Primary epithelial malignant mesothelioma of the pericardium with deciduoid features: cytohistologic and immunohistochemical study

Malignant mesothelioma with deciduoid features (MMWDF) is a recently characterized morphologic variant of epithelioid malignant mesothelioma, which frequently is misdiagnosed as peritoneal deciduosis or florid mesothelial hyperplasia. We report on the cytological, histological, immunohistochemical, and autopsy findings of a case of MMWDF arising in the pericardium of a 71-yr-old female patient. Cytology showed large, polygonal to round cells with pale to bright, eosinophilic cytoplasm, occasionally showing xantomatous pattern, containing a pleomorphic and vesicular nucleus with a single prominent nucleolus. Autopsy examination showed a neoplasm encasing the heart and great vessels. No other primary neoplasm was found. The histological analysis disclosed the typical features of MMWDF. Immunohistochemistry showed diffuse immunoreactivity for cytokeratin MNF116, HBME-1, and calretinin in the neoplastic cells, as well as focal positivity for epithelial membrane antigen positivity in a brush border-like pattern. All other markers were negative. We would like to stress that pathologists must be aware of the cytological and histological features of this rare variant of epithelioid malignant mesothelioma in order to avoid a misdiagnosis of a benign process or a metastatic malignancy.