Cartilage in children's lungs: a quantitative assessment using the right middle lobe.

The amount and development of cartilage in the lungs of 150 children dying between 24 week's gestation and 12 years has been studied using standard sections of the right middle lobe. Both the cartilage-bearing bronchi and the cartilage fragments increase in number until approximately two months after birth, after which time a constant level is maintained. There is a progressive increase in the total area of cartilage in the child's lung during infancy and childhood, and this appears to be more directly related to the crown-rump length of the child than to its age. Percentiles of the quantity of cartilage found in the standard lung sections are presented.