Background
Accurate interpretation of chest radiographs can be challenging especially for residents. Detection of subtle abnormalities is facilitated by the knowledge of several rules. This presentation aims to teach the viewer these rules using an image rich case-based approach. Each case will highlight a broken rule and use the case to teach the viewer the interpretation of chest radiography. In addition, CT correlates explaining the radiographic changes will be provided. The case will end with a teaching point.
Educational Goals / Teaching Points
Examples of this rule-based approach include the three laws of the hilum, including shape, density, and position of the hila with respect to each other. Chest radiograph examples of displaced paraspinal lines will differentiate the normal and abnormal appearances. Additional teaching points will review the density of the right paratracheal vasculature with respect to the aorta, the density of the cardiac silhouette on both sides of the spine, the size of the trachea in reference to the vertebral body, the position and the sharpness of the costophrenic angles, the size of the azygous vein, symmetrical apical pleural thickening, the density of the liver in the right upper quadrant, the distance of the stomach bubble from the left hemidiaphragm, and the aortopulmonary window interface, etc.
Key Anatomic/Physiologic Issues and Imaging Findings/Techniques
This presentation will help the viewer identify sometimes subtle abnormalities on chest radiographs on the basis of interpretation rules that when broken can indicate underlying pathology or anatomical variance. Some examples of these rules include: the right hilum is always lower or at the same level as the left, both hila should be equal in density, and the hilar vessels should maintain concavity towards the mediastinum. Right paratracheal opacity should be less than the aortic density. The azygous vein measures less than 1.1 cm in diameter. The aortopulmonary interface should be a straight line or concave inwards. The top of the liver should be half as dense as the middle.
Conclusion
This case-based review will outline a series of rules that when broken indicate a chest radiograph abnormality. In addition to improving one's ability to identify the abnormality, this presentation will help the learner consider and provide a differential as well as recommend further evaluation when indicated.
