Unusual Focal Muscle FDG Activity Related to Altered Biomechanics.

A 20 year old man suffered severe right knee pain, especially when his right foot touched ground. The MRI findings suggested periosteal osteosarcoma, which led to a staging FDG PET/CT. The images showed not only a hypermetabolic right knee lesion but also focally elevated activity in select muscles, which was attributed to altered biomechanics. The resected lesion was pathologically proven as periosteal chondrosarcoma instead of periosteal osteosarcoma. In a follow-up period of 4 years after the surgery, there was no recurrent disease, nor any abnormality in the muscles which showed focal FDG activity on the initial FDG PET/CT.