Disc degeneration may lead to changes of the vertebral body marrow, through abnormal forces exerted upon the vertebral body endplates. These reactive endplate changes have been grouped into three types discernible on MRI (20). Type I changes consist histologically of fibrovascu-lar tissue replacement of normal cellular marrow. These changes are seen as low signal intensity on T1 and high signal intensity on T2. Although they may resemble osteo myelitis, the lack of high signal in the disc on T2-weighted images can differentiate them from infection (27) (Fig. 6).
Type II change represents areas of fatty replacement of bone marrow. Accordingly, both T1- and T2-weighted images are of relatively high signal intensity, consistent with fat (Fig. 6). No significant amount of post-contrast enhancement is observed. Unlike type I changes, this stage usually does not revert and can proceed to type III (19,27).
The final stage consists of sclerotic changes and hyperostosis. There is a deficiency of normal marrow. These type III changes are seen as low signal intensity on both T1- and T2-weighted images (19).
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