Bone Marrow Signal Alteration in the Spine and Sacrum

Abstract

B one marrow signal abnormality in the spine and sacrum is a common, sometimes unexpected finding on MRI, and it can be a source of diagnostic dilemma to radiologists who interpret these examinations. The myriad causes of bone marrow signal alteration include variants of normal, marrow reconversion, tumor (myeloproliferative disorders, metastatic, or primary), radiation, fracture, degenerative change, infection, inflammatory arthritis, and osteonecrosis. A pattern-based diagnostic approach to bone marrow signal abnormalities in the axial skeleton frequently helps to generate a concise list of diagnostic possibilities, thereby potentially minimizing the need for biopsy. The three main components involved in assessing the pattern of perceived signal abnormality on MRI are its signal characteristics, distribution, and morphology. Much information can be gained by evaluating the signal characteristics of a lesion on the different pulse sequences generally used (described in the next section). The distribution of bone marrow signal abnormalities can be categorized as diffuse or infiltrative, focal, or multifocal (Table 1). In the spine, it is important to consider the distribution of the lesion, whether it is localized within the vertebral body, extends into the pedicles or posterior elements, or is confined to the endplates. The morphology of the lesion should be assessed in terms of its borders, whether it is discrete and well circumscribed, ill defined, or aggressive and whether there is destruction of the cortical margin or merely outward bulging and expansion. This pattern-based approach must be combined with the routine diagnostic workup of bone marrow signal abnormalities seen elsewhere in the appendicular skeleton, including comparison with prior MRI (if present), complementary imaging (if needed), and clinical chemistry and bone biopsy (where appropriate).