Pericardial Fluid Metastatic Tumor Distribution and Fluid Volume Analysis: A 10-Year Institutional Experience

Cytologic examination of pericardial effusions is critical for detecting malignant involvement, which carries a dismal prognosis. However, contemporary large-scale studies characterizing the distribution of metastatic tumors and the impact of submitted fluid volume on diagnostic yield remain limited. This study evaluates the distribution of metastatic tumors in malignant pericardial effusions and examines the relationship between specimen volume and likelihood of malignant cytologic diagnosis in a large institutional cohort.

A 10-year retrospective review was performed of all pericardial fluid cytology specimens accessioned at a large tertiary academic medical center. Clinical, radiologic, and cytologic findings were recorded. Cases categorized as suspicious for malignant cells (SFM) or malignant (MAL) were included in the metastatic tumor distribution analyses after reviewing tumor cytomorphology and immunohistochemical profiles in conjunction with clinical and radiologic data. Specimen volumes were stratified by diagnostic category, and threshold-based analyses at 50 mL and 100 mL were compared across diagnostic categories using statistical methods.

A total of 1,591 cases were identified from patients with a median age 65 years and a male-to-female ratio of 0.98. Most cases were negative for malignant cells (NFM) (78.6%), while 14.4% classified as malignant (MAL). Among malignant cases (SFM + MAL), carcinomas accounted for 83.5%, followed by hematolymphoid malignancies (14.0%); mesotheliomas, sarcomas, and melanomas were rare. Lung carcinoma was the most common primary tumor (48.0%), followed by breast carcinoma (16.0%) and B-cell lymphoma (7.8%). Submitted specimen volume increased progressively across diagnostic categories (p = 0.0010), with malignant cases demonstrating higher median volumes than negative cases. Specimens ≥50 mL showed a significantly higher malignancy rate compared with those <50 mL (18.4% vs. 10.6%, p < 0.001), corresponding to nearly twofold higher odds of malignancy (OR 1.91, 95% CI: 1.43-2.55). A smaller but statistically significant association was observed at the 100 mL threshold (OR 1.35, 95% CI: 1.06-1.82), with no additional benefit at higher thresholds.

In this 10-year institutional experience, malignant pericardial effusions were overwhelmingly metastatic in origin, most commonly arising from lung and breast carcinomas and hematolymphoid malignancies. Awareness of the metastatic distribution to the pericardium enhances diagnostic confidence and guides immunohistochemical workup on specimens with limited cellularity. Submitted fluid volume was significantly associated with a malignant cytologic diagnosis, with volumes ≥50 mL conferring nearly twofold increased odds of malignancy and diminishing incremental benefit beyond 100 mL. These findings support submission of at least 50 mL of pericardial fluid when clinically feasible to optimize diagnostic yield and inform appropriate ancillary testing.