STRUCTURAL alterations in the pulmonary arterial bed can profoundly affect the course and prognosis of patients with congenital malformations of the heart. The mechanism of production of these changes, their relation to pulmonary vasomotor activity, and their variation with age are as yet incompletely understood. It is believed, therefore, that a detailed definition of normal lung structure during growth and development might provide a useful baseline against which pathologic alterations could be evaluated.
The microscopic structure of pulmonary arteries has been extensively studied in the past.1-4 It is notable that histologic examination of the pulmonary arterial bed does not distinguish the lung of an adult from that of a child. Only in the newborn period is the appearance of the lung distinctive, marked by thick-walled pulmonary arteries and lobulations of the parenchyma. Within a few weeks or months after birth, the "fetal" pulmonary arteries become transformed into the thin-walled
Mary Libi-SyLora, Jetta Greco, Charlotte Ferencz. Postnatal Growth of the Pulmonary Arterial TreeMorphologic Characteristics. Am J Dis Child. 1968;115(2):191–201. doi:10.1001/archpedi.1968.02100010193007