Figure 7a. Interruption of the left main pulmonary artery in a 16-year-old boy. (a, b) Axial CT scans obtained at the level of the right main bronchus (a) and bronchus intermedius (b) (arrows) show interruption of the left main pulmonary artery. Note the compressed right main bronchus between the right-sided descending aorta (Ao) and a prominent right main pulmonary artery (RPA). The mediastinum is shifted to the left due to an associated hypoplastic left lung. (c) SSD reformatted image (superior view) delineates the spatial relationship between the prominent single pulmonary artery (blue), the right-sided descending aorta (AO [red]), and the compressed right main bronchus. (d) Virtual bronchoscopic reformatted image obtained at the level of the carina ("supine" position) shows the right main bronchus (R) with a compressed "fishmouth" shape. L = left main bronchus.