The aorta is the major artery carrying oxygenated blood out of the heart to the rest of the body. An aneurysm, which can form in any blood vessel, is a bulging or ballooning of the wall of the vessel. Aortic aneurysms can be classified according to their location, their shape, their size and the process that leads to their formation. The danger of an aneurysm is the risk of rupture due to the weakness they create in the vessel wall.
Types By Location
As the aorta exits the heart, it arches upward, then curves downward to descend through the chest and into the abdomen. In the lower abdomen, it divides into two branches that supply blood to the pelvis and legs. An aneurysm may form at any location, but most commonly does so in the abdomen, a condition known as an abdominal aortic aneurysm or AAA. If the ballooning is above the diaphragm, it is termed a thoracic aortic aneurysm. The Cedars Sinai website discusses more specific locations of aneurysms such as at the location where the aorta leaves the heart or in the aortic arch. They are also sometimes classified according to their position relative to the takeoff of the renal arteries which go to the kidneys. This terminology is suprarenal for above the split, or infrarenal for below.
Fusiform or Saccular
Aortic aneurysms may be one of two distinct shapes. The Mayo Clinic describes these shapes as fusiform and saccular. A fusiform aneurysm is symmetric with the bulging around the circumference of the vessel. Saccular aneurysms are more localized as a result of a more specific weakness in the wall. They appear as a blister or sac on one side of the aorta. The saccular form is more commonly caused by trauma to the blood vessel.
Size Definition
The Cedars Sinai website states that if the bulge is 1.5 to two times larger than the normal size of the vessel, it is termed an aneurysm. Alternatively, a diameter of 4 centimeters or greater can be the definition. The larger the aneurysm, the greater the risk of rupture, a life-threatening event.
Degenerative or Dissecting
The Society of Thoracic Surgeons uses the terms degenerative and dissecting when discussing types of aortic aneurysms. Degenerative refers to a process whereby the lining of the vessel breaks down and weakens. This can be the result of arteriosclerosis or hardening of the arteries. Risks for this include cigarette smoking, high blood pressure, and a family history.
A dissection of an aneurysm means there has been a separation of the inner layers of the blood vessel. This tear greatly increases the risk of a catastrophic event. Dissections can be further subdivided into type A and type B. Cedars Sinai notes that a type A dissection of the aorta occurs just at the outlet of the heart, and type B appears anywhere beyond this location. Type A is typically treated with emergency surgery while type B can sometimes be treated with medication and close monitoring according to the Society of Thoracic Surgeons.
