Occlusion of peripheral pulmonary vascular bed in a baby with idiopathic persistent fetal circulation.

Babies with a normal heart and persistence of the fetal circulation are frequently referred to the cardiologist because they present with severe cyanosis in the absence of parenchymal lung disease. Persistence of the fetal circulation may be associated with birth asphyxia, polycythaemia, hypoglycaemia,l and premature closure of the ductus arteriosus.2 Occasionally, however, no "trigger" factor can be identified. The present report concerns such an infant who died at 8 days, despite optimal medical management, because the peripheral pulmonary arterial bed was occluded by smooth muscle and swollen endothelial cells. The development of the pulmonary circulation was assessed by applying quantitative morphometric techniques to the injected and inflated lung. The structural changes found were more severe and extensive than those previously reported.3 4