The fluid sign is featured in acute vertebral compression fractures that show bone marrow edema. It can be an additional sign of osteoporosis and rarely occurs in metastatic fractures.
MR imaging with opposed gradient-recalled echo sequences and contrast enhancement provided data that allowed us to classify infiltration patterns and to quantify diffuse marrow involvement in multiple myeloma, both of which correlated to clinical staging and biopsy. Also, the MR data was of prognostic value. Therefore, like laboratory parameters, biopsies, and radiographs, MR imaging can be a supporting pillar in staging and planning treatment of patients with multiple myeloma.
This article reviews the principles of diffusion-weighted imaging (DWI) and recent results in DWI of the musculoskeletal system. The potential of DWI in the diagnosis of pathology of the musculoskeletal system is discussed. DWI is a relatively new MR imaging technique that has already been established in neuroradiology, especially in the early detection of brain ischemia. The random motion of water protons on a molecular basis can be measured with DWI. To date DWI of the abdomen and of the musculoskeletal system has only been employed in scientific studies, but first results indicate that it may also be beneficial in these fields. Different diffusion characteristics have been found in normal tissues such as muscle, fat and bone marrow. Also, pathologic entities such as neoplasms, post-therapeutic soft tissue changes and inflammatory processes can be differentiated. Normal muscle shows significantly higher diffusion values than subcutaneous fat and bone marrow, due to a higher mobility of water protons within muscle. Soft tissue tumors exhibit a significantly lower diffusion value compared with post-therapeutic soft tissue changes and inflammatory processes. Necrotic tumor tissue can be distinguished from viable tumor due to significantly higher diffusion of water protons within necrotic tissue.
Contrast material enhancement in healthy persons can vary greatly (range 3-59%, mean 21%, SD 11%). With increasing age there is a significant decrease in contrast enhancement (Pearson's correlation, P < 0.01). The percentage SI increase in patients with intermediate-grade (biopsy 20-50 vol%) and high-grade (biopsy > 50 vol%) diffuse malignant bone marrow infiltration was significantly higher than in normals (mean 67%, SD 34%, P < 0.001). Low-grade (biopsy < 20 vol%) diffuse malignant bone marrow infiltration can not be assessed by non-enhanced T1-weighted SE images or Gd-DTPA application. In conclusion, contrast material enhancement in healthy persons can vary greatly and is dependent on age, while intermediate-grade and high-grade diffuse malignant bone marrow infiltration can be objectively assessed with SI measurements.
Diffusion-weighted imaging allows for measurement of tissue microstructure and reflects the random motion of water protons. It provides a new method to study bone marrow and bone marrow alterations on the basis of altered water-proton mobility in various diseases. Different diffusion-weighted methods have proved to be capable of differentiating between benign edema and tumorous involvement of bone marrow. It is especially useful for the distinction of acute benign osteoporotic and malignant vertebral compression fractures. Diagnosis is based on the contrast to normal bone marrow. Hypo- or isointensity reflects acute benign collapse, whereas hyperintensity is indicative of the tumorous nature of a fracture. Apparent diffusion coefficients (ADC) are significantly lower in metastatic disease than in bone marrow edema. Furthermore, bone marrow cellularity can be estimated by ADC measurements. Diffusion-weighted imaging might be helpful for monitoring response to therapy in metastatic disease.
Response to neoadjuvant chemotherapy combined with RHT is predictive for an improved local tumor control resulting in a long-term survival benefit for patients with HR-STS at unfavorable RP/V sites; however, the impact of RHT has to be defined in a randomized phase III trial.
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