There’s More to Bone Scan Than Osseous Metastasis: Interesting Non-Metastatic Findings on Bone Scintigraphy

Objectives: To illustrate the low specificity of skeletal findings seen on bone scan. To demonstrate that benign conditions can have suspicious findings on bone scintigraphy. To exemplify that radionuclide bone imaging may be useful in solving diagnostic dilemmas, especially in cases with non-specific findings on anatomic imaging.

Background: Radionuclide bone imaging is a common nuclear medicine studies frequently requested by clinicians to aid in the staging and management of malignancies. Bone scans play an important role in the detection of osseous metastasis. Bone scintigraphy is usually performed using technetium-99m–labeled diphosphonates which rapidly accumulate in bone¹, especially in areas of active bone metabolism ^{2, 3}. The appearance of bone metastases on scintigraphy differ for blastic and lytic processes. Osteoblastic metastases usually appear as foci of increased activity while lytic metastases may manifest as areas of decreased uptake. Any process that increases bone turnover will also show increased radiotracer uptake on bone scan, hence mimicking osteoblastic metastatic disease. Conversely, any bony defect such as a sternal foramen, may also demonstrate photopenia, thereby mimicking osteolytic metastasis. Content: Abnormal bone scintigraphy findings are shown in common benign pathologies including, sternal foramen, facet arthrosis, Paget’s disease, fractures, thrombophlebitis, sarcoidosis, aseptic loosening of hardware and metastatic pulmonary calcification.

Conclusions: Bone scintigraphy plays an essential role in the staging of genitourinary malignancies. However, many benign conditions may show up on bone scans because it is highly sensitive to bone metabolism but low in specificity. Hence, bone scinitigraphic findings must be interpreted in light of the clinical context and correlated with other radiologic imaging. It is imperative that the radiologist be aware of such metastatic mimics in order to avoid upstaging cancers or excluding patients from therapeutic interventions that may otherwise be beneficial. Furthermore, some conditions with nonspecific findings on anatomic images can be diagnosed with radionuclide bone imaging and subsequently avoid invasive biopsy.