Disorders of Bone Marrow

Abstract

Bone marrow is one of the largest organs in the body, after the osseous skeleton, skin, and body fat, and is present on nearly every magnetic resonance image obtained of the human body. Hematopoietic (red) marrow is present throughout the entire skeleton at birth, but over the ensuing two decades of life different regions of hematopoietic marrow convert to fatty (yellow) marrow. This conversion begins in the periphery of the skeleton and then symmetrically extends into the central skeleton (Fig. 1a). An additional, superimposed sequence of marrow conversion occurs in the long bones, starting in the diaphyses and progressing towards the metaphyses (particularly the distal metaphysis) (Fig. 1b). In the second decade of life, marrow in the long bones becomes predominantly fatty, except in the proximal metaphyses. In the late third decade, the marrow distribution reaches its mature state, with hematopoietic marrow occupying the axial skeleton (skull, spine, sternum, clavicles, scapulas, pelvis) as well as the proximal metaphyses of the humeri and femurs; later in life, even those regions gradually convert to fatty marrow. Open image in new window Fig. 1a. Bone marrow conversion patterns. a The conversion of hematopoietic marrow at birth to fatty marrow occurs overall from the peripheral to the axial skeleton (arrows). Open image in new window Fig. 1b. Bone marrow conversion patterns. b In long bones, hematopoietic marrow first converts to yellow in the diaphysis, then proceeds to the metaphysis (double-headed arrows). During times of increased requirement for hematopoiesis, both sequences proceed in the opposite directions to reconvert fatty marrow to hematopoietic marrow. Bone scans are used here to demonstrate the directions of marrow changes