Atherosclerotic aneurysms are the most common form of aortic aneurysms. They are seen more commonly in males and the frequency increases after the age of 50 years when the incidence of complicated lesions of advanced atherosclerosis is higher. They are most common in the abdominal aorta, so much so that all forms of aneurysms of abdominal aorta (fusiform, cylindrical and saccular) should be considered atherosclerotic until proved otherwise. Other locations include thoracic aorta (essentially the ascending part and arch of aorta), iliac arteries and other large systemic arteries.
PATHOGENESIS.
Obviously, severe atherosclerotic lesions
are the basic problem which cause thinning and destruction of the medial elastic tissue resulting in atrophy and weakening of the wall. Since atherosclerotic lesions are most
common and severe in the abdominal aorta, atherosclerotic aneurysms occur most frequently here. In the thoracic aorta,
besides atherosclerotic lesions, medial degeneration is another additional factor implicated in pathogenesis.
MORPHOLOGIC FEATURES.
Atherosclerotic aneurysms of the abdominal aorta are most frequently infrarenal, above the bifurcation of the aorta but may extend into common iliac arteries. They may be of variable size
but are often larger than 5-6 cm in diameter.
Atherosclerotic aneurysm is most frequently fusiform in shape and the lumen of aneurysm often contains mural
thrombus.
EFFECTS. The clinical effects of atherosclerotic aneurysms are due to complications. These are as under:-
1. Rupture.
Rupture of the atherosclerotic aneurysm is the most serious and fatal complication. The risk of rupture depends upon the size and duration of the aneurysm and the blood pressure. Rupture of abdominal aneurysm may occur either into the peritoneum or into the retroperitoneum
resulting in sudden and massive bleeding. Occasionally, there may be slow progressive leak from the aneurysm. A ruptured aneurysm is more likely to get infected.
2. Compression.
The atherosclerotic may press upon some adjacent structures such as compression of ureter and erosion on the vertebral bodies.
3. Arterial occlusion.
Atherosclerotic aneurysms of the abdominal aorta may occlude the inferior mesenteric artery, or there may be development of occlusive thrombosis.
However, collateral circulation develops slowly and is nearly always sufficient so as not to produce effects of ischaemia.
Thromboembolism is rather common in abdominal aneurysms.
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