Alveolar Capillary Dysplasia (ACD) is a lethal developmental anomaly of the pulmonary vasculature: it is generally described as the failure of formation of the normal air-blood diffusion barrier in the newborn lung. Alveolar Capillary Dysplasia is usually associated with "misalignment" of the pulmonary veins.
Alveolar Capillary Dysplasia is a pulmonary disease that presents in very early infancy. Infants generally become critically ill in the first days of life with severe hypoxemia and pulmonary hypertension, although presentation has been reported at 6 weeks of life in an infant with a patchy distribution of disease. The majority of patients with ACD will have other associated anomalies of the cardiovascular, gastroinstestinal, urogenital, or musculoskeletal systems.
The initial presentation is identical to severe idiopathic pulmonary hypertension of the newborn. However, infants with Alveolar Capillary Dysplasia do not respond, or respond only transiently to therapies that are usually effective in reversing this condition. Infants with ACD do not improve despite maximal support in the intensive care nursery including mechanical ventilation, nitric oxide, and extracorporeal membrane oxygenation (ECMO).
The cause of ACD has not yet been determined. It was first identified in 1947.
The diagnosis of Alveolar Capillary Dysplasia should be considered in infants who present with severe hypoxemia and idiopathic pulmonary hypertension, and who do not respond appropriately after 7 to 10 days of neonatal intensive care treatment as described below. The majority of patients with ACD (approximately 75%) will have other associated anomalies of the cardiovascular, gastrointestinal, urogenital, or musculoskeletal systems. The initial chest radiograph is usually normal. If a cardiac catheterization is performed, there may be absence of the capillary blush phase.
The diagnosis can only be confirmed by lung biopsy or autopsy. Consulting a pathologist with experience in making this diagnosis may be helpful. Pathological features include a paucity of alveolar capillaries, widened alveolar septae, and increased muscularization of pulmonary arterioles. There is usually malpositioning ("misalignment") of pulmonary veins in the bronchovascular bundle, but this is not required for the diagnosis. A focal distribution of disease has been described, which makes it necessary to examine multiple lung sections if ACD is suspected.
Since treatment is seldom, if ever, effective, life expectancy of the infant is very short.
Standard therapies include mechanical ventilation, high concentrations of inspired oxygen, inhalational nitric oxide and ECMO support. These therapies prolong life by days to weeks, but have not led to long-term survival. The longest reported survival is to 2 months of age with the use of extracorporeal membrane support followed by inhaled nitric oxide.
Theoretically, alveolar capillary dysplasia could be treated by lung transplantation. However, successful transplantation has not yet been reported. Donor availability continues to limit the utilization of lung transplantation for neonatal diseases.