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What are the causes of cold or photopenic defects on bone scans?
There are numerous benign and malignant causes for photopenic regions on a bone scan.
Bones with avascular necrosis or infarction in the early stage have photopenia.
Lytic osseous tumors or metastases can be cold because there is an absence of osteoblastic activity.
Major Causes of Cold Defects on Bone Scintigraphy
- 1. Attenuation artifact due to prosthesis, pacemaker, jewelry, lead shield, barium contrast, etc.
- 2. Malignant bone tumors
- 3. Metastatic disease (particularly when lytic such as from thyroid or renal cell carcinomas)
- 4. Avascular necrosis or bone infarction
- 5. Disuse atrophy
- 6. Unicameral bone cyst
- 7. External radiation therapy
- 8. Early osteomyelitis
Any metal objects—either external, such as jewelry, or internal, such as a pacemaker or joint prosthesis—can attenuate or block emitted radiation from reaching the scan detector.
On the basis of CT morphometry of the sternum, the possible causes of photopenia in the lower sternum in patients without sternal foramen are as follows: thin middle portion of sternum bone marrow, a focal defect or notch in the posterior sternal cortex, high accumulation of peripheral lesions, and bone metastasis.
