Persistent pulmonary hypertension of the newborn due to alveolar capillary dysplasia.

Three unrelated female term infants died when less than 1 month old from intractable pulmonary hypertension associated with deficient capillaries in airspace walls, anomalous small pulmonary veins in bronchiolar-arterial rays, and medial thickening in small pulmonary arteries together with peripheral muscularization. This complex vascular abnormality in the lungs has been termed alveolar capillary dysplasia and/or misalignment of lung vessels in seven previously reported cases. Each infant also showed abnormally immature parenchymal development in the lungs, as was noted in four of the seven prior cases. One had phocomelia; four of the seven prior cases had a variety of congenital anomalies. The primary pulmonary vascular anomaly is likely to be a failure of fetal lung vascularization dating from the second trimester and to be due to action of an unknown teratogen. Centroacinar veins may represent bronchial veins that do not normally develop beyond the ends of cartilaginous bronchi. Pulmonary arterial occlusive changes are interpreted as reactive to obstruction at the level of pulmonary arterioles.