MAGNETIC RESONANCE IMAGING
This imaging technique is the best method to evaluate bone marrow, the first site of most metastatic cancers. It is especially sensitive for round cell lesions such as leukemia, lymphoma, and multiple myeloma that replace the marrow space. The high fat content of marrow translates to high signal intensity or brightness. This essentially provides a contrast medium juxtaposed with tumor. Three-dimensional anatomic delineation is also very good throughout the skeleton. MRI is especially suited to the spine because it is sensitive for tumor, and shows sagittal alignment, cross-section, and crisp detail of dural and spinal cord compression. Of particular concern is to distinguish pathologic fracture due to osteoporosis from that due to tumor. This distinction is particularly important for postmenopausal women, who may suffer from both conditions and be subject to hormone manipulation as well. MRI is a helpful but imperfect discriminator.
Angiography is used as a therapeutic adjunct more than for the diagnosis of metastatic disease. Embolization of tumor for pain relief or to reduce vascularity is of great therapeutic value. Diagnostic use is limited to the preoperative identification of the artery of Adamkowitz before treating thoracic spine lesions.
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Cancer precludes bone healing in most pathologic fracture situations. The rapid growth of metastatic cancers overwhelms the healing response. Few studies have been done to measure this process. Gainor and Bruchert evaluated 129 long bone fractures. Healing occurred in 45 cases (36%). Among patients who live 6 months or more, 50% of fractures healed. The best healing rates were in multiple myeloma (67%), kidney (44%), and breast cancer (37%). No patients with lung cancer healed their fracture. The length of patient survival correlated best with fracture healing rates, although healing was considered multifactorial. Five factors determined the healing of pathologic fractures.
Lung, colorectal, and melanoma tumors failed to heal. These lesions tended to occur late in the course of disease and were purely lytic. Multiple myeloma and breast and kidney cancers healed most frequently. These lesion often occurred early in the course of disease when patients had more therapeutic options available. Bone formation and reossification were often seen in these cases.
Rigid internal fixation supplemented with bone cement increases the probability of bone union. Alignment and position of bone fragments are also important as in the case of nonpathologic fractures. Bone cement not only contributes to stability but may present a mechanical obstacle to tumor regrowth in the fracture region.
Longer survival occurred in patients with earlier or more slowly progressing disease. This correlated with improved healing rates for patients living longer than 6 months.
High doses (greater than 3000 cGy) were associated with poor healing.
There were no data regarding the impact of chemotherapy of healing in this series.
Chemotherapy effects in animal models are difficult to extrapolate to the human condition because of the variation in dose intensity and treatment scheduling. Most studies suggest that healing is reduced 50% by common agents such as methotrexate or doxorubicin.
Other systemic factors may make a minor contribution to fracture healing. For example, osteoporosis, hormone manipulation, cachexia, and other factors may be important. Newly released bisphosphonates reportedly benefit bone healing in experimental animal models. These agents have not been shown to augment healing in a clinically significant way, however. The magnitude of osteoblast suppression and the adverse effect of radiation on healing is debated. Doses as low as 2000 cGy begin to interfere with normal fracture healing in animals. In adults, fracture healing is very difficult to achieve when more than 5000 cGy is administered, although healing has been reported in children with fractures through heavily irradiated bone treated for Ewing’s sarcoma.