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Aneurysm

An aneurysm (or aneurism) (from Greek ανευρυσμα, a dilatation) is a localized dilation or ballooning of a blood vessel by more than 50% of the diameter of the vessel. Aneurysms most commonly occur in the arteries at the base of the brain (the circle of Willis) and in the aorta (the main artery coming out of the heart) - this is an aortic aneurysm. more...

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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 (farthest from the flow of blood) is known as the tunica adventitia or the adventitia. This layer is composed of connective tissue.

Types

Aneurysms are also described according to their shape: Saccular or fusiform. 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.

Locations

Aneurysms can occur anywhere where there is a blood vessel, although they are most common in arteries. Most non-intracranial aneurysms (95%) 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 (e.g., the popliteal vessels in the knee). Arterial aneurysms are much more common, but venous aneurysms do happen (for example, the popliteal venous aneurysm).

  • While most aneurysms occur in an isolated form, the occurrence of berry aneurysms of the anterior communicating artery of the circle of Willis is associated with autosomal dominant polycystic kidney disease (ADPKD).
  • The third stage of syphilis also manifests as aneurysm of the aorta, which is due to loss of the vasa vasorum in the tunica adventitia.

Risks

Rupture and blood clotting are the risks involved with aneurysms. Rupture leads to drop in blood pressure, rapid heart rate, and lightheadedness. The risk of death is high except for rupture in the extremities. Blood clots from popliteal arterial aneurysms can travel downstream and suffocate tissue. Only if the resulting pain and/or numbness are ignored over a significant period of time will such extreme results as amputation be needed. Clotting in popliteal venous aneurysms are much more serious as the clot can embolise and travel to the heart, or through the heart to the lungs (a pulmonary embolism).

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Decrease in aneurysm deaths in men with AAA screening
From American Family Physician, 8/15/05 by Allen F. Shaughnessy

Clinical Question: In older men, does screening for abdominal aortic aneurysm (AAA) result in fewer deaths overall or fewer deaths caused by aneurysm over the next five years?

Setting: Population-based

Study Design: Randomized controlled trial (single-blinded)

Allocation: Uncertain

Synopsis: The researchers conducting this Danish study enrolled all 12,639 men born in years 1921 to 1929 and who lived in a single county. The men were 64.3 to 73.8 years of age (average: 67.7 years) at the time of the study. The men were assigned randomly to a control group or were invited to undergo ultrasonography to screen for the presence of AAA. Nonresponders to the invitation were reinvited once, and 76.6 percent of all invited men underwent screening.

Participants with an AAA of at least 5 cm in diameter (0.5 percent) were referred to a vascular surgeon; men with small AAAs were screened yearly and referred if their aneurysm had increased to 5 cm or more in diameter. There were nine deaths from AAA in the screened group and 27 deaths caused by AAA in the control group over the mean 4.33 years of follow-up. Rates of all-cause mortality in these older men were not affected by screening. These small numbers translate into a number needed to screen of 349 to prevent one AAA-related death over 4.3 years.

Bottom Line: Offering screening to older men will decrease their risk of dying because of an AAA but will not decrease their overall risk of dying within the next 4.3 years. This study evaluated screening in all men; other studies of screening have shown a benefit in men who smoke. (Level of Evidence: 1b)

ALLEN F. SHAUGHNESSY, PHARM.D.

Study Reference: Lindholt JS, et al. Screening for abdominal aortic aneurysms: single centre randomised controlled trial. BMJ April 2, 2005;330:750-2.

Used with permission from Shaughnessy AF. AAA screening decreases aneurysm deaths in men but not overall mortality. Accessed online June 1, 2005, at: http://www. InfoPOEMs.com.

COPYRIGHT 2005 American Academy of Family Physicians
COPYRIGHT 2005 Gale Group

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