Atherosclerotic enlargement of the human abdominal aorta

dAortic aneurysms usually develop in the atherosclerosis prone infrarenal a bdominal aorta. To assess the role of atherosclerosis in aortic enlargement , we studied the relation between plaque formation and aortic size in 30 pr essure-fixed male cadaver aortas (age 40-95 years, mean age 67 years). Morp hometric analysis of transverse sections of the mid-thoracic and the mid-ab dominal aortas included measurement of intimal plaque area, lumen area, pla que and media thicknesses. The area encompassed by the internal elastic lam ina area (IEL area) was taken to be an index of aortic size. IEL area incre ased with age at both the thoracic (r = 0.77, P < 0.01) and abdominal (r = 0.54, P < 0.01) aortic levels. The aorta also enlarged with increasing plaq ue area at the thoracic (r = 0.73, P < 0.01) and abdominal (r = 0.79, P < 0 .01) levels. Regression analysis of IEL area on age, body weight, height an d plaque area revealed that the primary predictor of thoracic aortic size w as age, whereas the primary predictor of abdominal aortic size was plaque a rea. Plaque thickness in the abdominal aorta was greater than in the thorac ic aorta (P < 0.01). Increased plaque area was associated with a significan t decrease in media thickness in the abdominal aorta (r = - 0.75, P < 0.01) but not in the thoracic aorta. Aortas with relatively enlarged abdominal s egments, i.e, those with a thoracic to abdominal ratio of < 1.2 (n = 13), w ere compared to those with a normal ratio (<greater than or equal to> 1.2, it = 17). Relatively large abdominal aortas had twofold greater plaque area (P < 0.001), reduced medial thickness (P < 0.05), fewer medial elastic lam ellae (P < 0.01) and greater mural tensile stress (P < 0.05) than relativel y normal abdominal aortas. We conclude that plaque formation in the infrare nal abdominal aorta in humans is associated with aortic enlargement and dec reased media thickness. These changes may be predisposing factors for the p referential development of subsequent aneurysmal dilation in the abdominal aorta. (C) 2001 Elsevier Science Ireland Ltd. All rights reserved.