Pertinent findings on a normal neonatal chest X ray
The appearance of the thymus is variable. The “sail” sign refers to the thymus creating a triangular shadow of soft tissue along the mediastinal border on chest x-ray.
Always check for the side of the aortic arch (normally left sided); this may be difficult to do in newborns, and the side of the aortic arch may need to be inferred by observing that the descending aorta runs to the left of the spine and that the trachea is mildly deviated to the right.
Look at heart size. In contrast to adults, the normal cardiac-thoracic ratio may be 60%. The apex of the heart should be on the left (i.e., levocardia).
Pulmonary vascularity should be assessed. This assessment may be difficult, but some clues to increased vascularity include seeing vessels behind the liver density or noting that the right descending pulmonary artery is larger in diameter than the trachea.
Look at the bones (especially the vertebrae for any segmental anomalies), and note whether the humeral heads have ossified (this happens at 40 weeks of gestation).
Look under the diaphragm for organomegaly and the position of the stomach bubble (normally in the left upper quadrant.)
Since you are generally not going to forget to look at the lung fields, try to do that last to make sure they are clear.