Ideally a clinical diagnosis treated emergently (without delay for studies)
CXR
Lung ultrasound
No lung sliding seen (not specific for pneumothorax)
May also identify "lung point": distinct point where you no longer see lung sliding (pathognomonic)
Absence of lung sliding WITHOUT lung point could represent apnea or right mainstem intubation
Evaluate other intercostal spaces because pneumothorax may only be seen in least dependent area of thorax
NO comet tail artifact
Bar Code appearance/"Stratosphere" sign on M-mode (absence of "seashore" waves)
Ultrasound has greater sensitivity than chest x-ray for pneumothorax in trauma patients 
NO comet tail artifact
Bar Code appearance/"Stratosphere" sign on M-mode (absence of "seashore" waves)
Tension pneumothorax
Spontaneous pneumothorax
Hemothorax
Catamenial pneumothorax
Chylothorax
Traumatic pneumothorax
Iatrogenic pneumothorax
Pneumopericardium