Background: Differentiation between pyopneumothorax and lung abscess can be difficult but has important therapeutic consequences. The role of chest ultrasonography in this issue remains undetermined. Sonographic features of hydropneumothorax and/or pyopneumothorax are characteristic and not difficult to recognize. In this study, the authors evaluate the usefulness of a panel of sonographic findings characteristic of hydropneumothorax in distinguishing pyopneumothorax from lung abscess.
Methods: This series included 16 patients with lung abscess and 19 with pyopneumothorax. A diagnosis of lung abscess or pyopneumothorax was based on the following criteria: pus aspiration from the lesion, appropriate clinical setting, thoracic computed tomographic findings, serial follow-up of chest radiograms, and consistent clinical course. The panel of sonographic features suggestive of hydropneumothorax, including the presence of air-fluid level, the curtain sign, loss of gliding sign above the air-fluid level, and the suspended microbubble sign, were recorded and analyzed by a consensus of blinded readers. In addition, sonographic features used to differentiate empyema and lung abscess were also evaluated.
Results: The results indicated that the presence of air-fluid level, the curtain sign, loss of gliding sign above the air-fluid level, and the suspended microbubble sign were valuable in distinguishing pyopneumothorax from lung abscess. All four sonographic findings were observed in 17 of 19 patients with pyopneumothorax. In contrast, two or fewer sonographic findings were seen in 16 patients with lung abscess. Our results confirmed that the wall characteristics, shape of the lesion, chest wall angle, and pleural separation were also useful.
Conclusions: The panel of sonographic findings is of considerable value in differentiating pyopneumothorax and lung abscess.