Study on the onset of atherosclerotic lesions in human coronary arteries.

The coronary arteries of 300 fetuses, neonates, infants and children were examined by light microscope in an effort to reconstruct the natural history of the first atherosclerotic lesions. The critical period for the passage from processes of growth and remodelling to atherosclerotic involvement appeared in this series at the age of 5 years. The incidence of the earliest lesions was distributed as follows: fibrous plaques in 2% of the subjects 6--10 years old and 4% of the subjects 11--15 years old; gelatinous plaques and fatty streaks in 6% of the subjects 11--15 years old. Indirect evidence was obtained that certain branch pads or cushions acted as precursors of the first fibrous plaques. Their conversion into atherosclerotic lesions was induced by insudation, histolysis (elastolysis, collagenolysis, ground substance depletion and degenerative cell changes), followed by nodular proliferation of smooth muscle cells and abundant neoformation of ground substance and collagen fibers. The onset of the first gelatinous plaques was also preceded by insudation and histolysis followed by swelling necrosis. The appearance of the first fatty streaks seemed to be not preceded by particular structural changes. The first fibrous plaques developed only in bifurcation and emergence areas, whereas the first gelatinous plaques and fatty streaks involved the proximal segments of the main coronary vessels.