Cytopathology of extramedullary hemopoiesis in effusions and peritoneal washings: a report of three cases with immunohistochemical study.

The clinical, cytopathologic, and immunohistochemical features of three cases of extramedullary hemopoiesis are presented. Differentiation of megakaryocytes from malignant cells can be difficult in cytologic material; we believe familiarity with cytologic features of megakaryocytes, along with factor VIII-related antigen immunoreactivity, is helpful in providing an accurate diagnosis.