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“No, definitely not.”
After confirming with the bone scan technician that the patient was not wearing any foreign objects, intern C began to carefully observe this bone scan image (Figure 1).
Figure 1
This is a 67-year-old female patient who underwent right breast cancer resection one year ago. Although no clear signs of tumor bone metastasis were found on today’s whole-body bone scan, what confused intern C was that the anterior phase showed a significant sparse distribution area of the radiotracer on the right chest and abdomen, and the posterior phase also revealed a sparse radiotracer distribution area on the right chest and back.
What is going on here?
Intern C quickly thought: if the local bone lesion is mainly osteolytic or in the early stage of blood supply impairment, it often leads to local decreased uptake of phosphate radiotracers, resulting in localized radioactive defects. The most common causes of radioactive defects on bone scans are none other than:
① Tumor lesions dominated by osteolytic changes;
② Multiple myeloma;
③ Early-stage blood flow obstruction caused by vascular lesions, such as ischemic necrosis or bone infarction;
④ Radiation therapy;
⑤ Bone cysts;
⑥ Bone sites removed by surgery;
⑦ Dense foreign substances inside or outside the body, such as barium, cardiac pacemakers, metal implants in bones and joints, or decreased upper abdominal radioactivity due to excessive stomach contents.
For this patient, all the above conditions were excluded during the inquiry phase. Looking more closely, although the radiotracer distribution on the right chest and abdomen was sparse, it did not affect the uptake of the tracer by normal bones. It was like an area erased by a rubber on a sketch; if not observed carefully, one might really think a piece of bone is missing.
Intern C quickly checked the patient’s previous bone scans and found that the same area showed sparse radiotracer distribution during last year’s whole-body bone scan as well, but the range was not as large as today. At that time, the corresponding SPECT/CT fused images showed a cyst in the liver about 14×10×12 cm in size (Figure 2).
So that’s it!
Combining this year’s ultrasound examination, which showed that the liver cyst had grown significantly since last year, it was inferred that the sparse radiotracer distribution in this area was caused by this large cyst.
This also explains why the bone scan appeared as if a piece of bone was “missing.”
In fact, changes in MDP metabolism in bone scans do not always indicate bone pathology. In many cases, MDP metabolic changes have soft tissue causes. For example, in this case, when the liver cyst grows large enough, the attenuation effect causes a region corresponding to that cyst on the bone scan image to show a significant sparse radiotracer distribution.
Therefore, detailed pre-examination inquiries, review of medical history, and necessary physical examinations of bone scan patients are extremely important. Ensuring quality control at every step helps explain unexpected findings in bone scan images, thus providing more accurate and effective diagnoses for clinical practice.
Author: Qin Shanshan
Affiliation: Nuclear Medicine Department, Shanghai Tenth People’s Hospital
Issue: 2019, Week 36, Total No. 113
Editor-in-charge: Qin Shanshan
Reviewer: Yu Fei