Misalignment of lung vessels and alveolar capillary dysplasia: a cause of persistent pulmonary hypertension.

Two infants with fatal persistent pulmonary hypertension are described. Morphologically there was misalignment of the lung vessels, with the veins and the arterioles anomalously related, often sharing the same adventitial sheet. The capillaries did not make contact with the alveolar epithelium. The arterioles had increased medial muscle, and there was extension of the arteriolar muscularization to the precapillary level. The fraction of the parenchyma that was septal and connective tissue was increased. The acini had a decreased complexity, with immature alveoli and with a decreased radial alveolar count. The cause appeared to be related to abnormal capillary and venous plexus formation and migration. This syndrome seems to be identical with that described in three previous reports and probably represents a specific cause of persistent pulmonary hypertension.