2025 Volume 64 Issue 3 Pages 148-154
Background : Reports of pleural mesothelioma with an abundance of lipid-rich mesothelial cells in the pleural fluid are extremely rare.
Case : The patient was a male in his 70 s. Chest CT revealed a tumor in the middle lobe of the right lung extending to the right chest wall, along with right pleural effusion. A percutaneous biopsy of the chest wall tumor revealed epithelial-like tumor cells within fibrous tissue. Immunohistochemical staining confirmed the tumor as an epithelioid mesothelioma. Concurrent cytology of the pleural fluid revealed numerous large cells with abundant vesicular cytoplasm. Giemsa staining showed that the cytoplasm of these cells was filled with numerous microvesicles that showed a negative reaction to PAS and Alcian blue staining, but a strongly positive reaction to neutral fat staining, indicating accumulation of neutral fat in the cytoplasm. Subsequent preparation of a cell block from the pleural fluid and immunocytochemical staining confirmed these large cells as malignant mesothelioma cells showing loss of BAP1 expression.
Conclusion : In cases of suspected mesothelioma in which cytology of body cavity fluids reveals abundant mesothelioma cells with vesicular cytoplasm rich in neutral fat, confirmatory immunocytochemical staining of cell blocks for mesothelioma is recommended.
