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. 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. Bone can also be affected by radiation therapy, in which there is an overall decrease in radiotracer uptake in a focal area. Soft tissue structures such as the breasts (or breast implants) can reduce activity observed in underlying bones such as the ribs. Finally, there have been several reports of cold defects occurring at the site of acute osteomyelitis.
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