Pulmonary shunt in a single lung evidenced by quantitative lung scan obtained in the erect and supine positions.

A 46-year-old woman had a nonfunctioning lung and pulmonary shunt resulting from trauma. She had shortness of breath when in the erect position but no symptoms when in the supine position. A chest radiograph and computed tomographic scan showed collapse of the left lung, hyperinflation of the right lung, and cardiomegaly. Body position and cardiomegaly are causes of nonuniform pulmonary artery perfusion revealed by quantitative lung scans obtained in different positions. After left pneumonectomy with left pulmonary artery ligation, the clinical symptoms subsided completely.