Clinical Practice: Thoracic and Cardiovascular Imaging
Core concepts
Chest radiography hinges on a systematic search pattern (airway, bones, cardiac silhouette, diaphragm, effusion, fields, gastric bubble, hila, hardware). Know the silhouette sign (loss of border indicates adjacent opacity) and air bronchograms as markers of alveolar rather than interstitial disease. For CT pulmonary angiography, understand the diagnostic criterion for pulmonary embolism (filling defect within a contrast-opacified artery) and the role of D-dimer and pretest probability (Wells score) in selecting imaging.
Traps in questions
- Mistaking a nipple shadow or companion shadow for a nodule; lateral or prior films resolve this.
- Calling a widened mediastinum traumatic aortic injury without mechanism and supporting signs (apical capping, left effusion).
- Confusing cardiomegaly with pericardial effusion on portable films.
- Forgetting that a normal chest radiograph does not exclude early interstitial lung disease; HRCT is more sensitive.
Rule of thumb
On an upright PA film, the right hemidiaphragm sits about one intercostal space higher than the left; if the left is higher, look for a cause (eventration, subphrenic process, prior surgery).
Worked example
A patient with pleuritic pain has a wedge-shaped peripheral opacity and a small effusion. The finding is most consistent with pulmonary infarction from PE; the next step is CT pulmonary angiography, not repeat radiography.