Conversion of bone marrow in the humerus, sternum, and clavicle: changes with age on MR images.

To study the normal conversion of bone marrow in the humerus, sternum, and clavicle, 101 T1-weighted magnetic resonance (MR) studies obtained in 91 patients aged 2 days to 37 years were retrospectively evaluated. Conversion from hypointense (red) to hyperintense (yellow) bone marrow was assessed by comparison of signal intensity of the bone marrow with that of muscle and fat. Conversion began in the proximal humeral epiphysis (in 16 of 21 adequate studies [76%]), humeral diaphysis (17 of 30 adequate studies [57%]), and distal metaphysis (16 of 25 adequate studies [64%]) before age 1 year and was nearly complete in these regions (20 of 22 adequate studies [91%], 20 of 21 adequate studies [95%], and five of seven adequate studies [71%]) in examinations of children aged 1-5 years. In the proximal humeral metaphysis, conversion was seen in 21 of 22 adequate studies (95%) in children aged 1-5 years and was nearly complete in all by age 20 years. Conversion began in the sternum (six of six studies [100%] in children aged 6-10 years) and clavicle (six of eight studies [75%] in children aged 6-10 years) before age 11 years but was never complete. Bone marrow conversion in the humerus, sternum, and clavicle follows a well-defined pattern and is depicted earlier by MR imaging than one would expect on the basis of histologic data.