Declining density of intimal smooth muscle cells and age as preconditions for atheronecrosis in the basilar artery.

The aging basilar artery has some differences and some similarities when compared with the aorta and coronary arteries. As the non-necrotic intimal thickness increases over time, the number of smooth muscle cells reaches a steady state around age 25-30 years in the coronaries and aorta, but continues to increase in the basilar artery, even to 90 years of age. The numbers of cells per unit of tissue (the cell density) declines with age, and the patterns of decline are quantitatively similar in all three arterial segments. All arteries so far examined behave alike in showing that atheronecrosis emerges in those specimens that have sufficiently low density of intimal smooth muscle cells. These results identify low intimal cell density as a criterion for recognizing arteries that are prone to atheronecrosis. One possible explanation is that depopulation of the fibrotically thickened and aged intima, by spreading apart the smooth muscle cells with expanding matrix materials, could be the conditioning factor that brings about the intrusion of atheronecrosis.