F-18 FDG PET/CT imaging of follicular dendritic cell sarcoma of the mediastinum.

A 52-year-old female smoker presenting with unexplained weight loss underwent CT and FDG PET/CT imaging, which demonstrated an extremely hypermetabolic mediastinal mass with calcification, necrosis, and features of local invasiveness. Mediastinoscopy and biopsy were followed by successful surgical resection of an encapsulated mass showing the typical histologic features of follicular dendritic cell sarcoma (FDCS). FDCS of the mediastinum is a rare neoplasm arising from accessory cells of the immune system. Integrated FDG PET/CT of mediastinal FDCS highlights the importance of histologic assessment of mediastinal tumors that may seem unresectable on initial imaging.