Avid uptake of [18F]-FDG in fibrous dysplasia can mimic skeletal involvement in Hodgkin’s disease

Abstract

Fibrous dysplasia is a common benign skeletal disorder that is assumed to result from a development failure during the bone maturization process. It can be either mono- or polyostotic. Most patients present before the age of 30 years [1]. To date, only a few descriptions of the appearance of fibrous dysplasia on [ 18 F]-fluorodeoxyglucose–positron emission tomography (FDG PET) images have been reported in the literature [2, 3]. We present here the case of monostotic fibrous dysplasia which was detected through the avid uptake of [ 18 F]-FDG. A 12-year-old boy was diagnosed with Hodgkin’s disease. The initial [ 18 F]-FDG PET images showed cervical lymphadenopathy and an avid tracer uptake in the right proximal femur. This finding was interpreted as skeletal involvement of lymphoma, thus defining clinical stage IV disease. After four courses of chemotherapy, a second [ 18 F]-FDG PET (a) was performed for response evaluation. At this time, pathologic tracer uptake was only seen in the right proximal femur (a, arrow), and we therefore considered residual lymphoma in the differential diagnosis. The corresponding radiograph (b) revealed an ill-defined area of ground-glass opacity and a cortical thickening (b, arrowhead). Magnetic resonance imaging showed the lesion to be hypointense in T1weighted sequences and hyperintense in T2-weighted sequences, and demonstrated a strong uptake of contrast medium (c). Due to the significant implications of possible residual lymphoma, open biopsy was performed. The hematoxylin and eosin-stained section (d) showed typical features of fibrous dysplasia with randomly organized trabeculae of woven bone surrounded by immature fibrous tissue.