Imaging description

In the adult, it is widely recognized that residual hematopoietic marrow is present throughout the axial skeleton. In addition, hematopoietic marrow is usually present within the proximal metaphyseal areas of the femur and humerus. Residual hematopoietic marrow may be observed within the proximal humeral epiphyseal area in normal adults. Hematopoietic marrow does not result in significant hyperintensity on images acquired with T2-weighted, fat-suppressed T2-weighted, or STIR sequences (Figure 13.1). Hematopoietic marrow is not associated with cortical destruction or an adjacent soft tissue mass. Hematopoietic marrow usually demonstrates bilateral symmetry, and evaluation of the contralateral extremity may be useful in problematic cases. The MR imaging characteristics of infiltrative lesions vary. All demonstrate some decreased signal intensity on T1-weighted images (Figure 13.2). Their appearance on T2-weighted sequences varies depending on tissue type, cellularity, water content, and the presence of fibrosis, necrosis, hematoma, or inflammatory debris.

Importance

Awareness of the normal physiologic variations of hematopoietic and fatty marrow distribution is important because these normal patterns can mimic marrow-based disease.

Differential diagnosis

Differential diagnosis includes marrow reconversion, marrow infiltration or replacement, myeloid depletion, and marrow edema.

Teaching point

When signal intensity variations are observed, the possibility of residual or reconverted hematopoietic marrow should be considered.