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.
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.
Cold or photopenic defects on bone scans refer to areas of reduced or absent radioactive tracer uptake during nuclear medicine bone scanning.
These defects can indicate various conditions affecting the bones.
Some of the common causes of cold or photopenic defects on bone scans include:
- Bone Fractures: Fractures in the bones can cause cold defects on bone scans, especially if they are healing and have reduced blood flow to the affected area.
- Bone Tumors: Malignant tumors, such as bone metastases from other cancers (e.g., breast, prostate, lung), or primary bone tumors (e.g., osteosarcoma, chondrosarcoma), can appear as cold defects on bone scans due to reduced metabolic activity in the tumor cells.
- Osteomyelitis: Osteomyelitis is a bone infection caused by bacteria. The presence of infection and inflammation can lead to reduced tracer uptake and photopenic defects on bone scans.
- Avascular Necrosis (Osteonecrosis): Avascular necrosis is the death of bone tissue due to a lack of blood supply. The affected bone area may appear as a cold defect on a bone scan.
- Bone Infarction: Bone infarction refers to the death of bone tissue caused by a disruption of blood supply. It can lead to a photopenic defect on a bone scan.
- Bone Marrow Replacing Lesions: Conditions like multiple myeloma or metastases that infiltrate the bone marrow can reduce normal bone marrow activity and result in cold defects on bone scans.
- Bone Healing after Surgery: Following orthopedic surgeries or joint replacements, areas of healing bone may show reduced tracer uptake during the initial healing stages.
It’s important to note that cold or photopenic defects on bone scans do not provide a definitive diagnosis. Additional imaging studies, laboratory tests, and clinical evaluations are usually necessary to determine the underlying cause of the abnormalities seen on the bone scan. A team of healthcare professionals, including nuclear medicine physicians, radiologists, and orthopedic specialists, will collaborate to interpret the findings and make a comprehensive diagnosis.
As with any medical imaging test, it’s essential for individuals to discuss the results and their implications with their healthcare provider to develop an appropriate treatment plan based on the underlying condition.
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.
