[Metastatic bone disease. Strategies for imaging]

Skeletal metastases represent the most common malignant bone tumor. They occur mainly in adults and even more frequently in the elderly. The most common metastases in men are from prostate cancer (60%) and in women from breast cancer (70%). Other primitive tumors responsible for bone metastases are: lung, kidney, thyroid, alimentary tract, bladder, and skin. The spine and pelvis are the most common metastatic sites, due to the presence of red (haematopoietic active) bone marrow in a high amount. As a general rule, the radiographic pattern was lytic type; other aspects were osteosclerotic, mixed, lytic vs mixed and osteosclerotic vs lytic patterns. The main symptom is pain, although many bone metastases are asymptomatic. The most severe consequences are pathologic fractures and cord compression. Clinical evaluation of patients with skeletal metastases needs multimodal diagnostic imaging, able to detect lesions, to assess their extension and localization, and eventually drive the biopsy (for histo-morphological diagnosis). These techniques give different performances in terms of sensitivity and specificity; but none of the modalities alone seems to be adequate to yield a reliable diagnostic outcome. Therefore multidisciplinary cooperation is required to optimize the screening, clinical management and follow-up of the patients. In other terms, what is the efficacy of these new diagnostic tests compared to the "older" diagnostic tests? Frequently the new procedures do not replace the older one, but it is added to the diagnostic workup, thereby increasing costs without impacting the "patient's condition". The aim of the present work is to propose an "algorithm" for the detection and diagnosis of skeletal metastases, which may be applied differently in symptomatic and asymptomatic oncologic patients. Bone scintigraphy remains the first choice technique in the evaluation of asymptomatic patients, in whom skeletal metastases are supposed. Although it has a high sensitivity, scintigraphy is unspecific. So that a negative scan response has to be re-evaluated with other methods: if clinical status remains "negative", the diagnostic route can stop. On the contrary, in patients with "positive" scan or with local symptoms and pain, the screening of metastatic lesions must be accomplished by a combination of radiography and CT: the result may be negative (for low sensitivity of conventional radiology), not conclusive (in this case bone biopsy is necessary) or symptoms are not due to metastatic lesions (i.e., osteoarthritis). CT represents an excellent mean of defining the extent of any metastatic lesions, especially those located at sites difficult to evaluate (vertebral column and pelvis). Before bone biopsy is carried out, MRI must be performed, because it is the only technique that makes it possible to distinguish between bone marrow components. It has been used most extensively in the evaluation of spine metastases. The limitation of MRI is the unspecificity of its findings, which may lead to an equivocal diagnosis, and because only part of the skeleton can be studied.