Introduction: Malignant pleural mesothelioma (MPM) is an aggressive malignancy arising from mesothelial cells lining the pleura. Most commonly, it presents as a unilateral pleural effusion. MPM usually develops on the parietal pleural surface and later spreads to the visceral pleura. Visceral pleural involvement entails a more advanced disease stage and is therefore an important prognostic factor. Pleural fluid (PF) cytology is often the first diagnostic test, but the sensitivity in the literature varies from 4 to 77%. However, no data are available for the diagnostic yield of cytological PF analysis with regard to the visceral pleural involvement. The aim of this study is to assess whether PF cytological yield is related to the extent and pattern of visceral pleural invasion, as assessed by thoracoscopy.
Methods: Medical records of all patients who underwent thoracoscopy for suspicion of malignant pleural effusion from two hospitals were reviewed. Patients were selected if they initially underwent a diagnostic thoracentesis before thoracoscopy, if visceral pleural appearance during thoracoscopy was clearly documented, and MPM confirmed on pleural tissue biopsy.
Results: Seventy-five patients were selected. Forty-five patients had a positive PF cytology on thoracentesis, while 30 had a negative PF cytology. Thoracoscopy showed parietal pleural invasion in all subjects. Interestingly, 82% of patients with positive PF cytology on thoracentesis had visceral pleural involvement, whereas only 30% of those with negative PF cytology had visceral pleural invasion. The pattern of visceral pleural invasion consisted of pleural masses, nodules, or pleural thickening. A multivariate regression identified visceral pleural invasion (p < 0.001) as the only independent factor predicting the positivity of cytology on pleural effusion.
Conclusion: In epithelioid MPM, PF cytological yield was significantly higher in patients with visceral pleural invasion assessed by thoracoscopy. Positive PF cytology is associated with a more advanced disease.