Which of the following terms or expressions refers to the presence of air that has dissected into the retroperitoneum?

A. pneumothorax.
B. pneumoperitoneum
C. pulmonary interstitial emphysema
D. tension pneumothorax

?ANS: B
A. Incorrect response: Pneumothorax is the presence of extra-alveolar air in the pleural space.
B. Correct response: Pneumoperitoneum is the presence of air or gas in the peritoneum. Pneumoperitoneum generally follows pneumomediastinum and results from air dissecting initially into the retroperitoneal space.
C. Incorrect response: Pulmonary interstitial pneumonia (PIE) refers to the dissection of air along vascular sheaths following alveolar rupture.
D. Incorrect response: A tension pneumothorax is a pneumothorax characterized by the continuous collection of air in the pleural space until the pressure reaches supra-atmospheric levels.