Fig. 1.

A 20-year-old man underwent a whole-body ¹⁸F-FDG PET/CT scan for the re-evaluation for recurred metastatic osteosarcoma of T2-T5 with paravertebral extraosseous soft tissue extension to the bilateral neural foramen and paravertebral soft tissues (blue arrows) shown on axial (a) and sagittal (b) magnetic resonance images. Three months ago, he had undergone a corpectomy of T3 with laminectomy of T2-T5, and posterior arthrodesis due to metastatic osteosarcoma after limb salvage surgery, and adjuvant chemotherapy for primary osteosarcoma of his right tibia. In addition to recurring tumors, axial tomographic (c-e) and maximum intensity projection (f) images of ¹⁸F-FDG PET/CT show asymmetric increased uptakes (red arrows) in the fatty tissues of the left cervical, supraclavicular, axillary, and thoracic paravertebral spaces, which were considered as increased brown fat activities