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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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Is there benefit of antioxidant supplementation in abdominal aortic aneurysm repair? - Nutrition and Surgery
From Nutrition Research Newsletter, 10/1/02

The process and mediators resulting in tissue injury following ischemia and reperfusion are multifactorial, but there is considerable evidence that supports the idea that they include reactive oxygen species. In healthy individuals, a wide range of antioxidant defenses protects against oxidative damage. However, free radicals can accumulate as a result of overwhelming production of inadequate defenses. The latter situation may reflect an inadequate supply of antioxidant micronutrients. Cross-clamping of the aorta during abdominal aortic aneurysmectomy (AAA) leads to ischemia-reperfusion, oxidative stress, cell dysfunction, and injury in the muscles of the lower extremities. Scientists hypothesized that supplementation with micronutrients with antioxidant properties would supplement antioxidant mechanisms and minimize the decreases in muscle strength and physical function, which occur following AAA.

In an attempt to evaluate this process, these researchers conducted a randomized, double-blind, placebo-controlled clinical trial of individuals undergoing AAA. Due to the synergistic and complementary actions of antioxidant micronutrients, investigators chose to supplement patients with a combination of vitamins and trace elements. A two-week period of preoperative supplementation was chosen because of data demonstrating that oral vitamin E supplementation for two weeks achieved increased tissue levels of alpha-tocopherol. Patients of both sex and any age who were identified at least two weeks before elective repair of an infrarenal abdominal aortic aneurysm were eligible to participate in the study. Subjects were randomly assigned to receive either micronutrient (MN) supplementation or placebo in a blocked design. MN supplementation consisted of beta-carotene (10 000 IU/d), vitamin C (1000 mg/d), vitamin E (400 IU/d), selenium (50 microgram/d), and zinc (24 mg/d). The supplement or placebo was taken orally for at least two weeks and not more than three weeks prior to surgery and continued on the morning of surgery and daily during the first postoperative week. Patients were instructed to maintain their routine diets before surgery. Clinical, functional, physiologic, and biochemical endpoints were evaluated. The duration of the surgical procedure and aortic clamping and other clinical variables were recorded. Organ system function was assessed on the first and second postoperative mornings. Pain was evaluated. Assessments of function status (Karnofsky Performance Status [KPS]), cognitive impairment (Mini-Mental State Examination, MMSE), health-related quality of life (HRQL) (SF36 Health Survey) and the ability to conduct physical and instrumental activities of daily living (PADL, IADL) were made at the Pre-Admission Unit visit before surgery and at the scheduled follow-up visit closet to four weeks following the operation. Thirty-six subjects participated in the study.

Handgrip strength decreased following surgery, with no significant difference observed between MN and placebo groups. Intravenous fluid administration, red blood cell transfusions, ICU stay, duration of mechanical ventilation, and hospital stay were similar in MN and placebo groups. There was no 30-day mortality in either group. KPS decreased following surgery, but the decrease did not differ between groups. MMSE did not change following surgery and a full diet was tolerated on postoperative day 6+2 in both groups. The decline in general health following surgery was more marked in the placebo group, and the difference in decline in vitality approached statistical significance.

The investigators concluded that perioperative supplementation with micronutrient with antioxidant properties has limited effects on strength and physical function following major elective surgery.

J. Watters, A. Vallerand, S. Kirkpatrick, et al. Limited effects of micronutrient supplementation on strength and physical function after abdominal aortic aneurysmectomy. Clinical Nutrition 21:321-327 (August, 2002). [Correspondence: James M. Watters, Ottawa Hospital 737 Parkdale Avenue, Ottawa, Ont., Canada K1Y 4E9].

COPYRIGHT 2002 Frost & Sullivan
COPYRIGHT 2002 Gale Group

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