Journal of Ultrasound in Medicine, Vol 20, Issue 12 1341-1345, Copyright © 2001 by American Institute of Ultrasound in Medicine
Usefulness of the suspended microbubble sign in differentiating empyemic and nonempyemic hydropneumothorax
F. C. Lin, C. W. Chou and S. C. Chang
Department, Veterans General Hospital-Taipei, and School of Medicine, National Yang-Ming University, Taiwan, Republic of China.
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%.
CONCLUSION: The suspended microbubble sign shown on ultrasonography might
be of considerable value in differentiating empyemic and nonempyemic
hydropneumothorax.
