NORMAL BONE-MARROW IN THE SACRUM OF YOUNG-ADULTS - DIFFERENCES BETWEEN THE SEXES SEEN ON CHEMICAL-SHIFT MR-IMAGING

OBJECTIVE, Age-related changes in the distribution of fatty and nonfat ty bone marrow in the pelvis and femur are well recognized, However, m apping not only of age-related MR appearance of normal bone marrow but also of potential variations in females versus males is necessary to differentiate normal findings from marrow disease, Accordingly, we stu died possible sex-related differences in the MR imaging appearance of sacral bone marrow in young adults, SUBJECTS AND METHODS, A population of 21 healthy men and 21 healthy women (17-42 years old) was prospect ively studied with chemical-shift pulse sequences. MR imaging (1.5 T) of the sacrum was done with frequency-selective fat images (SENEX [sel ective nonexcitation] 300/27) and water images (SENEX 1000/27) by usin g an elliptical surface coil. Two independent observers compared the s ignal intensity of sacral marrow with the signal of fatty tissue plane s adjacent to the sacrum (fat images) and the signal of gluteus muscle (water images), T2 relaxation times were estimated by using a two-par ametric monoexponential fit on SENEX 1000/27 and SENEX 1000/54 images. RESULTS, In both sexes, fat MR images showed a higher fat content and greater heterogeneity in the bone marrow of the lateral masses than i n the vertebral bodies of the sacrum (p<.05). Yellow marrow in the lat eral masses of the sacrum appeared brighter in men than in women (p<.0 5), The heterogeneity of fatty marrow did not differ significantly bet ween the sexes. On water MR images, the signal intensity of the sacrum was higher in women (p<.05). T2 relaxation times were longer in nonfa tty marrow with a high water signal intensity (41.8 +/- 5.5 msec versu s 33.4 +/- 2.6 msec p<.01). CONCLUSION, Our findings show that the nor mal appearance of the sacral bone marrow depicted on chemical-shift MR imaging differs between young men and women. Awareness of these diffe rences is important to avoid misinterpretation of normal MR findings s een in patients in this age group.