Figure 1.

a) PA chest radiograph. Normal lungs are visible as black fields (air) (*) with superposition of multiple white linear structures (vessels and walls of airways). The lung hila consist of bronchi (main stem (1) and lobar bronchi) and vascular structures (pulmonary arteries (2) and pulmonary veins). A normal pleura is not visible on a chest radiograph. In the mediastinum, we can visualise the trachea (3) as a translucent tube on the midline, the aortic arch (4), the pulmonary trunk (5), the left border of the heart formed by the left ventricle (6) and the right border of the heart formed by right atrium (7). A normal heart has a normal cardiothoracic index: (a+b)/maximal diameter of the chest (c) must be <0.5. The bony components of the chest visible on the frontal view are: the ribs (+), the manubrium sternum (8), the clavicles (9), the scapulae (10) and the vertebral bodies on the midline. The diaphragm (11) is sharply delineated and the costophrenic angles (12) must be sharp and free. b) Lateral chest radiograph. The lateral chest film can be used to localise better the findings on the frontal view. Numbers and symbols are as for a).