Fig. 2.

Pathologic changes in pulmonary circulation in neonatal HRF follows 4 patterns. Intravascular obstruction caused by increased viscosity as seen in polycythemia in the presence of normal pulmonary vasculature can cause PPHN. Asphyxia or parenchymal lung disease can lead to alveolar hypoxia and acute pulmonary vasoconstriction. Chronic pulmonary vascular remodeling can result from chronic intrauterine hypoxia, antenatal ductal closure, or CDH. Lung hypoplasia with paucity of pulmonary vasculature accompanies CDH; intrathoracic space occupying lesions, such as adenomatoid malformations; or chronic oligohydramnios syndromes, which could be secondary to chronic leakage of amniotic fluid or fetal oliguria from renal dysfunction. (Copyright © Satyan Lakshminrusimha.)