Clinical Utility of Pleural Tissue Debris Incidentally Obtained During Drainage of Pleural Effusion: A Retrospective Cohort Study

Background/Objective: The incidence and clinical utility of pleural tissue debris, occasionally encountered in drainage systems, have not been systematically evaluated. We aimed to determine the frequency of tissue debris detection in patients undergoing drainage for pleural effusion, and its utility for the differential diagnosis of exudative effusion and pathological diagnosis of malignant pleural effusion (MPE). Methods: This retrospective proof-of-concept analysis included 325 consecutive patients who underwent percutaneous effusion drainage. The incidence, histopathological findings, and potential predictors of tissue debris were evaluated. For patients with MPE, the adequacy of tissue for immunohistochemistry and molecular testing was evaluated, and the diagnostic sensitivity of tissue debris for MPE was calculated and compared with that of cytology with cell blocks. Results: Tissue debris was detected in 151 patients (46.5%), more frequently in exudates than in transudates (51.7% vs. 23.3%, p < 0.001), and most frequently in patients with MPE (64.6%, p < 0.001). MPE was the only independent predictor of tissue debris detection (adjusted odds ratio 5.74, 95% CI 2.25–9.31). The pathological findings of the debris were classified into metastatic carcinoma/lymphoma (49.0%), acute/chronic inflammation (30.4%), fibrinoid material with inflammation (17.2%), mesothelial reaction (2.6%), and acute suppurative pleuritis/abscess (0.7%). Among the 74 cases with MPE diagnosed using tissue debris, immunohistochemistry and molecular testing were feasible in 85.1% and 69.0% cases, respectively. Diagnostic sensitivity of tissue debris for MPE was significantly higher than that of cytology (77.9% vs. 66.3%; p = 0.035) with a combined sensitivity of 84.2%. Conclusions: Systematic collection of tissue debris, a previously underrecognized clinical specimen obtained during effusion drainage, may be highly valuable for the diagnosis of MPE and adequate for immunohistochemistry and molecular testing, reducing the reliance on invasive biopsy and supporting precise oncological decisions.