Extranodal Rosai-Dorfman Disease : Emperipolesis
Emperipolesis in a case of extranodal Rosai-Dorfman disease (RDD) involving terminal ileum. Emperipolesis refers to non-destructive phagocytosis of lymphocytes and plasma cells within histiocytic cytoplasm. The lymphocytes and plasma cells are contained in intracytoplasmic vacuoles (note the halo around contained lymphocytes) and thus protected from destruction by the hydrolytic enzymes of the histiocytes. Emperipolesis is a histologic hallmark which is required for the diagnosis; however, it is not specific for RDD and may be seen in other conditions. Erythrophagocytosis may also be present.