From the RSNA refresher courses - Evaluation of the marrow space in the adult hip

The adult pelvis and hip contain extensive marrow space in which a variety of processes may occur. Evaluation of this space requires an understanding of normal maturation and recognition that the marrow of the pelvis (axial skeleton) and that of the proximal femurs (appendicular skeleton) contain variable amounts of red and yellow marrow. At magnetic resonance (MR) imaging, this variability yields patterns in normal marrow ranging from very uniform and homogeneous signal intensity to patchy and heterogeneous signal intensity. The marrow space serves as a reflection of patient health and may herald developing anemia with reconversion of inactive to active marrow. Pathologic processes to be considered include marrow edema related to trauma, tumors, or infection; marrow ischemia and infarction; marrow infiltration from primary or secondary neoplasms or from infection; or complete loss of normal myeloid tissue in the marrow space. Each process can be effectively studied with MR imaging.