Abnormal dilatation of the pulmonary lymphatic vessels. Lymphatic fluid in the lung is derived from normal leakage of fluid out of the blood capillaries in the lung. In pulmonary lymphangiectasia, the pulmonary lymphatics are not properly connected and become dilated with fluid. The phenotype is Pulmonary lymphangiectasia (HP_0006521, a Human Phenotype Ontology identifier). Also known as: Pulmonary lymphangiectasis.