Bone Marrow Signal Alteration in the Extremities

TLDR: Although the pattern approach is useful for analyzing bone marrow signal abnormalities, evaluation of available clinical history; biochemical markers; complementary imaging; and, when appropriate, bone biopsy is often necessary to establish the diagnosis are often necessary.

Abstract: Received May 14, 2010; accepted after revision September 28, 2010. A lterations in bone marrow signal are encountered on a daily basis when interpreting MRI of the extremities. Distinguishing benign from malignant entities requires a thorough understanding of the pathologic processes that occur in the extremities. Disease entities can be broadly grouped into the categories of normal marrow or marrow reconversion, tumor, trauma, infection, inflammation, ischemia, radiation or chemo­ therapy, degenerative disease, and miscellaneous disorders (Table 1). Analysis of marrow abnormalities is based on a pattern approach that includes an evaluation of the distribution, location, signal characteristics, and morphology of the entity. Marrow signal distribution can be classified as diffuse, multifocal, or focal (Table 2), although there is considerable overlap among the entities. The location of the signal abnormality can further narrow the list of diagnostic possibilities. For example, osteochondral lesions, avascular necrosis, and degenerative changes have a predilection to involve subchondral bone. Neoplasms, such as giant cell tumors and chondroblastomas, occur in the epiphyseal region. Most processes affecting the bone marrow show low signal on T1­weighted imaging and increased signal on T2­weighted and STIR imaging. It is important to compare the T1 signal of the process with skeletal muscle because T1 hypointensity relative to skeletal muscle is often seen in pathologic conditions. Finally, there must be an evaluation of morphologic characteristics of the lesion, such as whether the margins are smooth or irregular and whether there is evidence of cortical penetration or soft­tissue extension. Characteristic morphologic appearances can be seen in such conditions as osteonecrosis, trauma, and Paget disease. Although the pattern approach is useful for analyzing bone marrow signal abnormalities, evaluation of available clinical history; biochemical markers; complementary imaging; and, when appropriate, bone biopsy is often necessary to establish the diagnosis. A thorough understanding of normal marrow conversion, as well as normal marrow variants and marrow reconversion, is also essential for accurate interpretation. Kung et al. Bone Marrow Signal Alteration