Answer: Rosai-Dorfman disease

Histology: none provided

Discussion: Diff Quik stained touch prep shows a mixed population of small lymphocytes admixed with foamy macrophages and scattered large histiocytes with lymphophagocytosis (emperipolesis). No lympho-glandular bodies are identified. H&E stained sections show marked dilatation of the sinuses with partial effacement of the lymph node architecture. The dilated sinuses are filled with lymphocytes, plasma cells, and large histiocytes with abundant eosinophilic cytoplasm. Numerous large histiocytes with lymphophagocytosis are also present. Immunostains demonstrate that the histiocytes filling the sinuses are S-100 positive and CD1a negative consistent with sinus histiocytosis with massive lymphadenopathy (Rosai-Dorfman disease).

The etiology of Rosai-Dorfman disease (RDD) is not known. In the majority of cases, RDD undergoes complete resolution, in others chemotherapy can be effective. The clinical course can also be protracted for years or decades. In other cases, the disease may show spontaneous resolution and then recurs years later.

The differential diagnosis includes non-specific sinus hyperplasia (the cells are S-100 negative and lack emperipolesis), Langerhans’ cell histiocytosis (the cells are both S-100 and CD1a positive) and sinus histiocytosis induced by cobalt-chromium or titanium in pelvic lymph nodes of patients with hip prosthesis. RDD-like changes can also occur in Hodgkin’s and non-Hodgkin’s lymphoma.