Spatial dispersion of spindle cells in the human thoracic aorta.

The intima of the human thoracic aorta thickens with age. Those portions of thickened intima that lack foci of atheronecrosis or foam cells are populated by smooth muscle cells, which are usually characterized in sections by spindle-shaped nuclei, and by occasional superficial monocytic macrophagic cells. Populations of these cells were censused by counting nuclear profiles at 40 anatomically defined sites in each of 200 aortas aged 10 to 69 years. The different depths within the intima between the lumenal surface and the media with minor exceptions did not significantly differ in cell numbers. The density of cells decreased with thickness at all ages and with age at all thicknesses after completion of growth and maturation. The total numbers of cells in 100-microns lengths of intima, assessed in longitudinal tissue sections, were virtually constant with aging after 20 to 29 years. The dispersion of cells over the intima in the lateral walls of the thoracic aorta followed a negative binomial distribution, which has an upward skewed unimodal form. Because of the sampling properties of this form of distribution the mean of eight to 12 measurements appears to be adequate to describe the spindle cell numbers in the nonnecrotic parts of an aorta.