The Lateral Chest Radiograph in the Diagnosis of Hilar and Mediastinal Masses

The left pulmonary artery superior and posterior to the left upper lobe bronchus is clearly seen on lateral chest films. The right pulmonary artery is surrounded by structures which make it less distinct. Both upper lobe bronchi are seen on end in the lateral view; the right bronchus is superior to the left, which is surrounded by the pulmonary artery and veins. The right superior pulmonary vein enters the left atrium directly inferior to the right pulmonary artery. The azygos vein is extrapleural; its horizontal portion is oriented in the anteroposterior direction and is seen only on anteroposterior films.