title: Usefulness of the suspended microbubble sign in differentiating empyemic and nonempyemic hydropneumothorax.
abstract: OBJECTIVE
  The suspended microbubble sign is defined as the image seen on ultrasonography consisting of a pleural effusion strewn with numerous hyperechoic pinpoints and more or less linear shadows that move synchronously with respiration. In this study, we intended to evaluate the clinical usefulness of the suspended microbubble sign in differentiating empyemic and nonempyemic hydropneumothorax.
  
  
  METHODS
  This series consisted of 8 patients with empyemic hydropneumothorax and 23 patients with nonempyemic hydropneumothorax. The finding of the presence of the suspended microbubble signs on ultrasonography was recorded. To further elucidate the generation of the suspended microbubble sign, the interaction between air and pleural fluid of different types was investigated in vitro.
  
  
  RESULTS
  The suspended microbubble sign was shown on ultrasonography in all 8 patients with empyemic hydropneumothorax but was absent in the 23 patients with nonempyemic hydropneumothorax. These findings were supported by the observation that the pus seemed to mix with and trap the air more easily than did the nonpurulent pleural fluid, as shown in vitro. In this selected population, the sensitivity and specificity of the suspended microbubble sign in aiding a diagnosis of empyemic hydropneumothorax were both 100%.
  
  
  CONCLUSIONS
  The suspended microbubble sign shown on ultrasonography might be of considerable value in differentiating empyemic and nonempyemic hydropneumothorax.
authors.affiliation: Department, Veterans General Hospital-Taipei, and School of Medicine, National Yang-Ming University, Taiwan, Republic of China.
authors.forename: F C
authors.initials: FC
authors.lastname: Lin
authors.forename: C W
authors.initials: CW
authors.lastname: Chou
authors.forename: S C
authors.initials: SC
authors.lastname: Chang
mesh_terms: D003937:Diagnosis, Differential; D016724:Empyema, Pleural / Q000000981:diagnostic imaging*; D005260:Female; D006801:Humans; D006872:Hydropneumothorax / Q000000981:diagnostic imaging*; D008297:Male; D008875:Middle Aged; D012680:Sensitivity and Specificity; D013492:Suppuration; D014463:Ultrasonography