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Rhythmic structures of the aorta in children and young adults.

517 samples of the aorta (descending thoracic and abdominal) from children aged 0 to 14 years and 70 men aged 20-29 years were investigated. Rhythmic structures (RS) were found in 4% of still-borns and in children in their first days of life. Thereafter, the occurrence of RS systematically increased with age, and after the first year of life they occurred in 60% of cases. In men aged 20-29 years RS were transformed in 40% into ribbon-shaped fibrous plaques (FP); in cases when RS were absent, small FP occurred only in 7% of cases. The initial phase of RS development is characterized by impaired and disorganized elastic fibres at the border between the intima and the media. This is followed by migration of smooth muscle cells from the media into the intima and intimal thickening, accompanied with neoformation of irregularly arranged elastic fibres. The next phase, is characterized by fibrous transformation of RS into FP. Similar to aortic RS coronary arteries of children develop "cushions" as a result of hyperplasia of intimal elastic fibres and smooth muscle cells.