Falsely Negative F-18 FDG PET of Osteosarcoma Arising In Paget Disease

We present the case of a large, painful pelvic bone tumor in a 53-year-old woman with severe Paget disease. Her presentation was complicated with bilateral total hip arthroplasty, history of spinal stenosis, and multiple lucent lesions in the spine and pelvis in severely affected pagetoid bone. This case features the rare but dreaded complication of osteosarcomatous transformation in Paget disease. A variety of imaging modalities including PET/CT were utilized in the evaluation of these lesions. The PET/CT findings were counter-intuitive with regard to the intense uptake of the underlying chronic disease process and the near-absence of uptake in the tumors. The histology of the pelvic mass is also intriguing, as it demonstrated a sarcoma with giant cell features. Conservative, non-operative management was chosen, due to the patient's poor medical condition, so we may never know the nature of the spinal lesion in this case, but will discuss the differential diagnosis for a lytic spinal lesion in a patient with severe Paget disease complicated by osteosarcoma with giant cell features.