Which projection best demonstrates a suspected pneumothorax when a patient can sit up?

• A. Upright chest radiograph (PA or AP)
• B. Supine chest radiograph
• C. Lateral chest radiograph
• D. AP oblique chest radiograph

Answer: (A)

Free air in the pleural space rises to the highest point in the chest, so an upright chest radiograph is the most sensitive way to detect a pneumothorax when the patient can sit up. In this position, air collects at the apices and pulls the visceral pleura away from the chest wall, creating a visible pleural line with absent lung markings beyond it. This makes even small pneumothoraces easier to spot.

A supine view distributes air along the front and back of the chest, often layering it over structures like the heart and mediastinum, which can hide a small pneumothorax and reduce visibility. A lateral view can reveal a pneumothorax, but it’s less reliable than an upright projection for capturing air at the apex. An AP oblique view isn’t the standard primary method for this indication and isn’t as effective at showing the pleural line clearly in this context.