MRI "road-map" of normal age-related bone marrow. II. Thorax, pelvis and extremities.

We retrospectively reviewed T1-weighted MR images of 381 patients aged from 7 days to 24 years to evaluate the bone marrow change in thoracic wall and shoulder, pelvis and proximal femur and upper and lower extremities. The patients included in the study were without history of bone marrow disease. A grade of from 1 to 4 was assigned to the marrow signal intensity of the examined anatomic segments. The signal intensity of all anatomic segments was as low as or lower than that of muscle in all patients younger than 2 months, reflecting underlying hematopoietic marrow. The first segments to become hyperintense were the epiphyseal/round bone ossification centers, followed by the phalanges, diaphysis, flat bones and metaphysis. Marrow signal intensity increased in all regions with age. While in the epiphysis, round bones and diaphysis bone marrow shows a diffuse and homogeneous increased signal intensity with age, in the sternum, ribs, scapulae, posterior ilium and metaphysis varying percentages of intermediate signal intensity are maintained. An orderly progression of red to yellow marrow was established.