Fibrous Dysplasia Presenting as a Cold Spot in 18F-FLT PET/CT Imaging.

Fibrous dysplasia (FD) is a benign bone lesion in which normal bone marrow is replaced by fibro-osseous tissue. The usual high fluorodeoxyglucose (F-FDG) uptake in FD may lead to the misdiagnosis of bone malignancy. Herein, we describe the case of a 42-year old man with histologically verified FD of the pubic bone, which has been subsequently examined during follow-up for rectal cancer, using both F-FDG and fluorothymidine (F-FLT) PET/CT imaging. The FD lesion was characterized by a high uptake of F-FDG (hot spot) but very low uptake of F-FLT (cold spot) as compared with the contralateral unaffected pubic bone.