Study objective: To report the etiology of large and massive pleural effusions, and to compare their biochemical fluid characteristics with those of smaller size, and between malignant and nonmalignant conditions.
Design: Retrospective chart review of all patients undergoing thoracentesis at an academic medical center in Lleida, Spain, during a 10-year period.
Patients: Posteroanterior chest radiographs were available in 766 patients during the study period. Large pleural effusions (ie, two thirds or more of the hemithorax without its complete obliteration) were identified in 70 patients (9%), and massive pleural effusions (ie, hemithorax was completely opacified) were identified in 93 patients (12%).
Results: A similar etiologic spectrum between large and massive pleural effusions was observed. The most frequent cause of these pleural effusions was malignancy (89 patients; 55%), followed by complicated parapneumonic or empyema (36 patients; 22%), and tuberculosis (19 patients; 12%). Compared with nonmalignant pleural effusions, patients with large or massive malignant pleural effusions were more likely to have pleural fluids with higher RBC counts (18.0 × 109 cells/L vs 2.7 × 109 cells/L, respectively; p < 0.001) and lower adenosine deaminase (ADA) activity (11.5 vs 31.5 U/L, respectively; p < 0.001), which were the two parameters that were selected by a stepwise logistic-regression model as independent predictors of malignancy. In addition, large/massive malignant pleural effusions showed higher median RBC counts (18.0 × 109 cells/L vs 4.3 × 109 cells/L, respectively; p < 0.001), higher lactate dehydrogenase levels (641 vs 409 U/L, respectively; p = 0.001), lower pH (7.39 vs 7.42, respectively; p = 0.006) content, but similar cytologic yield (63% vs 53%, respectively; p = 0.171) than smaller malignant pleural effusions.
Conclusions: The presence of a large or massive pleural effusion enables the clinician to narrow the differential diagnosis of pleurisy, since most effusions are secondary to malignancy or infections (either bacterial or mycobacterial). Bloody pleural fluid with low ADA content favors a malignant condition.