Isolated Extranodal Rosai-Dorfman Disease on 18F-FDG PET-CT Scan.

Rosai-Dorfman disease (RDD) is an uncommon proliferative histiocytic disorder. Patients usually present with painless massive cervical lymphadenopathy with fever and leukocytosis. Isolated extranodal disease is rare and more severe fibrosis, fewer histiocytosis in lesions make diagnosis more difficult as compared to nodal disease. Here, we report a case of isolated extranodal RDD on fluorodeoxyglucose (FDG) positron emission tomography-computed tomography (PET-CT) scan. FDG-avidity of RDD lesions is attributable to the intense glucose dependence of the proliferating histiocytes. PET-CT scan not only demonstrates the complete staging of the disease but also provide functional information about the disease activity to guide biopsy.