Bone and marrow imaging: do we know what we seeand do we see what we want to know?

Excerpt

In an interesting letter to the Editor of the Journal of Clinical Oncology, Sandip Basu and Abass Alavi from the Division of Nuclear Medicine, Hospital of University of Pennsylvania, Philadelphia, PA, USA remind us that [¹⁸F]fluorodeoxyglucose positron emission tomography (FDG-PET) and bone scintigraphy (BS) provide different information and this is the reason why skeletal scintigraphy detects metastatic skeletal involvement later than FDG-PET [1]. In fact, FDG-PET detects metastases located in the bone marrow, while bone scintigraphy depicts the osteoblastic reaction. Indeed, the skeletal regions where red marrow is distributed are also the most common locations for the spread of cancer cells as eventually seen by BS. The authors remark that bone marrow is the primary site for the initial metastasis and should therefore be the main focus when assessing skeletal disease and that in the twenty-first century we should start emphasising the concept that the bone marrow rather than the bone is the primary location for cancer spread. They point out the possibility of distinguishing between bone marrow metastases with FDG-PET and reactions to pathological fractures with BS in patients with cancer, as well as the added value of tomography endowed with a higher spatial resolution than planar scintigraphy. Furthermore, they observe that response to therapy can be best evaluated by assessing disease activity in the marrow space, which is the primary location for metastatic lesions from lung cancer, melanoma and breast cancer. They also point out that osteolytic lesions (including those due to multiple myeloma), which are commonly missed by bone scintigraphy because of the lack of osteoblastic reaction, will be readily detected by FDG-PET. In contrast, osteoblastic metastasis from slowly growing tumours, such as prostate and thyroid cancer, should be assessed with radiolabelled amino acids and other PET tracers. Finally, it is worth noting that whereas BS depicts exclusively the diffusion of the disease in the bones, FDG-PET provides information on the possible metastatic involvement of any body part. …