Purpose: To establish retrospectively a range of values for signal intensity change in normal vertebral marrow by using chemical shift magnetic resonance (MR) imaging and to assess the use of this technique in differentiating benign from malignant marrow abnormalities.
Materials and methods: Institutional Review Board approval for this retrospective, HIPAA-compliant study was obtained; informed consent was waived. A total of 569 normal vertebrae in 75 patients (42 women, 33 men; mean age, 57.5 years; age range, 26-84 years) (control group) and 221 lesions in 92 patients (50 women, 42 men; mean age, 59.0 years; age range, 27-85 years) (study group) who had focal vertebral marrow abnormalities were studied by using 1.5-T chemical shift MR imaging. Imaging time was less than 1 minute. The proportional change in signal intensity on in-phase compared with out-of-phase images was calculated by using 1 x 1-cm regions of interest (ROIs) in the control group and ROIs as large as possible for focal lesions in the study group. This change in signal intensity (expressed as a percentage) was compared with that of normal levels and benign and malignant lesions. For statistical analysis, a random effect model was used that was adjusted for multiple comparisons.
Results: A substantial decrease in signal intensity was noted for all normal vertebrae (mean, 58.5%) and for benign lesions, including endplate degeneration (mean, 52.2%), Schmorl nodes with edema (mean, 58.0%), hemangiomas (mean, 49.4%), and benign fractures (mean, 49.3%). Metastases exhibited either a minimal decrease or an increase in signal intensity (mean, 2.8%). Although there was some overlap in the range of signal intensity values among malignant lesions, benign lesions, and normal marrow, the differences in signal intensity loss for normal marrow and benign and malignant lesions were significant (P < .01 for all pairwise comparisons after adjusting for multiplicity).
Conclusion: Bone marrow in the vertebral bodies displays somewhat variable behavior at chemical shift MR imaging. Results suggest that a decrease in signal intensity greater than 20% on out-of-phase images compared with in-phase images should be used as a cutoff threshold for normalcy to allow distinction between benign and malignant causes of vertebral marrow abnormalities.