Fibrous dysplasia (FD) is a common benign bone disorder of an unclear etiology. It is known that FD can appear without an increased FDG uptake on F-18 fluorodeoxyglucose positron emission tomography/computed tomography (FDG-PET/CT). However, there are also several reports that FD showed increased FDG uptake and this mimicked malignant bone involvement on FDG-PET. Herein we describe a case of biopsy-proven FDG-PET positive FD in a patient with intestinal non-Hodgkin's lymphoma (NHL). A 45-year-old woman was diagnosed with intestinal NHL, which was removed by right hemicolectomy. After the operation, the FDG-PET/CT scan showed hypermetabolic activity in the right transverse process of the T10 vertebra. The patient then received a total of 6 cycles of R-CHOP (rituximab, cyclophosphamide, doxorubicin, vincristine, and prednisolone) chemotherapy every 3 weeks. After completion of the planned chemotherapy, the 2^nd FDG-PET/CT showed increased FDG uptake (SUVmax=6.0 g/mL) of the previous bone lesion. The MR images revealed a T1-hypointense lesion with sharp borders in the same region, and this showed homogenous contrast enhancement on the fat-suppressed T1-weighted images. After the radiologic studies were carefully reviewed, the bone lesion was assumed to be benign such as FD. We performed bone biopsy and the histological examination confirmed the diagnosis of FD. In conclusion, bone lesions with FDG uptake need to be carefully interpreted when evaluating patients with known malignancy.

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