Age-related marrow changes in the pelvis: MR and anatomic findings.

Short repetition time magnetic resonance images of the pelvis in 70 subjects (aged 1 day to 24 years) without history of bone marrow disease were retrospectively analyzed for the distribution and appearance of red and yellow marrow. The signal intensity and degree of mottling of marrow in six anatomic regions of the pelvis were observed and were assigned a grade. Anatomic correlation was provided with gross and microscopic examination of bone marrow biopsy specimens taken from selected pelvic sites in cadavers of children. Marrow signal intensity increased in all pelvic regions except the acetabulum from birth to age 24 years. Marrow heterogeneity was most prominent in the acetabulum at all ages. Patterns of bone marrow signal intensity and heterogeneity are recognized for four age groups: the infant, child, adolescent, and young adult. Regional and age-related differences in the signal intensity of pelvic marrow correlate with the percentage of fat seen microscopically in marrow.