A congenital malformation defined by underdevelopment of lung parenchyma characterized by abnormally small lungs, resulting in insufficient lung tissue and blood flow and inadequate gas exchange. A life-threatening condition that may result in neonatal death or stillbirth. Clinical presentation is variable. Typically presents unilaterally (although may present bilaterally) and ranges in severity from hypoplasia to agenesis. Newborns may present with pneumothorax, perinatal stress, severe acute respiratory distress, and persistent pulmonary hypertension of the newborn. Children with less severe hypoplasia may present with cough, tachypnea, wheezing, and recurrent pneumonia.

Usually occurs secondary to other congenital abnormalities, congenital diaphragmatic hernia being the most common cause. Other causes include pleural effusions, bladder outlet obstruction, and oligohydramnios, among others. Treatment is supportive and is dependent on the size of fetal lungs and cause of pulmonary hypoplasia. Prognosis is defined by the degree of pulmonary hypertension, extent of hypoplasia, and severity of underlying abnormalities. Survivors may experience long-term lung complications.