Abstract
The aorta was examined pathologically in 20 dogs ranging in age from 10 to 18 years. Macroscopically, rough appearance of the intimal surface of the aorta was found in 17 dogs : 6 animals showed white linear or streak-like plaque formation on the intimal surface. Microscopically, many portions of the aorta examined exhibited degenerative or sclerotic changes in the intima, internal elastic membrane and media. Intimal lesions characterized by mild to severe thickening were classified into 3 types according to their main components : muscular, fibrous and fibromuscular thickening. An alteration in the internal clastic membrane consisted of partial loss, splitting, fragmentation, reduplication, and calcium deposition, and almost always coexisted together with the intimal lesions in most sections. In the media, edematous swelling of the smooth muscle cells surrounded by edematous accumulation was observed as the earliest evidence of the medial degeneration, which was followed by the presence of relatively dense fibrous tissue with a focal loss of muscle, leading to extensive medial fibrosis. These fibrotic lesions were more frequently observed in the cases with pronounced intimal thickening. The severity of such lesions in the vascular walls appeared to be associated with increasing age. In addition, the severer lesions tended to occur frequently at more distal portions of the aorta. The vascular changes observed in the present study resembled those seen in senile arteriosclerosis in man.
