ANEURYSMS

ANEURYSMS

An aneurysm is an irreversible dilatation of an artery to at least one and one-half times its normal diameter. The most common sites are (aortic > iliac > popliteal > femoral arteries). The carotid, renal, visceral, and upper extremity arteries can also develop aneurysms.
Arterial ectasia refers to localized arterial enlargement less than 50% of normal diameter.

Classification
1. According to shape:-
It is helpful to further classify aneurysms as saccular or fusiform. Saccular aneurysms usually arise from a distinct portion of the wall and have a mouth, whereas fusiform aneurysms involve the total circumference of the artery and represent a diffuse dilatation.
2. According to wall layer involvement :-
Aneurysms may involve all layers of the arterial wall (true aneurysm) or only a portion of the vessel wall or surrounding tissue (false aneurysm).
Dissecting aneurysms most commonly occur in the thoracic aorta with possible involvement of the abdominal aorta.
3. According to cause :-
Aneurysms can be classified as ?nonspecific, ?traumatic, ?dissecting, ?mycotic, ?anastomotic, ?childhood, and those ?associated with pregnancy.

?Degenerative Aneurysms
The most common type of aneurysm has been called atherosclerotic, but since the role of atherosclerosis in aneurysmal disease is unclear, the term “degenerative” is more appropriate. This view is supported by histologic evidence that demonstrates degeneration of the arterial wall. The intima usually is absent and replaced with compacted fibrin in multiple layers; the media has fragmented and reduced numbers of elastic lamellae; and, most important, there is focal loss of elastic tissue. An imbalance between the two enzymes important in the metabolism of elastin, elastase (degradation) and ?1-antitrypsin (synthesis), has been identified in patients with aneurysms as compared to occlusive disease. This imbalance becomes even more pronounced in multiple aneurysms and ruptured aneurysms.

?Traumatic Aneurysms
Many early descriptions of aneurysms dealt with traumatic or false aneurysms or pseudoaneurysms. Most traumatic aneurysms today are due to arterial catheterization or penetrating injuries. These lesions are characterized by a focal defect in the arterial wall, with the hemorrhage contained by the surrounding tissues. With time, a fibrous capsule forms around the hematoma, but a definite risk of rupture is present because the surrounding tissues do not withstand arterial pressures and cannot contain the hemorrhage indefinitely.