PET imaging of Rosai-Dorfman disease: correlation with histopathology and ex-vivo beta-imaging.

We report the case of a woman who developed an early relapse of a squamous cell carcinoma (SCC) and was thus restaged twice within a year using [(18)F]fluorodeoxyglucose (FDG) positron emission tomography (PET). While there was no evidence of metastatic tumor outspread, focally increased FDG uptake was visible in numerous nodes but showed no change during the period between the two PET scans. These nodes, predominantly located at the proximal extremities, ranged in size from about 1 cm to over 6 cm. They were located subcutaneously, showed a red/bluish livid color and were of stout consistency. These nodes occurred first after radiochemotherapy for a non-Hodgkin's lymphoma (NHL) about 6 years earlier and slowly increased in size and number. One node of the right forearm was resected and ex-vivo beta-imaging, directly measuring the positron emission of the intranodal FDG distribution, was done and showed an overall increased glucose utilization with distinct spots of high metabolism. Histopathological work-up of the tumor showed widespread granulomatous tissue with lymphocyte follicles. Immunostaining showed the tumor to be positive for S100, CD68 and vimentin. Rosai-Dorfman disease (RDD) was diagnosed and no evidence of a potential relapse of the previous NHL was detected. RDD is a rare disease that is associated with the multifocal growth of benign tumors. The lesions are metabolically highly active. The correlation of the beta-imaging and histopathological results showed a high metabolism within granulomatous tissue with more intense metabolism within lymphocyte follicles.