Lumbosacral Paravertebral Tophaceous Gout on an Adolescent Mimicking Malignant Neoplasm in 18 F-FDG PET/CT.

Contrast-enhanced MRI was performed on a 17-year-old adolescent boy with chronic lumbar and lower-limb pain, which had worsened over the past 3 days. It revealed a suspicious malignant mass adjacent to right appendage of L5-S1 vertebrae, with mixed signals and heterogeneous and obvious enhancement. 18 F-FDG PET/CT was subsequently performed for staging. It showed an FDG-avid mass with mixed density in right psoas major muscle, involving adjacent appendage of L5-S1 vertebrae. Histopathological examination confirmed the mass to be gouty tophus, characterized by nodular homogeneous pink amorphous deposits around the cartilage tissue, surrounded by histiocytes and multinucleated giant cells.