Pneumothorax is air in the pleural space.

Radiological criteria:

Tension: Make a decision about tension by evaluating the clinical situation, BP and pulse. Radiologic signs are not reliable. The size of pneumothorax or shift of mediastinum do not suggest tension. Mediastinum will be shifted to the opposite side even without tension, as the negative pressure is relatively more compared to the side with pneumothorax. A very small pneumothorax in a patient with pre-existing lung disease can cause more symptomatic findings.