Figure 1: CT neck
CT neck showing a large left posterior neck mass involving several lymph nodes.
Figure 1-H&E
The low power H&E image demonstrates multifocal pale eosinophilic areas and higher power demonstrates that these pale areas comprise accumulations of large bland histiocytes with abundant pale eosinophilic cytoplasm with intermingled lymphocytes and plasma cells. Higher power demonstrates that these histiocytes have small but distinct nucleoli.
Figure 2-CD3, CD20 & CD138
CD3 immunostain (top left) highlights numerous background T cells. However, Rosai-Dorfman lesions frequently contain excess of CD20 positive B cells (top right). There is prominent plasmacytosis noted on the CD138 immunostain depicted on the bottom left. Frequently, there is excess of IgG4 positive plasma cells and Rosai-Dorfman lesions. However, in this case IgG4 positive plasma cells were not increased.
Figure 3-CD1a
CD1a, a marker of Langerhans cells is negative. This allows exclusion of Langerhans' cell histiocytosis.
Figure 4-S100
The Rosai-Dorfman histiocytes are strongly positive for S100 with nuclear and cytoplasmic staining. On higher power, emperipolesis with lymphocytes present in the cytoplasm of these histiocytes is apparent. Emperipolesis is characteristic features in this disease.
