Diagnostic Accuracy of Pleural Fluid Cytology and The Predictive Value of Visceral Pleural Involvement: Correlation with Pleural Biopsy Histopathology

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Background: Pleural effusion is a frequent presentation of infectious/inflammatory and neoplastic diseases. Despite its noninvasive nature, pleural-fluid cytology has a variable sensitivity for malignancy and can be negative or indeterminate, necessitating a definitive diagnosis by pleuroscopic biopsy. This study analyzed the diagnostic performance of pleural-fluid cytology and its associations with pleural biopsy results in relation to visceral pleural involvement and lymphocytic predominance. Methods: An analytical cross-sectional study with retrospective data retrieval and prospective case accrual was conducted among 65 patients with pleural effusion who had underwent medical pleuroscopy with pleural biopsy. The study retrospectively reviewed clinical, pleuroscopic, cytological and histopathological data. Cytology of pleural fluid was available for 58 patients, and it was classified according to the International System for Reporting Serous Fluid Cytopathology. The reference standard was histopathology of pleural biopsy specimens. Sensitivity, specificity, positive predictive value, negative predictive value and overall diagnostic accuracy were computed. Results: Of the 65 patients, histopathological examination revealed benign pleural lesions in 39 (60.0%) and malignant lesions in 26 (40.0%). Visceral pleural involvement was seen in 31 patients (47.7%) and correlated significantly with neoplastic nature. Biopsy results came back as malignant in 54·8% of patients with visceral involvement versus 26·5% without (P=0.020). The cytological classifications of the pleural fluid were strongly correlated with the histopathological diagnosis (P < 0.001). All 5 cases designated as atypia of undetermined significance and all 11 cases marked as suspicious for malignancy were malignant on biopsy. The sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV), and the overall accuracy of cytology was 65.4%, 96.9%, 94.4%, 77.5% and 82.8% respectively. The ratio of lymphocytic predominance was not significantly correlated with the biopsy (P = 0.072). Conclusions: Pleural-fluid cytology is both a highly specific and clinically useful first-line investigation for malignant pleural disease, but its moderate sensitivity limits the reliability of negative tests. Malignancy is more common with visceral pleural involvement and could help try to guide site of biopsy. While cytology analysis is the first-line test in a suspected malignancy, pleural biopsy continues to be indicated when cytology is negative, atypical or inconsistent with clinical or pleuroscopic suspicion.

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