Basic imaging - chest X-ray (CXR)

Role

Chest X-ray is the first-line thoracic imaging investigation - rapid, low-radiation-dose, widely available - used to assess for pneumonia, effusion, pneumothorax, and cardiac silhouette abnormality, and to screen for gross intrathoracic pathology before deciding whether cross-sectional imaging is needed
The most frequently performed imaging investigation in both inpatient and outpatient settings given its speed, low cost, and low radiation dose relative to CT

Standard posteroanterior (PA) erect film provides the most reliable assessment of heart size and lung fields; anteroposterior (AP) supine films (common in unwell/bedbound patients) exaggerate cardiac silhouette size and reduce diagnostic accuracy for subtle findings - this technical difference should be accounted for when interpreting a portable inpatient film

Systematic review (airway, breathing/lung fields, cardiac silhouette, diaphragm, edges/soft tissue, foreign bodies/lines/tubes) avoids missing a focal abnormality when an obvious finding draws attention elsewhere
Lateral decubitus views can confirm a small pleural effusion suspected on the frontal film alone

Findings directly guide further investigation - a new consolidation supports empirical pneumonia treatment; an effusion prompts consideration of diagnostic/therapeutic thoracocentesis; an equivocal finding in a clinically unwell patient should prompt CT rather than repeated plain films

Community-acquired pneumonia, pleural effusion (parapneumonic/empyema), pneumothorax, line/tube position confirmation

A CXR can lag behind the clinical picture - early pneumonia or a small effusion may not yet be radiographically visible, so a normal film does not exclude infection in a clinically convincing presentation, and short-interval repeat or CT should be considered rather than treating a normal CXR as definitively reassuring

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