METASTATIC DISEASE

      The spine is a common site for metastatic disease. The more common primary tumors to metastasize to the spine are lung and breast carcinoma, followed by prostatic carcinoma. Any malignancy has the potential to metastasize to bone, except perhaps CNS gliomas.

      Using the T1-weighted study, the normal medullary cavity should have a relatively homogeneous high-signal appearance due to the presence of marrow fat. Metastases, primary osseous neoplasm, and some hematopoietic or metabolic disorders result in replacement of the high-signal fat by lower signal substrates such as neoplastic tissue, fibrosis, or abnormally increased extracellular fluid. Varying degrees of decreased signal in the marrow cavity from osseous metastases can be seen on T1 images, depending on the amount of blastic reaction. Endnote Except for sclerotic metastases, bone metastases are hyperintense on T2-weighted images. The majority enhance with gadolinium on T1-weighted images. Fat suppression is recommended for both the T2-weighted and the gadolinium-enhanced images.

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      In older patients with osteoporosis and vertebral compression deformities, difficulty may arise in trying to distinguish this entity from neoplasm, but the marrow in osteoporosis maintains its fat component. In the case of metastases, as a general rule nearly all of the vertebral body fat is replaced before compression occurs. Morphology is also important in distinguishing benign from malignant vertebral collapse. Intervertebral fluid, an intervertebral vacuum cleft, wedge-shaped deformity of the vertebral body and preservation of the posterior cortical margin favor a benign process. End plate compression with herniation of disk material into the body is another sign of benign collapse. Paravertebral soft-tissue mass suggests malignancy. Acute benign fractures do not enhance initially, but after a week or two, enhancement of granulation tissue is observed. Finally, on diffusion-weighted images, benign fractures are hypointense, whereas pathologic vertebral compression fractures are hyperintense. Initial reports were very positive for diffusion weighted images distinguishing benign from pathologic fractures, Endnote however, subsequent reports have been less enthusiastic. Endnote

      Except in unusual circumstances, epidural metastatic disease occurs in association with osseous metastases. Once a soft-tissue mass is identified, additional features require characterization, including definition of the caudal-rostral and paravertebral extent, identification of any additional soft-tissue involvement, and quantification of the degree of cord, cauda equina, and root compression. Endnote Epidural neoplasm on T1 images is usually slightly lower in signal than spinal cord.

 

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