Final answer:
A non-traumatic pneumothorax occurs without any evidence of trauma or injury. The most common cause is spontaneous pneumothorax, which is related to abnormalities in connective tissue.
Step-by-step explanation:
A non-traumatic pneumothorax refers to a collapsed lung that occurs without any evidence of trauma or injury. The most common cause of non-traumatic pneumothorax is a condition known as spontaneous pneumothorax, which is believed to be related to subtle abnormalities in connective tissue. In this condition, the lung tissue becomes weakened, leading to the formation of air-filled spaces called blebs or bullae. These blebs or bullae can rupture spontaneously, causing air to escape into the pleural space and resulting in the collapse of the lung.