Emperipolesis in pleural fluid mesothelial cells. A phenomenon not associated with Rosai-Dorfman disease, report of a case.

Emperipolesis is a cell-within-cell phenomenon distinct from phagocytosis more often described in Rosai-Dorfman disease, where usually lymphocytes or other bone marrow cells (plasma cells, erythroblasts or neutrophils) are entirely surrounded but not engulfed by macrophages as the host cell, but occasionally megakaryocytes and neoplastic could be. Mesothelial cell has been described in a couple of cases of lymphomas affecting serous membranes, but never described in pleuritis. In the present work, the first case of emperipolesis by mesothelial cells in a patient with self-limited pleural effusion was demonstrated by immunohistochemistry and Electron Microscopy studies.