Imaging of malignant bone involvement by morphologic, scintigraphic, and hybrid modalities

Detection of bone involvement is essential for optimal therapy of oncologic patients. The purpose of imaging is to identify early bone involvement, to determine the full extent of the skeletal disease, to assess the presence of accompanying complications-such as fractures and cord compression-and to monitor response to therapy. Detection of bone involvement by various imaging modalities is based on either direct visualization of tumor infiltration or detection of the reaction of bone to the malignant process. MRI can identify early involvement of bone marrow. CT, which depends mainly on bone destruction, provides detailed bone morphology. In nuclear medicine, uptake of (18)F-FDG is directly into tumor cells, thus allowing for early detection and monitoring the response to therapy of tumor sites in the marrow, bone, and soft tissue, whereas increased uptake of (18)F-fluoride and (99m)Tc-methylene diphosphonate reflects the osteoblastic reaction of bone to the presence of tumor cells. The hybrid techniques SPECT/CT and PET/CT, recently introduced into clinical practice, provide a better anatomic localization of scintigraphic findings and may improve the diagnostic accuracy of SPECT and PET in detecting malignant bone involvement. The current review discusses the basis for the detection of malignant bone involvement by various morphologic and scintigraphic imaging modalities and the advantages and the limitations of each. Special emphasize is placed on the newer integrated technique of PET/CT. The role of imaging in identifying bone involvement in different malignant diseases is also discussed.