Lessons From the Friday Unknowns
Histologic sections show a nodule involving fibroadipose tissue. The nodule is composed of many lymphocytes and histiocytes and has some features suggestive of lymph node. However, there is no capsule or subcapsular sinus and therefore we believe this process is extranodal and mimicking a lymph node.
The lesion is composed of many histiocytes with abundant pale cytoplasm and central nuclei. Some of these histiocytes contain lymphocytes within their cytoplasm, evidence of emperipolesis. There are also many small lymphocytes and mature plasma cells.
Immunohistochemical studies show that the histiocytes are positive for S100 protein and cyclin D1, and are negative for CD3 and CD20. Many of the lymphocytes in the cells with emperipolesis are CD3+ T-cells.
These findings support the diagnosis of Rosai-Dorfman disease.
Link to digital slides : bit.ly/3w5aao1 | Slides labeled case 5