procedure, a ligature consists of a piece of thread tied around an anatomical structure, usually a blood vessel or another hollow structure to shut it off. With a blood vessel the surgeon will clamp the vessel perpendicular to the axis of the artery or vein with a hemostat,...

; by implanting small coils which stimulate the formation of clots; or, particularly in the case of cerebral aneurysm

Cerebral aneurysm

A cerebral or brain aneurysm is a cerebrovascular disorder in which weakness in the wall of a cerebral artery or vein causes a localized dilation or ballooning of the blood vessel.- Signs and symptoms :...

s, by clipping

Clipping (medicine)

Clipping is a surgical procedure performed to treat an aneurysm. If the aneurysm is intracranial, a craniotomy is performed, and afterwards an Elgiloy or titanium Sugita clip is affixed around the aneurysm's neck....

.