Focal fat deposition in axial bone marrow: MR characteristics.

One hundred fifty-eight magnetic resonance (MR) imaging studies of the spine were reviewed to assess the frequency and distribution of focal deposits with signal behavior typical of fat in the axial bone marrow. In addition, three fresh cadaveric spines were evaluated with MR imaging and subsequently sectioned for anatomic and histologic correlation. Macroscopic evaluation of the sectioned cadaveric specimens revealed well-defined, yellow areas within the bone marrow that correlated precisely with localized zones of signal intensity characteristic of fat on MR images. Histologic evaluation of these regions demonstrated typical focal fatty replacement of hematopoietic bone marrow. Their appearance was related to age and the presence of pathologic changes such as spondylitis, kyphoscoliosis, and spondylosis. Based upon these observations, focal fatty replacement of hematopoietic bone marrow appears to be a common phenomenon that should not be confused with localized disease processes.