Positive pleural cytology is an indicator for visceral pleural invasion in metastatic pleural effusions.

INTRODUCTION: In case of undiagnosed pleural effusions, it is necessary to conduct thoracentesis with pleural fluid (PF) cytology. Yet, sensitivity of PF cytology is widely variable as a result of sample size, experience, and preparation method.

OBJECTIVES: The aim of this study was to assess whether pleural fluid (PF) cytology is correlated to visceral or parietal pleural invasion as assessed by thoracoscopy in metastatic pleural effusions.

METHODS: All records of patients with pleural effusion were reviewed. The inclusion criteria were as follows: PF cytology, reported appearance of macroscopic pleural invasion during thoracoscopy and malignant diagnosis. Patients with mesothelioma were excluded. Finally, 287 patients who met all criteria were selected. According to the thoracoscopy findings, the extent of the disease on the pleura was analyzed in relation to the PF cytology.

RESULTS: In this study, 160 patients (55.7%) had a positive PF cytology (Group A) while 127 (44.3%) recorded negative PF cytology (Group B). From Group A, patients with visceral pleural invasion were 120 (75%) while only 49 patients (38.5%) were found from Group B and the difference was statistically significant (P < .00001). In univariate analysis, visceral pleural invasion was strongly associated with positive PF cytology (P < .001). Other significant associations with positive PF cytology included PF bloody aspect (P = .012), and endoscopic mixed pattern of pleural invasion (P = .0039). Only visceral pleural invasion was statistically significant in multivariate analysis (P < .001).

CONCLUSIONS: In patients with pleural metastatic disease, visceral pleural invasion is the only significant factor associated with positive pleural fluid cytology.