Role of ultrasound in differentiating simple parapneumonic from complicated parapneumonic pleural effusion

Thoracic ultrasound (TUS) is a standard procedure to identify pleural effusions, but its diagnostic accuracy in differentiating CPPE from simple parapneumonic effusions (SPPE) requires further investigation.

Can TUS accurately differentiate CPPE from SPPE in patients with parapneumonic effusions?

and Method: This is a retrospective analysis of all adult patients with parapneumonic effusion. TUS findings were categorized as echogenic (septated or non-septated) or non-echogenic. CPPE was biochemically defined if any of the PFA criteria were met (positive gram stain/culture, pH < 7.20, glucose <60 mg/dL, lactate dehydrogenase >1000 IU/L, or gross pus). Diagnostic test characteristics (sensitivity, specificity, PPV, NPV, LR+, LR-) were calculated.

A total of 175 parapneumonic effusions were analyzed. CPPE and SPPE distribution was nearly equal (52 % vs. 48 %). Echogenic findings seen in TUS had high sensitivity (92 %) and high NPV (89 %) for CPPE but low specificity (65 %). Notably, 29/83 (35 %) patients with biochemically defined SPPE had discordance in the TUS findings of echogenicity. Half of these discordant SPPEs required thrombolytics or surgery.

TUS demonstrating echogenicity is highly sensitive for detecting CPPE, and the absence of echogenicity makes CPPE unlikely. However, a third of patients with biochemically defined SPPE had echogenic effusions on TUS, and half of these discordant biochemical SPPE required additional interventions such as thoracic surgery or intrapleural enzyme treatment. Therefore, TUS findings should be integrated with PFA to guide management decisions in parapneumonic effusions.