Extranodal Soft Tissue Rosai Dorfman Disease with Floret Cells Involving the Inguinal Region, Masquerading as Inflammatory Liposarcoma. Report of a Case Featuring Increased IgG4 Positive Plasma Cells

Rosai Dorfman disease (RDD) is a rare histiocytic proliferative disorder of unknown pathogenesis that had been originally described in lymph nodes, but was found to occur in different visceral organs and anatomic sites as well. We report herein a patient who presented with a mass in the inguinal region which was initially diagnosed on core biopsy as inflammatory pseudotumor, then as inflammatory liposarcoma on excision of the mass. The patient was referred to our hospital for further management. On review of the histopathological material, we made the diagnosis of extranodal soft tissue Rosai Dorfman disease (ENST-RDD) by the identification of the characteristic S100-positive histiocytes demonstrating emperipolesis. We noted the presence of floret cells, which probably prompted the earlier diagnosis of inflammatory liposarcoma. The presence of these cells had not been documented in earlier reports on ENST-RDD. In addition, there was heavy IgG4 positive plasma cell infiltration associated with storiform fibrosis in the same lesion, probably pointing to a link between ENST-RDD and IgG4-related disorders.