How do you rule out empyema in a small pleural effusion that is not amenable to thoracentesis?  

Ultrasonographic findings indicate empyema, such as complex septated or non-septated/echogenic effusions Wang et al., PMID 35984158. However, if the effusion is too small, it may be difficult to characterize, limiting the diagnosis. Moreover, when the effusion is so small, the likelihood of empyema ...