Did you see the opacity on the right> But did you noticed the hyperlucent, widened and deepend left costophrenic sulcus?… aka Deep Sulcus sign .. signifying a basilar pneumothorax in this supine patient.

These aren’t easy but you can provide major clinical assistance to the clinical team when you see them (of course chances are the CT is on it’s way)

Short reference: http://radiology.rsna.org/content/228/2/415.full.pdf