Aneurysm

An aneurism is localized, blood-filled dilation of a blood vessel caused by disease or weakening of the vessel wall. Aneurysms most commonly occur in arteries at the base of the brain and in the aorta- this is an aortic aneurysm. This bulge in a blood vessel can burst and lead to death at any time, much like a bulge in an over-inflated innertube. The larger an aneurysm becomes, the more likely it is to burst. Aneurysms can be treated.

The layer of the artery that is in direct contact with the flow of blood is the tunica intima, commonly called the intima. This layer is made up of mainly endothelial cells. Adjacent to this layer is the tunica media, known as the media. This "middle layer" is made up of smooth muscle cells and elastic tissue. The outermost layer is known as the tunica adventitia or the adventitia. This layer is composed of connective tissue.

Aneurysms are also described according to size: Saccular or fusiform. A saccular aneurysm resembles a small sack; a fusiform aneurysm is shaped like a spindle. Aneurysms can be broken down into two groups: true aneurysms and false aneurysms. A true aneurysm involves an outpouching of all three layers of a blood vessel: the intima, the media, and the adventitia. True aneurysms can be due to congenital malformations, infections, or hypertension. A false aneurysm, also known as a pseudoaneurysm, involves an outpouching of only the adventitia. Pseudoaneurysms can be due to trauma involving the intima of the blood vessel, and are a known complication of percutaneous arterial procedures.

Aneurysms can occur anywhere where there is a blood vessel, although they are most common in arteries. Most non-intracranial aneurysms arise distal to the origin of the renal arteries at the infrarenal abdominal aorta, a condition mostly caused by atherosclerosis. The thoracic aorta can also be involved. One common form of thoracic aortic aneurysm involves widening of the proximal aorta and the aortic root, which leads to aortic insufficiency. Aneurysms occur in the legs also, particularly in the deep vessels. Arterial aneurysms are much more common, but venous aneurysms do happen.

Historically, the treatment of arterial aneurysms has been surgical intervention, or watchful waiting in combination with control of blood pressure. Recently, endovascular or minimally invasive techniques have been developed for many types of aneurysms.

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Related Links:

• US National Library of Medicine

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