Congenital pulmonary lymphangiectasis is a rare primary disorder that causes respiratory distress in the newborn. In severe cases it may be fatal within the first few days of life; however, there are less severe cases with prolonged survival with optimal management. Although usually sporadic, congenital pulmonary lymphangiectasis may be associated with malformation syndromes such as Turner, Noonan, and Down syndromes. It is often accompanied by a chylous pleural effusion, suggesting an intrinsic abnormality of lymphatic development in such cases. Grossly, the lungs are firm and bosselated, with visible distention of lymphatics across the pleural surface. Microscopically, the lymphatics in the interlobular septa and subpleural region are cystically dilated, forming empty spaces lined by a thin endothelium. If necessary, the endothelial lining may be demonstrated with the aid of immunohistochemistry using antibodies to CD31 or factor VIII-related antigen.

Pulmonary lymphangiectasis may be a secondary condition or may be part of a systemic lymphatic maldevelopment. It is categorized into three main groups: primary, secondary, and generalized. Primary lymphangiectasis is thought to result from failure of pulmonary lymphatics to connect with systemic lymphatics, for example, via the thoracic duct. Secondary pulmonary lymphangiectasis is associated with cardiac maldevelopment with obstruction of pulmonary venous drainage (e.g., total anomalous pulmonary venous return). Generalized lymphangiectasis is a systemic abnormality that involves not only the lung but also the soft tissue, viscera, or bone of the thorax, and sometimes extrathoracic sites.