Pericardial Fluid Cytology: Insights from a Five-Year Retrospective Review

Summary: Introduction: Pericardial effusion can occur in various medical conditions, including infections, malignancy, connective tissue disorders, and others. Cytologic evaluation of pericardial fluid (PF) is uncommon and primarily used to rule out malignancy. Materials and Methods: We conducted a retrospective study in our safety-net hospital, analyzing all pericardial fluid samples collected over the past five years (January 2019 - January 2024). Samples were obtained via ultrasound or image-guided pericardiocentesis. A total of 105 samples were collected from 97 patients (52 males and 45 females) aged 17 to 119. Results: Thin prep and cell block preparations were created for all 105 cases. Diagnostic categories were revised to fit The International System for Reporting Serous Fluid Cytology (TIS): nondiagnostic (ND), negative for malignancy (NFM), atypia of undetermined significance (AUS), suspicious for malignancy (SFM), and malignant (PFM). The distribution was as follows: 2 ND cases (1.9%), 76 NFM (72.3%), 9 AUS (8.5%), 4 SFM (3.8%), and 14 PFM (13.3%). Immunocytochemistry (ICC) was more frequently performed in AUS (3/9), SFM (4/4), and PFM (10/14) cases than in NFM cases. Adenocarcinoma was the most common malignant diagnosis (12/14), followed by squamous cell carcinoma (2/14), with the lung being the most frequent primary site. Molecular testing was conducted successfully in 6/14 PFM cases. ICC confirmed one SFM case as metastatic renal cell carcinoma, two AUS cases as reactive mesothelial cells, and one AUS as mantle cell lymphoma. Conclusions: PF specimens are uncommon. Despite the small volume submitted for cytologic evaluation, a specific interpretation was successfully rendered in the majority of cases, in conjunction with ICC (98.1%). Metastatic lung adenocarcinoma was the most frequent malignancy, with cell blocks being utilized successfully for molecular testing. ICC did not further refine the diagnosis in a significant number of AUS and SFM cases, emphasizing the importance of applying of TIS AUS criteria for such specimens to avoid overdiagnosis of atypia.