Pneumothorax ex vacuo.

Pneumothorax ex vacuo is a little-known complication of lobar collapse. In this condition, acute bronchial obstruction from mucous plugs, aspirated foreign bodies, or malpositioned endotracheal tubes causes acute lobar collapse and a marked increase in negative intrapleural pressure around the collapsed lobe. As a result, gas is drawn into the pleural space around the collapsed lobe while the seal between the visceral and parietal pleura of the adjacent lobe or lobes remains intact. The pneumothorax spontaneously resolves when the bronchial obstruction is relieved and the lobe reexpands. Recognition of pneumothorax ex vacuo is crucial in directing treatment to relieve the bronchial obstruction rather than inserting a chest tube into the pleural space.