Background: The American College of Chest Physician (ACCP) has identifi ed 4 categories of parapneumonic effusion (PPE) to guide treatment. The modality in assessing anatomy of pleural fl uid is not well-defi ned, making differentiation of category 2 from category 3 PPE diffi cult. We investigated whether sonographic septation predicts category 3 PPE in guiding early pleural drainage.
Methods: Medical records of patients with lung abscess or pneumonia at admission were reviewed retrospectively. All patients had a plain chest radiograph upon admission. Patients classifi ed as AACP category 2 or 3 who underwent chest sonography with thoracentesis revealing non-purulent parapneumonic effusions with neutrophils predominance were included. Inter-observer variations in determining PPE category were analyzed. Further, positive predictive value (PPV), relative risk (RR) and reading agreement of positive sonographic septation in predicting category 3 PPE were determined.
Results: 51 patients of the total 97 recruited had sonographic septation. The reading agreement between thoracic radiologists in determining the category of pleural fl uid by plain chest radiograph was low with a kappa coeffi cient (κ) of 0.29. In contrast, reading agreement of positive sonographic septation was substantial (κ = 0.73). A signifi cantly higher PPV for category 3 effusion was observed in patients with sonographic septation (86.3%) compared to those with no septation (43.5%) (p < 0.001). The RR of category 3 PPE with sonographic septation was 1.98 (95% CI: 1.40-2.81; p<0.001).
Conclusions: Sonographic septation is a useful sign in predicting category 3 PPE, and may in conjunction with plain chest radiograph, enable a more accurate diagnosis or screening way of patients with lung abscess and pneumonia.