Histological study of pulmonary vasculature in fatal cases of persistent pulmonary hypertension of the newborn.

Using our own morphometric technique, we examined pulmonary vasculature in eight neonates who died of persistent pulmonary hypertension of the newborn (PPHN). PPHN was judged to be idiopathic in three neonates and was associated with fatal meconium aspiration in the other five. Two characteristic structural features of PPHN were revealed in this study. First, medial thickening of the normally fully-muscularized pulmonary vessels occurred in the smaller and more peripherally located arteries. Second, fully-muscularized vessels extended as far as the intraacinar arteries, which are normally non-muscular vessels at this age. This structural abnormality appears not to merely represent a failure of the fetal pattern to regress, and it is suggested that PPHN is due to a structural abnormality of the pulmonary microcirculation in fatal cases.