Musculoskeletal ImagingDouble density sign
an indication of
intervertebral disc displacement on
myelography; alternatively, the appearance of bone on bone scans in patients with
osteoid osteoma.
In the former, when the spine is viewed in the lateral projection after opacification of the dural sac, the change in contour of the dural sac or root sheath of the herniated disc appears as a double density.
In osteoid osteoma, the double density sign is characterized by intense scintigraphic activity centrally in the region of the nidus and less intense accumulation of the radionuclide peripherally in the sclerotic bone (Fig.1).
DR/RB
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a. Axial CT scan of the ankle demonstrates a calcified nidus with surrounding bone eburnation in the anterior aspect of the talus.
b. Bone scan reveals a focus of intense radionuclide accumulation which corresponds to the site of the osteoid osteoma on the CT scan. A zone of less intense tracer activity surrounding the osteoid osteoma creates the appearance of a "double density".
(Courtesy of James Kirkham, MD, Minneapolis, MN)
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Double density sign, Fig.1 (a) | | Double density sign, Fig.1 (b) | |