What imaging modality is considered the gold standard for pleural effusion?

• A. Upright PA and lateral chest X-ray
• B. CT chest w/ or w/o contrast
• C. Ultrasound of chest
• D. MRI chest

Answer: (A)

The main idea is that an upright chest X-ray with both PA and lateral views is the classic first-line imaging to detect a pleural effusion. Fluid settles at the bases, causing blunting of the costophrenic angles on the frontal view and posterior layering on the lateral view. This modality is quick, widely available, and inexpensive, making it the standard initial test to confirm an effusion and to give a rough sense of its size.

While ultrasound is more sensitive for detecting small effusions and is excellent for guiding drainage, and CT provides detailed characterization when needed, the upright chest X-ray is traditionally regarded as the standard starting imaging in many clinical settings.