Double "Density" Sign on Bone Scan

The double "density" sign, more properly referred to as the double uptake sign, is the scintigraphic pattern on osteoid osteoma on bone scan. The more intense central uptake on blood-flow, blood-pool and delayed phases of the bone scan represents the nidus of the lesion, while the lower, peripheral uptake, represents activity in the surrounding sclerotic reactive bone. The main differential considerations on radiographs include osteomyelitis, which has a more uniform pattern of radiotracer uptake, and abscess, which has decreased activity in the central cavity.