Extranodal Rosai-Dorfman Disease : Ileum
Microscopic features of Rosai-Dorfman disease of the gastrointestinal tract are similar to those seen in nodal and other extranodal sites. The lesion is composed of sheets of large, foamy histiocytes admixed with lymphocytes and plasma cells. The overlying mucosa is not involved or shows minor non-specific changes. Many of the histiocytes demonstrate empeipolesis - which refers to non-destructive phagocytosis of lymphocytes and plasma cells within the histiocytic cytoplasm (best seen in the next four images). The adjacent lymph nodes, when involved, show follicular hyperplasia, pericapsular fibrosis, and dilated sinusoids with abundant histiocytes demonstrating emperipolesis. Immunohischemistry will show strong reactivity in the histiocytes for S100, lysozyme, and CD68 but no staining for CD1a.