Extranodal Rosai–Dorfman Disease Arising in the Right Atrium

Rosai–Dorfman disease is a rare, benign histiocytic proliferative disorder that commonly affects the lymph nodes. Although extranodal involvement has been reported in diverse sites, manifestation in the cardiovascular system is extremely uncommon. Specifically, the involvement of the heart by Rosai–Dorfman disease is an extraordinarily infrequent event. Here, the authors present a case of Rosai–Dorfman disease arising in the right atrium in a symptomatic 61-year-old man who initially presented with pleuritic chest pain and was found to have a large, lobulated, and circumscribed right atrial mass. The lesion exhibited an exuberant histiocytic and chronic fibroinflammatory process with focal emperipolesis within histiocytes. Immunohistochemical studies demonstrated strong S100 positivity in CD68+ CD1a− histiocytes. Although rare, Rosai–Dorfman disease should be considered in the differential diagnosis of a right atrial mass.