Extranodal Rosai-Dorfman disease involving appendix and mesenteric nodes with a protracted course: report of a rare case lacking relationship to IgG4-related disease and review of the literature.

Rosai-Dorfman disease (RDD), also known as sinus histiocytosis with massive lymphadenopathy, is a rare disease of unknown etiology that typically presents as nodal disease in young children. However, it also can present in various extranodal sites and can be difficult to recognize if not considered in the differential diagnosis. Here, we report a case of appendix involvement by extranodal RDD, which occurred in a 69-year-old woman with a long duration of 12 years for intermittent right lower quadrant pain. The patient underwent a right hemicolectomy for a clinical diagnosis of appendiceal cancer. A mixed inflammatory infiltration of mature lymphocytes, plasma cells and histiocytes exhibiting emperipolesis were indentified. Other areas had storiform fibrosis and sclerosis admixed with numerous plasma cells. These histologic features combination with immunoreactivity for CD68 and S100 protein were indicative of a diagnosis of extranodal RDD. We discuss the clinical, pathologic findings as well as differential diagnoses and consideration of a possible relationship of this entity to IgG4-related lesion.