Misalignment of lung vessels: diagnostic role of conventional histology and immunohistochemistry.

Misalignment of lung vessels represents a rare congenital anomaly that may cause respiratory failure in the newborn. It is characterized by abnormal position of pulmonary veins and venules that lie adjacent to arteries and bronchi, and it is usually associated with a decreased number of alveolar capillaries (i.e., alveolar capillary dysplasia), although these two conditions have been separately described. Awareness of this anomaly is required by pathologists because it can be easily overlooked on lung biopsy or autopsy, and because definite diagnosis relies on histology. We report the case of a newborn male baby who developed respiratory distress 18 h after an uncomplicated delivery. The patient died on the 7th day, after high frequency oscillatory ventilation, nitric oxide inhalation and extracorporeal membrane oxygenation were unsuccessful. On autopsy, histology and immunohistochemistry demonstrated diffuse changes, fulfilling diagnostic criteria of misalignment of lung vessels and of alveolar capillary dysplasia in both lungs, with muscularization of very peripheral pulmonary arteries and a prominent interstitial and periadventitial fibrosis. Diffuse distribution of vessel misalignment could explain the rapid onset of respiratory failure, and the presence of diffuse fibrosis might have contributed to irreversible respiratory dysfunction by impairment of lung parenchyma extensibility.