(in McClain et al). Sinus histiocytosis with massive lymphadenopathy involving a cervical lymph node.

A. Expanded lymph node sinuses filled with distinctive histiocytes in a background rich in plasma cells, foamy macrophages and small lymphocytes.

B. Distinctive histiocytes exhibiting emperipolesis where intact lymphocytes, some housed in vacuoles, are present within the cytoplasm.

C. Emperipolesis in a histiocyte with a prominent central nucleolus and a delicate nuclear membrane.

D. Immunohistochemical staining for the S100 protein highlights histiocytes with emperipolesis.