Persistent fetal circulation: Newly recognized structural features.

Three infants died with pulmonary hypertension of unknown cause during the first three months of life. Their lungs were examined using quantitative morphologic techniques. In all three cases the intra-acinar pulmonary arteries were more muscular than normal, as shown both by an increase in thickness of the muscle coat in arteries which are normally muscular, and by extension of muscle into smaller and more peripheral intra-acinar arteries not normally muscular at this age. It is suggested that "persistent pulmonary hypertension" of the newborn infant is, in some infants, due to a structural abnormality of the pulmonary circulation which is present at birth.