A. Pathogenesis
The abdominal aorta is commonly affected by atheroma and the process of atherosclerosis (see chapter Athero-sclerosis/Atherothrombosis). Atherosclerotic disease causes thickening of the intima. This thickening appears to reduce the diffusion of oxygen and nutrients from the aortic lumen to the strong middle wall of aorta. This causes degeneration of the elastic elements and weakening of the walls of the aorta. The elastic wall of the aorta may be stretched causing the vessel to dilate. Tension on the dilated aortic wall increases, thus, causing further expan¬sion of the artery with aneurysmal formation. Tension in the dilated vessel wall rises in accordance with Laplace’s law, which states that wall tension is proportional to the product of pressure and radius; as the diameter of the aorta increases its wall tension rises. The torrential blood flow imparts considerable hydrodynamic stress on the arterial wall, especially in the lower abdominal aorta.
Most aneurysms occur in the abdomen just after the aorta branches to the kidney and before the aorta ends in its division into iliac arteries to the pelvis (see Fig. 1). Fortunately, aneurysms that occur before the aorta branches off to the kidney are rare; at this location repair of an aneurysm is fraught with danger as kidney failure may occur. Other sites for aneurysmal formation are in the thoracic aorta, the iliac arteries in the pelvis, and the popliteal artery at the back of the knee.

Страницы: 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9